Numerical investigation on auto-ignition and knock behavior of a downsized aviation kerosene rotary engine with varying spark ignition energies

To clarify the role of spark-ignition flame propagation speed in end-gas auto-ignition and knock, this study numerically investigates a downsized dual-spark-plug aviation kerosene Wankel rotary engine using a three-dimensional CFD framework coupled with detailed chemistry. In this work, ignition energy is used as a control parameter to regulate early flame-kernel development and the subsequent spark-ignition flame propagation speed, thereby isolating its effect on end-gas thermochemical evolution and knock behavior. The results show that end-gas auto-ignition is initiated preferentially in the trailing-section regions near the front and rear end covers, where local high-temperature zones are formed by combustion chamber geometry and pressure-wave reflection/superposition. These regions first undergo low-temperature reactions and then enter the high-temperature decomposition stage, finally triggering knock. Increasing ignition energy accelerates spark-ignition flame propagation, strengthens flame-induced compression and heating of the unburned mixture, promotes the low-temperature reaction progress of the end-gas, and advances end-gas auto-ignition. However, its effect on knock intensity is non-monotonic. Knock intensity increases markedly from 0.05 J to 0.1 J, and then decreases gradually as ignition energy further increases from 0.1 J to 0.3 J. This is because knock intensity depends not only on auto-ignition timing, but also on the chemical reactivity of the mixture consumed by the auto-ignition flame. The findings reveal the mechanism by which spark-ignition flame propagation speed affects end-gas auto-ignition and knock in aviation-kerosene rotary engines, and provide theoretical guidance for knock suppression in downsized Wankel rotary engines.