Characterization of Commercial Vehicles' Start-Up Operations from In-Use Data

Chen Zhang, Eric Miller, Andrew Kotz, Kenneth Kelly, Matthew Thornton, Michael Geller, Rasto Brezny

Research output: Contribution to journalArticlepeer-review

5 Scopus Citations


Diesel engines produce disproportionate levels of emissions when the engine and after-treatment systems are operating at low temperatures. This situation arises most commonly when the vehicle is first started after overnight. To quantify emissions attributable to vehicle starts, a sizable collection of on-road commercial vehicle operating data is analyzed to identify start-up events and inspect associated emissions. Data was obtained from the National Renewable Energy Laboratory's (NREL's) Fleet DNA and from the Center for Environmental Research & Technology (CE-CERT). Included are 500 + diesel vehicles with more than 42,000 recorded days, drawn from 25 vocational categories across the United States. Analysis shows that vehicle behavior, in terms of engine cold- and warm-operation, starts per day, soak time, and warm-up duration, differs significantly between vehicle vocations. Also, weighting factors for cold- and hot-starts currently used in the U.S. Environmental Protection Agency's Federal Test Procedure (FTP) for heavy-duty emissions certification accurately represent real-world operations. Although the FTP includes a comparable fraction of cold operation, the hot fraction is much shorter than real-world operation due to limited test duration. The investigation also revealed that real-world engines operate for a significant amount of time when the engine coolant is in the “hot-stabilized” region, but the selective catalytic reduction (SCR) temperature is below its effective operating temperature of 200 °C. Of the vehicles under investigation, almost 20% of their operational time is within this condition. Thus, novel approaches to raise and maintain SCR temperature are highly required to further reduce engine emissions.

Original languageAmerican English
Article numberArticle No. 102694
Number of pages28
JournalTransportation Research Part D: Transport and Environment
StatePublished - Feb 2021

Bibliographical note

Publisher Copyright:
© 2021 Elsevier Ltd

NREL Publication Number

  • NREL/JA-5400-75066


  • Cold start
  • Commercial vehicle
  • Federal Test Procedure
  • In-Use data
  • Selective catalytic reduction


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