压缩比及EGR对直喷米勒循环汽油机性能影响的试验研究

Influences of Compression Ratio and EGR on DI Miller Gasoline Engine Performance

针对发动机小型化、节能减排的趋势及实现汽油机高热效率的目标,在一台3缸涡轮增压直喷汽油机上综合研究了压缩比及废气再循环(EGR)技术对发动机燃烧和排放的影响。结果表明:提高压缩比有助于改善汽油机中低负荷工况燃油经济性,但对于大负荷工况的改善效果不明显,尤其对于外特性工况,由于爆震的限制,提高压缩比会导致油耗明显恶化。通过引入再循环废气,可优化燃烧过程,抑制爆震的发生,中等转速中等负荷工况下,引入20%EGR后可使燃油消耗率降低达6.9%,但对于转速2000 r/min,平均有效压力0.2 MPa特征工况,油耗改善不明显。综合高压缩比与EGR的作用后,可扩大EGR的作用负荷工况范围,进一步改善燃油经济性。

Considering the trend of engine downsizing,energy saving and emission reduction and the requirement of high thermal efficiency for gasoline engine,the influences of compression ratio and exhaust gas recirculation(EGR)technology on engine combustion performance and emission were studied on a 3-cylinder direct-injection supercharged gasoline engine.The results show that the increase of compression ratio is helpful to improve the fuel economy at medium and low load conditions,but the improvement is not obvious at high load conditions.It is especially true for external characteristic conditions because the increase of compression ratio will lead to significant deterioration of fuel consumption due to the limitation of knock.With the introduction of EGR,the combustion process improves and the knock suppresses.After introducing 20% EGR,the specific fuel consumption reduces by 6.9% under the medium speed and medium load conditions,but reduces little under the condition of 0.2 MPa BMEP at 2000 r/min.Combining high compression ratio strategy with EGR can expand the operating range of EGR and further improve the fuel economy.