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Title: Certification and in-use compliance testing for heavy-duty diesel engines to understand high in-use NOx emissions : 2018 : final report

Principal Investigator / Author(s): Durbin, Thomas

Contractor: UC Riverside

Contract Number: 15RD001

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


In order to achieve ambient air quality standards for ozone and PM, CARB has taken significant steps to reduce the NOX emissions from on-road heavy-duty diesel engines (HDDEs). The certification standard for NOX has been tightened to 0.20 g/bhp-hr over engine dynamometer testing cycles, and the not-to-exceed (NTE) in-use compliance requirements have been implemented for heavy-duty diesel vehicles (HDDVs). However, in-use NOX emissions from HDDVs observed in recent real-world measurements were higher than their certification standard. It is important to investigate the differences between the certification and in-use NOX emission rates and to understand the factors contributing to these differences. A contract was awarded to the University of California, Riverside (UCR) to test two HDDVs equipped with 2010-compliant HDDEs from different manufacturers with diesel particulate filter (DPF) and selective catalytic reduction (SCR) technologies using an engine dynamometer, a chassis dynamometer for laboratory testing, and portable emissions measurement systems (PEMS). Emission testing was conducted over a number of different cycles and on-road driving conditions, representing both urban and freeway driving. The NOX emissions from both engines exceeded 0.20 g/bhp-hr over the Urban Dynamometer Driving Schedule (UDDS) and Federal Test Procedure (FTP) on the engine dynamometer. Under the same UDDS driving conditions, NOX emissions from the chassis dynamometer and on-road testing were up to 4 times higher than the emissions from the engine dynamometer testing. In the in-use compliance analysis, 4.0 to 50.2 percent of the on-road vehicle operations were subject to the NTE in-use compliance requirements, while all the vehicle operations were subject to the European work-based Moving Averaging Window (MAW) requirements. The results of this study indicate that in-use NOX emissions are above the 0.2 g/bhp-hr level for a wide range of operation, and that there are higher emitting trucks that also can contribute disproportionately to the NOX inventory. It is likely that a combination of expanded certification criteria, tightened certification limits, and expanded in-use compliance procedures will be needed to provide greater control of in-use NOX emissions.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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