大缸径点燃式天然气发动机爆震的影响因素

Knock Impact Factors in a Large Bore SI CNG Engine

爆震被认为是缸内燃烧火焰传播过程中末端混合气局部热点自燃引起的压力振荡.通过抑制局部热点自着火的反应速率可以降低爆震强度.通过一台缸径为190,mm的天然气发动机,研究不同过量空气系数对降低爆震强度的影响.在过量空气系数较小的工况下,当自着火发生时可以观察到压力振荡;在过量空气系数较大的工况下,当自着火发生时爆震强度较微弱.爆震强度随着缸内最高温度和最大压力变化而变化.在过量空气系数大于1.45的工况下,爆震的发生由局部热点反应速率决定;而在过量空气系数小于1.45的工况下,爆震的发生受自着火出现时刻控制.

The knock intensity is thought to be decreased by suppressing the reaction rate of auto-ignition.The effect of the mixture dilution which decreases the reaction rate on the knock intensity was investigated by using a large bore SI CNG engine.In the case of low dilution,the pressure oscillation was observed when the auto-ignition of the end gas occurred.On the other hand,in the case of high dilution,there was the condition that the knock intensity was weak even if the end gas auto-ignited.The knock intensity was shown as a function of the maximum temperature and the maximum pressure which affected the reaction rate.These results suggest that the condition that the knock occurs is controlled by the reaction rate in the case of high dilution although it is controlled by the auto-ignition timing of the end gas in the case of low dilution.