提高SI燃烧废气稀释极限

Improving Exhaust Gas Dilution Limit of SI Combustion

针对不同负荷之间,均质充量压燃着火和传统火花点燃两种燃烧模式的转换问题,在HCCI燃烧的边界外SI工况点上,通过内外部废气耦合控制燃烧结合气门参数调整的方法,在一台装有全可变气门机构的单缸进气道喷射实验发动机上,进行了拓展SI燃烧废气稀释极限的研究.目的是减少两种燃烧模式之间的热阶跃和稀释度阶跃,以实现无缝的负荷调节.研究发现:通过调整不同的内外部废气比例,结合气门参数的调节,可以有效拓展SI燃烧的废气稀释极限,从5%左右提升至30%左右,同时得到较好的燃油经济性.与此同时,气门参数的设定也可以与HCCI相接近,减少了两者气门参数之间的差距.但是在优化过程中,必须要规避由于热振荡现象造成的循环变动限制.

For improving the transition of HCCI and SI combustion between different loads,at the SI operation point beyond HCCI operating range,through coupling internal EGR,external EGR and valve parameters,the research on expanding exhaust gas dilution limit of SI combustion is carried out in a single-cylinder port injection gasoline en-gine with a fully variable valve actuation system.The purpose is to reduce heat step and RGF（residual gas fraction） step between the two combustion modes,further achieving load regulation with no switching process.It is found experimentally that,by adjusting the proportion of internal and external EGR,and valve parameters,the exhaust gas dilution limit of SI can be effectively expanded.At the same time,the better fuel consumption can be reached.The valve parameters can be close to those of HCCI.The gap of valve parameters between the two combustion modes is reduced.But in the two optimization process,the thermal oscillation phenomenon limits the design of control pa-rameters.