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Achieving Ultra Low NO X Emissions Levels with a 2017 Heavy-Duty On-Highway TC Diesel Engine and an Advanced Technology Emissions System - NO X Management Strategies
Abstract
Recent 2010 emissions standards for heavy-duty engines have established a limit of oxides of nitrogen (NOX) emissions of 0.20 g/bhp-hr. However, CARB has projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards, the National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and Ozone will not be achieved without further reduction in NOX emissions. The California Air Resources Board (ARB) funded a research program to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions. This paper details engine and aftertreatment NOX management requirements and model based control considerations for achieving Ultra-Low NOX (ULN) levels with a heavy-duty diesel engine. Data are presented for several Advanced Technology aftertreatment solutions and the integration of these solutions with the engine calibration. Further development is necessary for optimizing vocational test cycle emissions, but the results presented here demonstrate a potential pathway to achieving ultra-low NOX emissions on future heavy duty vehicles.
... However, when these systems are below 200 °C, during startup or low speed/load operation, their NOx conversion efficiency is low. One of the goals of the EPA and CARB partnership is to reduce or even eliminate these NOx emissions [3,4,5]. ...
... The LLC emissions requirements for NOx will be between 1 to 3 times the FTP and RMC-SET requirements (0.05 to 0.24 gNOx/bhp-hr) [3,6]. [1,4,5,8]. ...
... Storing NOx and HC emissions until the ATS is at operating temperature is a promising strategy. This can be achieved through the use of a PNA catalyst with zeolites to trap HC [1,5,8]. Figure 1.1 shows a schematic of proposed ULN ATS configurations compared to today's ATS systems [9]. ...
Medium and heavy-duty diesel engines contribute nearly a third of all NOx emissions nationwide. Further reduction of NOx emissions from medium and heavy-duty diesel engines is needed in order to meet National Ambient Air Quality Standards (NAAQS) for ambient particulate matter and ozone. Current diesel engine aftertreatment systems are very efficient at reducing NOx emissions at exhaust temperatures above 200 °C, however at exhaust temperatures below 200 °C there are significant NOx emissions at the tailpipe. Therefore, a reduction of diesel engine cold start and low speed/load operation emissions, where exhaust temperatures are below 200 °C, is needed. Utilizing a passive NOx adsorber (PNA) to adsorb NOx emissions at temperatures below 200 °C and reduce tailpipe NOx emissions is part of the solution. In this research, over 200 hours of experimental testing was carried out on a Johnson Matthey Diesel Cold Start Concept Catalyst (dCSC™), a passive NOx adsorber with hydrocarbon trapping ability on an oxidation catalyst. Storing NOx emissions while the aftertreatment system downstream of the PNA is at temperatures below 200 °C needs to be supplemented by externally heating the aftertreatment system downstream of the PNA. This would reduce the time the aftertreatment system is at temperatures below 200 °C. The faster the aftertreatment system reaches operating temperature the less risk of substantial NOx emissions at the tailpipe, because the storage capacity of the dCSC™ is finite. Methods such as electric heaters, fuel burners, engine calibration, engine hardware changes, and others to quickly reach desired aftertreatment temperatures are being researched. The EPA and CARB are preparing to monitor the emissions regulation compliance of medium and heavy-duty diesel engines by using on-board diagnostics, throughout the useful life of the engine. They are also investigating thermal and chemical catalyst poisoning in order to accurately age and predict the life of the aftertreatment system. Improving processes and reducing contaminants in fuels can reduce the risk of chemical catalyst poisoning. A 2013 6.7L Cummins ISB (280 hp) diesel engine was used for a series of experiments to quantify the NO, NO2, and NOx storage and release performance of the dCSC™. NOx storage experiments were performed at a range of temperatures from 80 to 250 °C and NOx release experiments were performed at temperatures from 200 to 450 °C. The portion of NO, NO2, and NOx that is converted and the portion that remains stored on the dCSC™ and the oxidation characteristics of the dCSC™ at these temperatures were also quantified. Peak NOx storage capacity of the dCSC™ was found to be at temperatures from 125 to 150 °C. Throughout the testing, a decrease in the total NOx storage capacity was observed. However, the 200-second dCSC™ NOx storage capacity remained constant throughout testing. The percentage of stored NOx released was observed to be over 70% if the dCSC™ temperature ramped through 200 to 265 °C and/or reached 350 °C. These temperatures coincide with the desired operating temperatures of current aftertreatment systems. The dCSC™ also shows over 50% NO to NO2 oxidation at temperatures from 200 to 400 °C and a peak oxidation performance of 90% at 300 °C. At temperatures of 150 °C and above, the dCSC™ oxides 90 to 100% of CO to CO2. At 80 to 125 °C, the dCSC™ oxidizes 50 to 70% of the CO entering the substrate to CO2.
... Thermal management is also possible by throttling the engine. An increase in pumping losses due to throttling on the intake side leads to a loss of efficiency with a corresponding increase in temperature [16,17] Figure 6. Nitrogen oxide conversion above the temperature before SCR (T before SCR) and temperature distribution before SCR of a 13-litre long-distance vehicle. ...
... External energy can be introduced into the system through electric heating catalysts or fuel burners to increase the exhaust gas temperature selectively and purposefully [17,21]. The introduction of the electrical energy at the position of the urea injection ( Fig. 9) additionally allows dosing of urea even at low exhaust gas temperatures without increased risk of deposits. ...
... An even closer position to the engine is possible with an additional SCR catalytic converter before the DOC [17,21,27]. ...
Despite of generally improving air quality, many European urban areas fail to comply with current immission rules. Therefore, in the automotive sector including commercial vehicles tighter limits and test procedures for real driving emissions are in discussion or have already been adopted. For the commercial vehicle sector corresponding regulations are discussed as well as challenges and measures to meet the upcoming more stringent requirements.
... [2,3,4] which culminated in the adoption of the Heavy-Duty California Low NO X Omnibus Rule [5] These efforts were conducted at SwRI starting in 2013 and continuing through 2020. The results of these earlier programs have been previously reported in other publications [6,7,8,9,10,11,12]. The Low NO X program was aimed at demonstrating the feasibility of technologies to reduce tailpipe NO X from heavy-duty engines by 90% from current standards, while at the same time maintaining a path towards meeting future greenhouse gas (GHG) standards. ...
Multiple areas in the U.S. continue to struggle with achieving National Ambient Air Quality Standards for ozone. These continued issues highlight the need for further reductions in NO X emission standards in multiple industry sectors, with heavy-duty on-highway engines being one of the most important areas to be addressed. Starting in 2014, CARB initiated a series of technical demonstration programs aimed at examining the feasibility of achieving up to a 90% reduction in tailpipe NO X , while at the same time maintaining a path towards GHG reductions that will be required as part of the Heavy-Duty Phase 2 GHG program. These programs culminated in the Stage 3 Low NO X program, which demonstrated low NO X emissions while maintaining GHG emissions at levels comparable to the baseline engine. Building on that prior program effort, EPA continued to support further Low NO X demonstration efforts in support of the development of new Federal Emissions Standards for heavy-duty highway vehicles and engines as part of the Clean Trucks Plan. Some of these efforts have been reported in previous publications, which focused on the evaluation of a modified Stage 3 architecture to extended useful life, as well as examination of various challenges related to field duty cycles, in-use measurements, sensors, and fuel. Beyond these efforts, EPA also undertook a redesign effort to produce an updated Low NO X aftertreatment system. The updated system incorporated many lessons learned from previous efforts, as well as recent catalyst process and formulation updates to improve performance and durability in key areas. This updated system was evaluated for emission control performance and durability using the Stage 3 Low NO X test engine. The updated system was aged to 800,000 equivalent miles using DAAAC accelerated aging techniques, and it was evaluated over both regulatory and field duty cycles. The results of these evaluations are presented within this paper.
... A model-based controller (Sharp et al., 2017;Rao et al., 2020;Sharp et al., 2021) was being used in this program to control the DEF dosing similar to the baseline work (Meruva et al., 2022) and also the thermal management strategies to power on the EH. The model tracks ammonia storage in each of the SCR substrates and has a target ammonia storage based on temperature. ...
Engine and aftertreatment solutions are being identified to meet the upcoming ultra-low NO x regulations on heavy duty vehicles as published by the California Air Resources Board (CARB) and proposed by the United States Environmental Protection Agency (US EPA) for the year 2027 and beyond. These standards will require changes to current conventional aftertreatment systems for dealing with low exhaust temperature scenarios. One approach to meeting this challenge is to supply additional heat from the engine; however, this comes with a fuel penalty which is not attractive and encourages other options. Another method is to supply external generated heat directly to the aftertreatment system. The following work focuses on the later approach by maintaining the production engine calibration and coupling this with an Electric Heater (EH) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) followed by a primary aftertreatment system containing a downstream Selective Catalytic Reduction (SCR). External heat is supplied to the aftertreatment system using an EH to reduce the Tailpipe (TP) NO x emissions with minimal fuel penalty. Two configurations have been implemented, the first is a Close Coupled (CC) LO-SCR configuration and the second is an Underfloor (UF) LO-SCR configuration. The CC LO-SCR configuration shows the best outcome as it is closer to the engine, helping it achieve the required temperature with lower EH power while the UF LO-SCR configurations addresses the real-world packaging options for the LO-SCR. This work shows that a 7 kW EH upstream of a LO-SCR, in the absence of heated Diesel Exhaust Fluid (DEF), followed by a primary aftertreatment system met the 2027 NO x regulatory limit. It also shows that the sub-6-inch diameter EH with negligible pressure drop can be easily packaged into the future aftertreatment system.
... Increased cylinder charge temperature promotes combustion stability and lowers unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions via enhanced charge thermal reactivity. Subsequently, a robust combustion process also improves the exhaust gas temperature to enhance the EAT system performance [13][14][15]. ...
By harnessing gasoline’s low reactivity for partially premixed combustion promotion, gasoline compression ignition (GCI) combustion shows the potential to produce markedly improved NOx-soot trade-off with high fuel efficiency compared to conventional diesel combustion. However, at low-load conditions, gasoline’s low reactivity poses challenges to attaining robust combustion with low unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. Increasing the in-cylinder charge temperature by using variable valve actuation (VVA) can be an effective means to address these challenges. In this numerical investigation, VVA strategies, including (1) early exhaust valve opening (EEVO), (2) positive valve overlap (PVO), and (3) exhaust rebreathe (ExReb), were investigated at 1375 RPM and 2 bar brake mean effective pressure in a heavy-duty GCI engine using a market-based gasoline with a research octane number (RON) of 93. The total residual gas level was kept over 50% to achieve an engine-out NOx target of below 1.5 g/kWh. For a complete engine system analysis, one-dimensional (1-D) system-level modeling and three-dimensional (3-D) computational fluid dynamics (CFD) analysis were close-coupled in this study. Performance of the VVA strategies was compared in terms of in-cylinder charge and exhaust gas temperatures increase versus brake-specific fuel consumption (BSFC). The EEVO strategy demonstrated in-cylinder charge and exhaust temperature increase up to 130 and 180 K, respectively. For similar in-cylinder charge temperature gains, the ExReb strategy demonstrated 11% to 18% lower BSFC compared to the EEVO strategy. This benefit primarily originated from a more efficient gas-exchange process. The PVO strategy, due to the valve–piston contact constraint, required excessive exhaust back-pressure valve (BPV) throttling for hot residuals trapping, thereby incurring higher BSFC compared to ExReb. In addition, the ExReb strategy demonstrated the highest potential for exhaust temperature increase (up to 673 K) among the three strategies. This was achieved by ExReb’s maximum air-fuel ratio reduction from high internal residuals mass and BPV throttling. Finally, the ExReb profile was optimized in terms of the peak lift, the duration, and the location for maximizing the fuel-efficiency potential of the strategy.
... Open loop feed forward control and close loop feedback control have been discussed and it was stated that the main challenge was how to actively manage NH 3 storage to maximize NOx reduction while reducing ammonia slip [3]. To achieve low NOx emissions, an integrated control strategy involving a selective catalytic reduction filter (SCRF) + selective catalytic reduction (SCR) scheme was applied [4,5]. Considering the temperature impact on SCR performance, thermal management was applied in the aftertreatment system [6]. ...
Urea-Selective Catalytic Reduction (SCR) is widely used to reduce nitrogen oxide (NOx) emissions. This paper presents a comprehensive experimental research work on aftertreatment emissions of NOx and ammonia (NH3) slip for three aftertreatment concepts by introducing the SCR sizing strategy on a 6-cylinder mid-range non-exhaust gas recirculation (EGR) diesel engine to meet China non-road Stage IV regulation limits. It can be observed that the three concepts could meet the regulation limits for NOx emissions and NH3 slip by selecting the appropriate length. There is little effect on emission results during a non-road transient cycle (NRTC) when the aftertreatment inlet/outlet with insulation and without insulation and the emission results on both strategies could meet non-road China Stage IV regulation limits. It is recommended to select Concept 2 which could meet regulation requirements considering multiple factors in the SCR sizing strategy. Substrate impact and NH3/NOx molar ratio (ANR) impact are investigated based on Concept 2. The results show that by applying the SCR substrate aftertreatment with a cell density of 600 cpsi, NOx conversion capability is stronger than that with cell density 400 cpsi for the same SCR size. Current dosing strategy is capable and recommended ANR is 0.9–1.1 if considering dosing strategy optimization. The methodology in this study provides an effective guidance and reference for future aftertreatment SCR sizing strategies in real applications.
... New engine designs and alternative fuels are expected to play a major role in controlling NOx emissions and subsequently improving air quality. Several studies have shown the pathway for ultra-low NOx emissions from stoichiometric compressed natural gas (CNG) engines, capable of achieving sub 0.02 g/bhp-hr of NOx emissions [12][13][14]. The use of natural gas has significantly increased in many fleets, such as refuse trucks, buses, delivery trucks, and yard tractors commonly used in on-terminal container movement [6,15,16]. ...
... However, to meet future emission reduction goals, it will be important to better control NO x emitted during low load operations with advanced engine and aftertreatment control strategies, such as implementing cylinder deactivation or using a mini-burner to keep the aftertreatment components at effective operating temperatures. 27,28 Brake-specific NO x emissions were the highest and showed the largest variations under low load conditions (Figure 2b). Meanwhile, instantaneous and distance-specific NO x emission rates were the lowest under low load conditions and showed comparable or even smaller interquartile ranges compared to medium and high load conditions ( Figure S4). ...
Real-world nitrogen oxides (NOx) emissions were estimated using on-board sensor readings from 72 heavy-duty diesel vehicles (HDDVs) equipped with Selective Catalytic Reduction (SCR) system in California. The results showed that there were large differences between in-use and certification NOx emissions, with 12 HDDVs emitted more than three times the standard during hot-running and idling operations in the real world. The overall NOx conversion efficiencies of the SCR system on many vehicles were well below the 90% threshold that is expected for an efficient SCR system, even when the SCR system was above the optimum operating temperature threshold of 250°C. This could potentially be associated with SCR catalyst deterioration on some engines. The Not-to-Exceed (NTE) requirements currently used by the heavy-duty in-use compliance program were evaluated using on-board NOx sensor data. Valid NTE events covered only 4.2 – 16.4% of the engine operation and 6.6 – 34.6% of the estimated NOx emissions. This work shows that low cost on-board NOx sensors are a convenient tool to monitor in-use NOx emissions in real-time, evaluate the SCR system performance, and identify vehicle operating modes with high NOx emissions. This information can inform certification and compliance programs to ensure low in-use NOx emissions.
This review provides a panoramic view of emission control technologies and key aftertreatment catalysts for vehicles using fossil fuels and carbon-neutral fuels.
div class="section abstract"> Currently, on-road transport contributes nearly 12% of India’s total energy related carbon dioxide (CO2) emissions that are expected to be doubled by 2040. Following the global trends of increasingly stringent greenhouse gas emissions (GHG) and criteria emissions, India will likely impose equivalent Bharat Stage (BS) regulations mandating simultaneous reduction in CO2 emissions and nearly 90% lower nitrogen oxides (NOx) from the current BS-VI levels. Consequently, Indian automakers would likely face tremendous challenges in meeting such emission reduction requirements while balancing performance and the total cost of ownership (TCO) trade-offs. Therefore, it is conceivable that cost-effective system improvements for the existing internal combustion engine (ICE) powertrains would be of high strategic importance for the automakers. In this second part of a two-part article, several component-level advancements are discussed, including both the engine and the aftertreatment system (ATS) for heavy-duty (HD) diesel engine based powertrains. For engine system level, the role of efficient air-handling systems (AHS), including turbochargers and EGR configurations to reduce engine out NOx emissions, was reviewed. For thermal efficiency improvements, potential of millerization and its implications on the AHS performance were presented. For an efficient ATS performance during the engine cold-start warm-up period, critical to meeting criteria emissions compliance, thermal management strategies, including valve variability, were reviewed. Finally, market-relevant HD engine system recipes with a minimal TCO implications were highlighted.
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The ultra-low NO x emission limits for heavy and mid-duty vehicles, which are expected to be imposed in both Europe and the USA by 2027, together with the enforcement of continuous decrease in CO 2 emission levels, make the need for adoption of newer technologies in the automotive industry imperative. To achieve low tailpipe NO x emissions, the accelerated warm-up of the exhaust aftertreatment system is of great importance. On the other hand, the thermal management strategies applied for this purpose result in fuel consumption penalty and consequently higher CO 2 as it can be widely found in the literature. Thus, the use and optimization of advanced thermal management technologies is critical to decrease the NO x – fuel penalty trade-off on the basis of complete driving cycles. In the present work an integrated modeled-based approach is implemented by coupling advanced, predictive 1D engine, and aftertreatment simulation models which are extensively validated via dedicated experimental data. The main goal of this approach is to define and investigate multiple engine or aftertreatment-based thermal management technologies, as well as a combination of them, creating a more efficient warm-up mode for the engine. Thermal measures such as cylinder deactivation, retarded start of the main injection, late intake valve closing (Miller cycle), intake throttling, elevated idle speed, and secondary fuel injection upstream the DOC are evaluated for their effect on the exhaust system heat-up time, the fuel consumption penalty and more importantly, for their impact on the tailpipe NO x emissions calculated by this holistic simulation approach.
div class="section abstract"> To achieve low tailpipe NOX emissions in Heavy-Duty engines, the rapid warm-up of the exhaust aftertreatment system (EAS) needs to be assisted by the adoption of new technologies to reduce engine-out emissions and increase the EAS conversion efficiency. Engine measures like cylinder deactivation, retarded start of the main injection, late intake valve closing, intake throttling and elevated idle speed can substantially increase the available exhaust gas enthalpy and temperature at the expense of additional fuel as has been shown in the literature. On the other hand, the exhaust system can be optimized in terms of hardware and controls, which is nowadays strongly supported by simulation. However, these simulation studies typically assume a fixed engine hardware and calibration and thus fixed engine-out simulation boundary conditions. Moving forward to tougher and real-world oriented legislation, the fixed cycle and engine-out boundary condition becomes insufficient. The present work proposes a model-based approach that covers both the engine and the aftertreatment system in a single simulation platform. To ensure the predictive nature of the simulation, all engine and aftertreatment models were calibrated with appropriate experimental techniques. The models are scalable depending on the application target; for most of the results of this work, we employ fast running 1d models. Using the holistic simulation approach, it is possible to virtually activate and optimize the settings of various engine parameters to obtain a good trade-off in terms of fuel penalty and tailpipe emissions. Due to the huge number of parameter combinations, the optimization process itself is a real challenge that is addressed in the present work and time-efficient workflows are demonstrated. The application cases presented emphasize on technologies expected to be relevant for upcoming legislation, including close-coupled SCR and active exhaust heating.
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Several NOx reduction technologies have been developed to alleviate the impact of NOx emissions on the environment and meet the more stringent upcoming emission legislation. Although UWS is the most commonly used NOx reduction technology, it has various issues listed in this article. Several alternative technologies based on solid materials as a gaseous ammonia source are developed to eradicate these issues. This article reviewed the solid SCR systems currently being developed as an alternative to UWS for deNOx applications. Furthermore, the chemistry of the various ammonia storage materials used in these systems and their potential to produce gaseous ammonia for use in SCR have been evaluated. Furthermore, the deNOx performance of ammonium salts-based and metal ammine chlorides-based solid SCR systems have been evaluated. Besides, we have discussed various numerical modeling and simulation approaches applied to develop these solid SCR systems. Due to gaseous ammonia injection solid SCR systems offer better NOx conversion efficiency compared with UWS systems, especially at low exhaust gas temperatures. The authors believe this article will be helpful for future studies in this field to further develop and establish these solid SCR systems as a viable alternative deNOx technology.
div>Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NOx) and carbon dioxide (CO2) regulations. This article focuses on the development and calibration of a model-based controller (MBC) for an advanced diesel AT system. The MBC was first applied to a standard AT system including a diesel particulate filter (DPF) and selective catalytic reduction (SCR) catalyst. Next, a light-off SCR (LO-SCR) was added upstream of the standard AT system. The MBC was optimized for both catalysts for a production engine where the diesel exhaust fluid (DEF) was unheated for both SCRs. This research shows that the tailpipe (TP) NOx could be reduced by using MBC on both catalysts. The net result was increased NOx conversion efficiency by one percentage point on both the LO-SCR and the primary SCR. The CO2 emissions were slightly reduced, but this effect was not significant. Finally, the MBC was used with a final setup representative of future AT systems which included standard insulation on the catalysts and optimal DEF dosing controls. This final configuration resulted in an improved NOx and CO2 such that the composite Federal Test Procedure (FTP) NOx was 0.060 g/hp-hr and the composite FTP CO2 was 508.5 g/hp-hr. The article details this cycle along with the low-load cycle (LLC) and beverage cycle. More technologies are required to meet the future California Air Resources Board (CARB) 2027 standard, which will be shown in future work.</div
White smoke emission from decrepit construction vehicles is one of the main causes of fine dust production. In particular, despite the fact that a large amount of white smoke is occurring in the vehicles such as decrepit construction machinery equipped with DPF (Diesel Particulate Filter), no technical solution has been found yet. This study aims to analyze the causes of white smoke emission that occurs in DPF system and propose technical solutions to resolve the issues. The performance and operational characteristics of the burner mounted to thermally manage the DPF performance are the main causes of the occurrence of white
smoke. The fundamental ignition mechanism of the diesel burners was investigated depending on the types of ignition sources; the rotating gliding arc for plasma burner and glow plug for conventional diesel burner. It was verified that plasma burner can be applied to drastically reduce the occurrence of white smoke.
The high emissions of diesel engines at cold start conditions have attracted more and more attention, because the exhaust gas temperature at this condition is too low to light-off the aftertreatment system. The electrically heated catalyst (EHC) has a high potential for increasing exhaust gas temperature and thus lowering emissions from diesel engines under cold start conditions. In this study, based on a diesel engine with an aftertreatment system that an EHC was installed in the inlet of a diesel oxidation catalyst (DOC), the engine was cold started to a low-load operating point (1000 r/min, 56 N·m) and the World Harmonized Transient Cycle (WHTC). The influence of the EHC on the exhaust gas temperature and emission characteristics under the two cold start conditions is investigated. When EHC-on as opposed to EHC-off, the time required for the exhaust gas temperature at post-DOC to reach 138 °C was shortened by 767 s during the low-load cold start process, and the time required to reach 200 °C was reduced by 418 s during the WHTC cold start process. The total conversion efficiencies of CO and HC increased by 92.8% and 50.8% respectively in the warm up process of the low-load cold start, and the increases were 39.8% and 38.5% respectively in the urban driving cycle of the WHTC cold start process. It was found that the particulate number (PN) concentration at post-DOC increased when EHC-on, and the proportion of nucleation-mode particulates also increased.
New regulations by the California Air Resources Board (CARB) demand a stringent 0.02 g/hp-hr tailpipe NO x limit by the year 2027, requiring Selective Catalytic Reduction (SCR) catalysts to provide high NO x conversions even at low (below 200°C) exhaust temperatures. This work describes utilizing an Electrically Heated Mixer System (EHM system) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) catalyst followed by a conventional aftertreatment (AT) system containing DOC, DPF, and SCR, enabling high NO x conversions meeting CARB’s NO x emission target. The AT catalysts were hydrothermally aged to Full Useful Life. Conventional unheated Diesel Exhaust Fluid (DEF) was injected upstream of both the LO-SCR and primary downstream SCR. The EHM system allowed for DEF to be injected as low as 130°C upstream of the LO-SCR, whereas, in previous studies, unheated DEF was injected at 180°C or dosed at 130°C with heated DEF. The combination of unheated DEF, EHM system, LO-SCR, and downstream SCR enabled the needed increase in NO x efficiency in low exhaust temperatures, which was observed in drive cycles such as in cold-FTP, LLC, and World Harmonized Transient Cycle (WHTC). There were several-fold reductions in tailpipe NO x using this configuration compared to its baseline: 3.3-fold reduction in FTP, 22-fold in Low Load Cycle (LLC), 38-fold in Beverage Cycle, 8-fold in “Stay Hot” Cycle, and 10-fold in WHTC. Finally, it is shown that the EHM system can heat the exhaust gas, such as during a cold start, without needing additional heating hardware integrated into the system. These results were observed without performing changes in the engine base calibration.
Balance of activity and thermal stability for diesel oxidation catalyst (DOC) is difficult to control in terms of different modification methods. We prepare SrMnO3-mixed SmMn2O5 (SMO) by the one-pot calcination, then followed in 5 M HNO3 treatment to yield Mn⁴⁺@SMO catalyst. Highly active Mn⁴⁺ cations form on SMO surface as amorphous MnO2 via removing nearly all the Sr in perovskite framework and surface Sm of SMO. Mn⁴⁺@SMO exhibits superior DOC performance compared with pristine and MnO2-doped SMO under a GHSV of 120000 mL·g⁻¹·h⁻¹ or even after 800 ºC hydrothermal aging, since it possesses higher average oxidation state of Mn, more oxygen vacancies, stronger covalent bonds of Mn-O, and larger NO adsorption above 200 ºC. DRIFTS, NAP-XPS, and isotopic analysis demonstrate that the exposed Mn⁴⁺ cations are the major sites for nitrate or nitrite adsorptions, while both CO and NO oxidation reactions follow the MvK mechanism.
The commercial vehicle industry continues to move in the direction of improving brake thermal efficiency while meeting more stringent diesel engine emissions requirements. This study focused on fuel efficiency when using an exhaust burner during cold starts. Selective catalyst reduction (SCR) systems are very efficient at eliminating NOx from the exhaust once its temperature has been raised to 250 °C. The exhaust burner is used during a cold start to raise the temperature of the SCR system quickly, and then it is turned off once thermal preparation of the SCR is complete. The exhaust burner converts fuel energy to exhaust heat directly, and thus more efficiently, in comparison to engine measures such as intake/exhaust throttling or elevating the idle speed. Therefore, if engine measures are scaled back because the burner is responsible for SCR system heating, total fuel efficiency should be improved.This hypothesis was tested at Southwest Research Institute (SwRI), making use of engine testing capabilities that allowed the results to be compared with those generated in the low-NOx technology demonstration funded by the California Air Resources Board (CARB). In addition to an exhaust burner, this testing made use of a conventional aftertreatment system (i.e. not a 2-stage SCR or “dual-dosing” system) that had been hydrothermally aged to end of useful life. FTP and WHTC cycles were run with the burner being responsible for more and more of the warm-up, allowing the tailpipe NOx vs. CO2 trade-off curve to be defined for this technology package.KeywordsEmissionsNOxCO2BurnerEfficiency
div class="section abstract"> The commercial vehicle industry continues to move in the direction of improving brake thermal efficiency while meeting more stringent diesel engine emission requirements. This study focused on demonstrating future emissions by using an exhaust burner upstream of a conventional aftertreatment system. This work highlights system results over the low load cycle (LLC) and many other pertinent cycles (Beverage Cycle, and Stay Hot Cycle, New York Bus Cycle). These efforts complement previous works showing system performance over the Heavy-Duty FTP and World Harmonized Transient Cycle (WHTC). The exhaust burner is used to raise and maintain the Selective Catalytic Reduction (SCR) catalyst at its optimal temperature over these cycles for efficient NOX reduction. This work showed that tailpipe NOX is significantly improved over these cycles with the exhaust burner. In certain cases, the improvements resulted in tailpipe NOX values well below the adopted 2027 LLC NOX standard of 0.05 g/hp-hr, providing significant margin. In fact, near zero NOX was measured on some of these cycles, which goes beyond future regulation requirements. However, burner operation on the tested cycles also resulted in a CO2 increase, indicating that a different burner calibration strategy, or possibly an additional technology, will be needed to achieve lower CO2 emissions.
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Commercial vehicles require fast aftertreatment heat-up in order to move the selective catalytic reduction catalyst into the most efficient temperature range to meet upcoming NOX regulations while minimizing CO2. This study is a follow-up study using an electric heater upstream of a LO-SCR followed by a primary aftertreatment system having an engine equipped with cylinder deactivation. The focus of this study is to minimize the maximum power input to the e-heater without compromising tailpipe NOX and CO2. A system solution is demonstrated using a heavy-duty diesel engine with an end-of-life aged aftertreatment system targeted for 2027 emission levels using various levels of controls. The baseline layer of controls includes cylinder deactivation to raise the exhaust temperature more than 100°C in combination with elevated idle speed to increase the exhaust mass flow rate through the aftertreatment system. The engine load is adjusted to compensate for generating electrical power on the engine. The combination of electrical heat, added load, cylinder deactivation, and elevated idle speed allows the aftertreatment system to heat up in a small fraction of the time required by today’s systems. This work was quantified over the cold federal test procedure, hot FTP, low load cycle (LLC), and the U.S. beverage cycle showing improved NOX and CO2 emissions. The improvement in NOX reduction and the CO2 savings over these cycles are highlighted.
The deNOx performance of a selective catalytic reduction (SCR) system using ammonium carbamate (AC) was investigated and compared with that of a urea water solution (UWS). The effects of the NH3/NOx (α) ratio, injection threshold temperature (Tinj), and a zero-dimensional ammonia adsorption-desorption model on NOx conversion efficiency were evaluated. World harmonized transient cycle (WHTC) and non-road transient cycle (NRTC) tests were conducted using a 3.9-L diesel engine over a Cu-zeolite catalyst. The NOx conversion efficiency of AC in the WHTC and NRTC was increased compared with that of UWS during the cold phase by 6.43% and 8.71%, respectively, and during the hot phase by 14.79% and 11.93%, respectively. Gaseous ammonia injection at a low Tinj can explain improved deNOx performance, as increasing Tinj leads to a decrease in NOx conversion efficiency. Increasing the α ratio effectively increases NOx conversion efficiency, but a high α ratio leads to ammonia slip. Ammonia injection using a model-based control increased cold-start deNOx performance. These promising results provide an alternative pathway to controlling NOx emissions from heavy-duty diesel engines.
Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the Exhaust Gas Recirculation (EGR) and high-efficiency SCR routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, selective catalytic reduction (SCR) for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH3. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.
The latest legislative tendencies for on-highway heavy duty vehicles forecast further tightening of the NOx emissions limits in the European Union and also in the US; a NOx limit of 0.02 g/bhp-hr – the so called ultra low NOx limit – has been already approved by the California Air Resources Board (CARB) starting MY2027. In addition, the already phased-in regulations regarding CO2 enforce also a continuous reduction in CO2 emissions resp. fuel consumption both in the EU and in the US. In order to meet low NOx emission limits, a rapid heat-up of the exhaust aftertreatment (EAT) system is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO2 emissions as shown in numerous previous works also by the authors. A NOx-CO2 trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EAT side. In the present study a systematic investigation is carried out by means of modelbased holistic approach targeting the definition of optimal engine and EAT layout and thermal management calibration for future legislative emission limits. Using holistic engine and EAT concept development approach, conventional and advanced EAT layouts are tested. The advanced EAT layout consist of a close-coupled dual-stage SCR system which is directly coupled to the engine model. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NOx-CO2 emissions of the investigated cycle are compared and evaluated. Also, multiple improvement measures for engine are discussed and an outlook of future powertrain concepts is given.
Schaeffler is inventing a new electromechanical, discretely switchable valve lift system for commercial vehicle applications: the Schaeffler eRocker Arm System. This modular valve train system can be integrated easily in existing engine setups regardless of the camshaft position and number. It can support exhaust aftertreatment by rapid heat-up and efficient thermal management at extended low load operation. To meet future emission legislations, Schaeffler and IAV investigated various thermodynamic strategies via GT Power on a 12.2 l inline six-cylinder heavy duty engine. Innovative valve lift strategies like early intake valve closure in combination with secondary exhaust valve opening are compared to existing conventional strategies like intake air throttling and combustion phasing. The results show significant potential to increase the exhaust temperature with optimized fuel consumption.
div class="section abstract"> Despite considerable progress over the last several decades, California continues to face some of the most significant air quality problems in the United States. These continued issues highlight the need for further mobile source NOX reductions to help California and other areas meet ambient air quality targets mandated by the U.S. EPA. Beginning in 2014, the California Air Resources Board (CARB) launched a program aimed at demonstrating technologies that could enable heavy-duty on-highway engines to reach tailpipe NOX levels up to 90% below the current standards, which were implemented in 2010. At the same time, mandated improvements to greenhouse gas emissions (GHG) require that these NOX reductions be achieved without sacrificing fuel consumption and increasing GHG emissions. The CARB demonstration program has progressed through several stages since it was initiated, and the Stage 3 Low NOX program completed in 2020 represents the culmination of these technology demonstration efforts. This effort, using a 2017 production diesel engine as a baseline, demonstrated a combination of technologies that enabled Low NOX emission levels near the 90% reduction target, while at the same time maintaining GHG emission rates at the same levels as the base engine.
Previous publications have gone into detail regarding individual elements of the Stage 3 technology package. This paper will present a summary of the final configuration and final results of the Stage 3 program, including results for the fully aged aftertreatment system after the equivalent of 435,000 miles of operation. The performance of the final test article will be shown over a variety of both regulatory duty cycles and other off-cycle operations. The final fuel consumption and GHG performance of the system will also be described based on the benchmarking methods specified by EPA in the Phase 2 GHG standards.
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div class="section abstract"> The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NOX standards of CARB or EPA’s memorandum forecast further tightening of the NOX emissions limits. In addition, the GHG Phase 2 legislation and also phased-in regulations in the EU enforce a continuous reduction in CO2 emissions resp. fuel consumption. In order to meet such low NOX emission limits, a rapid heat-up of the exhaust after-treatment system (EATS) is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO2 emissions as shown in numerous previous works also by the authors. A NOX-CO2 trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EATS side.
In the present study a systematic investigation is carried out by means of model-based holistic approach targeting the definition of a high efficiency engine layout and optimal thermal management calibration. First, the potentials of combustion process optimization (compression ratio, peak firing pressure) and of turbocharger efficiency increase are quantified aiming engine efficiency increase. Afterwards, using holistic engine and EAT concept development approach, conventional and advanced EATS layouts are tested. The advanced EATS layout consist of a close-coupled dual-stage SCR system. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NOX-CO2 emissions of the investigated cycle are compared and evaluated. Multiple improvement measures for both engine and EAT system are discussed and an outlook of future powertrain concepts is given.
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Urea SCR technology has been widely used to reduce NOx emissions of diesel engines. Despite remarkable
development for decades, more advanced control and optimization of urea SCR systems are still required as global NOx
emissions standards are expected to become more stringent. This study investigated several influential parameters of urea SCR
system to improve NOx reduction efficiency. This study uses a commercialized UWS (Urea Water Solution) supply system
and a SCR catalyst which was installed in the exhaust line of a non-road CRDI (Common Rail Direct Injection) diesel engine.
From this study, it was found that the low space velocity of SCR catalyst is essential for high NOx reduction efficiency,
especially at low temperatures. Early injection of UWS enhances the overall NOx reduction efficiency if UWS injection was
carefully controlled to avoid urea deposits. Rich injection of UWS with AOC is a good strategy for high NOx reduction
efficiency. However, NOx reproduction in the AOC, which has an adverse effect on the overall NOx reduction rate, occurs at
high exhaust gas temperatures. System insulation also can improve the NOx reduction efficiency by a few percentage points.
Ammonia/urea selective catalytic reduction is an efficient technology to control NOx emission from diesel engines. One of its critical challenges is the performance degradation of selective catalytic reduction catalysts due to the hydrothermal aging experienced in real-world operations during the lifetime. In this study, hydrothermal aging effects on the reduction of ammonia adsorption capacity over a commercial Cu-zeolite selective catalytic reduction catalyst were investigated under actual engine exhaust conditions. Ammonia adsorption site densities of the selective catalytic reduction catalysts aged at two different temperatures of 750°C and 850°C for 25 h with 10% H2O were experimentally measured and compared to that of fresh catalyst on a dynamometer test bench with a heavy-duty diesel engine. The test results revealed that hydrothermal aging significantly decreased the ammonia adsorption capacity of the current commercial Cu-zeolite selective catalytic reduction catalyst. Hydrothermal treatment at 750°C reduced the ammonia adsorption site to 62.5% level of that of fresh catalyst, while hydrothermal treatment at 850°C lowered the adsorption site to 37.0% level of that of fresh catalyst. Also, in this study, numerical simulation and kinetic analysis were carried out to quantify the impact of hydrothermal aging on the reduction of ammonia adsorption capacity by introducing an aging coefficient. The kinetic parameter calibrations based on actual diesel engine tests with a commercial monolith Cu-zeolite selective catalytic reduction catalyst provided a highly realistic kinetic parameter set of ammonia adsorption/desorption and enabled a mathematical description of hydrothermal aging effect.
Heavy duty (HD) vehicles are projected to be the largest fuel-use subsector in transportation, with current demand for diesel fuel projected to grow 30% by 2040. Historically, a primary strategy for increasing diesel engine efficiency has been to increase peak cylinder pressure (PCP). However, increasing PCP imparts greater mechanical and thermal loads on engine components and materials. In recent years, the material property limits for many components have been reached and further increases in PCP above ∼20 MPa have been difficult, while still maintaining the necessary affordability and longevity of on-road HD diesel engines. This paper reviews the historical evolution and major metallurgical advancements of high temperature materials in HD on road diesel engines (10–15 L displacement) up to the current state of the art, focusing on materials in the engine block, cylinder heads, pistons, valves, and exhaust components. These components cover a wide range of material classes, including cast iron, ferritic steel, austenitic steel, titanium alloys, nickel based super-alloys, and high temperature coatings. The microstructural degradation and failure mechanisms of the materials associated with the complex mechanical and thermal loading during service are discussed and key areas for future materials research are suggested that overcome technical barriers.
de Trotz sich stetig verbessernder Luftqualität werden die gesetzlich vorgeschriebenen Immissionsziele in urbanen Gebieten noch nicht eingehalten. Deshalb sind im Automobilbereich – auch im Bereich der Nutzfahrzeuge – weitere Verschärfungen der Grenzwerte und vor allem der Testprozeduren zur Überprüfung in Betrieb befindlicher Fahrzeuge angedacht bzw. bereits verabschiedet. Für Nutzfahrzeuge werden Verfahren zur Bestimmung von Realemissionen und anstehende Verschärfungen der gesetzlichen Prozeduren vorgestellt sowie mögliche Maßnahmen zur Einhaltung dieser strengeren Auflagen.
Abstract
en Despite of generally improving air quality, many urban areas fail to comply with current emission rules. Therefore, in the automotive sector including commercial vehicles tighter limits and test procedures for real driving emissions are in discussion or have already been adopted. For the commercial vehicle sector corresponding regulations are discussed as well as challenges and measures to meet the upcoming more stringent requirements.
The most recent 2010 emissions standards for heavy-duty engines have established a tailpipe limit of oxides of nitrogen (NOX) emissions of 0.20 g/bhp-hr. However, it is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards, the National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and Ozone will not be achieved without further reduction in NOX emissions. The California Air Resources Board (CARB) funded a research program to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions. This paper details the thermal management strategies employed by the engine and supplemental exhaust heat addition device as was needed to achieve Ultra-Low NOX levels on a heavy-duty diesel engine with an advanced technology aftertreatment solution Further development is necessary for optimizing vocational test cycle emissions, but the results presented here demonstrate a potential pathway to achieving ultra-low NOX emissions on future heavy duty vehicles.
The 2010 emissions standards for heavy-duty engines have established a limit of oxides of nitrogen (NOX) emissions of 0.20 g/bhp-hr. However, the California Air Resource Board (ARB) projects that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards, the National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter (PM) and Ozone will not be achieved without further reduction in NOX emissions. The California Air Resources Board (CARB) funded a research program to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions. This paper details the work performed on a heavy-duty diesel engine to explore the feasibility of various configurations of Traditional Technology (diesel oxidation catalyst-diesel particulate filter-selective catalytic reduction (SCR)) and Advanced Technology (passive NOX adsorber or diesel oxidation catalyst - SCR on Filter - SCR) to demonstrate ultra-low NOX emissions. Active and passive performance modifiers were also evaluated to demonstrate low NOX emissions, including heated dosing, gaseous dosing, and supplemental heat addition devices. The proposed Ultra Low NOX emission levels of 0.02 g/hp-hr require a significant shift in technology application to address cold start NOX emissions. Data are presented showing comparison in NOX reduction capability of the various configurations. All testing was conducted on the FOCAS-HGTR® system, which is a full flow, transient gas reactor bench for testing full sized catalyst systems.