Numerical Simulation Of Liquid Fuel Supercritical Injection Process In Internal Combustion Engine

This thesis mainly addresses the fuel spray development process under supercritical conditions, with emphasis on the applicability of two real gas equations of state (SRK、PR) for supercritical spray study, and position of the mixing layer and its evolution characteristics.Numerical simulation of the injection and atomization of n-heptane in the supercritical environment is performed using the software CONVERGE and LES、RANS turbulence models. The simulation used the experimental data provided by Sandia National Laboratories. Based on two cubic equations of state, i,e, SRK and PR equations, the effects of the two state equations on the mass fraction of n-heptane and the temperature distribution of the supercritical spray under LES and RANS, as well as the variation of mass fraction of n-heptane with temperature under LES were investigated, and the results were compared with experimental data; the jet density variation and, the variation of distribution of the density gradients and the vapor mass fraction contour under LES were also studied. The results show that under LES the n-heptane mass fraction and temperature distribution computed by the two equations of state have a significant difference, while the results under the RANS by the two equations are essentially the same; the fuel spray penetration obtained by PR equation is greater than that by SRK, but the swirling structure on the spray tip of SRK equation occurs earlier; a large density gradient appears on the jet surface under both equation; the variation of mass fraction of n-heptane with temperature agrees well with the experiment.The following conclusions are obtained:the RANS turbulence models is not suitable for engine spray; the n-heptane mass fraction, temperature and density distributions confirm mutually that the mass fraction of n-heptane decreases with increasing distance in both axial and radial directions; the PR equation for the calculation of supercritical conditions might be more precisely than the SRK equation; the rapidly changing density indicates the existence of a mixing layer on the interface between the liquid and the gas:the positions of the mixing layer can be estimated by the maximum density gradient position, the mixing layer moves outward with increasing axial distance; the vapor mass fraction contour map also confirm the change of n-heptane mass fraction.