LNG发动机低速工况下瞬态燃烧过程试验研究

对一台增压、液化天然气(LNG)发动机低速工况下的瞬态过程进行连续检测,将实测的瞬态缸压曲线进行二次处理,得出表征缸内燃烧过程的特征参数,在此基础上剖析了诸多瞬态燃烧特征参数的内在联系以及对LNG发动机性能的影响.结果表明,50%燃烧点位置随循环数变动范围约为5 oCA,其波动主要是由燃烧始点的变化引起的,50%燃烧点和燃烧始点的峰值(或谷值)相互对应;50%燃烧点的峰值对应着最高压力升高率和最高爆发压力的谷值,反之则相反.10%~90%燃烧持续期的变化范围为30~45 oCA,它随循环数上升是导致LNG发动机IMEP和NMEP下降的主要原因之一.燃烧特征参数的波动,主要归咎于燃烧始点的不稳定.实现对燃烧始点的精准控制,是保证LNG发动机在低速高增压瞬态过程具有较好工作稳定性的前提.

Experimental Study on the Transient Combustion Process of LNG Engine under Low-speed Conditions

A test was conducted on a liquefied natural gas (LNG) turbocharged engine in the transient process of low-speed working condition.By secondary treating the measured transient cylinder pressure curve, various combustion state parameters were obtained.On this basis, the internal relation among these transient combustion characteristic parameters and the effect of these parameters on LNG engine performances were analyzed.The results have shown that the variation range of 50% of the burnt point with the cycle number is about 5 oCA, and its fluctuation is mainly caused by the change of the combustion starting point.The peak values of 50% of the burnt point correspond to those of the combustion starting point, and so do the valley values.The peak values of 50% of the burnt point correspond to the valley values of maximum pressure rise rate and maximum cylinder pressure, whereas the opposite is true.The variation range of 10%~90% of the combustion duration is 30~45 oCA, and the rise of combustion duration becomes one of the main reasons for the decline of LNG engine IMEP (indicated mean effective pressure) and NMEP (net mean effective pressure).The fluctuations of combustion characteristic parameters are mainly caused by the instability of the combustion start point.To precisely control the combustion start point becomes an effective way to ensure that LNG engine has good transient performances at low speed and high intake pressure working condition.