The nature of 'superknock' and its origins in SI engines

摘要

Extremely high knock intensities are observed occasionally in turbocharged spark ignition (SI) engines. Such events have been informally described as "Superknock" and are often associated with pre-ignition. Knock is initiated by autoignition at one or more "hot spots". The mode of propagation of the resulting pressure wave depends on the propagation velocity of the autoignitive front. When this becomes coupled with the acoustic wave, a localised detonation begins to develop, resulting in a very high rate of pressure rise. It is shown, through semi quantitative analysis including chemical kinetic calculations, that developing detonation becomes more likely when end-gas pressures and temperatures increase and might be the reason for "Superknock".