In order to enhance the performance of gas generators and optimize the structures, combustion flows were simulated. The turbulence was solved by the RNG two-equation model, the reaction was settled by the simple chemical reacting system ( SCRC) of the infinitely fast chemical reaction assumption and the beta probability density function (PDF) without the intermediate reactions, the radiative heat transfer was calculated by P-1 radiation model, the physical nozzle was simulated by the pressure-swirl atomizer model, and the emission of NOx was simulated as well. The characteristic parameters of the non-premixed combustion flows between the air and the C12H23, such as pressure, temperature and velocity etc, were obtained with FLUENT program about different structures and air-inlet conditions. The follows were considered and demonstrated with simulation results: the resistance character of structures, the relationship between the mass of cooling-air and the temperature distribution on inner walls, the NOx emissions etc.
