Numerical study of performance of reverse flow combustor

The performance optimization of a reverse flow combustor in a mini-jet engine is studied numerically. Different turbulence models (with appropriate mesh resolutions), i.e. steady (RANS) and unsteady k-ε (URANS) and the Reynolds stress model is adopted to investigate and compare the performance of the combustor. The probability density function (PDF) model is used to include combustion to complete the simulation. The simulation results were validated against existing experimental data (experiment conducted with kerosene fuelled combustion chamber). From this study, the unsteady standard k-ε (URANS) performed best, giving the best combination between simulation accuracy and computational cost. 3D Flow structures induced in the combustion chamber were identified using Q-criterion and strong correlation with the high temperature spot on the liner wall was observed. A performance optimization of the combustor is then conducted. This investigation is done parametrically. The volume of the combustor chamber is first increased by reducing the thickness of inner duct. It is found that the thrust increased close to 16.5% when the volume of the combustion chamber increased by 15%. In addition, the specific fuel consumption (SFC) decreased by 14.2% indicating an enhanced working efficiency of the combustor. The impact of fuel injection is also studied by doubling the injection point density and increasing FAR using the geometry of the baseline case. It is found that the thrust can be increased by about 60% with an increment of 80% for FAR. However, the SFC increases by about 15% indicating less working efficiency. In addition, the temperature at outlet also increased by about 37% imposing potential damage of the downstream turbines. A combined case is then conducted with a 15% increment of the combustor chamber volume and 40% increment of FAR using doubled density of fuel injection points compared to the baseline case, thrust is increased by 46.7%, and the exit temperature is increased by 17.9% In addition, SFC is almost unchanged indicating the same level of combustion efficiency to the baseline case. The current work has provided good insight to the numerical prediction capabilities of the flow features of a mini turbojet engine combustor. Important flow characteristics have also been observed.