Experimental investigation of the influence of pre-chamber structural parameters on combustion and emission characteristics of a high compression ratio SI engine

Abstract

The passive pre-chamber exhibits great potential for practical applications in the internal combustion engine due to its simple structure. However, it faces difficulties in scavenging process, making optimization of pre-chamber structure particularly important. In this study, the effects of pre-chamber ignition systems with different structures and original spark ignition were conducted on a high compression ratio direct-injection SI engine to investigate the combustion, performance, and emission characteristics. The results show that the increase in pre-chamber volume weakens the in-cylinder combustion process and engine performance, while increasing the pre-chamber orifice diameter can enhance the combustion stability at medium to high loads, but will weaken the engine performance at low load. Compared to spark ignition, pre-chamber ignition results in an earlier 50% combustion position, a shorter combustion duration and lower COVIMEP, with these effects becoming stronger as load increases. At high load, the pre-chamber ignition (PC1) advances the 50% combustion position by 5.6°CA and shortens the combustion duration by 16.7%. In addition, the indicated thermal efficiency of the pre-chamber ignition achieves an increase of 0.84% at the optimal point and 2.5% at high load. Overall, using the smaller orifice diameter and volume in the pre-chamber can improve in-cylinder combustion process and increase thermal efficiency across the load range. For emission analysis, the pre-chamber ignition leads to an increase in NOx and HC emissions due to the influence of in-cylinder combustion temperature and quenching effect, while the CO emissions are similar to spark ignition.