Bryan Zavala’s research while affiliated with Southwest Research Institute and other places

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.

div class="section abstract"> Upcoming regulations from CARB and EPA will require diesel engine manufacturers to validate aftertreatment durability with full useful life aged components. To this end, the Diesel Aftertreatment Accelerated Aging Cycle (DAAAC) protocol was developed to accelerate aftertreatment aging by accounting for hydrothermal aging, sulfur, and oil poisoning deterioration mechanisms. Two aftertreatment systems aged with the DAAAC protocol, one on an engine and the other on a burner system, were directly compared to a reference system that was aged to full useful life using conventional service accumulation. After on-engine emission testing of the fully aged components, DOC and SCR catalyst samples were extracted from the aftertreatment systems to compare the elemental distribution of contaminants between systems. In addition, benchtop reactor testing was conducted to measure differences in catalyst performance. Sulfur was deposited uniformly on the aftertreatment components while the oil derived phosphorous deposited more heavily at the system inlet. Consistent with on-engine emission testing results, the reference system SCR had worse overall NO_X conversion performance, though the performance was still within the specification of commercially available aftertreatment systems. High levels of oil-derived phosphorous deposited on the DAAAC-Engine SCR inlet greatly inhibited NO_X conversion but improved as the phosphorous levels decreased axially along the SCR, suggesting more volatile oil was introduced into the DAAAC-Engine system. Improvements to the DAAAC protocol to better represent real world aging are discussed. </div

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 NO_X, 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 NO_X 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 NO_X 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 NO_X 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 NO_X 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 NO_X 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. </div

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 NO_X standards and a system with advanced aftertreatment and engine technologies designed to meet low NO_X 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 NO_X over the baseline cycle. With the low NO_X system, eco-driving achieved a similar reduction in CO₂. NO_X emissions increased 108% over the baseline but remained below the low NO_X standard. The eco-driving cycles generated lower exhaust temperatures than the baseline cycles, which inhibited SCR catalyst performance and increased tailpipe NO_X. Conversely, a port drayage cycle with eco-driving showed improvements in both CO₂ and NO_X 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. </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 NO_X 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 NO_X 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. </div

div class="section abstract"> In 2020, CARB adopted the low NO_X 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 NO_X conversion performance. The following work discusses the NO_X emissions performance impact in a low temperature ambient environment. The engine and aftertreatment system evaluated was designed to comply with CARB’s low NO_X 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 NO_X standards. Furthermore, low ambient temperature operation creates challenges for controlling emissions even with a low NO_X system. </div

div>Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NO_x) 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) NO_x could be reduced by using MBC on both catalysts. The net result was increased NO_x 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 NO_x and CO₂ such that the composite Federal Test Procedure (FTP) NO_x 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

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