Abstract: Knock occurrs in a spark ignition engine with four-cylinder and high compression ratio, resulted in deliberately piston damage of the engine while burning methanol(M100).Through monitoring pressure trace in cylinder and analyzing damaged part of piston from its surface and micro-structure inside body, the mode of piston damage and failure under stronger knocking combustion is proposed. The results observed show that the outbreak of pressure in combustion chamber varies acutely and then forms the detonation wave while strong knocking combustion occurrs. When the wave acts on surface, it would transmit its action and then cause quick oxidation corrosion inside of piston body. Metallographic analysis shows that the surficial material of the piston with silicon/aluminum alloy is distorted from the original uniform distribution of the alloy component under attack of detonation wave. Through further using scanning electron microscopy(SEM), surface piston damage occurred adiabatic shearing melt hole. Meanwhile, through the composition determined by X-ray diffraction(XRD), the surface crystal of the piston failed has changed. Based on pressure variation in cylinder and analysis of material, a piston destruction mode of engine with methanol as fuel is concluded.

Key words: Detonation wave, Knock, Methanol, Piston