Fuel Injection Optimization during Engine Quick Start by Means of Cycle-by-Cycle Control Strategy for HEV Application

Engine-off strategy are popular used in hybrid electric vehicles (HEV) for fuel saving. The engine of an HEV will start and stop frequently according to the road condition. In order to obtain excellent fuel economy and emissions performance, the fuel injection during engine quick start should be optimized. In this paper, the characteristic of mixture formation and the HC emissions at the first 5 cycles which contribute the most HCs were investigated. After the analysis of mixture preparation during start process, the HC emissions during engine quick start were optimized by means of cycle-by-cycle fuel injection control strategy. The fuel mixture concentration during start-up process fluctuates more dramatically under hot start condition. Typically, the mixture at 4^th and 5^th cycle is over-riched. Based on the original engine calibration, the fuel injection at the initial 5 cycles was optimized respectively. It is found that the first cycle need to increase fuel injection as general, while the 2^nd to 5^th cycle need to reduce fuel injection, so that maximum IMEP can be obtained for all of the initial 5 cycles. For the 4^th and 5^th cycle, it can still produce fairly high IMEP even there’s no fuel injection in these two cycles. By means of cycle-by-cycle fuel injection control strategy, a significant improvement of the HC emissions during engine quick start can be achieved.