Integration of a discrete multi-component fuel evaporation model with a G-equation flame propagation combustion model and its validation

Abstract

A discrete multi-component fuel evaporation model has been successfully integrated with a G-equation flame propagation combustion model. In the discrete multi-component fuel evaporation model, the individual components of the fuel during the evaporation process are tracked, and the characteristics of the fuel components are determined from fuel libraries. In the G-equation flame propagation combustion model, five improved sub-models developed previously by the authors are used. Two new methods that are necessary for the integration are proposed. To consider the change of local fuel vapor mixture composition, a ‘blending cetane number approach’ is proposed that formulates the relationship between the fuel vapor mixture cetane number and the mole fraction and cetane number of each component. With the mixture cetane number, the research octane number can be calculated locally, and with this research octane number, the flame speed can be calculated. In the combustion stage, a ‘group chemistry method’ is proposed in which one representative species can be selected to represent several fuel components that belong to the same chemical family. This treatment makes it possible to use a smaller size of multi-component fuel chemical kinetic mechanism. Each sub-model included in the integrated model was validated to see if the integration process was correct or not, and finally the integrated model was tested to model complicated gasoline direct injection engine cases. Simulations of single-droplet and spray evaporation with discrete multi-component fuel cases from normal evaporation to flash boiling were performed and compared with available experimental data. The match between simulations and experiments is excellent. The G-equation flame propagation combustion model was also validated with experimental data. Evaporation and the combustion process were simulated for a gasoline direct injection engine. The simulated in-cylinder pressures are in good agreement with the experimental data.