Effects of ignition methods and control parameters on the lean combustion performance and flame geometry of jet ignition based on constant-volume combustion chamber

Pre-chamber jet ignition provides one of the most reliable thermal efficiency improvement technologies for future gasoline engines, especially hybrid gasoline engines. The effects of jet ignition control parameters on the jet flame morphology and combustion characteristics are still unclear, for example, the fuel injection mass in the pre-chamber and the time interval between low-flow injection and ignition. The paper explored the effects of jet ignition stoichiometric and lean combustion performance on the flame propagation process of high-energy spark ignition, passive and active pre-chamber, using direct flame imaging in a constant-volume combustion chamber. The jet ignition performance under lean combustion conditions is further enhanced by optimizing the jet ignition control parameters. Based on the luminance characterization of the image, the active pre-chamber with additional low-flow injection can provide 281% of the ignition intensity equivalent to high-energy spark plug ignition. Increasing the fuel injection mass in the pre-chamber can improve heat release and enhance ignition performance. However, the jet ignition performance will drop sharply due to the too-rich pre-chamber gas mixture. Extending the mixing time interval after ignition will enrich the lean ambient mixture outside the pre-chamber and increase the ignition performance. Over-mixing will occur if the mixing time interval is too long, especially under a few injected fuel mass situations. The radial stretch coefficient of the jet flame is defined to characterize the flame geometry during the jet flame propagation process. The jet ignition performance reaches its best when the jet flame propagates at high speed in both radial and circumferential directions, namely a wide jet flame.