A laminar burning velocity and flame thickness correlation for ethanol-air mixtures valid at spark-ignition engine conditions

The use of biomass-derived ethanol in spark-ignition engines is an interesting option to decarbonize transport and increase energy security. An engine cycle code valid for this fuel, could help to explore its full potential. Crucial building blocks to model the combustion in ethanol engines are the laminar burning velocity and flame thickness of the ethanol–air–residuals mixture at instantaneous cylinder pressure and temperature. This information is often implemented in engine codes using correlations. A literature survey showed that the few available flame thickness correlations have not yet been validated for ethanol. Also, none of the existing ethanol laminar burning velocity correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. Moreover, most of these correlations are based on measurements that are compromised by the effects of flame stretch and the occurrence of flame instabilities. For this reason, we started working on new correlations based on flame simulations using a one-dimensional chemical kinetics code. In this paper the published experimental data for the laminar burning velocity of ethanol are reviewed. Next, the performance of several reaction mechanisms for the oxidation kinetics of ethanol–air mixtures is compared. The best performing mechanisms are used to calculate the laminar burning velocity and flame thickness of these mixtures in a wide range of temperatures, pressures and compositions. Finally, based on these calculations, correlations for the laminar burning velocity and flame thickness covering the entire operating range of ethanol-fueled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.