Laminar burning velocity correlations for methanol-air and ethanol-air mixtures valid at SI engine conditions

The use of methanol and ethanol in spark-ignition (SI) engines forms a promising approach to decarbonizing transport and securing domestic energy supply. The physico-chemical properties of these fuels enable engines with increased performance and efficiency compared to their fossil fuel counterparts. An engine cycle code valid for alcohol-fuelled engines could help to unlock their full potential. However, the development of such a code is currently hampered by the lack of a suitable correlation for the laminar flame speed of alcohol-air-diluent mixtures. A literature survey showed that none of the existing correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. For this reason, we started working on new correlations based on simulations with a one-dimensional chemical kinetics code. In this paper the properties of methanol and ethanol are first presented, together with their application in modern SI engines. Then, the published experimental data for the laminar burning velocity are reviewed. Next, the performance of several reaction mechanisms for the oxidation kinetics of methanol- and ethanol-air mixtures is compared. The best performing mechanisms are used to calculate the laminar burning velocity of these mixtures in a wide range of temperatures, pressures and compositions. Finally, based on these calculations, two laminar burning velocity correlations covering the entire operating range of alcohol-fuelled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.

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