The knock study of high compression ratio SI engine fueled with methanol in combination with different EGR rates

Abstract

Methanol, with a high octane index, is considered to be one of the most ideal fuels for high compression ratio engines. In this paper, the SAGE models combined with methanol chemical reaction kinetics (consisting of 46-species and 247-elementary reactions) are used to study knock combustion. Knock combustion is simulated in a high compression ratio SI methanol engine with different EGR rates. The results show that the introduction of EGR into the combustion chamber can reduce the knock intensity and delay the knock onset time. Without EGR, the intake side of the combustion chamber is prone to knocking mostly. As the EGR rate increases, the exhaust side of the combustion chamber is the most likely to knocking. OH radicals can be considered an indicator of the temperature, and H2O2 can be regarded as an indicator of the propagating flame front. OH marks the knock phase duration and HCO marks the onset of knocking. The reaction intensities of CH2O, H2O2, CO and OH species are higher than other species during knocking combustion. The greater the reaction rate is, the greater the knock intensity will be.