A Comparison of HEV Engine Operation and HD Engine Emissions Test Cycles

Currently, all heavy-duty on-road engines in the USA are certified for emissions compliance using the Federal Test Procedure (FTP) heavy-duty transient cycle. The engine in a hybrid drive system, on the other hand, is controlled at a more steady-state level to reduce emissions over conventional drive systems. In this study, Allison Electric Drive seeks a better standardized emissions test cycle to certify (in the near term) engines which will be used in parallel and series hybrid drive systems. Actual revenue service data from a transit hybrid electric vehicle (HEV) was compared to several standard engine test cycles including the US FTP, ISO 8178 (a collection of many steady-state cycles), the Euro III (ESC) 13-mode cycle, and the Japanese 13-mode cycle. Graphical analysis of actual hybrid engine data revealed that the ESC cycle reflects field data better than other cycles, including the US FTP, which has little correlation. Transient analysis of FTP verses HEV showed that the former has two times the average and four times the maximum rate of change of percent torque compared to the HEV. This result supports the consideration of a steady state engine emissions test cycle.