CNG缸内直喷发动机稀薄燃烧火焰传播过程影响因素的研究

摘要

在试验用单缸光学发动机上,采用可视化技术研究缸内CNG直喷稀薄燃烧过程中喷射方式和点火方式对火焰传播过程的影响,同时采用双喷油器、双火花塞,分析研究喷射时刻、喷射位置和点火时刻等参数对稀薄燃烧特性和NOx排放特性的影响.结果表明,在稀薄燃烧过程中,火花塞附近的混合气浓度梯度对火焰传播和燃烧稳定性影响很大；混合气浓度梯度越大,循环变动越小,燃烧更稳定,但NOx排放量也增加.可见,控制稀薄燃烧过程的关键是控制火花塞附近的混合气浓度梯度,而它又直接影响NOx的生成.%The effects of injection and ignition modes on flame propagation in the lean burn process of in-cylinder CNG direct injection are studied on an experimental single-cylinder optical engine, and the effects of injection timing, injection location and ignition timing on its lean burn characteristics and NO, emission are also investigated by adopting dual injectors and dual spark plugs. The results show that in lean burn process the concentration gradient of mixture around spark plug has great effects on frame propagation and combustion stability; the greater the concentration gradient of mixture, the less the cycle to cycle variation, and hence the more stable the combustion, but the worse the N0x emission. So it can be seen that the key to lean burn process control is concentration gradient of mixture around spark plug, which however in turn directly affects the formation of NOX.