Characterization of High-Power Cold-Start Emissions Part 1: Analysis of a Modern Plug-In Hybrid Electric Vehicle Tailpipe Emissions

The California Air Resources Board (CARB) and the United States Environmental Protection Agency (US EPA) have recently introduced targets for tailpipe emissions during high-power cold-start conditions for plug-in hybrid electric vehicles (PHEVs). However, the performance characteristics of hybrid powertrains and the effectiveness of cold-start strategies in PHEVs are not well known. In this two-part study, the performance of a production PHEV is examined with the objective of quantifying the impact of high-power cold-start events on overall tailpipe emissions. High temporal fidelity data of powertrain performance and tailpipe emissions generated during cold-start events for various driving conditions are presented for the first time. The selected P2 hybrid vehicle was tested using (i) the European Real Driving Emissions (RDE) test, (ii) the US06 (Supplemental Federal Test Procedure), and (iii) a custom drive cycle developed for this study. Results show that driving conditions leading to the events vary significantly between the drive cycles. Demand for high vehicle speed and/or high traction power triggered cold-start events despite the high battery state of charge. The results are discussed in detail in terms of the specific regulated air pollutants and powertrain performance monitored in the 50-seconds window following each cold-start event. In the companion study, tailpipe emissions characteristics and engine start strategies are compared across multiple hybrid topologies during a high-power cold-start event. The results from both studies provide valuable new information to enable design of hybrid powertrains for future PHEVs that meet the upcoming cold-start emissions regulations.