Investigation of Cold-start Based on Cycle-by-Cycle Control Strategy in an EFI LPG Engine 2004-01-3059

This paper presents an investigation of cold starts based on a cycle-by-cycle control strategy in an LPG EFI engine. Experiments were carried out in a four-stroke, water-cooled, single cylinder, 125cc SI engine with an EFI system. Effects of the first injection pulse width and the first combustion cycle on the characteristics of the 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 combustions were tested based on the single starting injection pulse width. Test results show that the first combustion cycle has an important effect on HC emission and combustion stability of following cycles at cold-start. The injection pulse width is the key factor determining the characteristics of an ignition cycle during the cold-start. It is possible to realize an ideal ignition cycle, which is the cycle following the first fuel injection or the first charge cycle, if the first injection pulse width and timing are controlled reasonably. The air fuel ratio of the starting mixture needed by the first combustion cycle is as rich as 2.2 times of that at normal idle condition based on the injection pulse width. When the single first starting-injection-pulse width is applied at 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 combustion cycle can be advanced to happen and the cold starting reliability can be improved when the engine is motored by a starter several cycles before the first fuel injection.