Interaction of pressure wave and propagating flame during knock

To determine the mechanism of interaction between a pressure wave and a propagating flame during knock, normal combustion and knock are numerically modeled in a simplified one-dimensional hydrogen-fueled spark ignition engine. The heat release rate of the flame front during knock abruptly increases when the pressure wave propagates through the reaction zone. The pressure wave in the diffusion zone perturbs temperature and thus causes thermal runaway at positions with low temperature and high reactant concentrations. Analysis of the Damköhler number (the ratio of gas dynamic time to chemical reaction time) and the estimated overpressure revealed that abruptly raised heat release rate during knock facilitates the amplification of the pressure wave and reinforces the interaction between pressure wave and chemical heat release.