Different Combustion Models Applied to High PressureLOX/CH4 Jet Flames

The combustion phenomena in liquid-propellant rocket engines are highly complex. The combustion occurs at operating conditions well above of the thermodynamic critical points of the fluid where reactants properties show liquid-like densities, gas-like diffusivities, and pressure-dependent solubility. Actually, there is a great interest in the development of reusable liquid rocket engines that operates with methane and liquid oxygen as propellants. In the numerical study of LOX/CH4 jet flames there are some critical aspects to be taken into account. The choice of the combustion model is a critical point: it should be accurate in the phenomena description but it should also characterized by a low computational cost. In the present study different combustion models were used as the Eddy-dissipation finite-rate approach based on Arrhenius chemical kinetics, the equilibrium mixture fraction model (PDF) and the Steady State Flamelet approaches. In the case of reacting models based on chemical kinetics, both simplified and more complex kinetics models can be used to numerically describe the flames but the critical point in the choice is the individuation of the best compromise between computational cost and accuracy. In this work different chemical kinetics schemes were used, as the Skeletal mechanism and the Jones- Lindstedt mechanism, that permit to limit the number of reactions and species but taking into account also the intermediate species in the flame. Finally a purpose of this work is also to develop a pure Eulerian (i.e., single-phase) methodology by using both ideal gas and real gas equation of state and to compare with the discrete phase approach that uses an Eulerian description of the gas phase and Lagrangian equations for the dilute spray. For all the models used, a comparison with experimental data from literature was performed.