ARB Research Seminar

This page updated March 6, 2019

Emission Comparisons between Engine, Chassis Dynamometer, and In-Use Testing for Heavy-Duty Diesel Engines to Better Understand the Causes for High In-Use NOx Emissions

Photo of Thomas D. Durbin, Ph.D.

Thomas D. Durbin, Ph.D., University of California, Riverside

March 27, 2019
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Heavy-duty diesel engines (HDDE) are certified to meet emission standards before the engines are integrated into vehicle chasses for commercial use. Because NOx certification standards for HDDEs have been tighten based on laboratory engine testing conditions, it is often questioned if the NOx reductions expected from the certification standard changes are fully realized for in-use HDDEs. Chassis dynamometer and on-road portable emission measurement system (PEMS) tests often showed that the NOx reduction from in-use HDDEs are smaller than the expected reduction based on the certification standards. The engines are also required to comply with in-use HDDE not-to-exceed (NTE) emission limits and testing requirements in US. However, this NTE requirement was not designed to control NOx emissions effectively during low-speed low-load heavy-duty diesel truck (HDDT) operation, where a substantial fraction of vehicle activity and NOx emissions occur.

Given the importance of achieving the expected NOx reductions over the road, it is important to investigate and understand the differences between certification and in-use emission rates and to understand the factors contributing to these differences and discrepancies. For this investigation, two 2010-technology HDDTs with diesel particulate filter (DPF) and selective catalytic reduction (SCR) aftertreatment technologies were tested using three emission measurement methods, including an engine-dynamometer, a chassis-dynamometer, and an on-road PEMS. Engine and chassis dynamometer testing were conducted over a number of different cycles or driving conditions to evaluate a wide range of engine and vehicle operations.

The data collected from the three measurement methods will be analyzed and compared with each other. The differences between the measurement methods will also be evaluated in terms of their theoretical principles, purposes, test requirements, and others factors. The on-road and chassis dynamometer test results will also be evaluated as they relate to the in-use compliance procedures. Of particular importance will be identifying portions of operation where high NOx emissions are found that occur outside of the Not-To-Exceed (NTE) control area or under conditions that generate invalid Moving Average Windows (MAWs). Other areas of interested could include operation that occurs in the NTE control area, but for which the duration is less than the 30 seconds needed to qualify as an event. Based on findings from this study, the effectiveness of current HDDE certification procedures and HDDT in-use test procedures are assessed, and possible enhancements or alternatives to those procedures are explored.

Speaker Biography

Dr. Durbin is a Research Engineer in the emissions from advanced vehicles and fuels research group of CE-CERT and an adjunct professor in the Chemical and Environmental Engineering Department. He is conducting research in the area of vehicle emissions with an emphasis on studying particle and in-use emissions, fuels, and advanced technology vehicles. Prior to joining the vehicle emissions group, Dr. Durbin was involved in several other areas of research at CE-CERT including renewable energy and fuel sources and advanced vehicle technologies. Tom Durbin received his doctorate degree in Physics from the University of California, Riverside, in 1994.

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