外部EGR对HCCI汽油机拓展运行范围的影响

Influence of External EGR on Expanding HCCI Combustion Operation Range

在Ricardo Hydra单缸四冲程发动机上,通过将外部废气再循环引入到使用全可变气门运动机构实现的基于内部废气重压缩策略的HCCI燃烧过程中,研究外部废气对HCCI燃烧的影响规律.在相同的气门参数下,外部废气可以推迟着火时刻,延长燃烧持续期,降低发动机的最大爆发压力和最大压力升高率.将外部废气再循环应用于原HCCI燃烧范围的上边界,可以有效避免限制发动机大负荷的爆震现象.结合气门参数的灵活调整,使用越多的外部废气可以得到越大的负荷,但是,当外部废气率增大到一定程度,出现失火的现象,限制负荷范围的进一步拓展.在不同的转速下,引入外部废气再循环的方法可以将基于内部废气重压缩策略HCCI发动机的负荷范围向大负荷方向平均拓展30%左右.

HCCI combustion could be achieved in a single-cylinder port injection Ricardo Hydra engine with varible valve actuation, using the internal EGR re-compression strategy. The influences of external EGR on HCCI combustion are analyzed. The results show that external EGR could postpone ignition timing, increase combustion duration, decrease peak pressure and increase the maximum rate of pressure rise. It could avoid the knocking effectively, and decrease emission on the boundary region of HCCI combustion. The more external EGR there is , the higher the load, but misfire could occur when there is too much external EGR. External EGR could break through the knocking limit, and expands the operation range with about 0.08 MPa. Due to lateness of ignition, misfire further limits the expansion of the operation range.