Optical experiments on the effect of turbulent jet ignition on lean burning and engine knocking

Abstract

Recently the turbulent jet ignition (TJI) configured by pre-chamber has been paid more attention as it can effectively achieve rapid combustion thus high thermal efficiency. In this work, using a single-cylinder optical engine with high compression ratios, the effects of turbulent jet ignition on lean burning and engine knocking were comprehensively investigated, with the conventional spark-ignition scenarios for comparisons. The results show that the pre-chamber with larger volume results in stronger flame jets and a higher promoting effect on the combustion. However, due to the higher heat dissipation and throttling loss, the pre-chamber with larger volume results in lower IMEP. For lean combustion, the optimized TJI (small volume) can reduce the combustion instability and improve the thermal efficiency when compared to spark ignition. The main reason is that TJI can increase the in-cylinder flame speed and achieve a concentrated HRR. For knocking combustion, TJI increases the knock tendency and knock intensity. The main reason is that the accelerated flame advances the auto-ignition and induces a high energy density. In summary, the effect of TJI on engine performance differs under different load conditions and the TJI strategy should be optimized especially under heavy load conditions.