Research on the calculation method of auto-ignition timing and the effect of combustion parameters on auto-ignition under knock condition

Auto-ignition triggering plays an important role in the study of knock, accurate and generalized calculation methods are of great significance. In this study, a brand new calculation method of end-mixture auto-ignition timing based on heat release rate (HRR) is proposed based on several sets of data with different knock intensities of a small turbocharged gasoline engine. The calculation method effectively eliminates the effect of fluctuations in the actual HRR data by setting the search range and the auto-ignition threshold, and also eliminates the calculation delay caused by the second-order derivatives of HRR in the regular calculation method. Under this calculation method, the auto-ignition and knock characteristics present a good fit. The effects of combustion parameters on auto-ignition are significantly different. The changes in engine coolant and inlet air temperature as well as the over-rich mixture significantly affected the auto-ignition trigger pressure, while the ignition timing and the over-lean mixture had no effect on it. The effects of methanol on auto-ignition trigger pressure were also significantly different under various injection timings. The calculation of auto-ignition timing provides a vital prerequisite for the study of auto-ignition triggering, which is of obvious significance for the study of knock.