ARB Research Seminar

This page updated May 31, 2017

Evaluating Technologies and Methods to Lower Nitrogen Oxide Emissions from Heavy-Duty Vehicles

Photo of Christopher Sharp

Christopher Sharp

Photo of Ian Smith

Ian Smith

Christopher Sharp, Staff Engineer, Diesel Engine and Emissions R & D Department and Ian Smith, Research Engineer, Spark Ignited Engine Research and Development Department, Southwest Research Institute, San Antonio, Texas.

June 15, 2017
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


The 2010 emission standards for heavy-duty engines have established a limit for oxides of nitrogen (NOₓ) emissions of 0.20 g/bhp-hr, a 90% reduction from the previous emission standards. However, it is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with the 2010 NOₓ emission standards, the upcoming National Ambient Air Quality Standards (NAAQS) requirements for ambient particulate matter (PM) and ozone will not be achieved in California without further significant reduction in NOₓ emissions from the heavy-duty vehicles.

The main goal of this project was to demonstrate that modern heavy duty engines can achieve a target of 0.02 g/bhp-hr for tailpipe NOₓ emission, which represents a 90% reduction from the 2010 standard, with currently available control technology. An additional goal of the project was that the final configurations of engine and aftertreatment systems should be consistent with a path toward meeting current and future heavy-duty greenhouse gas (GHG) and fuel economy standards.

The project team selected two different engine platforms: a compressed natural gas (CNG)-based engine system and a diesel-based engine system. To identify advanced, production feasible, ultra-low NOₓ control solutions for both of these platforms, extensive work on calibrating engine control strategies, screening advanced aftertreatment technologies, selecting optimal combinations of engine and aftertreament technologies, and demonstrating ultra-low NOₓ emissions was performed in sequence.

The final system selected for the CNG engine was a combination of advanced air-fuel control strategies, close-coupled three-way catalyst (TWC), and conventional under-floor TWC. NOₓ emissions measured from the final CNG engine were 0.010 g/bhp-hr over the FTP certification cycle, well below the project target level of 0.02 g/bhp-hr. The final system selected for the diesel engine was a combination of cold-start engine calibration and an advanced aftertreatment system. NOₓ emissions from the final diesel system were measured with three different aftertreatment catalyst aging stages: degreened, thermal aging, and thermal and chemical aging. The NOₓ emissions over the FTP cycle were 0.008 g/bhp-hr, 0.012 g/bhp-hr, and 0.034 g/bhp-hr for the degreened, thermal aging only, and thermal and chemical aging, respectively. The project team suspects that the slightly high NOₓ with the thermal and chemical aged catalysts was due in part to an incident happened during the final aftertreatment aging, failure and crumbling of the matting material holding the Passive NOₓ Adsorber (PNA) in its metal canister.

As a result of this incident, there was an abnormally large build-up of soot and hydrocarbon on the PNA that likely caused uneven flow distribution that resulted in localized soot build-up on the selective catalytic reduction filter (SCRF) system. This research project found multiple ultra-low NOₓ technology pathways applicable for many diesel engine and aftertreatment configurations. The results will be very important when developing air quality plans and regulatory priorities to achieve further NOₓ reductions from heavy-duty fleet in California.

Speaker Biography

Christopher Sharp, is a Staff Engineer in the Diesel Engine and Emissions R & D Department at Southwest Research Institute (SwRI), San Antonio, Texas. He has been at SwRI for the past 25 years, where he has been involved in numerous programs related to integration of advanced aftertreatment systems on diesel and natural gas engines, for both on-highway and nonroad engines. These programs have ranged from early technology and prototype demonstrations, to production development and calibration efforts. In addition he also has a strong focus on measurement methodology, and is involved in the development of methods and procedures to characterize low level emissions from advanced technology engines. He is currently leading the program effort under way at SwRI to demonstrate technologies to achieve very low heavy-duty on-highway tailpipe NOₓ emission levels, which is being conducted on behalf of the California Air Resources Board (CARB).

Ian B. Smith, is a Research Engineer at Southwest Research Institute (SwRI), San Antonio, Texas. Mr. Smith began work at SwRI in 2015 as an engineer in the Spark Ignited Engine R&D Department. He was the primary engine calibrator and research engineer for the natural gas engine in the CARB Low NOₓ demonstration program, as well as, the lead author for SAE Paper 2017-01-0957 "Achieving 0.02 g/bhp-hr NOₓ Emissions from a Heavy-Duty Stoichiometric Natural Gas Engine Equipped with Three-Way Catalyst." His contribution to the CARB Low NOₓ demonstration program consisted of calibrating the Cummins ISX 12G engine with a new ECU and hardware, evaluating engine performance and emissions over the regulatory and low-load, vocational test cycles and testing the engine to demonstrate 0.02 g/bhp-hr NOₓ emissions over the heavy-duty FTP, RMC-SET and WHTC. While at SwRI, Mr. Smith has contributed to various projects including vehicle testing on chassis dynamometers to examine fuel property effects on gaseous and particulate emissions, vehicle and engine benchmarking, and engine testing, simulation and modeling for SwRI's High Efficiency, Dilute Gasoline Engine IV (HEDGE IV) consortium. Ian Smith graduated from Colorado School of Mines with a Bachelor's and Master's degree in Mechanical Engineering, focusing on thermal science and combustion. During his graduate studies Mr. Smith focused on topics of heat transfer, combustion, and internal combustion engines. Additionally, Mr. Smith was a teaching and research assistant for the internal combustion engine course and aided in testing a natural gas engine.

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