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CARB Low NOx Stage 3 Program - Modified Engine Calibration and Hardware Evaluations
... [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. ...
... SwRI was given open access to the ECM to make modifications, and details of the calibration changes are given in a previous SAE paper. [7] A number of hardware options were provided by suppliers as in-kind contributions to the program, and these were explored using supplemental funding that was provided by U.S. EPA, MECA, and the SwRI-run CHEDE-VII consortium. Figure 2 shows a summary of the hardware options evaluated. ...
... Figure 2 shows a summary of the hardware options evaluated. Detailed results of the individual hardware evaluations are reported elsewhere [4,7]. After final down-selection, cylinder deactivation (CDA) was retained for the Stage 3 demonstration. ...
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.
... The potential fuel consumption reduction with this combined supercharging and mild hybridization technology for a passenger car application was reported at 16% by King et al. In another integrated approach called SuperTurbo [23,24,25], the main engine turbocharger was coupled to a CVT and connected to the engine crankshaft, thereby enabling supercharging as well as turbocompounding capability. The technology achieved 28% engine downsizing on a heavy-duty off-road application with a 13.1% reduction in engine fuel consumption [25]. ...
... The technology achieved 28% engine downsizing on a heavy-duty off-road application with a 13.1% reduction in engine fuel consumption [25]. The technology also provided benefits in achieving ultra-low NOx emissions on heavy duty engines by reducing transient NOx and by improving aftertreatment thermal management [24]. An alternate concept eTurbo, is an integrated air system technology that integrates an electric motor on the turbocharger shaft to provide electric supercharging and electric turbocompounding capability [26,27,28]. ...
... The rotor of the first electric machine (26) is connected to the ring gear of first planetary set while the rotor of the second electric machine (42) is connected to the ring gear of the second planetary set. Lastly, the ring gear of first planetary set (24) is connected to the carrier of second planetary set (34). The arrangement allows for variable speed control of the secondary compressor (2) while also providing high-efficiency power-split energy transfer to the secondary compressor (mechanical from engine and electrical from electric machine 42). ...
While many technologies such as electrically assisted turbocharging, exhaust energy recovery and mild hybridization have already proven to significantly increase heavy-duty engine efficiency, the key challenge to their widespread adoption has been their cost effectiveness and packaging. This research specifically addresses these challenges through evaluation and development of a novel technology concept termed as the Integrated Turbogeneration, Electrification and Supercharging (ITES) system. The concept integrates a secondary compressor, a turbocompound/expander turbine and an electric motor through a planetary gearset into the engine cranktrain. The approach enables a reduced system cost and space-claim, while maximizing the efficiency benefits of independent technologies. First, an assessment of design alternatives for integration of the identified key engine technologies on a heavy-duty engine was conducted. Once the ITES concept was down selected, the research then focused on model-based optimization and evaluation of the ITES system for a downsized medium heavy-duty diesel engine applied in Class 6-7 urban vocational application. As an outcome of the evaluation, a 1D simulation based sizing methodology of ITES system components was proposed. Furthermore, a novel control strategy for the ITES system was developed that combines equivalent consumption based steady-state offline optimization with functional controls for transient operation and smooth mode switching. The offline optimization method was also extended to evaluate the potential of ITES system in increasing aftertreatment temperature, which is critical for meeting future ultra-low NOx emission standards. Lastly, using 1D simulation of validated models, the efficiency benefit of ITES system on engine certification and vehicle drive cycles was predicted for the Class 6-7 urban vocational application. In comparison to baseline engine, the downsized engine with ITES system predicted an 8.5% reduction in engine fuel consumption on HDFTP cycle, 19.3% increase in fuel economy on ARB Transient cycle and 23.7% increase in fuel economy on a real-world drive cycle.
... With different EGR strategies, it is expected that the efficiency can be improved further while emission is reduced. Another important technology adopted for heavy-duty low-load NOx emission control is cylinder deactivation, where cylinders are partially deactivated at low loads to increase the exhaust temperature of the firing cylinders [14,15]. Gasoline and diesel engines present different emission challenges. ...
... This system has been widely deployed to meet the current legislation requirement. Future heavy-duty emission regulation on NO x will likely drive the adoption of close-coupled SCR technology to meet lower NO x limits, cold start performance, low-load conversion efficiency, and durability requirements [14]. This close-coupled SCR system is in conjunction with dual urea injection, whereby urea is dosed at two locations allowing achievement of low NO x emission targets under a wide range of operations. ...
In the last several decades, emission regulations have become a significant driving force for vehicle technologies, from powertrain design to emission control. These technologies will experience continuous improvement and may require a paradigm shift to address more stringent emission regulations. As essential components of powertrain systems, fuel and lubricant additives have uniquely enabled powertrain performance and durability. This review focuses on the complex interactions between the fluids and the emissions control system. Investigations into the impact of fuel aromatic content on both primary and secondary emissions are discussed. This work provides the methodologies and context to evaluate the studies into the interactions between fluids and the emission system components. Research on lubricants interactions with particulate filters shows that the lubricant, when formulated appropriately, does not substantively degrade particulate filter performance. In fact, it was found that the lubricant additives can have positive impact on carbonaceous accumulation in the filter and improve particulate emissions. This work provides an overview and context for assessing the role of lubricant additives in the performance of the complete emission system. Understanding the full impact of the fluids, lubricant and fuel, and the powertrain hardware provides the foundation to design additives to deliver optimized performance for the vehicle with advanced emission control systems.
... A study conducted on a heavy-duty engine using a CDA hardware similar to the one used in this study also showed a 10% decrease in brake-specific fuel consumption for a 50 C increase in turbine-out temperatures (Matheaus, Evans et al., 2020). An ultra-low NOx engine demonstration study showed that amongst all the engine and catalyst technologies previewed, CDA hardware ranked highest for achieving conditions for low NOx and reduction in fuel consumption (Neely, Sharp et al., 2020). CDA can be achieved through different hardware configurations, ranging from complex variable valve actuation systems to simple modifications to valve actuation mechanism. ...
... Although the VGT is flexible in delivering a wide range of boost requirements for a six-cylinder operation, CDA mode pushes the limits of VGT operation while certain EGR rates are required. Turbocharger concepts like a SuperTurbo was used in another demonstration study to assist the primary turbocharger during CDA mode operation (Neely, Sharp et al., 2020). Furthermore, the separation of the EGR delivery mechanism from the turbocharger can also help expand the range of operation of the VGT. ...
The upcoming ultra-low-NOx (oxides of nitrogen) emissions standard and in-use NOx emissions requirement requires engine manufacturers to further reduce tailpipe NOx emissions by over 90% from the current United States Environmental Protection Agency 2010 heavy-duty emissions standard. To meet ultra-low NOx standards, significant improvements to the NOx reduction capability of the Selective Catalytic Reduction (SCR) system is required. Low-temperature exhaust conditions and the associated fuel penalty in increasing the exhaust temperatures for improving catalyst activity is an engineering challenge to balance lowering NOx emissions while lowering fuel consumption. Cylinder Deactivation (CDA) in diesel engines has shown the ability to increase exhaust temperatures while maintaining a zero-fuel penalty. This study details the results of the performance of a CDA hardware installed in a modern heavy-duty diesel engine. The study was aimed at developing steady-state engine calibrations to maximize exhaust temperatures while realizing a zero-fuel penalty or improved BTE operation during low-load engine operating conditions for an on-road heavy-duty diesel engine. In addition, the study demonstrated the effect of CDA on lowering aftertreatment cooldown during motoring operation. The results of the study showed close to a 100°C increase in turbine out temperatures (TOT) at idle, 1,000 rpm and 1,200 rpm engine speeds with engine load at 10 and 20% of rated torque. The results also showed that deactivating three of the six cylinders during motoring operation of the low-load cycle delayed after treatment cool down and maintained exhaust temperatures above the SCR activity threshold for a longer duration.
... [4][5][6] In addition to improvements in aftertreatment system materials such as the coating of catalysts, researchers are paying more attention to advanced aftertreatment configurations and corresponding control strategies, such as dual-stage SCR aftertreatment systems. [7][8][9] With the emergence of RDE emission problems, precise control of diesel engine SCR aftertreatment systems is crucial for solving RDE problems. ...
With the advancements in deep learning and neural network technologies within the engine technology domain, intelligent control of exhaust after-treatment systems has become viable. The exhaust temperature significantly affects the NOx conversion efficiency of the SCR system. In this study, a time-series prediction model for exhaust temperature and NOx emissions was first developed using the LSTM neural network based on experimental data, and a Multi-Head Attention Mechanism was introduced to enhance the model’s predictive performance (LSTM-MA model). Subsequently, a dual-stage SCR system’s ammonia-to-NOx ratio control method (LSTM-ANR) was developed based on LSTM-MA model. The potential of the dual-stage SCR system using the LSTM-ANR control method to reduce NOx emissions during the WHTC cycle was analyzed using GT-Power and Simulink software. Finally, the experimental results show that the cold-state and hot-state WHTC cycle’ weighted NOx emission and conversion efficiency are 0.165 g/kW·h and 98.6%, respectively. Compared to the original data from the engine, NOx emission was reduced by 64.13%. This proves that the control method can effectively lower NOx emission.
... Further improvements in combustion characteristics are progressing through new types of combustion strategies, advanced piston designs, high-pressure piezoelectric fuel injection, cooled EGR systems, variable geometry turbochargers, cylinder deactivation, and variable valve lift and timing, among others [7]. Figure 6 summarizes some of the engine technologies that will help enable low NO x systems. Cylinder deactivation, in particular, appears to show great promise when compared with other hardware technologies from evaluations as part of the CARB low NO x demonstration program [53]. However, issues related to the commercial viability of this technology remain to be addressed. ...
Oxides of nitrogen (NOx) represent unwanted by-products from combustion of fossil fuels. NOx can cause significant harm to living beings through decreased air quality. This review summarizes the
sources of NOx emissions, regulations established to limit these emissions from on-road transportation, and the technologies developed by the automotive industry to meet these requirements. As
regulations continue to establish lower limits for NOx emissions, engine and power technologies are evolving to meet these requirements. Exhaust aftertreatment systems have enabled near-zero
tailpipe NOx emissions using NOx reduction catalysts. These catalysts are being further developed for improved low-temperature performance and higher durability. Such improvements are enabled
through fundamental understanding of the underlying chemistry governing these catalytic processes. Future modifications in exhaust aftertreatment system architectures and catalysts will require robust
system control to optimize system performance and ensure high NOx conversion throughout useful life.
... Additional examples of implementation of the same approach have led, for an X15 6-cylinder Cummins engine with variable geometry turbine (VGT) and high-pressure exhaust gas recirculation (EGR), to an increase of 40-100 °C of the turbo-out temperature, with an overall reduction of roughly 20% in fuel consumption together with a simulated reduction of NOx going from 45% to 66% and a 1.5-3.7% decrease in CO2 depending on the cycle considered (FTP (federal test procedure) or LLC (low load cycle), respectively) [74][75][76]. ...
This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH3 and N2O. The NOx, N2O, and NH3 emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH3 and N2O is observed in both Diesel and gasoline light-duty vehicles, whereby NH3 emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH3 emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N2O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles.
A diesel oxidation catalyst (DOC) outlet nitrogen dioxide (NO 2 ) ratio model based on the model-based calibration (MBC) method was proposed, which is an important part of the two-stage selective catalytic reduction (SCR) control strategy for heavy-duty diesel engines. Emissions regulations for heavy-duty diesel engines around the world have become more stringent in limiting nitrogen oxide (NOx), especially when the engine is cold starting, which brings serious challenges to the aftertreatment system. The two-stage SCR system with the close coupled selective catalytic reduction-diesel oxidation catalyst-diesel particulate filter-selective catalytic reduction (ccSCR-DOC-DPF-SCR) layout has the potential to achieve ultra-low NOx emissions due to its high technology maturity, but the two-stage SCR urea injection control strategy based on the chemical reaction kinetics model presents a new functional requirement for the prediction of NO 2 ratio at the DOC outlet. However, experiments show that the Euro VI method based on calibration to obtain DOC outlet NO 2 ratio was not suitable for the two-stage SCR system, because of the temperature delay effect of ccSCR in transient conditions. Therefore, a quadratic polynomial model using the MBC method was constructed to predict the DOC outlet NO 2 ratio in the two-stage SCR system. The proposed MBC model can predict the NO 2 ratio by using exhaust mass flow rate, DOC inlet temperature, and DOC inlet NOx concentration. Experiments show that the proposed MBC model has wide applicability, for the two-stage SCR system under transient conditions, whether ccSCR urea injection is enabled will not affect the accuracy of the model’s prediction of the NO 2 ratio for the DOC outlet or SCR inlet.
The continuous reduction of NOx emission limits for heavy-duty diesel engines poses challenges to the control strategies of diesel engine. Developing an accurate prediction model for NOx emission and exhaust temperature is of great importance in reducing NOx emission. In this study, a time-series prediction model for exhaust temperature and NOx emission is built using LSTM neural network. The model's inputs are determined using sensitivity analysis. It can be also found that the prediction of exhaust temperature is highly sensitive to the past values of exhaust temperature and NOx emission. The impact of different types of cost functions on the model is investigated. According to the predictive abilities (the average after ten training runs) of models using different cost functions, a combination of the Mean Absolute Error (MAE) cost function and Huber cost function is selected to further improve the model performance. By introducing a novel combination cost function, multi-head attention mechanism, and convolutional neural network approach into the LSTM model, the LSTM-CCF-MA model was found to yield the best prediction results for NOx and exhaust temperature. The goodness of fit for all the training and test datasets exceeded 0.97.
Selective catalytic reduction (SCR) catalysts is used widely to reduce NOx emissions from diesel engines. However, improvements in de-NOx performance are required to meet future standards of near-zero NOx emissions. This study examines the effectiveness of dual-point NH3 injection technology, in which gaseous NH3 is injected into both closed coupled and under floor SCR catalysts. The NOx removal efficiency of dual-point NH3 injection is compared with that of single-point injection in a World Harmonized Transient Cycle test. The results show that dual-point injection of NH3 gas can effectively reduce NOx emissions from diesel engines due to superior temporal and spatial distribution of NH3 gas in an SCR catalyst.
div class="section abstract"> Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.
This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation: 1 Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.
2 A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.
3 HDIUT assessment results and observations for LLC and custom transient cycles.
4 Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.
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div class="section abstract"> In 2020, CARB adopted the low NOX omnibus ruling, which provided revisions to on-road heavy duty engine compliance standards and certification practices. As part of the updates to the regulation, CARB has introduced a new in-use vehicle testing process that broadens the operation modes tested and considers the manufacturer’s intended vehicle application. Compared to the previous method, or the Not-to-Exceed approach, cold start and low ambient temperature provisions were included as part of the updates. The inclusion of low temperature operation requires the OEMs to design a robust engine and aftertreatment package that extends NOX conversion performance. The following work discusses the NOX emissions performance impact in a low temperature ambient environment. The engine and aftertreatment system evaluated was designed to comply with CARB’s low NOX regulations. The cycles tested included the CARB Southern NTE cycle and an FTP-LLC protocol. Both test sequences were intended to replicate drive cycles observed in the field. Overall, results indicated higher emissions for the low ambient temperature conditions. Utilizing the 3-bin moving average window method, emissions results were calculated for idle, low load, and medium / high load bins. While the CARB Southern NTE cycle showed an increase in the idle and low load bins, the system was able to maintain compliance. The medium / high load bin, however, exceeded the compliance limit by ~40% due to changes in the exhaust conditions. For the FTP-LLC protocol, LLC segments also increased, but maintained compliance based on the 2031+ in-use NOX standards. Furthermore, low ambient temperature operation creates challenges for controlling emissions even with a low NOX system.
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div class="section abstract"> Despite considerable progress towards clean air in previous decades, parts of the United States continue to struggle with the challenge of meeting the ambient air quality targets for smog-forming ozone mandated by the U.S. EPA, with some of the most significant challenges being seen in California. These continuing issues have highlighted the need for further reductions in emissions of NOX, which is a precursor for ozone formation, from a number of key sectors including the commercial vehicle sector. In response, the California Air Resources Board (CARB) embarked on a regulatory effort culminating in the adoption of the California Heavy-Duty Low NOX Omnibus regulation.[ 1 ] This regulatory effort was supported by a series of technical programs conducted at Southwest Research Institute (SwRI). These programs were 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, while maintaining a path towards compliance with current heavy-duty Phase 2 GHG standards. These efforts culminated in the Stage 3 Low NOX program, the results of which have been documented in previous publications.
In parallel with the completion of the Stage 3 technical effort, EPA began an effort to promulgate a national heavy-duty low NOX regulation, with the goal of completing the regulation in 2022 to support a 2027 model year implementation.[ 2 , 3 ] As part of that regulatory effort, EPA leveraged the test platform that was developed under the Stage 3 program to continue investigation of Low NOX technology capabilities and limitations. The emission control system was upgraded in several ways, and a number of topics were examined that expanded the scope of the evaluation. These included investigation of system performance under a variety of field duty cycles, examination of extended useful life out to 800,000 miles, the impact of low ambient temperatures on performance, and others. The performance of the updated system, and the results of the wider system investigations are summarized in this paper.
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div class="section abstract"> This program involved the detailed evaluation of a novel laser-based in-exhaust ammonia sensor using a diesel fuel-based burner platform integrated with an ammonia injection system. Test matrix included both steady-state modes and transient operation of the burner platform. Steady-state performance evaluation included tests that examined impact of exhaust gas temperature, gas velocity and ammonia levels on sensor response. Furthermore, cross sensitivity of the sensor was examined at different levels of NOX and water vapor. Transient tests included simulation of the FTP test cycles at different ammonia and NOX levels. A Fourier transform infrared (FTIR) spectrometer as well as NIST traceable ammonia gas bottles (introduced into the exhaust stream via a calibrated flow controller) served as references for ammonia measurement. Results suggested that Indrio’s sensor exhibits a strong linear relationship with reference ammonia measurement across the tested range of 0 ppm to 200 ppm with a regression factor (R2) ~ 0.99. Exhaust flowrate did not have a significant impact on sensor performance. With no temperature compensation applied, Indrio’s sensor performance was not impacted by temperatures of the order of 300°C to 400°C, however, it slightly overestimated ammonia levels at lower temperatures (~200°C). Cross-sensitivity experiments indicated that the presence of 200 ppm NOX resulted in less than 2.5% change in slope (Indrio sensor vs reference). Transient sensor response indicated that the sensor tracked reference ammonia concentration reasonably well. Overall, the sensor exhibited tremendous potential to serve as an accurate onboard ammonia sensor that could be used for real-time SCR control strategy optimization which will be invaluable for future low NOX platforms.
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Commercial vehicles require fast aftertreatment heat-up to move the SCR catalyst into the most efficient temperature range to meet upcoming NOX regulations while minimizing CO2. One solution to this challenge is to add a fuel burner upstream of the con`ventional heavy-duty diesel aftertreatment system. The focus of this paper is to optimize a burner based thermal management approach. The objective included complying with CARB’s 2027 low NOX emissions standards for on-road heavy duty diesel engines. This was accomplished by pairing the burner system with cylinder de-activation on the engine and/or a light-off SCR sub-system. A system solution is demonstrated using a heavy-duty diesel engine with an 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 mass flowrate through the aftertreatment system. The combination of operating the fuel burner, cylinder deactivation and elevated idle speed (during cold start) allows the aftertreatment system to heat up in a small fraction of the time demonstrated by today’s systems. Performance was quantified over the cold FTP, hot FTP, low load cycle (LLC) and the U.S. beverage cycle. The improvement in NOX reduction and the CO2 savings over these cycles are highlighted.
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.
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.
Worldwide automotive emission regulations for heavy-duty diesel engines are increasingly stringent, especially for nitrogen oxide (NOx) and particulate matter (PM). The development of high-efficiency aftertreatment technologies and the optimization of the urea injection strategies are key factors for the diesel engines to meet the future regulations. In this paper, the effects of temperature and space velocity on close coupled selective catalyst reduction (ccSCR) and SCR are investigated firstly. The highest NOx conversion efficiency of ccSCR and main SCR is observed at 350 ℃, and an increase of space velocity leads to a more significant decrease on NOx conversion efficiency of ccSCR than that of SCR. Then three phases of urea injection state for both nozzles are determined according to the catalyst inlet temperature in the Federal Test Procedure (FTP) cycle. Urea injection strategy is optimized by urea injection ratio calibration and urea injection strategy updating based on the characteristic of three phases, as well as NH3 sensor feedback. Finally, the composite tailpipe NOx emission under FTP cycle is reduced below 0.027 g/kW·h, satisfying California air resources board (CARB) ultra-low NOx emission regulation with a penalty of slight increase in CO2 emissions. However, adopting a high reactivity gasoline can improve the efficiency while maintaining the low level of NOx emissions.
div class="section abstract"> Compliance with future ultra-low nitrogen oxide regulations with diesel engines requires the fastest possible heating of the exhaust aftertreatment system to its proper operating temperature upon cold starting. Late post injections are commonly integrated into catalyst-heating operating strategies. This experimental study provides insight into the complex interactions between the injection-strategy calibration and the tradeoffs between exhaust heat and pollutant emissions. Experiments are performed with certification diesel fuel and blends of diesel fuel with butylal and hexyl hexanoate. Further analyses of experimental data provide insight into fuel reactivity and oxygen content as potential enablers for improved catalyst-heating operation.
A statistical design-of-experiments approach is developed to investigate a wide range of injection strategy calibrations at three different intake dilution levels. Thermodynamic and exhaust emissions measurements are taken using a new medium-duty, single-cylinder research engine. Analysis of the results provides insight into the effects of exhaust gas recirculation, oxygenated fuel blends, and fuel reactivity on exhaust heat and pollutant emissions. Late-cycle heat release is an important factor in determining exhaust temperatures. Intake dilution and fuel properties certainly affect late-cycle heat release, but the methods applied in this work are not sufficient to reproduce or explain the mechanisms by which improved fuel cetane rating promotes operation with hotter exhaust and lower pollutant emissions.
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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"> Dynamic Skip Fire (DSF®) has been shown to significantly reduce CO2 on gasoline engines and has been in mass production since 2018. Diesel Dynamic Skip Fire (dDSF™) builds upon the technology and extends it to diesel engine applications. dDSF is an advanced cylinder deactivation technology that allows the deactivation of any number of cylinders dynamically to deliver the requested torque while maintaining acceptable noise, vibration, and harshness (NVH) performance. NOx regulations are becoming progressively more stringent on light, medium and heavy-duty (HD) diesel engines. Meeting low NOx standards is becoming increasingly challenging, especially in lightly loaded operating conditions where maintaining ideal aftertreatment system efficiency is difficult. Most existing techniques to increase aftertreatment temperatures at low loads incur a fuel consumption penalty, which increases greenhouse gas emissions. In this study, dDSF is shown to combine benefits by reducing both NOx and CO2 simultaneously. Detailed studies were conducted on a Cummins X15 HD diesel engine. Engine testing and vehicle level simulation studies were followed by transient testing conducted on an engine dynamometer as well as on-road vehicle tests. NVH testing and evaluation was performed at the vehicle level to characterize vehicle response and ensure acceptability. dDSF calibrations were optimized to provide best thermal benefits at low loads. System level considerations such as coordination of air handling and fueling during transitions between firing densities, detection of valve actuation errors and mitigation of oil consumption concerns were studied. Results from system simulations using engine test data show 74% reduction of NOx and 5.0% reduction in CO2 on the Low Load Cycle (LLC) compared to the baseline engine with conventional thermal management. This simultaneous reduction helps compliance of NOx regulations while also reducing overall greenhouse gas emissions.
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This work explores pathways to achieve diesel-like, high-efficiency combustion with stoichiometric 3-way catalyst compatible combustion in a single-cylinder spark ignition (SI) research engine. A unique high stroke-to-bore engine design (1.5:1) with cooled exhaust gas recirculation (EGR) and high compression ratio ( r c ) was used to improve engine efficiency by up to 30% compared with a production turbocharged gasoline direct injection spark ignition engine. Engine experiments were conducted with both 91 RON E10 gasoline and liquified petroleum gas (LPG) (i.e. autogas) and were compared to legacy gasoline data on the production engine. Geometric compression ratio ( r c ) of 13.3:1 was used for both fuels with additional experiments at 16.8:1 for LPG only. Measurements of exhaust soot particle size and number concentrations were made with both fuels. Significant reduction in soot particles across the whole particle size range were achieved with LPG due to the elimination of in-cylinder liquid films. The effects of EGR, late intake valve closing (IVC) and fuel characteristics were investigated through their effects on efficiency, combustion stability and soot production. Results of 47% gross thermal efficiency, and 45% net thermal efficiency at stoichiometric engine operation, at up to 17 bar IMEP and 2000 r/min with 16.8:1 r c were achieved with LPG. Estimated brake efficiency values were compared to a contemporary medium duty diesel engine illustrating the benefits of the chosen path for achieving diesel efficiency parity.
This study presents an analysis of real-world emissions from two heavy-duty trucks using the Not-To-Exceed (NTE) and the European based Work-Based-Window (WBW) methodologies. The study also presents a sensitivity analysis of the NTE and WBW approach to key parameters such as window duration, torque, power, and exhaust aftertreatment thresholds. The analysis is performed on data collected from two heavy-duty diesel vehicles operated under real-world conditions in California over various routes that include a combination of urban and freeway type operation. The results presented show that only 10-30% of the total data meets the required exclusion criteria prescribed by the current NTE regulation. Reducing the NTE window duration from the existing 30 to 10 seconds increases the number of windows available to perform NTE analysis. The study also shows that exempting data that correspond to exhaust aftertreatment system (EATS) temperature threshold of below 250°C is the most dominant parameter influencing the number of available windows in an urban-type operation. The WBW approach produces a rich collection of data points that are representative of the in-use emissions characteristic of the vehicle. The results of NOx vs CO2 using a 4-quadrant analysis from the WBW approach is indicative of a difference in engine manufacturer design and emissions control strategy pertaining to real-world operation. The results of the study show that revisions to the boundaries and exclusions to the NTE zone would contribute to broadening the scope of in-use assessment of heavy-duty vehicle operation. However, even with such modifications, the NTE may not apply to highly transient urban vocations such as delivery, refuse and transit bus vocations. While comparing the moving average WBW approach to the NTE, the former approach produces a significantly larger number of data points for in-use assessment.
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.
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.
Simultaneous CO2 and NOX Reduction for Medium & Heavy-Duty Diesel Engines using Cylinder Deactivation
- J E Mccarthy