Air Resources Board Seminar: Activity Patterns of Heavy-Duty Vehicles and Their Implications on Real-World In-Use Emissions

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Kanok Boriboonsomsin, Associate Research Engineer, Center for Environmental Research and Technology, University of California, Riverside

Event Overview

Heavy-duty vehicles comprise a variety of vocations, each of which may have different operational requirements resulting in different vehicle and engine activity patterns. It is important to understand the extent of these differences so that appropriate emission control strategies and policies can be developed. For instance, many heavy-duty diesel vehicles employ the selective catalytic reduction (SCR) technology to meet the 2010 emission standards for nitrogen oxides (NOₓ). Typically, SCR needs to be at least 200 °C before significant NOₓ reduction is achieved. Some activity patterns may increase the likelihood that this SCR temperature requirement is not met, such as during start-up and idling. The frequency of the activity patterns contributing to low SCR temperature varies partly by the vehicle’s vocational use.

In this study, the researchers collected detailed vehicle and engine activity data from 90 California heavy-duty vehicles across several vocations including line haul, drayage, construction, food and beverage distribution, refuse, and utility repair, among others. The data were used to calculate a number of statistics related to trip, engine start, engine idle, SCR temperature, etc. This presentation will highlight some of the similarities and differences in these statistics among heavy-duty vehicles in different vocations. For example, it is found that the vehicles in this study operate with SCR temperature lower than 200 °C for 11-87% of the time, depending on their vocation type. As a result, the estimated reduction in engine-out NOₓ emission by SCR ranges from 16% for agricultural trucks to 69% for refuse trucks. This would have a significant impact on the real-world in-use NOₓ emission inventory of heavy-duty diesel vehicles in California.



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