California Air Resources Board

Principal Investigator/Author: Kanok Boriboonsomsin

Contractor: University of California, Riverside

Contract number: 13-301

Project Status: Completed

Relevant CARB programs: Diesel Vehicles, Heavy-Duty Low NOx, Mobile Source Emissions Research Program  

Topic areas: Air Pollution, On-Road Heavy-Duty Vehicles, Heavy-Duty Vehicles, Heavy-Duty Vehicle Research, State Implementation Plans (SIPs)

Research Summary:

A selective catalytic reduction (SCR) aftertreatment system on 2010-technology heavy-duty diesel vehicles reduces oxides of nitrogen (NOX) emission in the exhaust stream, but requires adequate temperature, typically at least 200°C, for the reduction to take place. However, there are times when this temperature requirement is not met, such as initial engine start and during low load operations experienced when the vehicle is idling or moving slowly to meet various vocational demands. To better quantify real-world NOx emissions achieved by SCR, it is thus critical to characterize heavy-duty diesel vehicle vocation-specific activity profiles, including duty cycles, number of engine starts, SCR temperature profiles, and engine soak time distributions. The project team recruited and collected instantaneous location and engine activity data for a minimum of 4 weeks for each of 90 heavy-duty vehicles with gross vehicle weight ratings (GVWR) of 26,000lbs or higher. Eight of the 90 vehicles were not equipped with SCR aftertreatment systems: five express buses powered by natural gas and three diesel trucks older than the 2010 model year. A total of 19 vocation types were identified, covering a range of vocational uses, GVWR, and geographic regions. Activity profiles of idling, diurnal distribution of activity, trips per day, soak time distribution, SCR temperature profiles, and characteristics of driving cycles were characterized for each vocation type. These activity profiles are extremely important for improving the heavy-duty NOx emission inventory and estimating the frequency of good SCR function.

Keywords: selective catalytic reduction (SCR), heavy duty vehicles (HDVs), emission, oxides of nitrogen (NOx), fleet, temperature, activity profiles

Final Report: Please email research@arb.ca.gov to request the Final Report generated by this research contract.