正庚烷均质压燃过程的燃烧稳定性和循环变动的研究

对正庚烷HCCI燃烧典型工况下的燃烧稳定性和循环变动进行了研究。在单缸HCCI发动机上,通过气口喷射正庚烷,记录了部分燃烧、正常燃烧、爆震燃烧下100个循环的示功图,据此对各个燃烧参数和性能参数的循环变动进行了分析。研究表明：低温阶段的冷焰反应时刻、起始反应温度和低温放热峰值时刻的循环变动系数小于3%,且受混合气浓度的影响不明显;高温阶段燃烧参数循环变动较大,但是着火时刻和峰值放热时刻随混合气浓度的增加显著减小;低温和高温峰值放热率循环变动系数较高。在性能参数方面：不发生爆震燃烧时,最高压力、压力升高率的变动较小;发生爆震燃烧时,循环变动系数迅速增加;不发生失火或者部分燃烧时,平均指示压力和指示热效率的变动较小,且随混合气浓度增加而减小。

Study of Combustion Stabilities and Cycle-to-Cycle Variations of n-Heptane Homogenous Charge Combustion Ignition (HCCI) Combustion

In this paper,the combustion stabilities and cycleto-cycle variations of n-heptane homogeneous charge compression ignition(HCCI) combustion were investigated.In-cylinder pressures of 100 combustion cycles under typical operation conditions including partial burn,normal combustion and knock combustion were recorded.Consequently,cycle-to-cycle variations of combustion parameters and performance parameters were analyzed.The results reveal that,the cycle-to-cycle variations of the ignition timing,initial temperature,and crank angle corresponding to the peak heat release value are less than 3%.The variations of the second combustion stage are strongly affected by equivalence ratio and substantially improved with the increase of the fuel concentrations.The cycle-to-cycle variations and COVs of peak values of the cool flame and hot flame show obviously increase with the increase of fuel supply rate.Regarding to the performance parameters,variations of maximum pressure and pressure rise rate is very small except for the knock combustion.On the contrary,cycle-to-cycle variations of mean indicated pressure and indicated thermal efficiency are very small except for the partial combustion,and variations decrease with the increase of the fuel supply rate.