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CARB Low NOX Stage 3 Program - Final Results and Summary
Abstract
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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... Although the system described above already yields low NO x emissions levels when the SCR reaches its maximum conversion efficiency of over 99% (Sharp et al., 2021), it is not as efficient at controlling NO x emissions under low-load and low-speed conditions (Posada et al., 2020). To meet the potentially more stringent requirements from Euro VII, several upgraded emissions control technologies and aftertreatment configurations have been proposed by industry suppliers and manufacturer associations. ...
... In Configuration 3 (Figure 7), which we assumed to have the highest NO x reduction potential of all three options, we assumed a 10% increase in the volume of the underfloor SCR stage for increased NO x conversion efficiency. This is also expected to improve the SCR system durability (Sharp et al., 2021). Additionally, as compared to Configuration 2, the LO-SCR was close-coupled (ccSCR) in the engine compartment and we therefore added a premium of 25% on substrate costs. ...
... In the closed-couple configuration, a smaller volume was assumed to accommodate for space constraints and reduce the thermal mass of the catalyst for faster warm-up. The ccSCR stage of Configuration 3 therefore has a SVR of 1.0, based on the reference study and according to previous research from Southwest Research Institute (Sharp et al., 2021). In Configuration 2 (Figure 6), the SCRF replaced the DPF and part of the underfloor SCR stage. ...
The European Commission is currently developing the requirements for the upcoming Euro VII standards. This paper assesses the total manufacturing costs of the emissions control systems—including both engine and aftertreatment technologies—that will likely be required to meet these limits. In particular, this study estimates the costs associated with deploying technologies in heavy-duty trucks that enable very low NOx emission levels under cold start and at low load, conditions that are representative of urban driving operation.
The analysis finds that the technologies required to achieve ultra-low pollutant emissions are already in production or close to commercialization. On the engine and powertrain side, technologies such as cylinder deactivation, EGR cooler bypass, and 48-volt systems could enable better low-load engine-out NOx control, faster catalyst warm-up, and stay-warm thermal management strategies. On the aftertreatment side, compliance with stricter NOx emissions limits is expected to require the use of close-coupled catalysts, increased catalyst volumes, dual urea injection, heated urea dosing, and electric catalyst heaters, as well as high filtration substrates, amongst others.
The estimated incremental costs of meeting the Euro VII standards compared to a typical Euro VI-compliant emissions control system will be between €1,500 and €4,700 in 2025, and between €1,400 and €4,300 in 2030. Therefore, Euro VII will likely result in a cost increase between 2% and 5% relative to the current price of new Euro VI tractor-trailer trucks. Engine-out emissions control represents 0%-41% of the incremental costs of compliance to Euro VII, while the rest accounts for improvements in the engine aftertreatment system.
Increasing the full useful life requirements of aftertreatment systems from the current 700,000 km to 970,000 km and 1,300,000 km would lead to average additional costs of approximately €700 and €1,000, respectively, in 2025.
... The motivation for this work was to meet the 2027 NO x regulations with no additional support from a production engine (without CDA or engine calibration change) with an external heat source on an AT system. The recent works on the AT system to meet the 2027 NO x regulations include using a LO-SCR (Kasab et al., 2021;Matheaus et al., 2021;Sharp et al., 2021). This catalyst was added to a conventional AT system in this work. ...
... This combination of LO-SCR and conventional downstream AT is considered the "baseline" in this demonstration (Meruva et al., 2022). Unlike previous studies that used a heated DEF doser upstream of the LO-SCR (Harris et al., 2021;Matheaus et al., 2021;Sharp et al., 2021;Zavala et al., 2022), this study uses a standard DEF doser in both locations. Catalyst specifications are shown in Table 1. ...
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.
... Most of the ongoing research works to achieve 2027 NO x regulations are with the addition of Light-Off Selective Catalytic Reduction (LO-SCR) to the current production aftertreatment systems (Kasab et al., 2021b;Sharp et al., 2021;Zavala et al., 2022). The LO-SCR gains a benefit of reaching the light off temperature faster than the primary SCR by staying closer to the engine. ...
... 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.
... Engine body technology alone cannot meet such stringent emission regulations. Researchers have proposed advanced aftertreatment technologies such as close-coupled selective catalytic reduction (ccSCR) , passive NO X adsorber (Gu & Epling, 2019), SCR on the filter (Okeleye et al., 2023), mini burner (McCarthy et al., 2022), and electrically heated catalyst (Kang et al., 2024) for the new emission regulations, with ccSCR attracting much attention due to its higher level of technological maturity (Harris et al., 2019;Lehtoranta et al., 2022;Liu et al., 2022;Sharp et al., 2021). However, there are still some challenges in fully utilizing the performance of ccSCR. ...
Diesel engine emission regulations are becoming stringent regarding nitrogen oxide (NOX) limits. The challenge is to improve the NOX conversion efficiency of the after treatment system under low temperatures. Although the two-stage selective catalytic reduction (SCR) has become a hot research topic, developing the urea injection strategy faces two challenges of accurately predicting ammonia (NH3) coverage and the complexity of two-stage SCR co-control. Therefore, first, control-oriented close-coupled SCR (ccSCR) and SCR models were established based on chemical reaction kinetic mechanism, mass conservation, and continuous stirred tank reactor law. The integrated model was established by coupling them with a control-oriented diesel oxidation catalyst model. Second, the effects of temperature, exhaust mass flow rate, oxygen concentration, NOX concentration, and nitrogen dioxide ratio on the NH3 coverage target value were investigated based on the integrated model. Third, a two-stage SCR co-control strategy was proposed. The NH3 coverage initial value and the threshold temperature for ccSCR to stop urea injection of the control strategy were optimized under the world harmonized transient cycle (WHTC). The results show that the NH3 coverage target value is most sensitive to temperature and decreases with increasing temperature. The composite tailpipe NOX under the WHTC is as low as 0.2 g/(kW·h).
... [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.
... These emission factors are approximately 25% lower than the Euro 7/VII NO x limits recommended by contractors of the European Commission; the CLOVE consortium [30], [31]. These stringency levels are informed by the emission limits adopted for LDVs and HDVs in other jurisdictions [32], [33], data stemming from demonstration programs by industry stakeholders [34], [35], and technology feasibility assessments carried out in the United States [36], among others. These reductions would correspond, approximately, to an 80% and 66% reduction in real-world NO x emissions for diesel and gasoline cars relative to current standing Euro 6d standards, respectively, 77% and 68% reduction for diesel and gasoline vans respectively, and a 79% reduction for trucks and buses compared to Euro VI-E. ...
Air pollution is the single greatest environmental health hazard in Europe, responsible for over 300,000 premature deaths in the EU27 in 2019. Transport is a significant contributor toward the emission of air pollutants which reduce life expectancy through increased likelihood of morbidity-associated diseases. The introduction of the Euro vehicle emission standards has been successful in driving down the overall level of transport related air pollutants. However, the current regulatory limits have not been updated in nearly a decade. Furthermore, deviations are still evident between the type-approval standards and real-world emission recorded through remote sensing. Based on the technology potential of current emission control systems, a feasible reduction in new vehicle emissions of nitrogen oxides (NOx) of up 80% applicable to light- and heavy-duty vehicles that could be realized through the upcoming revision of the Euro standards is modelled. A multi-model approach is employed, combining a stock simulation model and a health impact model which applies the latest methodology of the Global Burden of Disease to quantify the cumulative emissions reduction and corresponding health impacts in the EU27 through 2050. Mandating such a NOx reduction for new vehicles from 2027 would result in a 93-98% reduction in annual NOx emissions from transport by 2050, and reduce cumulative emissions by 4.2-5 million tonnes over the 2027-2050 period. The corresponding reduction in levels of particulate matter and ozone would prevent 34,675 - 41,645 premature deaths, and 568,374 - 682,513 years of life lost. Heavy-duty vehicles experience greater relative emissions reductions compared to their light-duty counterparts due to the current slower deployment of zero-emission vehicles in the sector.
... This is due to the higher volatility, lower viscosity, longer ignition delay, and better fuel-air mixing achieved with gasoline-like fuels. The improved soot-NOx tradeoff could also help alleviate the tremendous operational and durability demands placed on modern lean aftertreatment systems for meeting upcoming emissions regulations Lee et al., 2019;Sharp et al., 2021). Optimizing the combustion system for GCI (i.e., piston bowl shape, injector, and air system configurations) also has the potential to improve fuel economy compared to the most efficient internal combustion engines today (Kumar et al., 2019;Pei et al., 2019;Sellnau et al., 2019). ...
Gasoline compression ignition (GCI) is a promising combustion technology that could help alleviate the projected demand for diesel in commercial transport while providing a pathway to achieve upcoming CO2 and criteria pollutant regulations for heavy-duty engines. However, relatively high (i.e., diesel-like) injection pressures are needed to enable GCI across the entire load range while maintaining soot emissions benefits and managing heat release rates. There have only been a limited number of previous studies investigating the spray characteristics of light distillates with high-pressure direct-injection hardware under charge gas conditions relevant to heavy-duty applications. The current work aims to address this issue while providing experimental data needed for calibrating spray models used in simulation-led design activities. The non-reacting spray characteristics of two gasoline-like fuels relevant to GCI were studied and compared to ultra-low-sulfur diesel (ULSD). These fuels shared similar physical properties and were thus differentiated based on their research octane number (RON). Although RON60 and RON92 had different reactivities, it was hypothesized that they would exhibit similar non-reacting spray characteristics due to their physical similarities. Experiments were conducted in an optically accessible, constant volume combustion chamber using a single-hole injector representing high-pressure, common-rail fuel systems. Shadowgraph and Mie-scattering techniques were employed to measure the spray dispersion angles and penetration lengths under both non-vaporizing and vaporizing conditions. Gasoline-like fuels exhibited similar or larger non-vaporizing dispersion angle compared to ULSD. All fuels followed a typical correlation based on air-to-fuel density ratio indicating that liquid density is the main governing fuel parameter. Injection pressure had a negligible effect on the dispersion angle. Gasoline-like fuels had slower non-vaporizing penetration rates compared to ULSD, primarily due to their larger dispersion angles. As evidenced by the collapse of data onto a non-dimensional penetration correlation over a wide range of test conditions, all fuels conformed to the expected physical theory governing non-vaporizing sprays. There was no significant trend in the vaporizing dispersion angle with respect to fuel type which remained relatively constant across the entire charge gas temperature range of 800–1200 K. There was also no discernable difference in vapor penetration among the fuels or across charge temperature. The liquid length of gasoline-like fuels was much shorter than ULSD and exhibited no dependence on charge temperature at a given charge gas pressure. This behavior was attributed to gasoline being limited by interphase transport as opposed to mixing or air entrainment rates during its evaporation process. RON92 had a larger non-vaporizing dispersion angle but similar penetration compared to RON60. Although this seems to violate the original similarity hypothesis for these fuels, the analysis was made difficult due to the use of different injector builds for the experiments. However, RON92 did show a slightly larger vapor dispersion angle than RON60 and ULSD. This observation was attributed to nuanced volatility differences between the gasoline-like fuels and indicates that vapor dispersion angle likely relies on a more complex correlation beyond that of only air-to-fuel density ratio. Finally, RON92 showed the same quantitative liquid length and insensitivity to charge gas temperature as RON60.
div class="section abstract"> Internal combustion engines are expected to continue to play an important on-going role in the future of transportation, particularly in long haul transit and off-road applications. Substantially reducing criteria emissions of heavy-duty (HD) commercial vehicle engines while also reducing fuel consumption is the quickest way to achieve more sustainable transportation. The opposed-piston (OP) engine developed by Achates Power has demonstrated the ability to meet the most stringent ultralow NOx emissions requirements using only a conventional, underfloor aftertreatment system, offering reduced cost, complexity and compliance risk compared to other diesel engines. This paper is focused on the measurement results of Achates Power heavy-duty engine achieving CARB proposed ultralow NOx emission for 2027 and 2031+ full useful life requirements while also meeting the EPA Greenhouse Gas (GHG) Phase 2 limits with a conventional aftertreatment system (ATS), which was aged to 435k, 600k and 800k equivalent miles. The paper will describe EPA cycle results at each aging step and highlight the challenge of simultaneously meeting both criteria and CO2 emissions.
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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 amount of sulfate produced by SO 3 poisoning was significantly increased compared to SO 2 poisoning. Low-temperature sulfur poisoning and the presence of SO 3 resulted in a significant reduction in the number of active sites.
In colder climates, heavy-duty compression ignition (CI) engines and exhaust aftertreatment systems (EATS) may struggle to reach ideal operating temperatures under idling and low load conditions. This may lead to high emissions of pollutants, especially nitrogen oxides (NOx). The objective of this study is to evaluate performance of a heavy-duty CI engine operating at various idling conditions and determine suitability for EATS operation. Steady state tests are conducted at engine speeds of 650 and 1100 rpm, and cold weather operation is simulated by operating engine at sub-optimal coolant, lubricant, and intake air temperatures. These engine speeds correspond to two-mode Clean Idle Test (CIT) as specified in the United States' (US) Code of Federal Regulations (CFR). The steady state tests are used to determine suitable diesel injection timing for performing CIT under standard and simulated cold weather conditions. At lowest load and 650 rpm idling speed, use of multiple injections and exhaust gas recirculation (EGR) are insufficient for raising exhaust gas temperature above 200°C. A combination of higher load, EGR, and 1100 rpm idling speed can create conditions for light-off selective catalytic reduction (LO-SCR) operation at the expense of higher fuel consumption. The modified CIT results show that optional Clean Idle NOx emission standards can be met with the use of EGR at both test modes. The Mode 2 conditions at 1100 rpm may allow LO-SCR activation as well. There are also distinct differences between results under fully and partially warmed-up conditions.
div class="section abstract"> Options for CNVII emission legislation are being widely investigated in a national program organized by China Vehicle Emission Control Center (VECC) since early 2020. It is foreseen that this possibly last legislation in China will have more stringent emission requirements compared to CNVI, including among other changes especially a further reduction of nitrogen oxide (NOx), inclusion of nitrous oxide (N2O) and sub-23 nm particle number (PN).
This study investigates the technical feasibility to fulfill a CNVII emission legislation scenario, based on a modified CNVI 8 L engine operating under both cold and hot World Harmonized Transient Cycle (WHTC) and Low Load Cycle (LLC). Methods to address the challenges are discussed and validated, including application of a twin dosing system, electric heater, hybrid concepts of combining Copper (Cu-), Iron (Fe-) and Vanadium (V-) SCR technologies, filters with ultra-high filtration efficiency and optimization of engine calibration and urea dosing strategies.
Based on the results, an advanced aftertreatment system is then proposed that can meet the requirements of the discussed CNVII scenario.
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Mitigating CO2 emissions from long-haul commercial trucking is a major challenge that must be addressed to achieve substantial reductions in greenhouse gas (GHG) emissions from the transportation sector. Extensive recent research and development programs have shown how significant near-term reductions in GHGs from commercial vehicles can be achieved by combining technological advances. This paper reviews progress in technology for engine efficiency improvements, vehicle resistance and drag reductions, and the introduction of hybrid electric powertrains in long-haul trucks. The results of vehicle demonstration projects by major vehicle manufacturers have shown peak brake thermal efficiency of 55% in heavy-duty diesel engines and have demonstrated freight efficiency improvements of 150% relative to a 2009 baseline in North America. These improvements have been achieved by combining multiple incremental improvements in both engine and vehicle technologies. Powertrain electrification through hybridization has been shown to offer some potential reductions in fuel consumption. These potential benefits depend on the vehicle use, the details of the powertrain design, and the duty cycle. To date, most papers have focused on standard drive cycles, leaving a research gap in how hybrid electric powertrains would be designed to minimize fuel consumption over real-world drive cycles, which are essential for a reliable powertrain design. The results of this paper suggest that there is no “one-size-fits-all” solution to reduce the GHGs in long-haul trucking, and a combination of technologies is required to provide an optimum solution for each application.
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
div class="section abstract"> 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. The focus of this paper is to identify the technology levers when used independently and also together for the purpose of NOX and CO2 reduction toward achieving 2027 emissions levels while remaining CO2 neutral or better. A series of independent levers including cylinder deactivation, LO-SCR, electric aftertreatment heating and fuel burner technologies were explored. All fell short for meeting the 2027 CARB transient emission targets when used independently. However, the combinations of two of these levers were shown to approach the goal of transient emissions with one configuration meeting the requirement. Finally, the combination of three independent levers were shown to achieve 40% margin for meeting 2027 transient NOx emissions while remaining CO2 neutral. These independent levers and combinations were also quantified for meeting the new Low Load Cycle. This paper shows which combinations of technologies meets both the transient emission cycles and low load cycles for NOx with adequate margin while also saving CO2.
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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"> 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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div class="section abstract"> Eco-driving algorithms enabled by Vehicle to Everything (V2X) communications in Connected and Automated Vehicles (CAVs) can improve fuel economy by generating an energy-efficient velocity trajectory for vehicles to follow in real time. Southwest Research Institute (SwRI) demonstrated a 7% reduction in energy consumption for fully loaded class 8 trucks using SwRI’s eco-driving algorithms. However, the impact of these schemes on vehicle emissions is not well understood. This paper details the effort of using data from SwRI’s on-road vehicle tests to measure and evaluate how eco-driving could impact emissions. Two engine and aftertreatment configurations were evaluated: a production system that meets current NOX standards and a system with advanced aftertreatment and engine technologies designed to meet low NOX 2031+ emissions standards. For the production system, eco-driving on an urban cycle resulted in a CO2 reduction of 8.4% but an increase of 18% in brake specific NOX over the baseline cycle. With the low NOX system, eco-driving achieved a similar reduction in CO2. NOX emissions increased 108% over the baseline but remained below the low NOX standard. The eco-driving cycles generated lower exhaust temperatures than the baseline cycles, which inhibited SCR catalyst performance and increased tailpipe NOX. Conversely, a port drayage cycle with eco-driving showed improvements in both CO2 and NOX emissions over the baseline. The results demonstrate that eco-driving algorithms can be a technological enabler to meet current and potential future emissions targets for heavy-duty applications.
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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.
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
New EU7 emission standards are currently under development. While the timing and exact level of stringency of these standards is not available, both OEMs and suppliers are preparing to meet significantly reduced tailpipe NOx and particle number standards for both light- and heavy-duty vehicles. We present here some of the emission control systems that are likely to be implemented and details on the advanced component technologies.
Ammonia adsorption is a precondition for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) to take place and it influences catalyst performance under transient conditions. For a vanadium-based SCR catalyst NH3 adsorption takes place on multiple adsorption sites over the catalyst surface with different behaviours depending on temperature, gas concentration and catalyst oxidation state. In this study, a mechanistic NH3 adsorption model within the framework of Langmuir adsorption models was developed for describing the NH3 adsorption isotherms obtained with a gas flow reactor for a vanadium-based SCR. The model was created by a data-driven modeling process, which involves different steps. First, a large set of candidate models was created systematically by combining multiple feasible adsorption mechanisms. Then, a parameter estimation workflow was performed using three different objective functions with increased complexity. Finally, a model reconciliation step was executed and a quality assessment was done for creating a unified robust model with a high degree of validity. As a result of this method, an NH3 adsorption model with five adsorption sites with different mechanisms was obtained that captures the main features from the experimental data. Furthermore, the model parameters have physical significance and relate to the adsorption strength and spatial arrangement for NH3 and water molecules. The proposed model can be used in the development of transient models with increased validity over a wide experimental region.
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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div class="section abstract"> This review covers advances in regulations and technologies in the past year in the field of vehicular emissions. We cover major developments towards reducing criteria pollutants and greenhouse gas emissions from both light- and heavy-duty vehicles and off-road machinery. To suggest that the transportation is transforming rapidly is an understatement, and many changes have happened already since our review last year [ 1 ]. Notably, the US and Europe revised the CO2 standards for light-duty vehicles and electrification mandates were introduced in various regions of the world. These have accelerated plans to introduce electrified powertrains, which include hybrids and pure electric vehicles. However, a full transformation to electric vehicles and the required grid decarbonization will take time, and policy makers are accordingly also tightening criteria pollutant standards for internal combustion engines. California has published the Advanced Clean Cars II standards and Europe has held various workshops outlining the core elements of future Euro 7 regulations. These will likely be the last major regulations for criteria pollutants, and compliant vehicles will likely be zero-impact emitting, that is with tailpipe emissions at or lower than the ambient concentrations. Meeting these regulations will require adoption of several advanced engine and emission control technologies which we discuss here. Emphasis will be on reducing cold start emissions, likely requiring active thermal management strategies. The challenge will be to lower criteria pollutants while also reducing fuel consumption, and we review some approaches being considered. The story is similar for heavy-duty vehicles, where meeting California’s Low NOx regulations and Euro VII scenarios require significantly improved engine controls and after-treatment systems. New system solutions and hardware additions show a pathway to meeting the regulations, although we caution that much more work is needed ahead to achieve the reductions over extended durability limits and with healthy engineering margins. We also review the impact of alternative fuels on reducing well-to-wheels (WTW) greenhouse gas emissions, along with recommendations to continue improving market fuel quality to reduce negative impact on criteria pollutants. Finally, while this paper does not intend to provide a detailed review of battery electric or fuel cell vehicle technology, we touch upon a few studies which discuss the outlook of powertrain diversification from a total cost of ownership and greenhouse gas reduction perspective.
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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 year 2020 marked the 50th anniversary of the passage of the Clean Air Act in the United States. The subsequent creation of the Environmental Protection Agency (EPA) and establishment of national ambient air quality standards (NAAQS) for criteria air pollutants paved the way for increasingly stringent tailpipe emission limits for passenger cars and trucks. These limits have been met through significant advances in both engine hardware and controls, and after-treatment systems, the latter of which will be the focus of this chapter. Modern powertrains using advanced after-treatment systems can practically eliminate the harmful gases and particulates from entering the atmosphere. Three-way catalysts (TWC) can address NOx, CO and hydrocarbons (HC) emissions from stoichiometric gasoline vehicles with near 100% efficiency when operating above the light-off temperatures. Diesel vehicles, despite the bad press in recent years, can be emitting well below the regulated limits with the adoption of the latest technologies such as selective catalytic reduction of NOx (SCR). The key challenge in both technologies is addressing the “cold-start” emissions, which is the combination of high emissions following an engine start and after-treatment temperatures below light-off. We will review the latest options that are being pursued to address this challenge and lead to “zero-impact” emitting vehicles. Particulate filters are ubiquitous on diesel vehicles and are also making their way on to gasoline vehicles with the recent particle number regulations in Europe and China. Filtration efficiency is very high and only improves with vehicle age due to the accumulated ash layer. There is evidence that in highly polluted urban environments, the tailpipe particulate emissions can in fact be lower than the ambient concentrations. Emissions control technology is mature but still there is much more work to be done. New regulations such as Euro 7, LEV 4 and the heavy-duty low NOx regulations in US and Europe are looking for further deep cuts in pollutant limits, regulating new species and particulates down to 10 nm, and extending the testing to include “all” driving conditions. We will review the new component technologies and the after-treatment system layouts being developed to address these upcoming regulations.
Sulfur oxides are a common source for the deactivation of Cu-exchanged CHA zeolite based catalysts used for NOx reduction in diesel exhausts by selective catalytic reduction with NH3 (NH3-SCR). Since water and possible formation of SO3 affect the deactivation of Cu-CHA catalysts, the deactivation in the presence of SO2 or a mixture of SO2 and SO3 was studied by measuring the SCR activity in wet and dry gas at 200 and 550 °C. The estimated S-content in the catalysts before and after 4 h regeneration at 550 °C in NO, NH3, O2 and H2O was related to the deactivation. The deactivation can be divided into two parts: a reversible deactivation that is restored by the regeneration treatment, and an irreversible part. The irreversible deactivation does not affect the activation energy for NH3-SCR and display a 1:1 correlation with the S-content, consistent with deactivation by Cu-sulfate formation. The reversible deactivation results in a lower activation energy and a deactivation that is larger than expected from the S-content. The presence of SO3 at 200 °C leads to higher reversible and irreversible deactivation, but has no significant impact at 550 °C. Furthermore, the irreversible deactivation is always higher when exposed at 200 °C than at 550 °C, and in wet conditions, compared to a dry feed. The deactivation is predominantly reversible, making regeneration at 550 °C a realistic approach to handle S-poisoning in exhaust systems.
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.
Despite the recent remarkable advances in the development of Cu-zeolite materials for selective catalytic reduction (SCR) of NOx with NH3, their performance is not immune to the poisoning by sulfur oxide species SO2 and SO3, commonly referred as SOx. Periodic removal of SOx, i.e. deSOx, is needed to maintain high NOx conversion efficiency of these catalysts even when ultra-low sulfur diesel (ULSD) fuel is used. Such deSOx events require high temperatures, typically in excess of 550 °C, which can be detrimental to the durability of the SCR catalysts and other aftertreatment components, and may also result in a fuel penalty. In this work, a recently discovered method, herein referred to as chemical deSOx, was found to be effective for removal of sulfur and for recovery of NOx conversion at substantially lower temperatures. The method relies on the use of low concentrations of reductants under net oxidizing conditions, arguably by inducing a locally reducing environment on the catalyst surface through different chemical mechanisms. Reductants such as NOx + NH3, NH3, C3H6 and n-C12H26 were demonstrated to achieve the removal of sulfur species without resorting to high temperatures. It is proposed that the change of the oxidation state of Cu sites in response to these exposures, achieved through different chemical mechanisms depending on the reductant, was responsible for facilitating the removal of sulfur from the catalyst.
The different impacts of SO2 and SO3 on Cu/zeolite SCR catalysts were investigated by SCR performance tests and multiple characterization techniques including temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS). The results indicate that a larger amount of highly dispersed CuSO4 formed in the zeolite catalysts (Z–CuSO4) upon SO3 poisoning, explaining the much more significant deactivation of the Cu/zeolite catalysts that were exposed to SO3 compared to poisoning by SO2. This paper provides the first demonstration that active sites of Cu/zeolite SCR catalysts involved in the storage and removal of sulfur can react with SO2 and SO3 in very different ways. In particular, the significant differences in the extent of sulfur uptake account for the considerably different impacts of SO2 and SO3 poisoning on the performance of Cu/zeolite SCR catalysts.
Update on the Path to 2027 Emissions Stage 3 Low NOX Program Results,” Global Automotive Management Council
- C Sharp
Low NOx Demonstration - Stage 2 Final Report
- C Sharp