Numerical Simulation of Liquid Fuel Injection in Combustion Chamber

Combustion of cryogenic propellants is of great technological interest for researchers and scientists nowadays. Due to high specific impulse, the use of liquid oxygen and hydrogen as cryogenic propellants will have preferences in the years to come. In the present study, RCM-3 configuration of MASCOTTE test facility is used for the investigation of supercritical cryogenic fuel combustion. The injector of this test case is a shear-coaxial injector consisting of a core of liquid oxygen surrounded by a high-speed flow of gaseous hydrogen. Pressure-based steady-state 2D axisymmetric scheme with non-premixed combustion model and compressibility effect under non-adiabatic conditions is used in the present study. Rich fuel stream flammability limit of 0.2 is used to accommodate non-equilibrium effects. Simulations are carried out for different turbulence models with ideal and real gas assumptions. Pressure-implicit with splitting of operators is used for pressure-velocity coupling while standard k-epsilon, standard k-, and SST k- turbulence models are used for the parametric study. Effects of ideal gas and real gas assumptions are also studied. A very low value of under-relaxation factor for density (0.01) is used to encounter stability issues. Computed results show that SST k- turbulence model with real gas assumptions provide qualitatively as well as quantitatively reasonable and encouraging results. Although peak temperature value is under-predicted, its location and temperature profile along the axis are accurately predicted through real gas assumption, whereas results with ideal gas are far away from experimental values. This provides conclusive evidence that the ideal gas assumption is not appropriate for fluids in the cryogenic state as liquid oxygen in the present study. Improved modeling and inclusion of detailed chemical kinetic mechanism will provide much improved results. Present results are very promising and encouraging to use CFD for the simulation and modeling of cryogenic fuel combustion in the supercritical state.