Shock–wake–shear interaction control through novel strut injectors for enhanced hydrogen mixing and combustion in a supersonic combustor

To achieve efficient combustion with a hydrogen fuel, the mixing between the fuel and air and the growth of the reaction zone must be very fast within a short supersonic residence time, and the shock-induced compression and flow separation losses must be minimal. But there are still elements to the fundamental understanding of the strut geometry, shape of the shock, wake formation, turbulent fuel flow and the resulting combustion–pressure-loss compromise that have yet to be resolved. This study aims to solve this issue by systematically investigating the three different injector configurations of strut-injector using the same operating condition. The novelty is to create a mechanistic correlation between the mechanisms of strut-controlled shock distribution, low-Mach wake formation, hydrogen penetration, turbulence–fuel overlap, thermal field formation, and overall combustor performance, instead of assessing injector designs based on any single combustion parameter. Hydrogen-distribution analysis also indicates that Strut B yields the largest fuel-plume width and benefits the most in terms of reduction of the fuel mass fraction, dropping below 0.010, near the downstream location, due to a more uniform and extensive high-temperature reaction region compared to Strut A. All of the configurations achieve 99–100% efficiency of combustion after the principal region of reaction; however, Strut B provides very nearly complete mixing towards the combustor exit, while keeping the maximum total pressure loss of about 0.27 as compared to about 0.34 for Strut A. From the results, distributed shock induced compression and spatially extended shock–shear interaction have been shown to be more efficient to mix hydrogen than concentrated compression, and serve as a physics-based guideline for designing high performance hydrogen fuelled scramjet strut injectors.