Effects of Spark Ignition Timing and Fuel Injection Strategy for Combustion Stability on HEV Powertrain during Engine Restart and Deceleration Driving

Abstract

Stringent regulations of exhaust emission and fuel economy from vehicles have become major issues in the automotive industry. Hybrid Electric Vehicle (HEV) can be one of the crucial alternative plans over current conventional vehicle, but they have drawbacks such as the increase of engine out total hydrocarbon (THC) emission and the deterioration of combustion stability at frequent engine stop and restart. This study performs experimental investigation to obtain a better understanding of THC emission characteristic at engine restart and deceleration driving on a HEV powertrain of parallel motor/generator type using a Fast response Flame Ionization Detector (FFID) and specified tool for cycle by cycle, cylinder to cylinder combustion and engine control characteristic analysis during transient state of HEV powertrain. The experimental conditions cover variation of high voltage battery State of Charge (SoC), spark ignition timing and injected fuel mass. As an experimental result, the effect of the spark timing control is so little, but the reasonable injection duration for stable combustion is more than 7 (ms) at the first cycle shortly after engine start-up by motor although the injection rate is 2.7 ~ 3 (ms) at idle state. The reason why more fuel was injected was that the deposited fuel in the cylinder and intake port was reduced due to discharging and vaporization during deceleration step before idle stop.