Characterization of Gaseous Emissions from Blended Plug-In Hybrid Electric Vehicles during High-Power Cold-Starts

Paper #:
  • 2018-01-0428

  • 2018-04-03
There is a distinct difference between plug-in hybrid electric vehicles in the market today. A plug-in hybrid electric vehicle (PHEV) can be classified as a blended PHEV if it is necessary to start the internal combustion (IC) engine to help power the vehicle before the battery is fully depleted. The other type, non-blended PHEVs, turn on the IC engine only after the battery is depleted. In contrast to non-blended PHEVs, blended PHEVs can have a high-power cold-start where the initial IC engine start occurs under high vehicle torque demand, even when the battery state of charge (SOC) is high. This occurs when the electric portion of the drivetrain has sufficient charge but cannot meet the desired vehicle torque, causing the IC engine to start. Testing of various blended PHEVs found that high-power cold-starts have different emission characteristics compared to conventional vehicle cold-starts that typically occur under a very low initial torque requirement when the vehicle is stopped, in park or in neutral. California Air Resources Board (CARB) staff conducted vehicle tests to investigate the effects of high-power cold-starts on the gaseous exhaust emissions of blended PHEVs. Conditions that triggered high-power cold-starts were characterized from on-road driving and the resulting vehicle speed traces were then used to conduct chassis dynamometer exhaust emission tests. A new methodology was developed to compare the cold-start emissions from the high-power cold-start acceleration cycles to emissions from regulated emission certification test cycles. The results from these tests indicated that high-power cold-starts may be yielding significantly higher exhaust emissions than those observed during the regulated emission test cycles that are conducted for vehicle exhaust emission certification. This paper provides a summary of the high-power cold-start test cycle development, the methodology that was utilized to compare test cycle emissions, and the high-power cold-start gaseous emissions results.
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