Integration of a Continuous Multi-Component Fuel Evaporation Model with an Improved G-Equation Combustion and Detailed Chemical Kinetics Model with Application to GDI Engines

A continuous multi-component fuel evaporation model has been integrated with an improved G-equation combustion and detailed chemical kinetics model. The integrated code has been successfully used to simulate a gasoline direct injection engine. In the multi-component fuel model, the theory of continuous thermodynamics is used to model the properties and composition of multi-component fuels such as gasoline. In the improved G-equation combustion model a flamelet approach based on the G-equation is used that considers multi-component fuel effects. To precisely calculate the local and instantaneous residual which has a great effect on the laminar flame speed, a “transport equation residual” model is used. A Damkohler number criterion is used to determine the combustion mode in flame containing cells. 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 variance of the fuel vapor mixture composition in each cell. The laminar flame speed has been updated to consider multi-component fuel effects, as a function of pressure, temperature, equivalence ratio, residual, and fuel vapor mixture PRF number. To model the chemistry process in the unburned region in front of the flame and in burned regions behind the flame, a recently developed PRF mechanism is used to describe the multi-component fuel mixture. Simulations of the vaporization of a single droplet with a single-component fuel (iso-octane) are compared with multi-component fuel cases. The vaporization of a spray of multi-component fuel injected into a chamber is simulated for both normal and flash-boiling conditions. The new PRF mechanism is validated against shock tube data. In addition, gasoline direct injection engine combustion is simulated at different manifold absolute pressures, different end-of-fuel injection timings, and different spark ignition timings. The simulated in-cylinder pressures and heat release rates are compared with experiment data and good agreements are found.