Development and validation of a quasi-dimensional model for methanol and ethanol fueled SI engines

Methanol and ethanol are promising alternative SI engine fuels. Engine simulation tools could help to unlock the full potential of these fuels. Previous work by the current authors has focused on building submodels to predict the gas dynamics, combustion and knock occurrence in alcohol engines. Here, these building blocks are implemented in a quasi-dimensional engine simulation code, which is subsequently validated against measurements on two engines for various working conditions. The power cycle predictions for varying mixture composition are significantly improved by the introduction of new laminar burning velocity correlations. A comparison of turbulent combustion models indicates that models including thermodiffusive properties perform slightly better than simpler formulations. Finally, a preliminary evaluation of a new knock prediction model for methanol engines confirms useful results can be obtained for quantities relevant to knock. The largest inaccuracies occur for varying equivalence ratios. Including the effects of methanol on evaporation cooling and wall heat transfer might resolve this. The higher heat of vaporization relative to gasoline also required the inclusion of fuel puddling dynamics for a correct prediction of the volumetric efficiency by the breathing cycle model.