Numerical comparative study on knocking combustion of high compression ratio spark ignition engine fueled with methanol, ethanol and methane based on detailed chemical kinetics

Methanol, ethanol and methane are three kinds of common high-octane alternative fuels, which are ideal fuels for SI engines with high compression ratio. High compression ratio generates high thermal efficiency and also causes knocking combustion. Knock is one of the main obstacles for improving performance of SI engine. In this paper, the SAGE models combined with detailed chemical reaction kinetics were used to study knock combustion. The effect of equivalence ratio was discussed on the knocking combustion of SI engines fueled with methanol, ethanol and methane. The evolution of important components were analyzed in details during the combustion of methanol, ethanol and methane. The results showed that as the equivalence ratio increased, the intensity of knocking increased and the onset time occurred in advance for all three fuels. The knocking intensity of methane was significantly weaker than that of methanol and ethanol at any equivalent ratio. When the equivalence ratio was less than 0.9, the knocking combustion of methane disappeared. The knocking intensity of methanol was larger than that of ethanol. The ignition delay of methanol at low temperature depended largely on the consumption rate of H2O2, the auto-ignition was triggered by the dissociation of H2O2. For ethanol, the hydrogen abstraction by HO2 radicals suppressed auto-ignition, while the decomposition of H2O2 promoted autoignition. CH2O radical was important intermediate for the low-temperature reaction process of methane, which mainly distributed in the flame front region. The formation of CH2O radical could reflect the degree of low temperature oxidation of methane.