天然气发动机稀燃工况燃烧循环变动特性研究

Study on Characteristics of Cycle-to-cycle Combustion Variations in a Natural Gas Engine under Lean Burn Operating Conditions

对一台点燃式多点电喷天然气发动机在稀燃工况下进行试验，获得了各工况下的连续循环缸内压力数据，并计算了每循环与压力相关的燃烧循环变动特征参数及循环变动系数，进而研究了稀燃工况下天然气发动机的燃烧循环变动特性。结果表明，在稀燃条件下，每循环缸内峰值压力与平均指示压力有稳定的线性相关关系，每循环缸内峰值压力出现时刻与峰值压力和平均指示压力的线性相关关系随当量比的减小，均出现了由负相关到正相关的转变，并且混合气当量比越小，天然气发动机的燃烧循环变动越明显，在当量比为0．60～0．65时，平均指示压力变动系数有加速增长的趋势。

The experiment was conducted with a multi-point fuel injected and spark ignition natural gas engine under lean burn conditions. Successive in-cylinder pressure data were recorded under conditions with different equivalence ratio Ф , and the characteristics of cycle-to-cycle combustion variations （CCV） under lean burn condition was investigated by calculating characteristic parameters of CCV of each cycle and the coefficient of variations of them. The results show that in-cylinder peak pressure .（ Pmax ） and indicated mean effective pressure （ Pi ） have a stable linear correlation, but the correlations between crank angle at which the in-cylinder peak pressure occurs （ θpmax ） and ether pmax or Pi have a transition from inverse ratio to direct ratio. Moreover, smaller equivalent ratio can increase the level of cycle-to-cycle in-cylinder combustion pressure variations and there is always a sharp acceleration when Ф0.6-0.65.