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.

Automated summary

This study experimentally investigated the combined impact of excess air ratio (lambda) and injection strategy on the performance of a spark-ignition port-plus direct-injection (PI + DI) dual-injection gasoline engine at half load. The experimental results showed that brake mean effective pressure decreased with increasing lambda, while brake thermal efficiency initially increased and then decreased with increasing lambda. The lambda also had significant effects on various emissions such as carbon monoxide, hydrocarbon, nitrogen oxides, and soot.