Combined impact of excess air ratio and injection strategy on performances of a spark-ignition port- plus direct-injection dual-injection gasoline engine at half load

Spark-ignition direct-injection gasoline engine is one of the main power of passenger cars. In this study, com-bined impact of excess air ratio (lambda) and injection strategy on performances of a spark-ignition port-plus direct -injection (PI + DI) dual-injection gasoline engine at half load was investigated experimentally. Experimental results show that the brake mean effective pressure decreased with increasing lambda at half load; the brake thermal efficiency first increased, then reached the highest value at approximately lambda = 1.1 or 1.2 for different injection strategies, and finally decreased with increasing lambda; the maximum cylinder pressure, maximum heat release rate and maximum cylinder temperature decreased with increasing lambda, and their corresponding crank angles delayed; the starting of combustion (CA05) increased with increasing lambda, the CA05 at PI0DI100 (0 % PI and 100 % DI per cycle), late DI mode and any lambda values was the closest to top dead center; for early DI mode, combustion center (CA50) of PI0DI100 was greater or lower than that of PI50DI50 (50 % PI and 50 % DI per cycle) at roughly lambda < 1.15 or lambda > 1.15, respectively; combustion stability (COVimep) of early DI mode can be controlled within 2 %; the lambda had a significant effect on brake-specific carbon monoxide (BSCO) emission at rich mixture and a little effect on BSCO emission at lean mixture; the brake-specific hydrocarbon (BSHC) emission of early DI mode was much higher than that of late DI mode, the injection strategy had an important effect on HC (hydrocarbon) emission; for early DI mode, the brake-specific nitrogen oxides (BSNOX) emissions first increased with increasing lambda, then reached the highest value at lambda = 1.1, and finally rapidly decreased with further increasing lambda; for late DI mode, the BSNOX emissions decreased with increasing lambda; the soot emission decreased with increasing lambda; the soot emission of late DI mode was much higher than that of early DI mode; at a constant lambda, sootPI50DI50,early DI mode approximate to sootPI0DI100, early DI mode MUCH LESS-THAN sootPI50DI100, late DI mode < sootPI0DI100, late DI mode.