NUMERICAL SIMULATION OF A HYDROGEN FUELED SCRAMJET COMBUSTOR AT MACH 1.5 USING STRUT INJECTORS AT MACH 2.47 AIR SPEED

摘要

In the arena of design of combustion chamber of scramjet engine lots of development are still going on. A properly designed combustor shall promote sufficient mixing of the fuel and air so that the desired chemical reaction and thus heat release can occur within the limited residence time of the fuel-air mixture. In the present work two different types of strut fuel injectors are investigated numerically, strut with circular injector and strut with alternating wedge injector. The combustor and strut dimensions are same as DLR Scramjet model. It consists of a divergent channel with a flame -holding, wedge shaped structure in the middle of the flow field from the base of which hydrogen is injected. Comparative study of mixing and combustion enhancement has been performed for Mach number 2.47 for air and Fuel (hydrogen) is injected at Mach 1.5.Simulations have been performed using ANSYS14- FLUENT. Density based approach is chosen and Standard k-ε model is used for modeling turbulence and single step finite rate chemistry is used for modeling the H_2-Air kinetics. k- ε model is based on a finite volume discretization of the continuity, momentum, energy equations. Dirichlet and Neumann boundary conditions are applied at inflow and outflow boundary conditions respectively and fixed walls are subjected to no slip conditions. For the purpose of validation, the k-ε results are compared with experimental data. The numerically predicted profiles of static pressure, axial velocity, turbulent kinetic energy and static temperature are compared for each model. It is seen that due to combustion the recirculation region behind the wedge becomes larger and acts as a flame holder for the hydrogen diffusion flame. The leading edge shock reflected off the upper and lower combustor walls makes the setting of combustion when it hits the wake in a region where large portions of the injected fuel have been mixed up with the air. The shear layers at the base of the wedge becomes more pronounced due to the fact that continuous ignition occurs within these shear layers. Maximum temperature occurred at the recirculation area which is produced due to shock wave-expansion, wave jet interaction and fuel jet losses concentration. It was found that mixing and combustion was considerably better with the more flow-disturbing alternating wedge injector strut and the rise in static temperature is enhanced with higher Mach number of air.