Collection of Activity Data from On-Road Heavy-Duty Diesel Vehicles

This page last reviewed November 23, 2015


For the State of California to meet upcoming ambient air quality standards for ozone and particulate matter, considerable reductions in NOx emissions are needed. To achieve some of these reductions the NOx emission standard for heavy-duty on-road engines was reduced by 90% in 2010. Diesel engine manufacturers are in most cases using advanced engine exhaust aftertreatment, specifically Selective Catalytic Reduction (SCR), to meet the new standard. SCR reduces NOx in the exhaust stream, but requires adequate temperatures for the reduction to take place. Typically the SCR needs to be at least 200C before significant NOx reduction is achieved. However, there will be times when this temperature requirement is not met, such as right after engine start and during low loads experienced when the engine is idling, or when the vehicle is moving slowly on flat terrain. The frequency of low temperature and low duty operations varies for a truck depending on its type of vocation. In line-haul application a truck operates mostly with high load to maintain high-speed cruise, while the other trucks operate with frequent stops in local goods delivery application. As truck activity changes, SCR functionality of the truck changes with implications for NOx reduction using SCR. Therefore, it is critical to characterize heavy-duty diesel truck activity profiles including duty cycles, number of engine starts, and engine soak time distributions, for trucks by vocation. The heavy-duty diesel truck activity profiles are fundamental for updating emission inventories, quantifying real-world NOx emissions from trucks meeting the new 2010 NOx certification standard, and determining if the certification standard should be revised.

The objective of this research is to characterize the heavy-duty truck activity profiles (e.g., duty cycles, starts and soak time) for different types of vocational uses (line haul, drayage, delivery, etc.) with the specific goal of identifying what fraction of the vehicle operation may be such that SCR functionality is challenged. The research should also put these results in context of the emission certification test cycle and provide an analysis of the representativeness of the certification cycle to real world emissions of NOx for the different types of heavy duty vehicles. The results will be used to improve heavy duty NOx emissions models, and to take a critical look at whether certification and compliance procedures need to be updated to account for the functionality of SCR.