The detonation combustion phenomenon is supersonic combustion process and follows on thermal explosion in combustor. Deflagration to detonation transition occurs in detonation tube due to pressure oscillation in PDE combustor, which is driven by acoustic combustion phenomena in detonation tube. As this combustion process has great significance role for future propulsion system, the present objective is to investigate the effect of modify ejector having half angles of α = (− 4°, 0°, + 4°) on detonation combustion wave propagation regime. Further the propulsion thrust of liquid kerosene and gaseous hydrogen–air mixture are also analyzed. This numerical simulation has been analyzed by LES turbulence model for DDT and shock wave pressure oscillation in pulse detonation combustor at Fluent based CFD plat form. The one-step irreversible chemical kinetics model analyzes the details exothermic chemical reaction mechanism inside the combustor. However, the shrouded ejector with taper angle of α = +4° performed the strong starting vortex generation and shortest possible time of 0.032 s for fully developed detonation wave. The simulation results also shows that thrust force augmentation of hydrogen–air mixture is greater compared to combustion process of liquid kerosene–air mixture with significant magnitude of 38 N. Although kerosene–air mixture produces less pollutant number but the propagation flame velocity is 2550 m s−1 for hydrogen/air mixture, which is near about C–J velocity and comparatively higher than kerosene/air combustion process.