In this paper numerical studies have been carried out to examine the intrinsic flow features of cavity based scramjet combustors with backward facing step and forward ramp using 3D, density-based, implicit, SST k-omega turbulence model. The preliminary results show a wide variety of flow features resulting from the interactions between the injector flows, shock waves, boundary layers, and cavity flows. In all the cases the C2H6-CO2-H2O fuel is injected at three different jet angles for the optimization of the jet orientation. Through the 3D numerical simulation we have corroborated that an optimized cavity is a good choice to stabilize the flame in the scramjet combustor as it generates a benign recirculation zone in the scramjet combustor. We comprehended that the cavity based scramjet combustors have a bearing on the source of disturbance for the transverse jet oscillation, fuel/air mixing enhancement, and flame-holding improvement. We concluded that the cavity shaped combustor with backward facing step and 45° forward ramp having an injector location of 1.6 times of its hydraulic diameter from the inlet facilitating at an angle of injection of 45° opposing the inlet flow is a good choice to getting relatively higher temperature at the exit.