缸内直喷式汽油机废气滞留条件下的燃烧特性

Combustion Characteristics of Gasoline Direct Injection Engine with Exhaust Gas Trap

研究了缸内直喷式汽油机废气滞留条件下,负气门重叠角、点火提前角、压缩比及分层混合气对废气滞留燃烧的影响。研究结果表明:GDI发动机在部分负荷时利用废气滞留可减小泵气损失,但使燃烧持续期增长、循环波动增大;负气门重叠角增大导致循环波动增大;适当地提前点火时刻有助于降低循环波动;废气滞留燃烧采用高压缩比会产生点燃触发压燃的组合燃烧方式,可缩短燃烧持续期但使循环波动增大;利用2次喷射策略形成分层混合气有助于降低废气滞留燃烧时的循环波动,缩短滞燃期和燃烧持续期,从而提高循环热效率,第2次喷射比例和时刻对性能产生重要影响。

The combustion characteristics of a gasoline direct injection （GDI） engine with exhaust gas trap （EGT） were studied. The results show that the engine cyclic variation increases with adding negative valve overlap （NVO） angle~ this can be overcome by advancing properly ignition timing to stabilize combus- tion. The flame propagation and compression combustion occur simultaneously under conditions of increased NVO angle and high compression ratio, this combined combustion can shorten combustion duration and enhance engine cyclic variation. Stratified mixture created by two stage injection may decrease engine cyclic variation, firing delay and combustion duration, thus improving thermal efficiency. Moreover, the second injection fraction and timing play an important role in combustion and emission characteristics in the GDI engine with EGT.