Shiyou Yang

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

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.

A Two-Zone Multigrid Model for SI Engine Combustion Simulation Using Detailed Chemistry

An efficient multigrid (MG) model was implemented for spark-ignited (SI) engine combustion modeling using detailed chemistry. The model is designed to be coupled with a level-set-G-equation model for flame propagation (GAMUT combustion model) for highly efficient engine simulation. The model was explored for a gasoline direct-injection SI engine with knocking combustion. The numerical results using the MG model were compared with the results of the original GAMUT combustion model. A simpler one-zone MG model was found to be unable to reproduce the results of the original GAMUT model. However, a two-zone MG model, which treats the burned and unburned regions separately, was found to provide much better accuracy and efficiency than the one-zone MG model. Without loss in accuracy, an order of magnitude speedup was achieved in terms of CPU and wall times. To reproduce the results of the original GAMUT combustion model, either a low searching level or a procedure to exclude high-temperature computational cells from the grouping should be applied to the unburned region, which was found to be more sensitive to the combustion model details.

A Continuous Multi-Component Fuel Flame Propagation and Chemical Kinetics Model

A continuous multi-component fuel flame propagation and chemical kinetics model has been developed. In the multicomponent fuel model, the theory of continuous thermodynamics was used to model the properties and composition of fuels such as gasoline. The difference between the current continuous multi-component fuel model and previous similar models in the literature is that the source terms contributed by chemistry in the mean and the second moment transport equations have been considered. This new model was validated using results from a discrete multi-component fuel model. In the flame propagation and chemical kinetics model, five improved combustion sub-models were also integrated with the new continuous multi-component fuel model. To consider the change of local fuel vapor mixture composition, a “PRF adaptive” method is proposed that formulates a relationship between the fuel vapor mixture PRF number (or octane number) and the fuel vapor mixture composition based on the mean molecular weight and/or variance of the fuel vapor mixture composition in each cell. Simulations of single droplet vaporization with a single-component fuel (iso-octane) were compared with multi-component fuel cases.Copyright