This study presents the method of improving the scramjet combustor's performance by enhancing the mixing and penetration of the fuel. The mixing enhancement was done through a strut cavity, and the increased penetration was achieved through a Tandem-Hole injector.
The strut cavity induces pressure oscillations in supersonic flow with distinct dominant modes and broadband noise. The schlieren results showed seven kinds of waves associated with strut cavity pressure oscillations. Furthermore, the strut cavity had two shear layers, which moved in and out of the strut cavity at the trailing edges in synchronous and asynchronous modes. The Sturt cavity with the highest amplitude of pressure oscillation was implemented in a scramjet combustor for the reacting flow experiment. The results showed improved combustion due to the enhanced mixing of fuel and air.
Three Tandem-Hole injectors and a Single-Hole injector with the same injection area were studied for the plume penetration under cold flow conditions. The Tandem-Hole injector showed 12% higher penetration than the Single-Hole injector for the same fuel flow rate. The Tandem-Hole injector's higher penetration was due to the first liquid jet's shielding to the second jet. The second jet penetrated higher than the first jet, demonstrating overall penetration higher than the Single-Hole injector. Reacting flow experiments with Single-Hole and Tandem-Hole injectors in a scramjet combustor showed that the Tandem-Hole injector consistently demonstrated the superior performance for all the equivalence ratio tested.
Combining the strut cavity for mixing enhancement and the Tandem-Hole injector for higher penetration demonstrated the highest performance among the configurations tested due to the two-level of enhancement. The first level of improvement was obtained through the mixing-strut cavity, and the Tandem-Hole injector gave the second level of improvement. The injection system with strut cavity and Tandem-Hole injector was found to be the optimum configuration.