Spark timing and fuel injection strategy for combustion stability on HEV powertrain

Stringent regulations on exhaust emission and fuel economy for vehicles have become major issues in the automotive industry. Hybrid electric vehicles (HEVs) are one of the crucial alternative plans over current conventional vehicles, but they have drawbacks, such as the increase of engine-out total hydrocarbon (THC) emission and the deterioration of combustion stability with frequent engine stopping and restarting. This study is an experimental investigation to obtain a better understanding of THC emission characteristics during engine restart and deceleration driving on a HEV powertrain of a parallel motor/generator type. Using a fast response flame ionization detector (FFID) and a specified tool for cycle by cycle and cylinder to cylinder investigation, the combustion stability and engine control characteristics were analyzed during the transient state of the HEV powertrain. The experimental conditions cover variations of the 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 was slight, but the reasonable injection duration for stable combustion was more than 7 ms at the first cycle shortly after engine start-up, although the injection rate was 2.7-3 ms in the idle state. The reason for the greater volume of fuel being injected was that the fuel deposited in the cylinder and intake port was reduced due to discharge and vaporization during the deceleration step before the idle stop. A basic control algorithm for combustion stability under engine restart conditions was built by considering the experimental results. (C) 2010 Elsevier Ltd. All rights reserved.