基于循环控制的LPG电喷发动机冷起动初探

Investigation of Cold-Start Based on Cycle-by-Cycle Control Strategy in a LPG EFI Engine

基于循环控制策略,利用单循环和多循环燃烧分析方法研究了LPG发动机的冷起动特性。试验在一台四冲程、水冷125mL单缸电控喷射点燃式发动机上进行。通过对冷起动循环的缸压和瞬时转速的实时测量和分析,研究了LPG首次喷射脉宽及着火循环的关系对冷起动着火特性的影响,特别对如何实现可控循环着火进行了基于单次起动喷射脉宽的单循环和多循环燃烧研究。试验结果表明:冷起动首次着火循环对整个起动过程的HC排放及着火稳定性起着至关重要的作用;起动喷射脉宽对冷起动着火特性的影响最大,合理控制起动喷射脉宽和喷射时刻,即可实现"即喷即着"的理想可控循环着火。LPG首次着火循环所需的混合气浓度约是稳定怠速时的2.2倍;单循环起动喷射脉宽起动与多循环起动脉宽起动相比,具有HC排放低和起动可靠性好的优点。在首次喷射之前空转几循环可以使发动机的首次着火循环序数提前,并能提高冷起动可靠性。

This paper presents an investigation of cold start by the method of single-cycle and multi-cycle combustion analysis in a LPG EFI engine based on cycle-by-cycle control strategy. Experiments were carried out in a four-stroke, water-cooled, single cylinder, 125 mL SI engine with EFI system. Effects of the first injection pulse width and the first firing cycle on the characteristics of cold start were analyzed based on the histories of transient engine speeds and cylinder pressures. The study focuses on how to realize the controllable ignition cycle, and the single-cycle and multi-cycle combustion were tested based on the single starting injection pulse width. Test results showed that: the first firing cycle has an important effect on HC emission and combustion stability during cold-start. The injection pulse width is the key factor for the characteristics of ignition cycle during the cold start. It is possible to realize the ideal ignition cycle, such as injection on time, combustion on time if the first injection pulse width and timing are controlled reasonably. The air fuel ratio of the starting mixture needed by first firing cycle is 2.2 times of that at normal idle condition. When the single starting injection pulse width is applied during cold start, the HC emission is lower than that of multi-cycle starting injection pulse width, and the starting reliability is also better. The first firing cycle can be advanced and the cold starting reliability can be improved when the engine is motored by starter several cycles before the first injection.