STUDY ON THE ACTIVE CONTROL OF LEAN COMBUSTION IN THE ENGINE CYLINDER BY MEANS OF FLAME IGNITION PROCESS

本文在以甲烷为燃料的单缸试验机上，研究了涡流对早期火焰发展和后期燃烧特性的影响，并与火焰核的数目和间隔有关。火焰核心在旋流混合物中被一个点火源的多个火花点燃。通过控制间歇火花点火系统的点火时间间隔，在缸内旋流的外部产生一个连续的小火焰。燃烧试验分析表明，适当的点火正时和核心系列可以提高平均有效压力，降低最高压力，并有可能防止NOx生成量的增加。1）在贫燃火焰中，通过利用涡流中火焰的对流运动，在宽范围的发动机操作中，热释放速率的控制变得可能。点点火对于通过改变第一点火正时和随后的点火正时来主动控制燃烧是有用的。3）第一点火正时的延迟有效地减少了NOx排放，而由于改进的燃烧而没有明显的性能变差4）根据燃烧室中的流动条件和火焰速度，可以最佳地选择火花正时。

In this study, the effects of swirl on the early flame development and late combustion characteristics are investigated in relation to the number of and the intervals of flame kernels using the single cylinder test engine fueled with methane. The flame kernels are ignited in the swirling flow of mixture by means of multiple sparks with one ignition source. A sequential flamelet appears in the outer part of the swirling flow in the cylinder by the intermittent spark ignition system at controlled intervals. The analysis of the combustion tests show that adequate spark timing and series of kernels could improve the mean effective pressure, keeping the maximum pressure down, and also showed a possibility of preventing the increase of NOx formation.The important results are as follows :1) in a lean combustion flame, the control of heat release rate becomes possible in a wide range of engine operation by utilizing convective motion of flame in a swirl.2) multiple ignition and/or multi-point ignition are useful for the active control of combustion by changing the first ignition timing and the subsequent ignition timing.3) retardation of the first ignition timing effectively reduces NOx emission without appreciable change of performance for the worse due to improved combustion by the subsequent flames.4) The optimum selection of the spark timings becomes possible depending on the flow conditions and flame speed in the combustion chamber.