Christopher Sharp’s research while affiliated with Southwest Research Institute and other places

div class="section abstract"> Diesel aftertreatment (AT) systems are critical for controlling emissions of CO, HC, NO_X, and PM in the on-road transportation sector. Ensuring compliance with regulatory standards throughout the AT system's lifespan requires precise prediction of various degradation mechanisms under real-world operating conditions and mitigating their impact through proper catalyst sizing and advanced controls. In the SwRI A2CAT-II consortium, a medium-duty diesel engine production aftertreatment system was subjected to full useful life aging, involving chemical poisoning with phosphorus (P) and sulfur (S) species, along with hydrothermal aging following the DAAAC protocol. This study was aimed to model and predict the aging trajectory of this production AT system thereby capturing changes in system dynamics under both steady-state and transient conditions. The system, designed to meet the 0.2 g/bhp-hr standard, comprised a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). It was aged to 3600 hours equivalent to the DAAAC protocol and tested across a series of steady-state and regulatory cycles (HFTP, RMC, and LLC) at degreened, 33%, 66%, and 100% aging points. A linear decrease in system NOx conversion was observed between 0% to 66% aging, followed by a nonlinear drop from 66% to 100%. The cumulative decline in NOx conversion was 0.8%, which could significantly impact systems designed to meet a 0.05 g/bhp-hr target. IntroductionAftertreatment durability demonstration is a mandatory validation exercise for on-road medium and heavy-duty diesel engine certification. This requirement ensures that the emission compliance can be achieved for the intended full useful life (FUL) of the engine system or multiple vehicle families. Conventional Deterioration Factor (DF) approach considers linear effect of sulfur and phosphorous poisoning on the catalysts over the entire useful life based on performance from 33% of aging the catalysts and extrapolating them to FUL. However, based on various studies, the impact of fuel derived Sulfur on diesel aftertreatment components was found to be exponentially significant particularly on the SCR due to the sulfur poisoning effect which require an active means to liberate sulfur to maintain appropriate SCR NOx conversion performance. Phosphorous from lubricating oil is known to adversely affect the activity of the oxidation catalyst in a catalyzed DPF thereby reducing the passive regenerative performance of DPF. For these reasons, an extensive understanding of chemical poisoning (particularly Sulfur and Phosphoros) and hydrothermal aging are warranted to design, validate and demonstrate the durability of aftertreatment components that are subjected to the prolonged chemical exposure. To address the extensive challenges in durability demonstration, the Diesel Aftertreatment Accelerated Aging Protocol, or DAAAC, was developed by Southwest Research Institute as a part of consortium effort that includes input from diesel engine manufacturers [ 1 , 2 , 3 ]. DAAAC is an accelerated aging cycle developed for each application based on the available field data. It includes the exposure from hydrothermal aging, sulfur and lubricant derived poison at accelerated rates. The protocol also requires the entire aftertreatment system to be aged as a complete system, since the upstream components, such as DOC, can impact the chemical makeup of sulfur derived constituents. The protocol does not introduce chemical constituents not normally observed in the field. The accelerated chemical exposure rate is limited only to a degree that has previously demonstrated successful correlation to normal, unaccelerated aging. The Protocol also requires that chemical aging mechanisms are to be introduced and / or consumed in a manner representative of the engine’s defined consumption pathways. Examples include sulfur exposure via high sulfur fuel or gaseous SO₂ and oil consumption via pre-combustion / post-combustion pathways. The Protocol also does not introduce chemical components that are not normally present in oil or fuel (other than doping the fuel with higher concentrations of sulfur, but this amount is relatively small). A comprehensive step by step breakdown of DAAAC protocol is presented elsewhere [ 2 ]. The primary objective of this paper is to disseminate the observation of long-term impacts of chemical poisoning and hydrothermal aging on a production aftertreatment catalyst subjected to FUL DAAAC protocol. The results of this experimental campaign were used to develop and validate a model capable of predicting hydrothermal and chemical aging mechanisms of conventional diesel aftertreatment to optimize long term emissions reduction performance. The paper is divided into following sections: 1 Introduction: An overview of the system 2 Background: A review of literature in the field of diesel AT aging 3 Test Campaign: Description of experimental setup used for collection of both steady state and transient data. 4 Experimental setup: Description of burner stand used for data collection. 5 Results and Discussion: Description of experimental results followed by discussion about underlying degradation mechanism identified through simulation work. 6 Summary and conclusion </div

div class="section abstract"> The heavy-duty low NOx program funded by EMA at Southwest Research Institute (SwRI) evaluates a combination of engine and advanced aftertreatment systems to achieve a 0.035 g/bhp-hr tailpipe NOx standard. This work emphasizes improvements to the light-off SCR (LO SCR) model used for low NOx controls. Two key mechanisms drive these improvements: the first is a real-time feedback system that utilizes the LO SCR outlet NOx sensor for short-term corrections to the model state, and the second involves adjustments to the dosing mechanism based on long-term trends in dosing signals compared to predicted NH3 consumption, derived from LO SCR inlet and outlet NOx sensors, referred to as long-term trim. An algorithm is incorporated to differentiate the LO SCR outlet NOx sensor readings into NOx and NH3 components based on cross-correlation between inlet and out NO _x sensors termed as speciation. The integration of this speciation algorithm with both short-term and long-term trim mechanisms significantly enhances the accuracy of the model estimated NH₃ storage state, as well as the prediction of outlet NOx, and NH3 levels under various transient conditions, including CFTP, HFTP, RMC, and LLC cycles. This improved accuracy in the LO SCR observer model enables more precise control of transient tailpipe NOx in the system. </div

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"> This work is a part of medium-duty Low NO _x technology development project with a focus on evaluating a combination of engine and advanced aftertreatment for 0.02 g/bhp-hr NO _x regulation proposed by CARB (California air resource board). In this project, a control oriented chemical kinetics model of SCR (Selective catalytic reduction) was used in the aftertreatment controller that is susceptible to performance degradation due to hydrothermal and chemical aging. This paper focuses on modeling the NO _x conversion and NH3 storage characteristics using a controls oriented SCR plant model which is further used for a model-based urea dosing scheme. A set of steady state reactor tests were used to calibrate the SCR performance at degreened, hydrothermal only and hydrothermal + chemical aging conditions and also to determine inhibition factors related to aging. The resultant model is capable of simulating SCR performance deterioration such as a reduction in NO _x conversion and NH3 storage. A non-linear aging profile was observed for Lo-SCR and downstream SCR showing a change in the NO _x conversion in the aged system when compared to a degreened system. Upon chemical aging further deterioration of low temperature performance was observed. This aging phenomenon impacts the dosing control strategy of the system. The results on controller performance for a set of Heavy Duty Federal Test Protocol(FTP), Ramp Modal Cycle (RMC), and Low Load Cycle (LLC) are presented. </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"> Typical two-site storage-based SCR plant models in literature consider NH₃ stored in the first site to participate in NH₃ storage, NO _x conversion and second site to only participate in NH₃ storage passively. This paper focuses on quantifying the impact of stored NH₃ in the second site on the overall NO _x conversion for an ultra-low NO _x system due to intra site NH₃ mass transfer. Accounting for this intra site mass transfer leads to better prediction of SCR out NH₃ thus ensuring compliance with NH₃ coverage targets and improved dosing characteristics of the controller that is critical to achieving ultra-low NO _x standard. The stored NH₃ in the second site undergoes mass transfer to the first site during temperature ramps encountered in a transient cycle that leads to increased NO _x conversion in conditions where the dosing is switched off. The resultant NH₃ coverage fraction prediction is critical in dosing control of SCR. This phenomenon is evaluated and quantified with different aging conditions, where the increased second site storage and reduced standard SCR activity due to hydrothermal aging leads to further increase in the reported phenomena. Although this phenomenon was observed for both light-off SCR (Lo-SCR) and downstream SCR based on analysis of the data, the impact on Lo-SCR performance was found to be higher compared to the downstream system due to the transient thermal conditions and higher temperatures experienced by the Lo-SCR system. This mass transfer mechanism also plays a role in determining NH₃ slip characteristics of Lo-SCR for real world conditions where the gradual transfer of NH3 in the axial direction leads to NH3 slip. This phenomenon is demonstrated using experimental data collected on a production engine for a set of HFTP, CFTP, RMC and LLC cycles </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