Co-Flow injection strategies for hydrogen scramjet engines: A numerical study of H2O, O2, and mixed injections in the cavity region

The current numerical study investigates the impact of co-flow injection strategies on the performance of a scramjet combustor via computational fluid dynamics analysis. The motivation of this research is to enhance mixing, combustion efficiency, and thermal stress distribution inside the supersonic combustor. A three-dimensional, steady-state, pressure-based solver was employed to simulate the scramjet combustor. Six different cases were developed to assess the effects of co-flow composition, mass flow rate, and injection location on scramjet combustion efficiency. The proposed cases were, conventional scramjet mlocodel (S1), H2O co-flow with mass flow rates of 0.48 kg/s (S2) and 0.96 kg/s (S3), O2 co-flow with mass flow rates of 0.48 kg/s (S4) and 0.96 kg/s (S5), and a mixed O2 and H2O co-flow case with mass flow rates of 0.48 kg/s each (S6). The results show that the introduction of H2O co-flow reduces the temperature at the combustor exit by up to 8 % compared to S1. On the other hand, O2 co-flow enhances combustion efficiency, which results in a temperature decrease of 17.4 % at the same location. The combined O2 and H2O co-flow case achieves a 12.5 % temperature reduction, balancing improved combustion efficiency with effective heat absorption. Co-flow injection also significantly impacts the turbulence intensity, with O2 co-flow producing the strongest effect by reporting up to 236 % increase in the intensity at the injection point. These findings provide design guidelines for advanced scramjet engines and offer a pathway to improve combustion efficiency while managing thermal loads in hypersonic propulsion systems.