Effect of rapid combustion on engine performance and knocking characteristics under different spark strategy conditions

Rapid combustion is considered as an effective way to improve engine performance but there is lack of investigations about the effect of rapid combustion on engine knock. In this study, a highly-strengthened engine, equipped with double spark system, was chosen for investigating the influence of rapid combustion on engine performance and knocking characteristics. The results show that under synchronous double spark ignition condition, output power and effective thermal efficiency are improved because of shortened combustion duration. However, engine knock is more prone to occur and knock intensity is more sensitive to spark timing. Then, considering the ability of solving detailed chemical kinetics, an engine simulation software was chosen to simulate auto-ignition and knocking characteristics at different spark intervals and locations. The results show that the compressing and heating effects of two ignited flames are the main reasons for end-gas auto-ignition. Further investigation on asynchronous ignition shows that early heat release of end-gas mixture before auto-ignition can reduce maximum explosive pressure and knock intensity can be decreased by more than 50%. Besides, the results of different spark location show that additional spark is more effective in reducing knock intensity if the location is closed to the position where auto-ignition occurs. (C) 2019 Elsevier Ltd. All rights reserved.