基于循环控制的LPG点燃式发动机冷起动首循环NO瞬态排放特性研究

从循环控制的角度，详细研究了LPG点燃式发动机冷起动首循环NO瞬态排放特性。实验在一台电控LPG进气道喷射单缸风冷四冲程125cm^3发动机上进行。通过高速采集系统记录发动机首循环瞬态NO排放、瞬时缸压和转速，从实验结果中分析发动机NO瞬态排放与其他参数之间的关系。研究表明：在稀燃工况下NO排放能更准确地反映着火的发生，可以作为首循环着火的判断依据；NO排放和循环缸压都随过量空气系数先增大后减小，最大缸内爆发压力发生在略浓的混合气浓度，而最大NO排放发生在较稀的混合气浓度；NO瞬态排放随循环缸压在稀燃、过渡和浓燃区呈现出不同的变化规律，首循环最佳过量空气系数应控制在过渡区域。

Study of Real Time NO Emission Characteristics Based on First Firing Cycle Analysis of Cold-Start

Based on the analysis of engine's first firing cycle (FFC) , this paper investigates the transient NO emission characteristics of cold-start in a small electronically controlled fuel injection (EFI) SI engine fuelled with LPG. At the same time, the experiment collected the real time cylinder pressure and instantaneous engine speed. The results show that transient NO emission could be used as a criterion to study the in-cylinder combustion of the first firing cycle. Transient NO emission and cylinder pressure increase initially and decrease subsequently with reducing excess air ratio. Maximum value of transient NO emission occurs at relatively lean mixture while maximum value of cylinder pressure is presented at relatively rich mixture. Transient NO emission versus cylinder pressure gives different behaviors at lean combustion, transition combustion and rich combustion. The best excess air ratio for the first firing cycle should be controlled within the transitional range.