Continuous multicomponent fuel film vaporization model for multidimensional engine modeling

A multicomponent fuel film vaporization model using continuous thermodynamics is developed for multidimensional spray and wall film modeling. The vaporization rate is evaluated using the turbulent boundary-layer assumption and a quasi-steady approximation. Third-order polynomials are used to model the fuel composition profiles and the temperature within the liquid phase in order to predict accurate surface properties that are important for evaluating the mass and moment vaporization rates and heat flux. By this approach, the governing equations for the film are reduced to a set of ordinary differential equations and thus offer a significant reduction in computational cost while maintaining adequate accuracy compared to solving the governing equations for the film directly. The new model was verified against accurate numerical solutions obtained with the finite difference method solving the governing equations, and good agreement was achieved for the vaporization process of a film on a flat plate. The simulations show that continuous multicomponent fuel vaporization is relatively fast initially with lighter components, while later on the vaporization process is dominated by heavier components. The model can reasonably predict the vaporization characteristics of a wall film of multicomponent fuel with many components. For comparison, the results using the infinite diffusion liquid model are also presented, and the results indicate that the new model predicted the vaporization process more accurately than the infinite diffusion model. Finally, the model was applied to study the film evolution of a spray/wall impingement process, and the simulation indicates that the multi-component nature of the fuel has a significant influence on the time-space distribution of the fuel concentration and composition.