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Reactivity controlled compression ignition engine: Pathways towards commercial viability
Abstract
Reactivity-controlled compression ignition (RCCI) is a promising energy conversion strategy to increase fuel efficiency and reduce nitrogen oxide (NOx) and soot emissions through improved in-cylinder combustion process. Considering the significant amount of conducted research and development on RCCI concept, the majority of the work has been performed under steady-state conditions. However, most thermal propulsion systems in transportation applications require operation under transient conditions. In the RCCI concept, it is crucial to investigate transient behavior over entire load conditions in order to minimize the engine-out emissions and meet new real driving emissions (RDE) legislation. This would help further close the gap between steady-state and transient operation in order to implement the RCCI concept into mass production. This work provides a comprehensive review of the performance and emissions analyses of the RCCI engines with the consideration of transient effects and vehicular applications. For this purpose, various simulation and experimental studies have been reviewed implementing different control strategies like control-oriented models particularly in dual-mode operating conditions. In addition, the application of the RCCI strategy in hybrid electric vehicle platforms using renewable fuels is also discussed. The discussion of the present review paper provides important insights for future research on the RCCI concept as a commercially viable energy conversion strategy for automotive applications.
... Reactivity-controlled compression ignition (RCCI) has emerged as a promising concept among state-of-the-art combustion technologies. Enabled by low temperature combustion (LTC) technology, RCCI offers twin benefits of improved thermal efficiency and reduced emissions [1]. As a dual-fuel concept, it facilitates greater control over combustion performance and is higher on the technology readiness level ladder [2] than other LTC strategies. ...
... Despite improved combustion control, RCCI is nevertheless driven by chemical kinetics [1]. Consequently, the parameters for solely controlling combustion phasing include injection timing, fuel blending, IVC thermal management, and reactivity stratification. ...
... Consequently, the parameters for solely controlling combustion phasing include injection timing, fuel blending, IVC thermal management, and reactivity stratification. Furthermore, RCCI operation is characterised by high pressure rise rate (PRR) and peak cylinder pressure (P max ) levels [1] which limit high-load operation. Under part-and low-load conditions, unburnt hydrocarbons (UHC) and CO emissions become an issue [9]. ...
... By changing the ratio between low-and high-reactivity fuels and their injection timing, it is possible to optimise combustion phasing, duration, and magnitude. However, continuous monitoring of the combustion process and regulation of this ratio and timing is required to guarantee robust and safe operation [7,8]. ...
... Cylinder-pressure-based control (CPBC) is a key concept for guaranteeing safe and stable operation of these advanced combustion concepts [8]. Typically, the measured incylinder pressure is used in next-cycle combustion control strategies to minimise cyclic variations in key combustion metrics. ...
... In both sweeps, the predicted standard deviations do not always match the measurements. In (8), w i (s IVC ), and w j (s IVC ) ∀i, j ∈ {1, 2, . . . , n PC } are assumed to be independent to align with the available GPR literature; however, this independence is not necessarily the case. ...
Cylinder-pressure-based control is a key enabler for advanced pre-mixed combustion concepts. In addition to guaranteeing robust and safe operation, it allows for cylinder pressure and heat release shaping. This requires fast control-oriented combustion models. Over the years, mean-value models have been proposed that can predict combustion metrics (e.g., gross indicated mean effective pressure (IMEPg), or the crank angle where 50% of the total heat is released (CA50)) or models that predict the full in-cylinder pressure. However, these models are not able to capture cycle-to-cycle variations. The inclusion of the cycle-to-cycle variations is important in the control design for combustion concepts, like reactivity-controlled compression ignition, that can suffer from large cycle-to-cycle variations. In this study, the in-cylinder pressure and cycle-to-cycle variations are modelled using a data-based approach. The in-cylinder conditions and fuel settings are the inputs to the model. The model combines principal component decomposition and Gaussian process regression. A detailed study is performed on the effects of the different hyperparameters and kernel choices. The approach is applicable to any combustion concept, but is most valuable for advance combustion concepts with large cycle-to-cycle variation. The potential of the proposed approach is successfully demonstrated for a reactivity-controlled compression ignition engine running on diesel and E85. The average prediction error of the mean in-cylinder pressure over a complete combustion cycle is 0.051 bar and of the corresponding mean cycle-to-cycle variation is 0.24 bar2. This principal-component-decomposition-based approach is an important step towards in-cylinder pressure shaping. The use of Gaussian process regression provides important information on cycle-to-cycle variation and provides next-cycle control information on safety and performance criteria.
... Ultimately, the study showed a clear route towards 50 % brake thermal efficiency for heavy-duty engines working in RCCI mode. The recent review by Paykani et al. [37] focused on RCCI control techniques to enable engine operation in transient conditions, including multi-mode combustion. The study put forward arguments for commercial feasibility of RCCI engines, also addressing life cycle analysis and cradle-to-grave CO 2 emissions. ...
... Note, however, that the complete model-based development framework with MZM so far has not been demonstrated: individual studies have focused on individual elements of the framework. A recent RCCI review by Paykani et al. [37], aiming to map out the "pathways towards commercial viability," highlighted the development of a proper control-oriented model (COM) as one of the key enablers. The authors examined two physics-based multizone models incorporating chemical kinetics. ...
... First, the equalised zonal pressure (P cyl ) is calculated according to Eq. (6). Based on it, the zonal mass is computed, as in Eq. (37). In order to quantify the interzonal mass exchanged, the change in mass of a zone over a time step is calculated by Eq. (38). ...
Many researchers believe multi-zone (MZ), chemical kinetics–based models are proven, essential toolchains for development of low-temperature combustion (LTC) engines. However, such models are specific to the research groups that developed them and are not widely available on a commercial nor open-source basis. Consequently, their governing assumptions vary, resulting in differences in autonomy, accuracy and simulation speed, all of which affect their applicability. Knowledge of the models´ individual characteristics is scattered over the research groups´ publications, making it extremely difficult to see the bigger picture. This combination of disparities and dispersed information hinders the engine research community that wants to harness the capability of multi-zone modelling.
This work aims to overcome these hurdles. It is a comprehensive review of over 120 works directly related to MZ modelling of LTC extended with an insight to primary sources covering individual submodels. It covers 16 distinctive modelling approaches, three different combustion concepts and over 60 different fuel/kinetic mechanism combination. Over 38 identified applications ranging from fundamental-level studies to control development. The work aims to provide sufficient detail of individual model design choices to facilitate creation of improved, more open multi-zone toolchains and inspire new applications. It also provides a high-level vision of how multi-zone models can evolve.
The review identifies a state-of-the-art multi-zone model as an onion-skin model with 10–15 zones; phenomenological heat and mass transfer submodels with predictive in-cylinder turbulence; and semi-detailed reaction kinetics encapsulating 53-199 species. Together with submodels for heat loss, fuel injection and gas exchange, this modelling approach predicts in-cylinder pressure within cycle-to-cycle variation for a handful of combustion concepts, from homogeneous/premixed charge to reactivity-controlled compression ignition (HCCI, PCCI, RCCI). Single-core simulation time is around 30 minutes for implementations focused on accuracy: there are direct time-reduction strategies for control applications. Major tasks include a fast and predictive means to determine in-cylinder fuel stratification, and extending applicability and predictivity by coupling with commercial one-dimensional engine-modelling toolchains. There is also significant room for simulation speed-up by incorporating techniques such as tabulated chemistry and employing new solving algorithms that reduce cost of jacobian construction.
... This makes it robust for the selection of future sustainable transport fuels. In this work, we focus on the combination of diesel and E85, which are commercially available and show good combustion properties, see, e.g., [4][5][6]. Although massive progress has been made in the understanding of the RCCI concept, four main challenges are encountered in competing with alternative concepts, and they bring this promising concept "on the road: [6]: ...
... In this work, we focus on the combination of diesel and E85, which are commercially available and show good combustion properties, see, e.g., [4][5][6]. Although massive progress has been made in the understanding of the RCCI concept, four main challenges are encountered in competing with alternative concepts, and they bring this promising concept "on the road: [6]: ...
... This includes new fueling and air management hardware, such as direct injection dual-fuel injection, advanced turbocharging, variable valve actuation, and new after-treatment technologies. To guarantee robust and stable engine operations, advanced combustion control concepts are essential [6,7]. ...
Reactivity controlled compression ignition (RCCI) is a highly efficient and clean combustion concept, which enables the use of a wide range of renewable fuels. Consequently, this promising dual fuel combustion concept is of great interest for realizing climate neutral future transport. RCCI is very sensitive for operating conditions and requires advanced control strategies to guarantee stable and safe operation. For real-world RCCI implementation, we face control challenges related to transients and varying ambient conditions. Currently, a multivariable air–fuel path controller that can guarantee robust RCCI engine operation is lacking. In this work, we present a RCCI engine controller, which combines static decoupling and a diagonal MIMO feedback controller. For control design, a frequency domain-based approach is presented, which explicitly deals with cylinder-to-cylinder variations using data-driven, cylinder-individual combustion models. This approach enables a systematic trade-off between fast and robust performance and gives clear design criteria for stable operation. The performance of the developed multivariable engine controller is demonstrated on a six-cylinder diesel-E85 RCCI engine. From experimental results, it is concluded that the RCCI engine controller accurately tracks the five desired combustion and air path parameters, simultaneously. For the studied transient cycle, this results in 12.8% reduction in NOx emissions and peak in-cylinder pressure rise rates are reduced by 3.8 bar/deg CA. Compared to open-loop control, the stable and safe operating range is increased from 25 °C up to 35 °C intake manifold temperature and maximal load range is increased by 14.7% up to BMEP = 14.8 bar.
... Reactivity-controlled compression ignition (RCCI) demonstrated significant commercial potential for automotive applications in the short to medium term [25]. Nevertheless, the implementation of accurate feedback control systems is essential to regulate engine parameters, thereby reducing cycle-to-cycle variability and ensuring reliable and safe operation [25]. ...
... Reactivity-controlled compression ignition (RCCI) demonstrated significant commercial potential for automotive applications in the short to medium term [25]. Nevertheless, the implementation of accurate feedback control systems is essential to regulate engine parameters, thereby reducing cycle-to-cycle variability and ensuring reliable and safe operation [25]. ...
Internal combustion engines (ICEs) currently account for approximately 25% of global power generation. Notably, this technology still plays a crucial role in a large segment of the transportation sector. In this editorial, a short overview of the latest developments and current research trends related to internal combustion engines is presented. Furthermore, the 11 contributions of this Special Issue are introduced. They cover three main topics: the use of new fuels for internal combustion engines for both automotive and railway applications; testing of additives for ICEs fed with conventional fuels; and CFD simulation applied to the analysis and design of ICE components.
... Similar considerations have been reported for engines using reactivitycontrolled compression ignition (RCCI) strategies, which require transition from part-load RCCI to high-load conventional combustion. Paykani et al. [10] reported slower load response during such mode shifts while combustion stability, in-cylinder conditions and engine-out emissions were sensitive to the conditions encountered during the transient. While RCCI offers ultra-low emissions at part load, the cost and operational implications of multiple fuels are barriers [10,11]. ...
... Paykani et al. [10] reported slower load response during such mode shifts while combustion stability, in-cylinder conditions and engine-out emissions were sensitive to the conditions encountered during the transient. While RCCI offers ultra-low emissions at part load, the cost and operational implications of multiple fuels are barriers [10,11]. High-dilution LTC and conventional diesel combustion modes with intermediate EGR levels (between 30% and 60%) remain a topic of interest for diesel engines [12] and can be applied to both conventional diesel and alternative low net carbon diesel-like fuels [13,14]. ...
Using high charge dilution low temperature combustion (LTC) strategies in a diesel engine offers low emissions of nitrogen oxides (NOx). These strategies are limited to part-load conditions and involve high levels of charge dilution, typically achieved through the use of recirculated exhaust gases (EGR). The slow response of the gas handling system, compared to load demand and fuelling, can lead to conditions where dilution levels are higher or lower than expected, impacting emissions and combustion stability. This article reports on the sensitivity of high-dilution LTC to variations in EGR rate and fuel injection timing. Impacts on engine efficiency, combustion stability and emissions are assessed in a single-cylinder engine and compared to in-cylinder flame temperatures measured using a borescope-based two-colour pyrometer. The work focuses on low-load conditions (300 kPa gross indicated mean effective pressure) and includes an EGR sweep from conventional diesel mode to high-dilution LTC, and sensitivity studies investigating the effects of variations in charge dilution and fuel injection timing at the high-dilution LTC condition. Key findings from the study include that the peak flame temperature decreased from ~2580 K in conventional diesel combustion with no EGR to 1800 K in LTC with low-NOx, low-soot operation and an EGR rate of 57%. Increasing the EGR to 64% reduced flame temperatures to 1400 K but increased total hydrocarbon (THC) and carbon monoxide (CO) emissions by 30–50% and increased fuel consumption by 5–7%. Charge dilution was found to have a stronger effect on the combustion process than the diesel injection timing under these LTC conditions. Advancing fuel injection timings at increasing dilution kept combustion instability below 2.5%. Peak in-cylinder temperatures were maintained in the 2000–2100 K range, while THC and CO emissions were controlled by delaying the onset of bulk quenching. Very early injection (earlier than 24 °CA before top-dead-centre) resulted in spray impingement on the piston crown, resulting in degraded efficiency and higher emissions. The results of this study demonstrate the potential of fuel injection timing modification to accommodate variations in charge dilution rates while maintaining low NOx and PM emissions in a diesel engine using low-temperature combustion strategies at part loads.
... Hitherto, these results have not been achieved by any other commercially applied engine concepts [6,11]. Contemporary applied-level RCCI research [1,12] focuses on challenges such as limited high-load operation, excessive unburned hydrocarbon emission at low loads and how to tackle controller design to suit system complexity. For example, Reitz & Duraisamy [1] discuss the use of high octane-number fuels like natural gas and alcohols to rein back RCCI´s maximum pressure rise rate (PRR). ...
... Addressing this restraint could help push BTE beyond 50%. Reviewing RCCI control techniques, Paykani et al. [12] conclude that physics-based, controloriented models are the key enablers for the concept to become commercially feasible. ...
With low-temperature combustion engine research reaching an applicable level, physics-based control-oriented models regain attention. For reactivity controlled combustion concepts, chemical kinetics-based multizone models have been proven to reproduce the governing physics for performance-oriented simulations. They offer accuracy levels similar to high-fidelity computational fluid dynamics (CFD) models but with a fraction of their computational effort. Nevertheless, state-of-the-art reactivity controlled compression ignition (RCCI) simulations with multizone model toolchains still face challenges related to predictivity and calculation speed. This study introduces a new multizone modelling framework that addresses these challenges. It includes a C++ code, deeply integrated with open-source, thermo-kinetic libraries, and coupled to an industry standard 1-D modelling framework. Incorporating a predictive turbulence mixing model, it aims to eliminate dependence on CFD-based initialisation, while applying a novel zonal configuration to achieve sensitivity to the combustion chamber´s geometrical features. Basic sensitivity simulations performed for zonal resolution and chemical kinetic mechanisms prove the approach is fit for purpose. Aiming for optimal trade-off between accuracy and simulation speed, the 12-zone model has a simulation time below three minutes per closed cycle. These achievements are validated against a medium-speed, large-bore, single-cylinder research engine, running in a dual-fuel mode with natural gas and light fuel oil. Using basic submodels, the framework reproduces measured in-cylinder pressure trace within an RMS error of 0.85 bar, and combustion performance indicators within a 5% error margin target. Ultimately, this is the first time the multi-zone kinetic framework has been proven suitable to reproduce RCCI combustion on a state-of-the-art marine engine geometry.
... They indicated an expressed need for additional controls to avoid undesirable effects to achieving the RCCI combustion mode. A comprehensive review of the transient operation under RCCI combustion mode was presented by Paykani et al. [319]. The main theme was that the RCCI combustion concept was mostly tested under stationary conditions, and there could be differences under transient conditions. ...
... Although cetane improvers theoretically require only one fuel tank for the RCCI combustion mode to work, the single fuel alternative does require an additional tank of a similar size as that of a diesel exhaust fluid (DEF) [319], which would be required to be recharged periodically. The fuel reformation strategy to obtain a secondary fuel having different reactivity from the same fuel to achieve RCCI combustion mode has been proposed to bypass this hurdle completely. ...
Several advanced low-temperature combustion (LTC) strategies have been developed to reduce the harmful emissions from diesel engines. These LTC strategies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and reactivity-controlled compression ignition (RCCI), can reduce engine-out nitrogen oxides (NOx) and soot emissions simultaneously. LTC investigations exhibit several limitations of HCCI and PCCI combustion modes, such as lack of combustion control and other operational issues at higher engine loads, making their application in production-grade engines challenging. RCCI combustion mode exhibited promising results in combustion control, engine performance, and applicability at higher engine loads. The potential of the RCCI concept was demonstrated on different engine platforms, showing engine-out NOx levels below the limits proposed by the emissions regulations, together with ultra-low soot emissions, eliminating the need of after-treatment devices. However, the RCCI combustion mode has several challenges, such as excessive hydrocarbons (HC) and carbon monoxide (CO) emissions at low loads and excessive maximum pressure rise rate (MPRR) at high loads, which limit its effective operating range and practical applications. This review article includes recent advancements in RCCI combustion mode, its potential for using alternative fuels, the effects of different parameters on RCCI combustion mode and its optimization, and the ability of RCCI combustion mode to extend the engine operating limit to reach higher loads, which prevents the application of this concept in commercial applications. The findings of different optical diagnostics have also been included, which have been performed to understand the detailed chemical kinetics of the fuel-air mixtures and the effect of fuel reactivities on the RCCI combustion mode. The first part of this article focuses on these studies, which provide important outcomes that can be used for the practical implementation of RCCI combustion mode in production-grade engines. The second part of this article covers different RCCI combustion mode strategies that can be used to eliminate the restrictions of RCCI combustion mode at high loads. Among the different techniques, dual-mode concepts have been extensively investigated. The dual-mode concept is based on switching between two different combustion modes, typically an LTC mode and conventional compression ignition (CI) combustion mode, to cover the entire operational range of the engine. Many studies showed that the NOx and soot emissions from stationary engines with dual-mode RCCI/CI combustion had substantially improved versus a single-fueled CI combustion mode engine. Results related to the measurements of emissions and performance in transient conditions and driving cycles have also been included, which exhibit promising results for RCCI combustion mode. A comprehensive review on overcoming the challenges and real-world applicability of RCCI combustion mode is not available in the open literature yet. This article includes the results of relevant RCCI combustion mode investigations carried out in single-cylinder and multi-cylinder engines, intending to fill this research gap. Finally, the results from alternative RCCI combustion mode concepts such as the dual-mode, hybrid-RCCI, simulations, and experiments in transient conditions using various driving cycles make this article uniquely relevant for researchers.
... Also, more stringent diesel engine emissions regulations have directed research towards further development of advanced combustion engines. Meanwhile, dual-fuel operation [379][380][381] with a premixed fuel and pilot-injected diesel has shown interesting advantages in terms of efficiency and emissions over conventional diesel combustion (CDC). Similar to compressed natural gas (CNG) and liquefied petroleum gas (LPG) [382], syngas is also a good candidate for the premixed fuel in dual fuel mode owing to its variable composition, flexible feedstocks, and possibility of on-board production on a vehicle [383,384]. ...
... This concept has been presented by Kokjohn et al. [413], who named it reactivity-controlled compression ignition (RCCI). In terms of commercialization, RCCI [380,381,414,415] is under more investigation for single-fuel operation, where high reactivity like diesel as the parent fuel, can be converted into a low-reactivity fuel by suitable in-situ on-board fuel reforming [34,[416][417][418][419][420][421][422][423][424]. ...
The adverse environmental impact of fossil fuel combustion in engines has motivated research towards using alternative low-carbon fuels. In recent years, there has been an increased interest in studying the combustion of fuel mixtures consisting mainly of hydrogen and carbon monoxide, referred to as syngas, which can be considered as a promising fuel toward cleaner combustion technologies for power generation. This paper provides an extensive review of syngas production and application in internal combustion (IC) engines as the primary or secondary fuel. First, a brief overview of syngas as a fuel is presented, introducing the various methods for its production, focusing on its historical use and summarizing the merits and drawbacks of using syngas as a fuel. Then its physicochemical properties relevant to IC engines are reviewed, highlighting studies on the fundamental combustion characteristics, such as ignition delay time and laminar and turbulent flame speeds. The main body of the paper is devoted to reviewing the effect of syngas utilization on performance and emissions characteristics of spark ignition (SI), compression ignition (CI), homogeneous charge compression ignition (HCCI), and advanced dual-fuel engines such as reactivity-controlled compression ignition (RCCI) engines. Finally, various on-board fuel reforming techniques for syngas production and use in vehicles are reviewed as a potential route towards further increases in efficiency and decreases in emissions of IC engines. These are then related to the research reported on the behavior of syngas and its blends in IC engines. It was found that the selection of the syngas production method, choice of the base fuel for reforming, its physicochemical properties, combustion strategy, and engine combustion system and operating conditions play critical roles in dictating the potential advantages of syngas use in IC engines. The discussion of the present review paper provides valuable insights for future research on syngas as a possible fuel for IC engines for transport.
... Still, considerable scope for improvement in this technology exists which withholds it from widespread adoption. These include hydrocarbon emissions at low and part loads [10], combustion stability [11], high PRR [12], and thermal management for efficient after-treatment [13]. In addition, the diverse production pathways that affect the composition of future fuels, combined with the need for flexible fuel operation, position H 2 in an admixed form as a promising solution to address the identified challenges. ...
Hydrogen (H2) admixing in Reactivity Controlled Compression Ignition (RCCI) technology engines is touted to enhance indicated efficiency (ITE>50%), optimize combustion and reduce greenhouse gas emissions. However, many pending issues remain regarding engine durability, nitrogen oxide (NOX) emissions and blending limits. These issues are addressed by employing a novel performance-oriented model which simulates under 3 min, combustion physics with similar predictivity (>95% accuracy) as computational fluid dynamic results. This so-called multizone model is parameterized to real-world operating cycles from a dual-fuel mid-speed marine engine. By considering port-fuel injected H 2 , the simulations show that combustion phasing advances at an average rate of 0.3⁰CA/% H 2 , accompanied by a peak reduction in methane slip of 80% achievable at 25% H 2 energy share. Also, engine control-oriented issues are addressed by demonstrating either intake temperature or diesel fuel share optimization to negate the drawbacks of combustion harshness and NO X emissions, while improving ITE 1-1.5pp over baseline operation. Nomenclature Abbreviations BR Blend ratio CA50 Crank angle at 50% energy released CFD Computational fluid dynamics CHR Cumulative heat release CL Combustion losses HCCI Homogeneous charge compression ignition HRF High reactivity fuel HRR heat release rate iEGR Internal exhaust gas recirculation IMEP indicated mean effective pressure IMEP720 net indicated mean effective pressure IMO International maritime organization ISx Indicated specific quantity (x: fuel, NO X , UHC) ITE Indicated thermal efficiency IVC Intake valve closing LFO Light fuel oil LHV Lower heating value (continued on next column) (continued) Abbreviations LRF low reactivity fuel LTC low temperature combustion MPRR Maximum pressure rise rate MZM Multizone model NG Natural gas NHR net heat released NOX Oxides of nitrogen PCCI Premixed charge compression ignition PMEP pumping mean effective pressure pp Percentage points PRR pressure rise rate RCCI Reactivity controlled compression ignition RMSE root mean square error SE Standard error SOC Start of combustion SOI Start of injection TDC top dead centre TDR Turbulent dissipation rate (continued on next page)
... Simultaneously, longer mixing time and therefore a more homogeneous air-fuel mixture, can effectively reduce the proportion of diffusion combustion, allowing for control of soot emission [5]. But this combustion control is not straightforward because ignition and combustion onsets are determined indirectly by fuel reactivity or thermal stratification [6]. The dual-fuel concept of RCCI excels over the mentioned LTCs as combustion can be controlled in a fast, cycle-by-cycle manner by changing the blend ratio (BR) between high-and low-reactivity fuels (further referred to as HRF and LRF respectively). ...
Hydrotreated vegetable oil (HVO) is becoming a widely accepted renewable drop-in alternative fuel to diesel. However, conventional diesel combustion does not fully exploit HVO's superior physicochemical parameters. Its high cetane index should significantly improve the performance and emission of next-generation, dual-fuel, reactivity-controlled compression ignition (RCCI) engines. These have a promising future in marine and off-road sectors. This study is the first comprehensive verification of HVO's benefits towards achieving superior RCCI combustion with natural gas. It used a sophisticated, single-cylinder research engine with a fully controllable air/ fuel paths, calibrated in conventional compression ignition mode. The calibration experiments in a corresponding RCCI setpoint covered the cross-sensitivity of high-reactivity fuels (HVO and diesel) to boost pressure, excess air ratio, exhaust gas recirculation and start of injection, investigated at 85 % and 93 % energy-based blending ratios with natural gas. Extensive measurement instrumentation provided combustion and emission characterisation, enabling observations regarding both the phenomenology and applied potential of HVO-activated RCCI. Best performance was observed at the boundary of mixture dilution, restricted by the misfire or combustion variability limits. High reactivity of HVO allows for extending combustion stability limits, enabling increasing both, the local dilution (earlier injection timings) and the global dilution (higher mixture strengths or higher exhaust recirculation ratios). Calibrated along these phenomenological outcomes, HVO and diesel allow achieving efficiency over 2 percentage points superior in RCCI mode, compared to conventional diesel reference. With HVO, RCCI can be calibrated to comfortably meet EPA Tier 4 emission limits in all legislated species, without aftertreatment. Particular merits are in NO X reduction, for which the best case HVO-RCCI tested at 0.7 g/kWh vs 2.8 g/kWh of diesel-RCCI. HVO further cuts down methane slip by more than 45 %, while PM emissions for RCCI are generally measured ultra-low. Corresponding conventional diesel reference exceeds the EPA NO X and PM limits by respectively 1500 % and 400 %.
... In the dual-fuel combustion mode known as Reactivity Controlled Compression Ignition (RCCI) [16], ammonia is considered an effective method for engine application. The RCCI mode blends high-octane fuel with low-octane fuel. ...
The combustion of diesel fuel in internal combustion engines faces challenges associated with excessive emissions of pollutants. A direct solution to this issue is the incorporation of cleaner energy sources. In this study, a numerical model was constructed to investigate the characteristics of ammonia–diesel dual-fuel application in a medium-speed diesel engine. Effects of ammonia–diesel blending ratios on engine performance and emissions were investigated. The results indicate that for this engine model, the optimal diesel energy ratio is about 22%. When the diesel energy ratio is less than 22%, the engine’s output performance is significantly affected by the diesel energy ratio, while above 22%, the influence of the intake becomes more pronounced. When the diesel energy ratio is below 16%, the cylinder cannot reach combustion conditions. Diesel energy ratios below 22% can cause ammonia leakage. With increasing diesel energy ratio, the final emissions of carbon oxides increase. With a higher diesel energy ratio, NO emissions become lower. When the diesel fuel energy ratio exceeds 22%, the N2O emissions can be almost neglected, while below 22%, with poor combustion conditions inside the cylinder, the N2O emissions will increase.
... Numerous research centers have conducted experiments to demonstrate the effectiveness of various combustion strategies, including pre-chamber combustion [3,4], Homogeneous Charge Compression Ignition (HCCI) [5,6], and Reactivity Controlled Compression Ignition (RCCI) [7][8][9][10][11][12]. These strategies, combined with innovative methodologies and low-cost sensors for cylinder-to-cylinder combustion phase control [13][14][15], have exhibited high fuel conversion efficiencies and low emissions [16][17][18][19][20][21][22][23][24]. Given these circumstances, a research initiative has been conducted by a collaboration between the University of Alabama and the University of Bologna aimed at exploring the potential of an ultra-low emissions combustion methodology, the Reactivity Controlled Compression Ignition (RCCI), during idling engine conditions in a heavy-duty single cylinder research engine [25,26]. ...
In the field of internal combustion engines, the Low Temperature Combustions (LTC) appear to have the potential to reduce the formation of both soot and nitrogen oxides. One of the most promising LTC is Reactivity Controlled Compression Ignition (RCCI) which is based on the combustion of a lean low reactivity fuel-air mixture generated in the intake manifold and autoignited by small injections of high reactivity fuel introduced at high pressure in the combustion chamber. By the combination of net-zero natural gas and biodiesel, such LTC methodology might represent a suitable solution moving toward zero-emissions in transportation sector.
Despite the potential to reduce pollutant emissions, Low Temperature Combustion strategies face a challenge in controlling the angular position where the combustion takes place which can be overcome by a proper management of the high-pressure injections.
One potentially interesting application is related to trucks, mainly because they have long periods of idling, since emissions can be drastically reduced by means LTC. A single cylinder research engine for heavy duty application is operated under steady state conditions at low load and speed to analyze the possibility of controlling the engine behavior in dual fuel RCCI mode. The results indicate that the combustion mode switches from the dual-stage to gaussian within a narrow angular range. A further advance of the start of injection can generate misfires and significant variations in typical combustion indexes, while a delayed start of injection can cause impulsive combustion that rises the cylinder temperature and results in high-frequency pressure oscillations inside the combustion chamber. These oscillations are related to the combustion chamber typical resonance frequency, and if relevant in amplitude and persist for a long time, they might generate a potential source of failures.
... Some of the most promising techniques are low-temperature combustions (LTC), and in particular dual fuel (DF) and reactivity controlled compression ignition (RCCI). These techniques are able to deliver at the same time ultra-low NO x and soot emissions and excellent brake thermal efficiency (BTE) [5,6]. LTC can be implemented also adopting low-carbon and renewable fuels, merging the advantages in terms of regulated emissions and GHGs. ...
div>The numerical study presented in this article is based on an automotive diesel engine (2.8 L, 4-cylinder, turbocharged), considering a NG–H2 blend with 30 vol% of H2, ignited by multiple diesel fuel injections. The 3D-CFD investigation aims at improving BTE, CO, and UHC emissions at low load, by means of an optimization of the diesel fuel injection strategy and of the in-cylinder turbulence (swirl ratio, SR). The operating condition is 3000 rpm – BMEP = 2 bar, corresponding to about 25% of the maximum load of a gen-set engine, able to deliver up to 83 kW at 3000 rpm (rated speed). The reference diesel fuel injection strategy, adopted in all the previous numerical and experimental studies, is a three-shot mode. The numerical optimization carried out in this study consisted in finding the optimal number of injections per cycle, as well as the best timing of each injection and the fuel mass split among the injections. The analysis revealed that combustion can be improved by increasing the local concentration of the more reactive fuel (diesel): in detail, the best strategy is a two-shot mode, with SOI1 = −35°CA AFTDC and SOI2 = −20°CA AFTDC, injecting 70% of the total diesel fuel mass at the first shot. As far as the SR is concerned, the best compromise between performance and emissions was found for a relatively low SR = 1.4. The optimization permitted to extract the full potential of the H2 enrichment in the DF H2/NG–diesel combustion also at low loads: in comparison to the DF NG case, combustion efficiency, and gross indicated thermal efficiency have been improved by 45.7% and 61.0%, respectively; CO- and UHC-specific emissions have been reduced by about 85.0%. Comparing CDC to the optimized DF 30 vol% H2/NG–diesel case, soot emissions are completely canceled, CO2-specific emissions have been reduced by approximately 42.0%, NOx-specific emissions by 33.8%. However, further work has to be done in order to reach comparable values of HC and CO, which are still higher than in a standard diesel combustion.</div
... T he transport industry is highly dependent on the use of fossil fuels for its energy demands [1]. This is attributed to the use of thermal engines for the combustion of liquid fuels to convert the produced thermal energy into useful mechanical energy or work [2]. However, combustion of carbon-based fossil fuels emits carbon dioxide (CO 2 ), which is a greenhouse gas (GHG) [3]. ...
div class="section abstract"> The transportation industry has been scrutinized for its contribution towards the global greenhouse gas emissions over the years. While the automotive sector has been regulated by strict emission legislation globally, the emissions from marine transportation have been largely neglected. However, during the past decade, the international maritime organization focused on ways to lower the emission intensity of the marine sector by introducing several legislations. This sets limits on the emissions of different oxides of carbon, nitrogen and sulphur, which are emitted in large amounts from heavy fuel oil (HFO) combustion (the primary fuel for the marine sector). A 40% and 70% reduction per transport work compared to the levels of 2008 is set as target for CO2 emission for 2030 and 2050, respectively. To meet these targets, commonly, methanol, as a low-carbon fuel, and ammonia, as a zero-carbon fuel, are considered. But for the well-being of the marine ecosystem, nitrogen and sulphur oxides, emitted from ammonia combustion, are more harmful due to their acidification and eutrophication impacts. Thus, the evaluation of the emission impact and the production cost must be done for the different production pathways of both fuels to estimate the most efficient way for a sustainable transition of marine transportation. Therefore, in this study, a well-to-wake enviromental and techno-economic analysis of methanol and ammonia is done to evaluate the most feasible pathway to meet those targets. Results show that, despite methanol’s carbon-based fuel nature, it is a more sustainable option for the shipping sector in terms of meeting the emission reduction targets as well as having a lower impact on the hydrosphere.
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... Reactivity-controlled compression ignition (RCCI) [19][20][21][22][23][24][25][26][27] and dual fuel low temperature combustion (LTC) [28][29] are dual fuel combustion strategies that demonstrate the ability to achieve drastic NOx emissions reduction. ...
Dual fuel combustion leverages a high-reactivity fuel (HRF) to ignite a premixed low reactivity fuel (LRF)–air mixture to achieve high efficiencies and low engine-out emissions. The difference in the relative amounts of these fuels and in-cylinder fuel reactivity stratification profoundly impacts dual fuel combustion. The effect of increasing LRF energy substitution on dual fuel combustion at various fixed HRF (diesel) quantities was experimentally studied for two different LRFs (natural gas and propane) on a heavy-duty single cylinder engine at a constant intake pressure of 1.5 bar and injection pressure of 500 bar. Further, this effect was studied for three different HRF start of injection (SOI) timings of 310 CAD (50° BTDC), 330 CAD (30° BTDC), and 350 CAD (10° BTDC). For 310 CAD SOI, increasing the LRF substitution at a fixed HRF resulted in higher loads, peak cylinder pressures, and peak apparent heat release rates (AHRR). The onset of low temperature heat release (LTHR) was advanced as the LR fuel flowrate increased at a given pilot quantity for diesel–NG but remained constant for diesel–propane dual fuel combustion at these SOIs due to the impact of propane on the temperature at which the onset of LTHR occurs. The indicated fuel conversion efficiency (IFCE) ranged from 35% at 4 bar IMEPg to 47% at 9 bar IMEPg with NG as the LRF and from 35% at 3 bar IMEPg to 51% at 8 bar IMEPg with propane as the LRF. For 330 CAD SOI, the HC and CO emissions decreased at a higher fixed HRF quantity and an increasing LRF substitution. However, this was accompanied by significantly higher oxides of nitrogen (NOx) emissions for both NG and propane as LRFs. For 350 CAD SOI, increasing the LRF substitution at constant HRF consistently led to a higher second stage AHRR, whereas the first stage AHRR remained relatively unchanged for both NG and propane as LRFs. This was accompanied by higher IFCE for all fixed HRF quantities as LRF substitution was increased. For all SOIs studied, the HC and CO emissions were substantially lower and combustion stability was significantly improved as the LRF substitution (and consequently, the load) was increased. To the best of the authors’ knowledge, the present work is unique in that it involves the first systematic experimental study of the impact of LRF energy substitution at fixed HRF quantities over a range of SOIs, providing comparative results for two different LRFs (NG and propane) on the same engine platform.
... Nad tym problemem w wielu badaniach bardzo wnikliwie skupia się profesor Rolf Reitz, m.in. w [76], gdzie pochyla się nad systemem sterowania silnikiem, lub w innych pracach, gdzie szczegółowo opisuje problemy, z jakimi muszą się zmagać konstruktorzy tych silników, np. w [77], gdzie szczegółowo została także opisana problematyka kształtu komory spalania takiego typu silnika. ...
The article presents synthetically the methods of ignition of the air-fuel mixture in Internal
Com-bustion (IC) engines along with the characteristics of their advantages and disadvantages, the
problems of their use and the possibility of development. The further development of piston engines
will require a drastic reduction in the emission of harmful exhaust components and carbon dioxide,
which is the most important greenhouse gas emitted by IC engines. For this reason, not only the
engines themselves must be changed but fuels as well. For the most effective use of them, self-ignition of
a homogeneous fuel-air mixture should be implemented. In the present state of technical development is
not possible to widespread use the most ad-vanced ways of self-ignition methods. Typical homogeneous
charge compression ignition (HCCI), where an engine uses only one type of the fuel and correctly
self-ignite in the full scope of work is still not implemented in a serial production.
In the foreign literature, there is a significant number of publications on various methods of Compression
Igni-tion (CI) in IC engines, including IC in Dual Fuel (DF) engines. The Polish literature, however,
is extremely sparse in this matter, and one can find a number of works on CI in single-fuel engines
[1-10], but the topic of DF fueling is not too extensively described. For this reason, it seems important
to publish an article on this important topic today.
Keywords: internal combustion engines, CI engines, homogeneous mixture, dual-fuel engines, RCCI,
DUAL FUEL, HCCI, ENGINES, PCCI, PPCI, PCI, SPCCI, SACIThe article presents synthetically the methods of ignition of the air-fuel mixture in Internal
Com-bustion (IC) engines along with the characteristics of their advantages and disadvantages, the
problems of their use and the possibility of development. The further development of piston engines
will require a drastic reduction in the emission of harmful exhaust components and carbon dioxide,
which is the most important greenhouse gas emitted by IC engines. For this reason, not only the
engines themselves must be changed but fuels as well. For the most effective use of them, self-ignition of
a homogeneous fuel-air mixture should be implemented. In the present state of technical development is
not possible to widespread use the most ad-vanced ways of self-ignition methods. Typical homogeneous
charge compression ignition (HCCI), where an engine uses only one type of the fuel and correctly
self-ignite in the full scope of work is still not implemented in a serial production.
In the foreign literature, there is a significant number of publications on various methods of Compression
Igni-tion (CI) in IC engines, including IC in Dual Fuel (DF) engines. The Polish literature, however,
is extremely sparse in this matter, and one can find a number of works on CI in single-fuel engines
[1-10], but the topic of DF fueling is not too extensively described. For this reason, it seems important
to publish an article on this important topic today.
Keywords: internal combustion engines, CI engines, homogeneous mixture, dual-fuel engines, RCCI,
DUAL FUEL, HCCI, ENGINES, PCCI, PPCI, PCI, SPCCI, SACI
... WER can be implemented through thermomechanical regeneration (no chemical reactions), such as organic Rankine cycle (ORC) [39,40], Brayton cycle [41], turbocharger [42], etc. WER also can be employed using thermochemical regeneration, such as fuel reforming (with chemical reactions). This wasted thermal energy (exergy), can be reduced in advanced combustion strategies like homogeneous charge compression ignition (HCCI) [43] or reactivity-controlled compression ignition (RCCI) [44,45] (see Fig. 1), since these combustion strategies have lower exergy destruction than conventional diesel combustion due to higher proportions of premixed combustion with more homogeneous in-cylinder distributions of equivalence ratio and gas temperature [46,47]. The exergy destruction related to the combustion occurring inside the engine cylinder will be discussed in the following paragraph. ...
There has been a growing demand to develop new energy conversion devices with high efficiency and very low emissions for both power and propulsion applications in response to the net zero-carbon emission targets by 2050. Among these technologies, solid oxide fuel cells (SOFCs) have received attention due to their high electrical efficiency (above 60%), fuel flexibility, low-emission, and high-grade waste heat, which makes them particularly suitable for a large number of applications for power and propulsion systems. The higher operating temperatures make SOFCs suitable candidates for integration with an additional power generation device such as an internal combustion engine (ICE) by (a) using the residual fuel of the anode off-gas in the engine, which further increases overall system efficiency to values exceeding 70%, (b) decreasing combustion inefficiencies and (c) increasing waste heat recovery. This paper reviews the published work on hybrid SOFC-ICE systems considering various configurations. It has been found that integrated SOFC-ICE systems are promising candidates over conventional engines and stand-alone SOFCs to be used in stationary power generation and heavy-duty applications (e.g., marine and locomotive propulsion systems). The discussion of the present review paper provides useful insights for future research on hybrid electrochemical-combustion processes for power and propulsion systems.
... Researchers propose several technical solutions to improve the performance, emission, and combustion characteristics of Hoang et al. Fuel xxx (xxxx) 124981 diesel engines, as illustrated in Fig. 1, including the modification of the design of the engines [7,8], the change in the operational parameters [9,10], the use of low-temperature combustion mode (such as Premixed Charge Compression Ignition [11,12], Homogeneous-Charge Compression Ignition [13,14], Reactivity Controlled Compression Ignition [15,16]), the improvement of combustion quality [17], and the installation of additional systems for exhaust treatment [18]. Among these, engine combustion and performance adjustment is the most popular approach due to its simplicity compared to changing engine designs or utilizing additional equipment. ...
In recent years, searching for efficient solutions to improve the emission and performance characteristics of diesel engines is considered as one of the essential and urgent work. Metal nanoparticles with a large surface area and high heat transfer coefficient could provide the impressive additive ability to the fuel reactivity and atomiza-tion. Therefore, the critical role of metal nanoparticles in the support of diesel engine behaviors using biodiesel and diesel is thoroughly evaluated in this current review. Indeed, preparation methods and critical properties of metal nanoparticles and metal nanoparticles-laden fuels are fully introduced. More importantly, the performance, combustion, emission characteristics, and tribology behaviors of diesel engines running on metal nanoparticles-laden biodiesel are compared to diesel fuel in detail. Generally, metal nanoparticles-included biodiesel facilitates the formation of a more homogeneous oxygen-containing mixture of fuel-air, resulting in a more complete combustion process than that of diesel fuel. As a result, the use of biodiesel with the presence of metal nanoparticles is considered as the potential strategy for promoting spay and atomization, enhancing the combustion process, increasing brake thermal efficiency (BTE), reducing toxic emissions (including carbon monoxide (CO), unburnt hydrocarbon (HC), and smoke), and improving tribology characteristics. However, some drawbacks are also indicated, such as increased NOx emission and brake-specific fuel consumption. In addition, it is also concluded that studies on other environmental impacts (such as PM emission), the stable properties of metal nanoparticles, and economic aspects should be made more extensively before commercial applications of metal nanoparticles in the real world.
... The RCCI combustion strategy was introduced to overcome the drawbacks of HCCI combustion, such as limited operating range and difficulties in control over combustion [6,7]. The RCCI combustion demonstrates excellent commercial viability in automotive applications along with hybrid electric vehicles [8]. In the RCCI combustion strategy, a low reactivity fuel (gasoline-like fuels) is injected in the intake manifold during suction stroke along with air, and a high reactivity fuel (diesellike fuels) is injected directly into the cylinder. ...
This study uses nonlinear dynamical and chaotic methods to investigate the cyclic combustion dynamics of a CNG-Diesel reactivity control compression ignition (RCCI) engine. The experiments of RCCI combustion mode are conducted on a single-cylinder automotive diesel engine with the development ECU. Low reactivity fuel (i.e., CNG) is injected into the intake manifold, and high reactivity fuel (i.e., diesel) is injected directly into the engine cylinder during the RCCI experiments. Mass of fuel injection per cycle and their injection events are controlled by using ECU. The engine is tested for fixed engine load and speed of 3 bar BMEP and 1500 rpm, respectively. A double diesel injection strategy is used for injecting the diesel fuel into the engine cylinder. In-cylinder pressure is measured using a piezoelectric pressure transducer on a crank angle basis with a resolution of 0.1 CAD. Combustion parameters are calculated on a cyclic basis from measured in-cylinder pressure. In this study, the effect of diesel injection timing (SOI-2) on the behavior of combustion dynamics for two different masses of port-injected CNG fuel (mc) is investigated. The CA50 time series of 1000 consecutive engine cycles is analyzed for combustion dynamics analysis using symbol sequence analysis, return maps, recurrence plots (RPs), recurrence quantitative analysis (RQA), and 0–1 test. The peaks in symbol sequence histograms and the corresponding symbol series depict the period-2 nature of the cyclic combustion dynamics at the intermediate SOI-2 of 30° and 40° bTDC. Return maps also confirm the onset of noisy period-2 bifurcation at 30° bTDC SOI-2. The dominance of deterministic period-2 characteristics is found in the cyclic combustion dynamics at 30° and 40° bTDC SOI-2 using recurrence plots. The 0–1 test method depicts stronger chaotic cyclic combustion dynamics at 20° and 50° bTDC SOI-2. In summary, the present study supports the existence of a periodic window in between the chaotic combustion for the intermediate values of SOI-2. The dominance of the deterministic characteristics makes this regime of intermediate SOI-2 values suitable for a better cycle resolved control.
... RCCI-DF combustion (either PFI or DI mode of MeOH) allows an explicit control of mixture's in-cylinder reactivity stratification by adopting various fuel injection strategies. This is generally considered an advantageous procedure for improving combustion efficiency together with low NO x and soot emissions [25][26][27][28]. Duraisamy et al. [29] studied single pilot (SOI = -10 CA ATDC) MeOH-diesel PFI-RCCI combustion to explore the effects of MSR and hot/cold EGR. ...
Methanol (MeOH) is a promising low-carbon liquid fuel to provide global energy security with a potential to achieve net-zero greenhouse gas emissions in transport sector. However, its utilization in diesel engines at high MeOH substitution ratios (MSR) suffers from misfire or high pressure rise rates owing to its distinct physio-chemical properties. This issue is addressed in the present study by adopting negative-valve overlap (NVO) and hot residual gases from the previous cycle. Experiments are performed in a single-cylinder heavy-duty CI engine for a constant MSR (90% energy based) and an engine speed of 1500 rpm. The aim of the study is to investigate the effects of 1) NVO period, 2) charge-air temperature (T air), 3) MeOH lambda (λ MeOH) on the MeOH-diesel dual-fuel (DF) combustion in NVO mode, and 4) to demonstrate the implications of NVO in yielding high net-indicated efficiency (η ind) together with low pollutant emissions at a wide range of engine operating loads (40-90%). The results show that the hot residual gases from the previous cycle enhance the reactivity of the fresh MeOH-air mixture by inducing slow oxidation processes before TDC f. The slow pre-flame oxidation processes are disruptive or oscillatory in nature, wherein NVO period, T air and λ MeOH can be used to control these processes and their induced reactivity enhancing capability. It is noticed that the pre-flame oxidation processes and the main combustion have a direct correlation between them. Based on the control strategy, the MeOH-diesel combustion in the NVO mode produced on average η ind of approx. 53% accompanied with very low NO x emission of 1.1 g/ kWh at a wide range of engine operating loads (40-90%). Additionally, on average the combustion phasing (CA50) is maintained at ~ 2 o CA aTDC, while the combustion stability remains high (COV IMEP ~ 3.5%).
Biodiesel/n-pentanol blend fuels have been regarded as the attractive alternatives for the utilization of diesel engines. However, the fundamental studies of low temperature combustion and soot formation characteristics of biodiesel/n-pentanol blend fuels in diesel engines are still scarce. The low temperature combustion and soot emission characteristics of pure waste cooking oil (WCO) biodiesel (B100) and 70% WCO biodiesel/30% n-pentanol blend (B70P30) were experimentally studied in an optical engine in the present study. Results reveal that B70P30 has longer ignition delays than B100 at low exhaust gas recirculation (EGR) rate, but the ignition delays of B70P30 become similar or even shorter when the EGR rate is over 12%. Adding n-pentanol into biodiesel increases the in-cylinder combustion pressure peak and maximum pressure rise rate. In addition, the delay in the appearance of ignition kernels and two-color images are observed for B70P30 fuel. In the initial stage of fuel combustion, B70P30 has less ignition kernels and lower soot KL factor distribution area. In the middle and late stages of combustion, flame area of B70P30 is small and flame brightness is weaker. Also, at the end of combustion, the two-color images of B70P30 show that the soot KL factor distribution around the periphery of the chamber is decreasing at a higher rate compare to B100.
Incorporating hydrogen into the fuel blend of ammonia/diesel in reactivity controlled compression combustion (RCCI) engines, while maintaining high indicated mean effective pressure (IMEP) and combustion efficiency (CE), presents a promising approach for mitigating nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), unburnt ammonia emissions and nitrous oxide (N2O) greenhouse gas (GHG)-a pressing challenge in the field. By supplementing ammonia/diesel combustion with hydrogen, potential issues related to incomplete combustion can be mitigated, along with a reduction in intake valve close temperature (TIVC). This study aims to assess the impact of hydrogen enrichment on combustion characteristics in RCCI engines utilizing ammonia and diesel as fuels, employing the kinetic mechanism of combustion reactions within Converge software. The effect of TIVC on key engine parameters, including in-cylinder pressure, heat release rate (HRR), CE, IMEP, and exhaust emissions, are analyzed by considering chemical reaction pathways. The findings reveal that introducing hydrogen into the ammonia /diesel RCCI combustion blend, leads to significant enhancements in CE and IMEP while simultaneously lowering emissions of CO, HC, unburnt ammonia, and N2O greenhouse gas (GHG). Specifically, when utilizing 80 % ammonia energy fraction (AEF) without hydrogen, minimum TIVC of 440 K is necessary to prevent incomplete combustion, increasing NOx emissions by approximately 20 g/kWh. However, by addition of 20 % hydrogen energy fraction (HEF) into the fuel mixture, the TIVC requirement drops to 380 K, thereby reducing NOx emissions to around 13 g/kWh, while maintaining consistent level of N2O GHG (2.7 g/kWh).
Global transport today is mainly powered by the Internal Combustion Engine (ICE) and throughout its century and a half of development it has become considerably more efficient and cleaner. Future prospects of the ICE rely on the scientific work conducted today to keep this trend of higher efficiency and cleaner emissions in new engines going. The aim of this article is to give a comprehensive review of development directions in novel piston engine designs, which seek to overcome the drawbacks of the ubiquitous 4-stroke piston engine. One of the directions of development is devoted to improving the mechanisms and the general layout of the piston engine to reduce losses within the engine. Research teams working with alternative engine work cycles like the 5- and 6-stroke engine and technologies for extracting waste heat seek to reduce thermal losses while novel layouts of valve trains and crank assemblies claim to significantly improve the mechanical and Volumetric Efficiency (VE) of piston engines. These novel ideas include camless or Variable Valve Action (VVA) and engines with Variable Compression Ratio (VCR) or opposed pistons. One alternative approach could also be to totally redesign the reciprocating mechanism by replacing the piston with some other device or mechanism. Additional scientific work is investigating Low Temperature Combustion (LTC) technologies such as Turbulent Jet Ignition (TJI) and Homogeneous Charge Compression Ignition (HCCI) and its derivatives like Premixed Charge Compression Ignition (PCCI) and Reactivity Controlled Compression Ignition (RCCI) that have shown improvements in thermal and fuel conversion efficiency while also significantly reducing harmful emissions. These combustion strategies also open the path to alternative fuels. The contemporary work in the combustion engine fields of research entail technical solutions from the past that have received a modern approach or are a completely novel idea. Nonetheless, all research teams work with the common goal to make the piston engine a highly efficient and environmentally friendly device that will continue to power our transport and industry for years to come. For this, solutions must be found to overcome the mechanical limitations of the traditional layout of the piston engine. Similarly various improvements in combustion technology are needed that implement state of the art technology to improve combustion characteristics and reduce harmful emissions.
Experimental results of the split injection were compared to single injection dual-fuel and conventional diesel
operation. Single injection case resulted in slightly lower HC emissions and cyclic variations and higher NOx
emissions than split cases in a narrow injection timing interval. Apart from that, split injections increased
combustion efficiency and decreased cyclic variations in a broader timing interval. For split cases, early first
injection timing prevented high premixed heat release peak, suppressed NOx emissions and knocking. Especially,
using 70% split ratio with retarded second injections increased combustion efficiency, decreased knocking level
and provided simultaneous reduction of HC and NOx emissions compared to lower split ratio cases. In short,
despite not giving the minimum values at all conditions, split injection showed potential to find a remedy to high
HC emissions and cyclic variations issues by keeping robust operation in a wider injection timing interval.
The numerical results support the experiments in which better combustion and decreased HC emissions are
attained using sufficiently early diesel injections. Simulations show that, compared to late single injection, early
single injection dual-fuel case enables more homogeneous temperature distribution and better oxidization of
methane near the cylinder wall and central region above the piston crown. Besides, split injection shows
improved methane oxidation near the cylinder wall and inside top-land crevice volume.
50 days free access link: https://authors.elsevier.com/a/1g~ky3iH4M3Ze
In-cylinder heat release features and nanoparticle emissions have been investigated in this study for CNG–diesel reactivity-controlled compression ignition (RCCI) engine. Study aims to determine the effect of low-temperature heat release (LTHR) and high-temperature heat release (HTHR) on the particles emissions from the RCCI engine. LTHR is obtained as a small peak (curve) before the main HTHR in the heat release rate curve. The LTHR and HTHR are not separated in heat release rate curve. The low-temperature heat release rate (LTHRR) is determined by extracting the heat release between start of combustion (SOC) to the intersection point of slope between LTHR and HTHR. The high-temperature heat release rate (HTHRR) is determined by fitting the trace between the intersection point of slope between LTHR and HTHR to the end of HTHR (the crank angle where the main HTHR turns negative after attaining the peak). This study calculates the amount of LTHR and HTHR by determining the absolute area under the LTHRR and HTHRR trajectories. Experiments are performed for different port-injected CNG masses (mc) and engine loads at a fixed engine speed of 1500 rpm. Single- and double-fuel injection strategy is used for injecting diesel. In the double-injection strategy, two cases are investigated. In the first case, diesel mass is split in the ratio of 50:50% between the first and second injection, whereas in the second case, diesel mass is divided into the proportion of 70:30%. CNG fuel mass, diesel start of injection (SOI), and the number of injections are controlled by engine electronic control unit (ECU). Results indicates that at a lower load with single-injection strategy, the lower amount of LTHR promotes the formation of small particles for 30° bTDC diesel SOI. It is found that increase in mc per cycle results in reduced and delayed LTHR and HTHR. With an increase in mc, the amount of LTHR decreases, and the total PN increases. The reduction in LTHR with an increase in mc leads to an increase in the formation of nucleation mode particles (NMPs) and a decrease in the accumulation mode particles (AMPs).
Due to energy shortage and environmental problems, the application of natural gas in internal combustion engine has attracted extensive attention. Therefore, diesel pilot ignition natural gas engine is a promising technology. However, the different sources of natural gas lead to the change of composition, which has a great impact on engine combustion and emission. In this study, the relationship between Wobbe index (WI), swirl ratio (SR), and the start of diesel injection (SOI) of six different natural gas mixtures was studied by numerical simulation method. Besides, reactivity controlled compression ignition (RCCI) combustion strategy was evaluated. The results showed that increasing the WI increased the in-cylinder pressure and temperature, increased the ignition delay and shortened the combustion duration, the gross indicated efficiency (GIE) of the six gases exceeded 50%. In addition, the increase of WI increased the nitrogen oxides (NOx) emissions, and reduced the hydrocarbons (HC) and carbon monoxide (CO) emissions. Moreover, the peak pressure rise rate (PPRR) increased with the rise of WI, which may lead to engine knock. The results also showed that the increase of SR increased the in-cylinder pressure and temperature and improved the PPRR. When the SR was 0.7 and the WI was 51.7, the combustion and emission performance of the RCCI engine was relatively better. Furthermore, the in-cylinder pressure, temperature, and NOx emission were reduced when the SOI was advance.
Improved combustion and reduction in emissions levels could be achieved with optimization of in-cylinder fuel–air mixing. According to the engine operating condition, the spatial and temporal features of in-cylinder mixture can be flexibly and accurately adjusted by methanol/diesel dual direct injection in real time. Present research investigated the effect of dual direct injection strategy on the operating range, combustion and emissions characteristics of a methanol/diesel dual direct injection engine. The results showed that the limits of the engine operating range could be obtained by observing the unstable and roar combustion in the cylinder when the methanol was injected directly during the intake stroke. The onset of roar combustion provided the upper bound of operating range at the methanol injection timing (SOIM) of − 60 °CA aTDC. High indicated thermal efficiency (ITE) could be achieved accompanied by widening the operating range of the engine. Systematic analysis results of combustion characteristics indicated that the increments of engine load and methanol energy substation ratio (ESR) were conducive to improving the combustion stability of the engine. Because of the reduced diffusion-controlled combustion, the methanol/diesel dual fuel direct injection strategy could realize a relatively low NOx emissions, which were insensitive to the SOIM at low ESR conditions. With the increase of ESR, injecting methanol close to TDC resulted in lower CO and HC emissions, especially at higher engine load conditions. This study confirms that the implementation of dual direct injection strategy has the potential to extend the operating range of a methanol/diesel engine, accompanied with high fuel economy and low emissions.
In this paper, Reactivity Controlled Compression Ignition (RCCI) with an electrically-assisted turbocharger (E-turbo) is investigated. This is a promising concept for future green transport, since it can realize very high thermal efficiencies for a wide range of renewable fuels. The combination of RCCI with an E-turbo requires a new approach to manage the energy flows of the engine due to constraints on the storage of electrical energy. The E-turbo shows most potential to increase the engine's thermal efficiency by improved tracking performance of the desired intake conditions. To exploit the full potential of the E-turbo during transients, a dynamic decoupling feedback controller is designed. A supervisory controller based on Pontryagin's Minimum Principle is composed to maximize the brake thermal efficiency while the battery of the E-turbo remains charge sustaining. The supervisory controller determines setpoints for the feedback controller and ensures therefore optimal engine operation during transients. For the simulated, real-world based transient-cycle, fuel savings of 0.64 [%] are realized by the developed supervisory control, while remaining charge sustaining.
For advanced pre-mixed combustion concepts, Cylinder Pressure-Based Control is a key concept for robust operation. It also opens the possibility for on-line heat release shaping. For cost and time efficient development of these controllers, fast control-oriented combustion models that predict average in-cylinder pressure traces have been proposed. However, they are not able to capture cyclic variations. In this study, a data-based modelling procedure is proposed to predict the in-cylinder pressure trace and cyclic variation during the combustion cycle. The inputs to the model are the in-cylinder conditions at intake valve closing and the fuelling settings. The proposed model is based on experimental data, Principal Component Analysis and Gaussian Process Regression. This new data-driven approach is applied to model the combustion behaviour of a Reactivity Controlled Compression Ignition engine running on Diesel and E85. The resulting model has a root-square-mean-error of average behaviour and cyclic variance of 0.8° and 0.2°² in CA50, 0.1bar and 0.03 bar² in Gross Indicated Mean Effective Pressure, and 0.1% and 0.001 %² in the Gross Indicated Efficiency, respectively.
Due to energy shortages and environmental issues, the application of reactivity controlled compression ignition (RCCI) combustion in internal combustion engines has received extensive attention. Through the verification of the model, RCCI combustion can be accurately simulated. In this study, the combustion and the emission performance of a single-cylinder heavy-duty natural gas/diesel RCCI engine have been optimized through numerical simulation. Six important parameters including start of injection (SOI) timing, intake valve closing temperature, intake valve closing pressure, exhaust gas recirculation (EGR), swirl ratio and spray angle have been investigated. The goal is to meet the requirements of European VI emission regulations while maintaining a high gross indicated efficiency (GIE). A strategy to achieve clean and efficient combustion of RCCI engine is proposed. The results showed that the addition of EGR can effectively reduce nitrogen oxide (NOx) emissions. SOI had the greatest impact on RCCI combustion and emission performance. Earlier SOI can improve the uniformity of the fuel mixture in the cylinder. Under the combined optimization of 6 important parameters, NOx, hydrocarbons and carbon monoxide emissions can meet European VI emission regulations, and fuel consumption can meet Environmental Protection Agency consumption regulations, improving the GIE.
Air pollution has reached critical levels in many major industrial cities, endangering public health, deteriorating the environment, and causing harm to property and landscape. The particulate emissions (PM) from propulsion which contribute to air pollution vary greatly in size and composition, conveying carcinogenic polyaromatic hydrocarbons (PAHs) present on the particle surface. Although it has been found that replacing fossil fuels with renewable oxygen-bearing fuels reduces the mass of PM released, not much is known on how this change in fuel composition affects soot levels, PAH production, and toxicity during the pyrolysis processes that occur in combustion engines. Biofuels such as alcohols, esters, ethers, and ketones are considered to be potentially sustainable alternatives fuels and can be produced by various biological and thermochemical processes from a range of renewable feedstocks. The effects of these oxygenated functional groups on the soot mass and PAHs produced during pyrolysis in a laminar flow reactor were investigated quantitatively in this study. The 16 PAHs identified as priority pollutants by the US Environmental Protection Agency (EPA) were investigated in this research, with particular focus on the probable mechanisms for production of the most carcinogenic PAHs (group B). The oxygenated fuels were pyrolyzed at temperatures ranging from 1050 to 1350 0C under oxygenfree conditions with a constant carbon atom content in nitrogen of 10,000 ppm and at a consistent residence period. Both soot bound PAH collected on filter papers and gaseous PAHs collected on XAD resin were extracted using accelerated solvent extraction (ASE), with PAH identification and quantification carried out using gas chromatography combined with mass spectroscopy (GCMS). An effect of the oxygenated functional groups on soot mass was readily apparent, with consistently lower production of soot by methyl acetate, and which has a higher oxygen to carbon ratio than ethanol, acetone, and diethyl ether. At all temperatures except 1350 0C, methyl acetate pyrolysis yielded much lower GP PAH levels than acetone and diethyl ether, but somewhat higher than that from ethanol pyrolysis. The concentration of PP PAH per unit volume of gas is much lower than the corresponding GP PAH, which suggests that PP PAH that condensed onto particulate surface, subsequently experienced surface reaction and were therefore not recoverable during the extraction process. The production of pyrene via acenaphthylene was found to dominate at higher temperatures for all fuels, regardless of molecular structure. At 11500C the relative abundance of the soot particles was low, however, the toxicity of the soot particles formed was substantially higher at lower temperatures, particularly in the case of pyrolysis of methyl acetate soot.
Our world is experiencing rapid change with high consumption rate of fossil fuel from internal combustion engine usage from all of economy sectors. Reactivity controlled compression ignition (RCCI) engines are capable of producing high thermal efficiency while emitting less NOx and PM. To maximize combustion phasing, duration and magnitude, RCCI engine uses in-cylinder fuel blending with two different reactivity inclination. Using dual-injection strategy, Low Reactivity Fuel (LRF) can be introduce through Port Fuel Injection (PFI) system and Higher Reactivity Fuel (HRF) with greater latent heat of vaporization is injected through Direct Injection (DI) system. The HRF is injected before ignition the premixed fuel occurs through DI combustion chamber. The ignition causes the LRF and HRF mixture to ignite and causes the remaining gas to ignite. In-cylinder temperature and combustion temperature can be reduced because of cool flame effects. This paper will review the effect of PFI using gasoline, alcohol and natural gas and DI strategy where diesel, biodiesel is used. NG and alcohol fuel combination with one constant HRF offer more reactivity inclination compared to gasoline. Thus, in term of the engine management strategies, effect of engine advance and retard timing, injector pressure and various direct injection pulse also being reviewed. Higher fuel injection pressure leads to better combustion and fuel atomization. To date, research on the RCCI engine mode had conclude that with low and medium engine load, engine will able to produce almost 60% thermal efficiency and emitted lower NOX and PM emissions in comparison to a conventional diesel engine.
Due to the excellent physicochemical properties, coal to liquid (CTL) is suitable for use as an alternative fuel in internal combustion engines. It is conducive to promoting efficient and clean utilization of coal. In this study, the experiment of using CTL and conventional diesel as pilot fuel and gasoline as the premixed fuel was carried out on a modified dual-fuel engine. The combustion boundary conditions, including gasoline ratio, intake flow rate, and intake temperature, were modulated at an engine speed of 1400 rpm and under low load. The combustion parameters and emission characteristics were fully discussed. The results show that both gasoline/CTL reactivity controlled compression ignition (RCCI) mode and gasoline/diesel RCCI mode contain low temperature heat release (LTHR) and high temperature heat release (HTHR) phases. Among them, the gasoline/CTL RCCI mode has a higher proportion of LTHR, and the low-temperature combustion occurs later than gasoline/diesel. Besides, the ignition delay (ID) of gasoline/CTL RCCI mode is generally shorter, and CA50 is more forward than that of gasoline/diesel RCCI. Compared with gasoline/diesel RCCI mode, the intake air flow has a more significant effect on the indicated thermal efficiency (ITE) and particle emissions of gasoline/CTL RCCI. In particular, the problem of high accumulation mode particles brought by the CTL can be solved by appropriately increasing the intake flow rate. There is an optimal intake temperature for the ITE of gasoline/CTL RCCI mode, while the ITE of gasoline/CTL RCCI mode remains almost constant as the intake temperature increases. Compared with diesel, when using high cetane number (CN) CTL as a pilot fuel, the combustion is more stable, and the ITE of that at each operating condition is about 3% higher. Under optimum intake conditions, the gasoline/CTL RCCI mode achieves higher thermal efficiency and products lower CO, HC, and particle emissions, but NOx emissions increase slightly.
The behaviors of spray, in Reactivity Controlled Combustion Ignition (RCCI) dual fuel engine and subsequent emissions formation, are numerically addressed. Five spray cone angles ranging between 5° and 25° with an advanced injection timing of 22° Before Top Dead Center (BTDC) are considered. The objective of this paper is twofold: (a) to enhance engine behaviors in terms of performances and consequent emissions by adjusting spray cone angle and (b) to outcome the exergy efficiency for each case. The simulations are conducted using the Ansys-forte tool. The turbulence model is the Renormalization Group (RNG) K-epsilon, which is selected for its effectiveness in strongly sheared flows. The spray breakup is governed by the hybrid model Kelvin–Helmholtz and Rayleigh–Taylor spray models. A surrogate of n-heptane, which contains 425 species and 3128 reactions, is used for diesel combustion modeling. The obtained results for methane/diesel engine combustion, under low load operating conditions, include the distribution of heat transfer flux, pressure, temperature, Heat Release Rate (HRR), and Sauter Mean Diameter (SMD). An exergy balance analysis is conducted to quantify the engine performances. Output emissions at the outlet of the combustion chamber are also monitored in this work. Investigations show a pressure decrease for a cone angle θ = 5° of roughly 8%, compared to experimental measurement (θ = 10°). A broader cone angle produces a higher mass of NOx. The optimum spray cone angle, in terms of exergy efficiency, performance, and consequent emissions is found to lie at 15° ≤ θ ≤ 20°.
For the requirements of rigorous CO2 and emissions regulations, the water injection technique is a promising solution to improve fuel economy. The establishment of an optimum water injection strategy is still a challenge when this technique is applied as a method of thermal efficiency enhancement. The present study proposes an evaluation index for the energy conservation potential of water injection strategies, which optimizes water consumption and minimizes the negative influence on energy conservation. An evaluation approach based on Brent’s method is adopted to search the optimum combination parameters of objection function, in which constraints consider fuel cost, usage cost, and space cost. A comprehensive vehicle dynamics model is established and validated to evaluate the energy conservation potential of proposed water injection strategies. The results present the proposed index provides an effective approach to assessing the trade-off relationship between water and fuel consumption. The fuel cost strategy improves fuel economy by 5.2% along the WLTC driving cycle, but this strategy consumes a large amount of water (1.08 L/100 km). In contrast, the proposed usage and space cost strategies save water consumption to 0.58 L/100 km and 0.29 L/100 km, respectively, although their ability to fuel conservation reduces to 4.8% and 4.5%, correspondingly. The comparison results provide considerable guidance on the selection of water injection strategies for vehicle designers and customers according to their purposes and demands.
Apart from electric vehicles, emissions targets for 2025 and 2030 in the heavy-duty transportation sector could be achieved with hybrid powertrains. Moreover, alternatives such as the use of synthetic or e-fuels may also offer a feasible path for transport decarbonization. This work explores different pathways to reduce CO₂ emissions considering the city of Valencia as a case study. The 10 most used bus lines operating in the city are evaluated using their GPS based vehicle speed information with 0D GT Suite simulations. First, the hybridization level for the share of buses was varied from 0 to 100% and the number of different bus types operating in each line was optimised for minimum CO2. Next, the battery and E-motor sizing is optimised for each bus line. Further, an assessment was done assuming 100% electrified fleet, with the 2030 and 2050 electricity generation CO2 footprint projections. Moreover, the potential of e-fuels in the current fleet is also evaluated. The results show that to meet the 2050 target, 100% electrified fleet (with 2050 electricity mix) as well as using e-fuels (generated from renewable sources) in the current fleet are feasible options. However, the e-fuel pathway is more economical than 100% electric fleet.
The present work focuses on the development and validation of a CFD simulation setup of diesel-methane dual fuel combustion in a single-cylinder research engine (SCRE). The validated setup is used to provide insight about dual fuel combustion at low-load operation. The computational campaign consisted of evaluating three different diesel injection timings of 310, 320, and 330 CAD at a methane percent energy substitution (PES) of 80%, 5.1 bar gross IMEP, 500 bar diesel injection pressure, and 1.5 bar manifold air pressure where 360 CAD corresponds to firing top dead center. The computational setup ability to capture combustion, performance, and emissions trends accurately is demonstrated by good agreement with experimental data. The validated setup is further utilized to provide insights into the nature of dual fuel combustion, particularly, the effect of methane on diesel autoignition. Analysis of the computational results showed that the onset of both low-temperature heat release and high-temperature heat release of n-dodecane (the chemical surrogate used for diesel) is delayed by the presence of methane in the system. For early diesel injection in a dual-fuel engine at low-load, initial high-temperature combustion arises from the burning of n-dodecane followed by methane combustion. Most of the methane present in the piston compression ring crevices, areas near the piston top and the liner, remained unreacted after combustion is done. The effect of diesel and methane fuel amount on engine performance at low-load was also explored.
Reactivity controlled compression ignition (RCCI) strategy uses two different fuels with different reactivities which provides more control over the combustion process and has the potential to dramatically lower combustion temperature and NOX and PM emissions. The objective of the present study is to numerically investigate the impact of syngas composition on the combustion and emissions characteristics of an RCCI engine operating with syngas/diesel at constant energy per cycle. For this purpose, different syngas compositions produced through gasification process have been chosen for comparison with the simulated syngas (mixture of hydrogen and carbon monoxide). The results obtained indicate that using syngas results in more soot, CO and UHC emissions compared with simulated syngas. Even though more NOX reduction can be achieved while operating with syngas, the engine could suffer from poor combustion and misfire at low loads due to the presence of nitrogen in the mixture. In terms of exergy, both syngas mixtures lead to more exergy destruction by the increase of syngas substitution. Nevertheless, the magnitude of exergy destruction for simulated syngas is less than the normal syngas.
Reactivity controlled compression ignition (RCCI) engines suffer from low thermal efficiency at low loads due to the high hydrocarbon and carbon monoxide emissions. Correspondingly, a direct dual fuel stratification (DDFS) combustion mode is investigated by directly injecting methanol and diesel into cylinder. Multi-objective optimization and detailed comparison are first conducted for the two engine strategies. Compared to RCCI, the optimized DDFS case shows higher thermal efficiency, lower emissions, lower demand for the in-cylinder initial temperature, and higher potential of energy recovery. Different from the single-stage combustion in RCCI, DDFS shows a two-stage combustion, the second stage of which is owing to its near-top dead center injection of methanol. Compared to RCCI, DDFS requires a lower initial temperature to retard combustion phasing, and a larger amount of exhaust gas recirculation rate to control nitrogen oxide and ringing intensity. The optimized methanol fraction and injection timings of diesel are similar for RCCI and DDFS, and they are determined in compromise of combustion efficiency and heat transfer loss. A large spray-included angle of diesel injector is preferable for RCCI to target diesel spray to the piston lip. In DDFS, a small spray-included angle of diesel injector is needed for more complete fuel oxidation, and a medium spray-included angle of methanol injector is required to avoid excessive heat transfer loss. Due to the non-sooting nature of methanol, DDFS produces as low soot emissions as RCCI. The present study shows that the co-optimization of operating parameters and fuel properties offers a promising approach to meet the more stringent regulation on efficiency and emission.
Dual-fuel reactivity controlled compression ignition combustion offers potentially superior overall efficiency and ultra-low nitrogen oxides and soot emissions. Using natural gas as the low reactivity fuel also provides high knock-resistance and carbon dioxide emission reduction. However, the concept suffers from relatively low combustion efficiency at low engine loads, causing unacceptable methane slip. This study tackles this issue, applying numerical simulations to investigate the application of negative valve overlap to improve combustion efficiency of reactivity controlled compression ignition at low engine loads. The objective is modification of in-cylinder thermal and chemical state before combustion, by varying timing and amount of fuel injected directly into the recompressed hot exhaust gases. The study uses TNO's multi-zone, chemical kinetics-based combustion model with variable valve actuation functionality. The simulation is based on two experimentally validated cases: an uncooled exhaust gas recirculation strategy and a lean burn concept. In both cases, negative valve overlap elevates in-cylinder temperature and cuts methane emissions by 15%, without combustion optimization. Crucially, it enables peak exhaust recompression temperatures above 850 K, sufficient for diesel reforming/ oxidation. The lean RCCI strategy takes greater advantage of fuel reforming than the exhaust gas recirculation case. Optimum conditions give almost 99% combustion efficiency and ultra-low methane emissions. Net indicated efficiency is 40.5% (@15% load), despite negative valve overlap's substantial pumping losses. Low-load net efficiency is 5.5 percentage points above the lean strategy baseline and 3 pp. better than the exhaust gas recirculation baseline. This strategy is considered applicable on state-of-the-art dual-fuel gas engines without hardware changes.
Reactivity Controlled Compression Ignition (RCCI) is commonly mentioned as a potential efficient and clean combustion concept. This study makes the first evaluation of natural gas-diesel RCCI combustion for mid-speed marine engines.
A state-of-the-art dual-fuel engine with 350 mm bore diameter is the basis for numerical simulations. GT-Power is used to create a one-dimensional air-path model. RCCI is simulated using TNO’s multi-zone combustion model incorporating detailed chemical kinetics. The simulations aim to optimize engine efficiency, with peak in-cylinder pressure and emissions as constraints.
The study shows best-point Indicated Efficiency of 47.8% is achievable (@75% load) using RCCI mode on stock engine hardware, while meeting IMO Tier III’s NOx limit. This performance is similar to the best contemporary marine gas engines, but RCCI also provides additional methane and CO emission reductions. Thus, RCCI combustion can meet Europe’s new rigorous Stage V limits, offering significant improvements in a marine engine’s GHG footprint.
Crucially, the study indicates an engine using hardware optimized for RCCI could deliver outstanding indicated efficiencies of 52%, with emissions of below 1g/kWh for all legislative species. This combination of high efficiency and ultra-low emissions would make RCCI combustion an attractive proposition for future marine propulsion and gen-set applications.
The global demand for transport energy is large, growing, and primarily met by petroleum-derived liquid fuels powering internal combustion engines (ICEs). Moreover, the demand for jet fuel and diesel is projected to grow faster than the demand for gasoline in the future, and is likely to result in low-octane gasoline components becoming more readily available. Significant initiatives with varying motivations are taking place to develop the battery electric vehicle (BEV) and the fuel cell as alternatives to ICE vehicles, and to establish fuels such as biofuels and natural gas as alternatives to conventional liquid fuels. However, each of these alternatives starts from a very low base and faces significant barriers to fast and unrestrained growth; thus, transport—and particularly commercial transport—will continue to be largely powered by ICEs running on petroleum-based liquid fuels for decades to come. Hence, the sustainability of transport in terms of affordability, energy security, and impact on greenhouse gas (GHG) emissions and air quality can only be ensured by improving ICEs. Indeed, ICEs will continue to improve while using current market fuels, through improvements in combustion, control, and after-treatment systems, assisted by partial electrification in the form of hybridization. However, there is even more scope for improvement through the development of fuel/engine systems that can additionally leverage benefits in fuels manufacture and use components that may be readily available. Gasoline compression ignition (GCI), which uses low-octane gasoline in a compression ignition engine, is one such example. GCI would enable diesel-like efficiencies while making it easier to control nitrogen oxides (NO x ) and particulates at a lower cost compared with modern diesel engines. Octane on demand (OOD) also helps to ensure optimum use of available fuel anti-knock quality, and thus improves the overall efficiency of the system.
This work presents a closed-loop combustion control concept using in-cylinder pressure as a feedback in a dual-fuel combustion engine. At low load, reactivity controlled compression ignition combustion was used while a diffusive dual-fuel combustion was performed at higher loads. The aim of the presented controller is to maintain the indicated mean effective pressure and the combustion phasing at a target value, and to keep the maximum pressure derivative under a limit to avoid engine damage in all the combustion modes by cyclically adapting the injection settings. Various tests were performed at steady-state conditions showing good abilities to fulfil the expected operating conditions but also to reject disturbances such as intake pressure or exhaust gas recirculation variations. Finally, the proposed control strategy was tested during a load transient resulting in a combustion switching-mode and the results exhibited the closed-loop potential for controlling such combustion concept.
This work evaluates the potential of a series hybrid vehicle concept that combines low temperature combustion (LTC) and biofuels as power source. To do this, experimental data from a previous work obtained in a single-cylinder engine running under ethanol-diesel dual-fuel combustion is used. Then, vehicle systems simulations are used to estimate performance and emissions of the LTC hybrid vehicle and compare them versus conventional diesel combustion (CDC). The vehicle selected to perform the simulations is the Opel Vectra, which equips the compression ignition engine used in the experimental tests.
The results from the simulations used for the analysis are firstly optimized by combining design of experiments and the Kriging fitting method. The multi-objective optimization allows to determine some characteristics and controls of the hybrid vehicle. The comparison of the estimated performance and emissions of the LTC-hybrid concept versus CDC over the worldwide harmonized light vehicles test cycle (WLTC) and real driving cycle (RDE) revealed clear benefits in terms of energy consumption, CO2 and NOx and soot emissions. In this sense, the hybrid concept enabled a reduction of the final energy consumed of 3% in the RDE cycle and 6.5% in the WLTC as compared to CDC. In terms of engine-out emissions, the CO2 was reduced around 16% versus CDC, and engine-out NOx and soot were reduced below the levels imposed by the Euro 6 regulation. As a penalty, the engine-out HC and CO emissions increased to more than double than CDC. However, based on previous experimental results, it is expected that a conventional diesel oxidation catalyst can reduce the tail-pipe HC and CO levels below the Euro 6 limits.
This article presents experience curves and cost-benefit analyses for electric and plug-in hybrid cars sold in Germany. We find that between 2010 and 2016, the prices and price differentials relative to conventional cars declined at learning rates of 23 ± 2% and 32 ± 2% for electric cars and 6 ± 1% and 37 ± 2% for plug-in hybrids. If trends persist, price beak-even with conventional cars may be reached after another 7 ± 1 million electric cars and 5 ± 1 million plug-in hybrids are produced. The user costs of electric and plug-in hybrid cars relative to their conventional counterparts are declining annually by 14% and 26%. Also the costs for mitigating CO2 and air pollutant emissions through the deployment of electrified cars tend to decline. However, at current levels, NOX and particle emissions are still mitigated at lower costs by state-of-the-art after-treatment systems than through the electrification of powertrains. Overall, the observation of robust technological learning suggests policy makers should focus their support on non-cost market barriers for the electrification of road transport, addressing specifically the availability of recharging infrastructure.
Reactivity controlled compression ignition (RCCI) is found promising low temperature combustion mode that has recorded tremendous success towards improving thermal efficiency and reducing NOx and soot emissions to nearly zero but has high specific fuel consumption, unburned hydrocarbon (UHC) and carbon monoxides (CO) emissions. Besides, RCCI requires combustion phasing control and loads extension to higher levels. Numerous researchers employed different strategies like use of exhaust gas recirculation (EGR) rate and dual fuel control to improve RCCI combustion performance and emission characteristics but little attention was paid to some strategies such as use of dual direct injection, oxygenated biofuels, and fuel additives. In addition, most of the researchers do consider one strategy without exploring the combined effects of many strategies at a time; hence, the technique requires combined strategies and methods for effective control and improved performance. This paper reviewed previous research activities and recent reviews on RCCI engine performance and emission characteristics with the view to finding information on current RCCI combustion methods and strategies while identifying its shortcomings. Eventually, some challenges of RCCI that affects its adaptability for effective commercialization were identified with respect to strategies integration and areas that require more efforts for more advances in the combustion mode were suggested.
Reactivity controlled compression ignition (RCCI) combustion has been shown to provide simultaneous ultra-low NOx and soot emissions with similar or better thermal efficiencies than conventional diesel combustion (CDC). Nonetheless, RCCI still has several challenges that restrict its operating range and limit its practical application. The dual-mode operation, which involves switching between different combustion modes, has been found as a promising alternative to operation in the whole engine map. However, the combustion mode switching requires difficult engine control, particularly during transient operation. The series hybrid vehicle (SHV) architecture allows the thermal engine to operate in a limited operating range by decoupling it from the drivetrain. Therefore, it could be an interesting alternative to the dual-mode concept. This work explores the potential of the RCCI series hybrid vehicle architecture to provide low engine-out emissions and CO2 by means of vehicle systems simulations. The results show the influence of the main parameters and control strategies of the SHV vehicle on its efficiency and emissions under different driving cycles. Finally, the optimal RCCI-SHV configuration is compared to CDC and dual-mode combustion strategies, confirming its potential as a future vehicle architecture for high efficiency and low emissions.
The great development of engine technologies can help to improve the engine characteristics and performance: a better thermal efficiency and an extending fuel economy area, which will subsequently decrease the fuel consumption and thus influence the overall architecture of the vehicle. In this paper, an investigation is carried out to assess the influence of the high-efficiency engine on the transmission gear numbers. First, according to the relevant studies and the integration of the advanced engine technology, a future engine fuel consumption map is obtained, based on which, the preliminary simulations are applied to explore the best match between the transmission and the proposed future engine from the perspective of fuel consumption. The simulation results indicate that the transmission with four gears is the best option to match the future engine while maintaining good fuel economy and meeting the driving demands. Then, based on this conclusion, a new hybrid powertrain architecture, which includes four gears for the engine, is introduced and analyzed in detail, with the advantage of seamless gear shift due to the compensation torque of the motor. Finally, to further examine the fuel economy and gear shift quality of the proposed powertrain, the dynamic model is established and the simulation results demonstrate that the new powertrain architecture shows a good fuel consumption performance and the gear shift process can be achieved without power interruption.
Reactivity controlled compression ignition (RCCI) is a promising low temperature combustion (LTC) regime that offers lower nitrogen oxides (NOx), soot and particulate matter (PM) emissions along with higher combustion efficiency compared to conventional diesel engines. It is critical to control maximum pressure rise rate (MPRR) in RCCI engines in order to safely and efficiently operate at varying engine loads. In this paper, a data-driven modeling (DDM) approach using support vector machines (SVM) is adapted to develop a linear parameter-varying (LPV) representation of MPRR for RCCI combustion. This LPV representation is then used in the design of a model predictive controller (MPC) to control crank angle of 50% of fuel mass fraction burn (CA50) and indicated mean effective pressure (IMEP) while limiting the MPRR. The results show that the LPV-MPC control strategy can track CA50 and IMEP with mean tracking errors of 0.9 CAD and 4.7 kPa, respectively, while limiting the MPRR to the maximum allowable value of 5.8 bar/CAD.
The fast rate of depletion of fossil fuel resources due to increasing demands and the adverse environmental impact by the automotive engines forced researchers to develop alternative strategies to meet the stringent emission norms in terms of oxides of nitrogen and particulate matter. In this regard, low temperature combustion is one of the promising advanced in-cylinder combustion strategies for reducing both oxides of nitrogen and particulate matter emissions simultaneously with a beneficial effect on specific fuel consumption. The low temperature combustion is achieved through homogeneous charge compression ignition, premixed charge compression ignition, reactivity controlled compression ignition and gasoline compression ignition. In this paper, an attempt is made to assemble and summarize a listing of important research articles on low-temperature combustion using a wide variety of conventional and alternate renewable fuels. The effect of low-temperature combustion on engine performance and emission characteristics over a wide range of engine test conditions and the challenges faced in these strategies are also described. From the assemblage of articles on low-temperature combustion using conventional and renewable fuels, it is understood that this strategy can help in achieving better performance, lower cylinder pressure and heat release rate, and simultaneous reductions of nitrogen oxides and particulate matter, but typically with an increase in carbon monoxide and hydrocarbon emissions. This literature review is expected to be useful to the researchers for understanding the concept, challenges, and the state-of-the-art of the different modes of low-temperature combustion using conventional and sustainable alternate fuels.
The European commission is targeting a 15% reduction in CO2 emissions for medium and heavy-duty transportation starting in 2025. Moreover, the next European normative (EU VII) will impose a decrease of 50% for NOx and particulate matter emissions with respect to the current EUVI normative. Meeting these requirements pose a significant challenge to truck and bus manufacturers. Several proposals appeared in the last few years as improve the cabin aerodynamics, decrease the friction losses and improve the powertrain efficiency. The last point involves improving the current combustion systems as well as the transmission and energy management. This work proposes to couple two potential technologies to reduce at the same time the global (CO2) and local pollution (NOx and soot). For this, two truck platforms representative of medium-duty applications (18 ton and 25 ton) are tested using the reactivity controlled compression ignition (RCCI) combustion mode with diesel and gasoline as fuels. In addition, the trucks are electrified to full hybrid technology in a parallel pre-transmission (P2) architecture. A 0D vehicle numerical model is used to evaluate the trucks under four different driving cycles representative of homologation and real driving conditions. The numerical model is validated against on road measurements. The RCCI combustion is modeled by means of a map-based approach with 54 points measured in steady-state conditions. This work presents a complete engine map calibration with measurements up to 350 hp using two combustion modes inside the map (so-called dual-mode dual-fuel). As a baseline, the commercial diesel no-hybrid trucks and the dual-fuel no-hybrid trucks are used. The results show the potential of the dual-mode dual-fuel combustion to achieve ultra-low NOx and soot emissions. In addition, the CO2 target reduction is achieved for several truck platforms and driving conditions due to the hybridization of the driveline. The cycles with large phases of urban driving are the most favorable due to the ability of recovering energy by means of the regenerative braking system and the possibility to avoid large idling phases with respect to the no-hybrid versions. In addition, the decrease of the payload improves the CO2 reduction with respect to the baseline cases.
A new concept of single-fuel RCCI has been proposed through the catalytic partial oxidation reformation of diesel fuel. The reformed fuel mixture is then used as the low reactivity fuel and diesel itself is used as the high reactivity fuel. In this paper, two selected reformates mixture from the reformation of diesel were selected for further analysis. Each reformate fuel mixture contained a significant fraction of inert gases (89% and 81%). The effects of the difference in the molar concentrations of the reformate mixtures were studied by experimenting with diesel as the direct injected fuel in RCCI over a varying start of injection timings and different blend ratios (i.e., the fraction of low and high reactivities fuels). The reformate mixture with the lower inert gas concentration had earlier combustion phasing and shorter combustion duration at any given diesel start of injection timing. The higher reactivity separation between reformate mixture and diesel, compared with gasoline and diesel, causes the combustion phasing of reformate-diesel RCCI to be more sensitive to the start of injection timing. The maximum combustion efficiency was found at a CA50 before TDC, whereas the maximum thermal efficiency occurs at a CA50 after TDC. The range of energy-based blend ratios in which reformate-diesel RCCI is possible is between 25% and 45%, limited by ringing intensity (RI) at the low limit of blend ratios, and COV of IMEP and combustion efficiency at the high limit.
Dual-mode dual-fuel (DMDF) combustion stands over other low temperature combustion strategies as it is able to operate over the entire engine map by transitioning between reactivity controlled compression ignition and diffusive combustion depending on the engine load. In combination with non-sooting e-fuels, it is able to achieve low NOx and soot levels even at high loads. Oxygenated fuels like poly-oxymethylene dimethyl ethers (OMEx) have been already proved to present an outstanding NOx-Soot trade-off improvement when used in combination with a DMDF combustion strategy. One drawback of OMEx is that, despite having a high reactivity, it has a low lower heating value, which requires considerably longer injection events compared to other traditional fuels in order to achieve the same engine power output. The long injections limit the flexibility of the injection strategy and result in extremely long combustion durations. A possible solution to this problem resides in moving towards injectors with higher flow rate capacities, but this may compromise the mixing and combustion processes. This work aims to shed some light on the implications of changing the engine hardware to overcome this limitation by testing a DMDF multi-cylinder engine using gasoline as the low-reactivity fuel and diesel or OMEx as the high reactivity fuels with injectors of different flow capacity. The results show that a concise analysis of the involved phenomenology of the combustion process allows to find out the trade-off between the engine-out emissions and the mixing capacity of the injection system while the engine performance is not significantly affected.
In recent years, improved combustion controllability through in-cylinder reactivity stratification by using two different fuels have led to introduction of dual-fuel reactivity controlled compression ignition (RCCI) strategy. In conventional RCCI, gasoline or natural gas can be used as the low-reactivity fuel, and diesel or biodiesel can be used as the high-reactivity fuel. This strategy has the potential to operate with a single low-reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver. In the present study, numerical simulations have been carried out to study injection strategy in a single-fuel RCCI engine fueled with isobutanol – isobutanol + 20% di-tert-butyl peroxide (DTBP). Firstly, the effects of start of injection (SOI) timing, injection pressure (pinj), spray cone angle (SCA), and DI fuel ratio were explored. Then, the effect of DI fuel ratio was discussed in each best case in order to decrease the high DI requirement. The results indicate that SOI = −88° ATDC, pinj = 1400 bar, and SCA = 45° can improve the single-fuel RCCI engine performance and emissions compared to the baseline case (SOI = −58° ATDC, pinj = 600 bar, SCA = 72.5°). Moreover, it is shown that by advancing the SOI timing to −88° ATDC, a 20% reduction in DI ratio, 3.3% increase in gross indicated efficiency (GIE) together with reductions in CO, and NOx emissions by 3.56 g/kW-h and 0.254 g/kW-h, could be achieved, respectively.
Reactivity Controlled Compression Ignition combustion technology potentials are well known for the capability to drastically reduce the engine-out nitrogen oxides and soot emissions simultaneously. Its implementation in mid-term low-duty diesel engines can be beneficial to meet the upcoming regulations. To explore the potential of this solution, experimental data are used from a compression ignition 1.9 L engine, which is operated under two combustion-modes: Reactivity Controlled Compression Ignition and conventional diesel combustion. Meanwhile, also the carbon dioxide emissions limitations must be fulfilled. To achieve this goal, the benefits associated to powertrain electrification in terms of fuel economy, can be joined with the benefits of RCCI combustion. To do so, two different supervisory control strategies are compared: Adaptive Equivalent Minimization Control Strategy and Rule-Based Control strategy, while dynamic programming is used to size the electric grid of the powertrain to provide the best optimal solution in terms of fuel economy and emissions abatement. The analysis of the designed hybrid powertrain is carried out numerically with GT-Suite and Matlab-Simulink software. The results show a great potential of the parallel full-hybrid electric vehicle powertrain equipped with the dual-mode engine to reduce the engine-out emissions, also to increase fuel economy with respect to the homologation fuel consumption of the baseline vehicle. The optimal supervisory control strategy was found to be the emissions-oriented Adaptive Equivalent Minimization Control Strategy, which scores a simultaneous reduction of 12% in fuel consumption, 75% in engine-out nitrogen oxides emissions and 82% in engine-out soot, with respect to the baseline conventional diesel combustion engine vehicle.
From previous results in a single-cylinder engine platform, it can be concluded that the dual-mode dual-fuel (DMDF) concept can be a potential solution to overcome the major constraints found with other single-fuel low temperature combustion modes. To extend these findings to a real application, this work evaluates the potential of the diesel-gasoline DMDF concept on a multi-cylinder 8L engine in terms of performance and emissions. To do this, a full engine calibration map was obtained following a specific methodology. The emissions results show that diesel-gasoline DMDF allows to achieve EURO VI NOx and soot emissions in a great portion of the engine map. Nonetheless, the levels of these pollutant at high load conditions exceed the EURO VI limits by far due to the need of implementing a diffusive combustion strategy with high EGR levels to avoid excessive in-cylinder pressure gradients. To mitigate this issue, the use of Oxymethylene ether (OMEx) instead of diesel fuel is proposed. A dedicated engine calibration was developed for the OMEx-gasoline DMDF concept following the same methodology. The results show that the oxygen content in the OMEx molecule allows to achieve a fully EUVI compliant engine calibration in terms of NOx with engine-out soot levels lower than 0.01 g/kWh. Moreover, due to the lower stoichiometric air–fuel ratio with this fuel, the air management system requirements are lower, reducing the pumping losses and increasing the brake thermal efficiency in most of the calibration map.
Reactivity controlled compression ignition (RCCI) is a promising combustion concept which uses two fuels to combine high thermal efficiencies and low engine-out NOx and soot emissions. The combustion concept relies on controlled auto-ignition and is sensitive for changing injection pressure, fuel quality, etc. Consequently, modeling and control of this complex combustion concept is not straightforward. In this work, Gaussian process regression is used to arrive at a data-driven model for a gasoline-diesel RCCI engine. This data-driven model is employed in a robust optimization approach that uses a nested particle swarm optimization. The designed (feedforward) control inputs maximize the efficiency of the RCCI engine while satisfying safety and emissions constraints under various disturbed conditions. In the simulation study, robust performance is obtained, and the robust efficiency is very similar to the efficiency under nominal condition.
Reactivity controlled compression ignition (RCCI) engines as one of low temperature auto ignition combustion strategies have shown a good performance to reduce NO x and soot emission while increasing engine thermal efficiency. Combustion control of these types of engines is relatively complex because of their ignition type which makes it difficult to have a direct control on the start of the combustion. In this research, combustion phase of an RCCI engine was modeled with using a control-oriented method. The combustion properties such as start of the combustion, crank angle degree where 50 percent of the fuel is burnt(CA50) and the burn duration were modeled in this research. A modified knock integral model was used for start of combustion estimation. Using the effect of spontaneous front speed, burn duration was modeled where a mathematical model is developed; and Wiebe function is used to model CA50. Indicated mean effective pressure(IMEP) also estimated in this modeling. To validate the developed models, five experimental data sets from a heavy-duty RCCI engine were used. The results show the maximum mean errors of 1.7, 1.9 and 2.3 crank angle degree (CAD) for start of combustion, burn duration(BD) and the CA50, respectively and this quantity is 0.5 bar for IMEP in steady state condition. The transient condition of the engine operation was also investigated. The results and trends are promising in all characteristics of the combustion process especially in the modeling of the indicated mean effective pressure where the majority of the data have errors less than 1.5 bar.
Diesel-ignited gas engines show high emission of hydrocarbons at low load and thus have to be operated there in Diesel-only mode. The transition between the combustion modes typically results in a significant torque deviation as well as in additional tailpipe emissions of pollutants. This paper presents a study on the transition between the two combustion modes, namely Diesel-only mode and dual-fuel mode. Optimal actuator trajectories are derived by solving a nonlinear optimal control problem. With the optimized trajectories implemented in a feedforward controller, the transition is significantly improved in terms of torque deviation, cumulative nitrogen oxide emissions, as well as cumulative hydrocarbon emissions.
A single-fuel RCCI concept has been proposed to avoid the need for a secondary fuel system required for conventional RCCI by generating the secondary fuel from the primary fuel through catalytic partial oxidation (CPOX) reformation. In conventional RCCI, gasoline or natural gas can be used as the low-reactivity fuel, and diesel can be used as the high-reactivity fuel. In this study, two reformate mixtures generated by reforming diesel fuel at different operating conditions were used as the low-reactivity fuel, with the parent diesel as the high reactivity fuel. The combustion characteristics of reformate-diesel RCCI were compared with the conventional RCCI. A CFD model was also developed and validated against the experimental results. The model was then used to validate a necessary approximation of the reformate mixture's species concentrations.
Compared to conventional RCCI fuel pairs, reformate-diesel RCCI shows marginally better thermal efficiency, approximately 10% better THC emissions, approximately 50% lower NOx emissions, and good controllability. Because the reformate mixture has a high concentration of diluents it displaces a large fraction of intake air and acts similarly to EGR. The combustion behavior of reformate-diesel RCCI is in between that of gasoline-diesel and natural gas-diesel conventional RCCI. From the results, it can be concluded that reformate-diesel RCCI is not overly sensitive to the reformation process itself and the exact species concentrations in the reformate mixture. A small change in the start of injection of diesel, blend ratio, and EGR fraction can be used to compensate for reformate mixture concentration differences.
The diesel/gasoline dual-mode dual-fuel (DMDF) combustion concept was optimized in a compression-ignition engine by combining the computational fluid dynamics (CFD) simulations with the genetic algorithm. Seven operating parameters with remarkable influences on the engine performance were chosen as the variables to be optimized for simultaneously minimizing the fuel efficiency, nitrogen oxides (NOx), and soot emissions. Moreover, the potential of the further improvement of the DMDF combustion concept was discussed, and the rationality of this strategy was demonstrated. The results indicate that, at low load, simultaneous improvement of the fuel economy and emissions can be realized by strengthening the homogeneous combustion. At mid load, the fuel economy can be improved by reducing the heat transfer losses, while the NOx emissions are sacrificed to some extent. At high load, improved fuel economy can be realized by transferring a part of diffusion combustion to premixed reactivity-controlled compression ignition (RCCI) combustion. Concerning the operating parameters, lower intake temperature is beneficial to decrease the transfer losses, and the control of intake temperature is crucial for the stable operation of DMDF combustion under wide load conditions. Overall, gross indicated thermal efficiency above 45% is achieved, and the NOx and soot emission can be maintained under the Euro 6 standard for the test load range.
After the diesel emissions scandal, also known as Dieselgate, Direct Injection Spark-Ignited (DISI) internal combustion engines (ICE) appears as the most promising alternative to mitigate the harmful tailpipe emissions from passenger cars. In spite of that, the current ICE technologies are not enough to achieve the fuel consumption/CO2 emissions targets set by the new transportation legislation (4.1 Lgasoline/100 km, 95 gCO2/km for 2021). In this complex scenario, the electrification of the powertrain using high efficiency electric motors and battery package together with sophisticated DISI engines appears as potential solution to meet these requirements. The aim of this work is to study the fuel consumption and pollutant emissions in transient conditions from a passenger car equipped with a variable compression ratio (VCR) DISI engine and electrified powertrain technologies. The vehicle behavior was simulated by means of a 0D GT-Suite model fed by experimental results obtained in an engine test bench. Mild hybrid electric vehicle (MHEV) and full hybrid electric vehicle (FHEV) architectures using a VCR DISI engine were studied. Moreover, an optimization methodology is presented to select the best vehicle configuration in terms of hardware and control strategies by means of a design of experiments (DoE). The results show that VCR allows a fuel improvement of 3% with respect to the conventional DISI fixed CR along the worldwide harmonized light vehicles test cycles (WLTC). The benefits found when combining the VCR technology with hybrid powertrains are even higher. In this sense, the fuel improvements were higher as the electrification levels increased, with 8% for MHEV-VCR and around 20% for FHEV-VCR. In terms of emissions, the two clear benefits with FHEV-VCR were the reduction of particle number (PN) and unburned hydrocarbons (HC) of around 60% and 15%, respectively, as compared to the conventional DISI.
The strong new restrictions in the vehicle CO2 emissions together with the instability of the fossil fuels
reserves reinforces the necessity to continue developing high efficiency combustion engines that operate
with renewable energy sources. Bio-ethanol appears as a potential fuel to replace well-established fossil
fuels, such as gasoline, due to the overall carbon neutral emission. In addition, the high-octane number
allows to increase the compression ratio of the engine to improve the thermal efficiency. Apart from the
CO2, the emissions legislation restricts the NOx and particle matter emissions to ultra-low values, and
they will continue decreasing down to almost zero. In this work, two advanced dual-fuel combustion
modes using bio-ethanol as main fuel are studied. A pre-chamber ignition system (PCIS) using bioethanol
and hydrogen, and a reactivity-controlled compression ignition (RCCI) combustion mode operating
with bio-ethanol/diesel was selected due to the potential to reduce NOx emissions. These combustion
technologies were studied by a numerical 0-D vehicle simulations in homologation and real-life
driving cycles for a range extender hybrid powertrain. As a baseline, the original manufacturer spark
ignition (SI) no-hybrid powertrain fueled with pure bio-ethanol was used. The powertrain components
and control system were optimized to obtain the maximum overall vehicle efficiency, and low CO2-NOx
emissions. Finally, a life cycle analysis (LCA) was performed to study the global potential of the bioethanol
to reduce greenhouse gas (GHG) emissions. A battery electric vehicle (BEV) and a gasoline SI
no-hybrid vehicle were added for comparison. The results show that the RCCI mode presents the highest
potential to reduce the NOx emissions. However, the PCIS allows to reduce the tank to wheel CO2
emissions up to 60 g/km when high rates of H2 are used. The LCA-GHG for the vehicles using bio-ethanol
is 50% and 95% lower than a BEV and SI-gasoline vehicle, respectively.
Carbon-neutral synthetic fuels can be produced from renewable electricity by the hydrogenation of carbon dioxide captured from air or exhaust gas. A promising class of these synthetic fuels are long-chain oxymethylene ethers (OMEs), which exhibit good auto-ignition characteristics for compression-ignition engine application. This study aims to investigate the auto-ignition of three oxymethylene ethers (OMEn, n = 2–4) numerically and experimentally. A shock tube is applied to measure ignition delay times over a range of initial conditions and the obtained results serve as the validation and optimization targets for a chemical mechanism of OME2-4 developed in this work. This model is derived first using an automatic reaction class-based mechanism generator. To ensure the chemical validity of the mechanism, the automatic generator applies reaction classes and rate rules consistently for OME2-4, which are adopted from a recently published OME1 mechanism. For improved model prediction accuracy of ignition delay times, the mechanism is then optimized automatically by calibrating these rate rules within their uncertainties using data for all OMEn fuels. It is shown that this highly automated model development process is able to provide accurate chemical mechanisms for large fuel components in a very efficient manner, if accurate prior kinetic knowledge exists for their short-chain counterparts.
Reactivity controlled compression ignition (RCCI) engines center on a combustion strategy with higher thermal efficiency, lower particulate matter (PM), and lower oxides of nitrogen (NOx) emissions compared to conventional diesel combustion (CDC) engines. However, real time optimal control of RCCI engines is challenging during transient operation due to the need for high fidelity combustion models. Development of a simple, yet accurate control-oriented RCCI model from physical laws is time consuming and often requires substantial calibrations. To overcome these challenges, data-driven models can be developed. In this paper, a data-driven linear parameter-varying (LPV) model for an RCCI engine is developed. An LPV state space model is identified to predict RCCI combustion phasing as a function of multiple RCCI control variables. The results show that the proposed method provides a fast and reliable route to identify an RCCI engine model. The developed model is then used for the design of a model predictive controller (MPC) to control crank angle for 50% fuel burnt (CA50) for varying engine conditions. The experimental results show that the designed MPC with the data-driven LPV model can track desired CA50 with less than 1 crank angle degree (CAD) error against changes in engine load.
The dual-mode dual-fuel combustion is a promising combustion concept to achieve the required emissions and carbon dioxide reductions imposed by the next emissions standards. Nonetheless, since the combustion concept relies on the reactivity of two different fuels (diesel and gasoline), the fuel formulation requirements are stricter. This work investigates the effects of the low reactivity fuel sensitivity for different octane numbers at different operating conditions representative of the combustion regimes found inside the dual-mode dual-fuel engine map. For this, experimental evaluations were performed using fuels with research octane number 92.5 and 80 and different sensitivities (0, 5 and the maximum one achievable for each fuel). The combustion development was assessed by means of the heat release rate characterization. Moreover, numerical simulations in a constant volume homogeneous reactor were used to explore and understand the impact of the different fuels on the ignition delay time. The results suggest that the sensitivity increase affects the different research octane number fuels in a different way. For the fuel with research octane number 92.5, the sensitivity variation increases the experimental ignition delay, impairing the combustion process and increasing the fuel consumption. In the case of the fuel with research octane number 80, the sensitivity increase does not affect the combustion development. This was justified by the numerical investigation, which points to a wider temperature range where the sensitivity does not affect the final ignition delay for research octane number 80. Moreover, generally, the ignition delay times for research octane number 80 considering the experimental gasoline fraction used are half than those of research octane number 92.5. At full load conditions, the trend is inverted, where the experimental ignition delay for research octane number 80 is affected by the sensitivity whilst research octane number 92.5 presents only modifications after the combustion start.
Hybrid Electric Vehicles (HEVs) can be considered as a potential technology to promote the change from conventional mobility to e-mobility. However, the real benefits in terms of CO2 emissions depend on a great extent on their mode of use, vehicle design and electricity source. On the other hand, in the last few years, advanced combustion modes as Reactivity Controlled Compression Ignition (RCCI) showed great advantages in terms of NOx and soot emissions reduction. This paper has the purpose of assessing, through numerical simulations fed with experimental results, the potential of different hybrid vehicles when used together with a low temperature combustion mode. In particular, the dual-fuel Mild (MHEV), Full (FHEV) and Plug-in (PHEV) hybrid electric vehicles are tested and compared to the original equipment manufacturer (OEM) and the conventional dual-fuel powertrain, both no-Hybrid vehicles. The powertrains are optimized to meet the current European homologation legislation Worldwide Harmonized Light Vehicle Test Procedure (WLTP). After that, a deep analysis is performed in terms of performance and emissions. Lastly, a life-cycle analysis (LCA) is performed to evaluate the real potential of the different technologies. The results show that the PHEV has the highest benefits in terms of fuel consumption and engine-out emissions. With this technology, it is possible to achieve the 50 g/km CO2 target for the PHEVs with a medium battery size (15 kWh), while NOx and soot levels are under the Euro 6 limits. In addition, the RCCI technology shows great benefits to achieve the Euro 6 soot level for the other hybrid platforms. The LCA shows that the PHEVs can achieve 12% reduction of the total CO2 with respect to the FHEVs, and 30% with respect to the no-hybrid diesel platform.
The increasingly stringent emissions regulations together with the demand of highly efficient vehicles from the customers, lead to rapid developments of distinct powertrain solutions, especially when the electrification is present in a certain degree. The combination of electric machines with conventional powertrains diversifies the powertrain architectures and brings the opportunity to save energy in greater extents. On the other hand, alternative combustion modes as reactivity controlled compression ignition (RCCI) have shown to provide simultaneous ultra-low NOx and soot emissions with similar or better thermal efficiency than conventional diesel combustion (CDC). In addition, it is necessary to introduce more renewable fuels as ethanol to reduce the total CO2 emitted to the atmosphere, also called well-to-wheel (WTW) emission, in the transport sector. Therefore, the combination of these two growing technologies with the use of ethanol (E85) could be a potential way to achieve clean and efficient vehicles. In this work, numerical simulations of full hybrid electric vehicles (series, parallel and series-parallel) and mild hybrid vehicles were performed and compared versus the conventional powertrain in the WLTC driving cycle. The hybrid vehicles are simulated with both CDC and diesel-ethanol RCCI combustion engines as power source. Each powertrain was optimized in terms of electric components (battery capacity, electric motors...), internal combustion engine operating points, power management strategy and transmission/differential ratio to obtain the minimum fuel consumption and NOx emissions. The results show a significant reduction of the total mass consumption as the complexity of the hybrid system increases (more electrical devices needed). In this sense, the series-parallel architecture, which represents the most complex hybrid system, allows reducing the energy consumption around 20% compared to the conventional powertrain operating under CDC. In addition, the combined use of CDC and RCCI in the same engine map showed improvements in NOx, soot and CO2 emissions versus CDC. Moreover, the series hybrid powertrain obtained the lowest NOx and soot emissions values due to using fixed operating conditions in RCCI mode for the thermal engine. Lastly, the mild hybrid technology showed an acceptable balance between complexity and fuel consumption.
The dual-mode dual-fuel combustion strategy allows operating over the entire engine map by implementing a diffusive dual-fuel combustion at high engine loads. This requires increasing the amount of exhaust gas recirculation to control the NOx emissions, which penalizes the soot levels. At these conditions, the use of non-sooting fuels as the e-Fischer Tropsch Diesel (e-FT) and oxymethylene dimethyl ethers (OMEx) could be a potential way to avoid the NOx-soot trade-off. The experimental results acquired in a compression ignition multi-cylinder medium-duty engine evidence that the higher oxygen content of OMEx allows reducing the soot emissions at high loads to near zero levels, while e-FT promotes a soot reduction of around 20% as compared to diesel. Nonetheless, the low lower heating value of OMEx leads to excessive injection durations, enlarging the combustion process and increasing the fuel consumption around 1.3–7.2% and 1.4–5.3% as compared to diesel and e-FT, respectively, depending on the engine load. Finally, the well to wheel analysis confirms the potential in reducing the carbon dioxide footprint of OMEx (14.8–69%) and e-FT (0.3–38.5%) compared to diesel, as they can be synthetized via direct air capture as a source of carbon and using renewable energy.
The application of a low-temperature combustion concept, such as RCCI combustion under real engine operating conditions is extremely complex. However, the implementation of the dual-mode dual-fuel (DMDF) strategy allows operating in low-medium load with the RCCI combustion and in high load with dual-fuel diffusive combustion. This allows taking advantage of the benefits of RCCI combustion as the simultaneous reduction of PM and NOx emissions. However, there are still serious challenges that required to solve, such as the high-pressure rise rate and the excessive CO and HC emissions. In this sense, this work shows how the implementation and an adequate adjustment of the cooled LP-EGR rate significantly minimize these problems and also shows how the LP-EGR has a greater impact on the DMDF than on the CDC concept.
This work has been performed in a modern medium-duty diesel engine fueled with standard gasoline and diesel fuels, with which a cooled LP-EGR loop has been coupled. A TSI Scanning Particle Sizer (SMPS 3936L75) was used to measure the particles size distribution and the Horiba MEXA-ONE-D1-EGR gas analyzer system to determine gaseous emissions. A parametric variation of the LP-EGR rate was experimentally performed to analyze the effect over each combustion process that encompasses the DMDF concept (fully premixed RCCI, highly premixed RCCI and dual-fuel diffusion) and its consequent impact on gaseous and particle emissions. In addition, results were compared against the CDC concept to state the benefits of the DMDF concept. Among the different results obtained, it can be highlighted that during the RCCI strategy the increase in LP-EGR rate provided a reduction in NOx emissions. Nonetheless, unlike that fully premixed RCCI in highly premixed RCCI combustion, the PM emissions increased with this increment in the LP-EGR rate, shifting the size distribution of particle toward larger sizes, but decreasing the HC and CO emissions. Finally, with the exception of the high HC and CO emissions in fully premixed RCCI, in all the combustion strategies of the DMDF concept, a reduction of the analyzed pollutants was observed when compared with the CDC mode.
Reactivity controlled compression ignition is a promising combustion strategy due to the combination of excellent thermal efficiency with ultra-low nitrogen oxides and particulate matter raw emissions. However, very high levels of unburned hydrocarbons and carbon monoxide emissions are found. It limits the reactivity controlled compression ignition use at very low loads and presents an additional challenge for the diesel oxidation catalyst. The low exhaust temperature and high carbon monoxide and hydrocarbon concentration can penalise the catalyst conversion efficiency. The objective of this work is to evaluate the response of an automotive diesel oxidation catalyst when used for reactivity controlled compression ignition combustion combining experimental and modelling approaches. For this purpose, dedicated tests have been done using diesel-gasoline as fuel combination in a single-cylinder engine. This way, the catalyst conversion efficiency has been determined within a wide operating range covering hydrocarbon adsorption conditions and the pollutants abatement dependence on the mass flow and temperature. The experimental results in the full-size catalyst has been analysed by modelling. A lumped diesel oxidation catalyst model has been applied to extend the results to multi-cylinder engine conditions and to determine the light-off curves for both carbon monoxide and hydrocarbons. These tests evidence the penalty in light-off temperature due to high pollutants mass fraction, which promotes inhibition limitations to the reaction rate.
Variable compression ratio (VCR)and variable valve timing (VVT)are two effective strategies to adjust the effective compression ratio, which is beneficial for controlling the combustion process of advanced combustion modes. In this study, systematic evaluation of the two strategies was conducted based on reactivity controlled compression ignition (RCCI)engine in terms of combustion process control, fuel efficiency, and emission characteristics. By coupling an updated KIVA-3V code with the genetic algorithm, the combustion of a heavy-duty RCCI engine with VCR and VVT strategies was respectively optimized, aiming to simultaneously realize high fuel efficiency and low emissions. The optimal VCR and VVT strategies were compared under a wide load range. The results indicate that, at low and mid loads, high effective compression ratio, large premix ratio, and early fuel injection can be utilized to realize Euro 6 nitrogen oxides (NO x )limit with ultra-low soot emissions and low fuel consumption for both VCR and VVT strategies. The increase of load from low to mid narrows the optimal range of exhaust gas recirculation (EGR)rate for VVT strategy whereas the range for VCR strategy is still wide. At high load, compared to VVT strategy, a further decreased effective compression ratio can be utilized for VCR strategy, which allows early fuel injection, leading to the improvements of fuel efficiency and soot emissions. This suggests that the VCR strategy is more practical for high-load operation of RCCI combustion and the commercialization the RCCI engine in the future compared to VVT strategy.
The stringent regulations, increased global temperature and customer demand for high fuel economy have led to rapid developments of different alternative propulsion solutions in the last decade, with special attention to the electrified vehicles. The combination of electric machines with conventional powertrains allows to diversify the powertrain architectures. In addition, alternative combustion modes as reactivity controlled compression ignition (RCCI) have been shown to provide simultaneous ultra-low NOx and soot emissions with similar or better thermal efficiency than conventional diesel combustion (CDC). Therefore, the combination of both technologies creates a promising horizon to be implemented in commercial vehicles of the near future. In this work, experimental and numerical simulations were combined to study the potential of the parallel full hybrid electric vehicle (P2-FHEV) and mild hybrid vehicle (MHEV) to obtain lower fuel consumption and NOx emissions than a conventional powertrain in the Worldwide Harmonized Light Vehicles Cycle (WLTC). The hybrid vehicles are simulated with both CDC and diesel-gasoline RCCI combustion engines as power source. Each powertrain was optimized in terms of components (battery, electric motors…) capacity, internal combustion engine operative points, energy management strategy and gear ratios. The results show a significant fuel consumption reduction as the complexity of the hybrid system increases. The parallel architecture, which represents the most complex hybrid system tested in this work, allows obtaining a fuel consumption reduction of around 20% as compared to CDC. The dual-mode CDC-RCCI concept showed improvements in NOx and soot emissions with comparable values in terms of energy consumption and CO2 emissions than CDC. Additionally, the mild hybrid technology with the functionality of start-stop, torque assist and regenerative braking showed an acceptable balance between complexity and fuel consumption gain.
The objective of this work is to examine in a systematic way, how conflicting requirements such as maximum ignition delay time and laminar flame speed can be met by adding gaseous components to methane in order to obtain the optimal fuel blend under engine-relevant conditions. Low-dimensional models are coupled with a multi-objective optimization algorithm in order to compute optimal methane/hydrogen, methane/syngas and methane/propane/syngas blend compositions that maximize simultaneously the ignition delay time, the laminar flame speed and the Wobbe number. The non-dominated sorting genetic algorithm (NSGA-II) is used to generate a set of Pareto solutions, and the best compromise solutions are then determined by the technique for order preference by similarity to ideal solution (TOPSIS).It was found that the GRI-Mech 3.0 mechanism could not accurately predict ignition properties of methane-based fuel blends under engine-relevant conditions. The optimization results revealed that initial conditions have a significant effect on the optimal fuel blend composition. For methane/hydrogen and methane/syngas blends, pure methane was the optimal fuel at high temperatures and low equivalence ratios, while high hydrogen contents were beneficial at lower temperatures. When the ignition delay time is of higher importance, the optimal composition shifted towards higher carbon monoxide contents. Blends with higher hydrogen and syngas contents resulted in reduced ignition delay times and higher laminar flame speeds. Regarding the methane/propane/syngas blend, the presence of propane in the optimal blend was found to be more favorable than hydrogen and carbon monoxide to satisfy the objectives.
Dual-mode dual-fuel combustion stands as one of the promising techniques to allow the dual-fuel operation along the whole engine map. This concept relies on using different combustion strategies as reactivity controlled compression ignition up to medium load, then migrating to diffusive dual-fuel combustion to reach full load. With this strategy, it is possible to obtain sensible reductions in NOx and soot while providing improvements in fuel consumption and CO2 emissions. However, the excessive quantities of HC and CO together with the low exhaust temperature can compromise the diesel oxidation catalyst (DOC) efficiency. In addition, the diffusive dual-fuel combustion applied at high engine load produces considerable soot amounts that should be reduced within the diesel particulate filter (DPF). Based on these facts, this work intends to evaluate the efficiency of a commercial aftertreatment system (DOC + DPF) while operating in dual-mode dual-fuel combustion. Additionally, fundamental studies where developed to understand the impact of the combination of fuels on the exhaust hydrocarbon species. First, the DOC performance was evaluated at steady-state and transient conditions under different operating conditions fulfilling the EUVI NOx and soot limits. In parallel, the different engine-out hydrocarbon species were measured by means of a Fourier-transform infrared spectroscopy (FTIR) gas analyzer. Finally, the passive and active regeneration processes were assessed by means of different methodologies aiming to evaluate the low NOx-low soot interaction and the capability of the active regeneration in dual-fuel dual-mode (DMDF) operating conditions. The DOC results showed an improper conversion efficiency at low load operating condition, where the exhaust temperature is low. By contrast, the thermal inertia at transient conditions allowed to improve the DOC behavior at low load, reaching DOC-out emissions one order of magnitude lower than those from the steady-state tests. Concerning the DPF, it was demonstrated that the low concentration of NOx and soot produced during the combustion does not lead to sensible changes in the NO2/NOx ratio before and after the DPF, indicating a low level/absence of passive regeneration. In the case of the active regeneration, both conventional diesel combustion (CDC) and DMDF operating conditions can obtain satisfactory reduction in the total soot trapped, being the increase in the exhaust temperature consequence of the HC and CO conversion the supporting mechanism for the active regeneration in the DMDF concept.
This work evaluates the performance and emissions of the series hybrid vehicle concept powered by a gasoline partially premixed internal combustion engine. To do so, experimental data was collected from a Volvo VED-D4 Euro 6 four-cylinder compression ignition engine running under gasoline partially premixed combustion. Two series hybrid vehicle models were developed in GT-Power®, which were fed with the experimental data to evaluate the potential of the hybrid concept. First of all, the battery charging strategy of the hybrid vehicles was optimized in terms of number of power levels and operating conditions. For this, a design of experiments was performed in GT-Power®, which enabled to obtain a predictive model of the performance and emissions. The predictive model was used to obtain the optimized NOx-fuel consumption Pareto frontiers for each charging strategy proposed. Finally, the GT-Power® vehicle models were run with the optimal operating conditions (selected from each Pareto) in both the new European driving cycle and worldwide harmonized light vehicles test cycle. The results show that the hybrid powertrain running with partially premixed combustion is able to achieve similar or better performance than the commercial diesel vehicle with low engine-out emissions. Moreover, comparing the results from both vehicles, it was confirmed that the hybridization results in better improvements when applied to urban traffic than for highway conditions where the power request is higher and the potential for regenerative braking is reduced.
A computational system optimization was conducted to explore the efficiency potential of an electrochemical-combustion combined system for distributed power generation. A solid oxide fuel cell model was developed and validated to simulate the electrochemical conversion process and a zero dimensional model was implemented to simulate the engine combustion process. A system level approach was used to evaluate the trade-offs and efficiency potential of the system. A design of experiments of simulations was conducted to explore the design space and a genetic algorithm was used to search the resulting response surface for optimal operating conditions. Metal engine experiments were used to validate that the internal combustion engine is capable of operating under the desired operating conditions and the results were used to obtain final system efficiencies. The results showed that under fully homogeneous and stratified engine conditions the system is capable of achieving electrical efficiencies of 70% (LHV) at a 1 MWe power level while producing minimal soot and NOx emissions.
Reactivity controlled compression ignition (RCCI) is a low temperature combustion strategy that offers one of the highest reported indicated thermal efficiencies for internal combustion engines, while having ultra-low nitrogen oxides (NOx) and soot emissions. The complex nature of RCCI makes it challenging to control combustion for an optimum heat release shape at broad engine operation with low cyclic variability and without exceeding maximum allowable in-cylinder pressure rise rate. This study aims at developing a control oriented model (COM) and a model predictive controller (MPC) to adjust combustion phasing, including crank angle by which 50% of fuel mass is burnt (CA50) and load, including indicated mean effective pressure (IMEP) during both steady-state and transient RCCI operations. A new COM is developed using a combination of physics-based and empirical models. An MPC with a 5-cycle prediction horizon is developed and implemented on an experimental RCCI engine setup. The IMEP and CA50 are controlled by adjusting injected fuel quantity, dual-fuel premixed ratio (PR), and start of injection (SOI) timing. To extend the controller operating range, switched MPCs are developed using PR as the scheduling variable. In addition, a sensitivity-based control strategy is developed to select between PR and SOI as the control variable. Experimental validation results show that the designed controller can track desired CA50 and IMEP with less than 1.4 CAD and 15 kPa tracking errors on a range of RCCI operation.
This work aims to determine the potential and benefits of cylinder pressure-based control (CPBC) to meet future emission legislation for heavy-duty automotive applications. Focus is on resulting engine performance. From a literature study, it is seen that CPBC is a crucial enabler for ultra high efficient and clean combustion concepts, such as PPC and RCCI. For these advanced concepts, combustion phasing and heat release control is key to guarantee stable and safe operation. RCCI also supports the transition towards sustainable fuels by allowing for the use of a wide range of fuels. In addition, CPBC is seen to reduce the calibration effort and to improve performance robustness for all combustion concepts. This results in reduced engine out emission dispersion and improved torque response. Installation of cylinder pressure sensors opens the route to real-time and robust estimation and monitoring of fuel efficiency, combustion noise, and NOx and opacity emissions. This permits new OBD functionality and sensor removal, and thus system cost reduction. For PPC and RCCI, the main control challenges are stable operation with maximal efficiency over the full load range, transient control, and fuel flexibility. To fully exploit the CPBC potential, better understanding of coordinated air-fuel path control, self-learning control capabilities for on-line fuel optimization, and in-cycle control of the heat release shape is needed.
Reactivity controlled compression ignition (RCCI) combustion is one of the most promising low temperature combustion (LTC) techniques, as it is able to provide ultra-low NOx and soot emissions together with higher thermal efficiency than conventional diesel combustion (CDC) in a wide range of operating conditions. However, the unburned hydrocarbon (UHC) and carbon monoxide (CO) emission levels are orders of magnitude higher than CDC, which can result in a major problem for implementing the RCCI concept in real engines. In this sense, the high levels of UHC and CO emissions together with the low exhaust temperatures during RCCI operation could compromise the diesel oxidation catalyst (DOC) conversion efficiency.
The objective of this work is to evaluate the efficiency of a conventional DOC in oxidizing the UHC and CO emissions from RCCI combustion. To do this, a medium-duty multi-cylinder diesel engine equipped with its original after treatment system has been used. First, the DOC conversion efficiency is evaluated under some steady-state conditions. Later, the influence of the thermal inertia on the DOC response has been evaluated by means of transient tests. In this sense, different engine load-speed steps as well some simplified conditions from the worldwide harmonized vehicle cycle (WHVC) and the supplemental engine transient cycle (SET) are evaluated. In steady-state conditions, with DOC-inlet temperatures of 200–300 °C, the results show conversion efficiencies of 100% for CO and 85–95% for HC. At 10% and 25% load, the DOC-outlet UHC levels are unacceptable considering the EURO VI regulation, while at 50% load the tailpipe emissions fulfill the emissions standard. The results in transient conditions are more promising thanks to effect of the thermal inertia, showing 100% conversion efficiency for CO and greater than 90% for UHC during large periods of engine operation.
This work compares the performance and emissions of two dual-mode combustion concepts over different driving cycles by means of vehicle systems simulations. The dual-mode concept relies on switching between the dual-fuel concept known as reactivity controlled compression ignition (RCCI) and conventional diesel combustion (CDC) to cover the whole engine map. The experimental RCCI maps obtained with diesel-E85 and diesel-gasoline used as inputs to perform the simulations were obtained in a high compression ratio light-duty diesel engine (17.1:1) following the same mapping procedure in both cases. The driving cycles simulated to perform the comparison were the Real Driving Emissions cycle (Europe), Worldwide harmonized Light vehicles Test Cycle (Europe), Federal Test Procedure FTP-75 (United States) and JC08 (Japan). The results show that the dual-mode concept has potential to be implemented in flexible-fuel vehicles. Using gasoline as low reactivity fuel (LRF) for RCCI, the vehicle mileage would be equal to CDC, but having reductions in NOx and soot emissions of 16% and 50%, respectively, along the RDE cycle. Using E85 instead of gasoline, the reductions in NOx and soot emissions increase up to 50% and 85%, respectively, but in this case promoting higher thermal efficiency than CDC.
Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide variety of engine platforms. However, a major challenge of this concept comes from the high hydrocarbon (HC) and carbon monoxide (CO) emission levels, which are orders of magnitude greater than CDC, and similar to those of port fuel injected (PFI) gasoline engines. The high HC and CO emissions levels combined with the low exhaust temperatures during RCCI operation could present a challenge for the current exhaust aftertreatment technologies.
The objective of this work is to evaluate the potential of a conventional diesel oxidation catalyst (DOC) for light-duty diesel engines when operating under dual-fuel RCCI diesel-gasoline combustion and to define its necessary size to accomplish with the current emissions standards. For this purpose, a 1-D model has been developed and calibrated through gas emissions measurements upstream and downstream the DOC under different engine steady-state conditions. After that, the DOC response in transient conditions has been evaluated by means of vehicle systems simulations under different driving cycles representative of the homologation procedures currently in force around the world. The results show that the HC and CO levels at the DOC outlet are unacceptable considering the different emissions regulations. By this reason, a dedicated study to define the DOC size needed to accomplish the different emissions standards is carried out. The results suggest that, the DOC volume needed to fulfill the type approval regulation limits ranges from four to six times the original volume.
This research focuses on the potential of the dual-fuel combustion engine fueled with regular gasoline and diesel to meet the Euro V emission standard over the whole operating range with a simple after-treatment system. For this purpose, a mode-switching strategy was investigated in this work. The engine maps of this strategy were obtained using a dedicated experimental procedure on a modified heavy-duty multi-cylinder engine. The switching of dual-fuel modes mainly depended on the engine load. At 25% engine load, fully premixed reactivity controlled compression ignition combustion was applied to achieve high efficiency and low emission combustion. At operating conditions higher than 50% load, homogeneous charge induced ignition combustion with up to three diesel injections (pre-, main and post-injections) was applied. Then, the effects of compression ratio on the dual-fuel combustion over the full operating map were explored and analyzed in detail. It was found that in spite of a slight increase in the fuel consumption, better combustion and emission performance over the whole operating map could be achieved in the dual-fuel combustion with a lower compression ratio. Finally, the effects of diesel oxidation catalyst were also investigated. The exhaust temperatures of this dual-fuel strategy were higher than the diesel oxidation catalyst light-off temperature, ensuring an effective conversion of the total hydrocarbon and carbon monoxide emissions. Furthermore, from the particle number-size distribution analysis, it was found that reactivity controlled compression ignition was dominated by the nucleation mode particles, while homogeneous charge induced ignition was dominated by the accumulation mode particles which tended to increase as the load increased. In addition, with a lower compression ratio of 16:1 and the application of diesel oxidation catalyst, the cycle-averaged regular emissions of the mode-switching combustion strategy could meet the Euro V emission standard simultaneously in the European Stationary Cycle test.