Large Eddy Simulation Of The Subcritical/Supercritical Fuel Spray Under IC Engine Conditions

With the development of the engine technology, the turbocharge technology and high injection pressure have obtained a wide range of applications, this means that the research of the process of the atomization and evaporation of transcritical/supercritical fuel sprays has very important theoretical and practical significance. To explore the mechanism and factors influencing the transcritical/supercritical fuel sprays, in this thesis numerical simulations of fuel sprays of n-heptane in a constant volume bomb are conducted based on the Euler-Lagrange method and Euler-Euler method combined in the computing platform OpenFOAM.The characteristics of the Lagrange method is the particles tracking. Breakup and atomization of the liquid jet occur during the injection process, following by burning in the cylinder after the liquid phase has changed to the gas. For comparison of the simulating results, this paper takes the RANS and LES turbulent model as the computational models. Besides, the ETAB model is taken to describe the breakup of the droplets. In the simulation, with the fuel injection pressure increasing and the temperature rising by the flame burning, the pressure and temperature in cylinder will exceed the critical value of the fuel.The characteristics of the VOF model is the surfaces tracking, which means capturing the vapor-liquid interface. And the turbulent model used is LES. Under the subcritical conditions, the uncompressible and insoluble solver is employed, while the compressible solver is adopted to simulate the spray under the supercritical conditions, which means it uses the real gas equations of state (P-R equations) instead of perfect gas equations of state.The results of the numerical simulation reveal that:(1) With the particles tracking method, the simulation results of LES is closer to the experimental values of the parameters characterized by the penetration of the fuel and the distribution of the temperature and the distribution of the particles, relative to the RANS method. Under the supercritical conditions, the transient effect is very significant and the thermodynamic properties of the liquid and gas also have significant changes, showing a drop of the latent heat of evaporation and a sharp change of the temperature. (2) With the VOF method, the subcritical condition simulation results shows that disturbance waves obviously exist on the jet surface. Under the influence of the disturbance waves, the surface of the jet will breakup and form droplets. And the simulation results under supercritical shows that no droplet exists anymore, instead a highly pleated surface separates the high-density jet fluid and the surrounding low-density fluid, which means a mixed layer interposed between gas and liquid exits.