Novel two-stage injector for flame stabilization in supersonic flows

A novel injector was developed as the result of numerical and experimental studies of the self-ignition of hydrogen and the flame stabilization in a supersonic flow (Ma = 2.1, T₀ = 900 K). The injector was realized as a serial system of a conventional supersonic diffuser and a nozzle dividing the flow into two parts. Most of the air flows into the combustion zone almost undisturbed. A small amount enters a shaped channel with a supersonic-subsonic- supersonic flow. Hydrogen is injected into both flows. The incomplete preburning in the subsonic area increases the total temperature and produces a large radical concentration, which acts as source for the ignition of the main flow. It is shown that the flame propagation is much faster under the presence of radicals. This allows the reduction of the required residence time of the fuel and the length of the chamber. The lower total temperature limit of proper ignition and flame stabilization is decreased to 900 K compared to 1200 K for the limit of the strut injection concept investigated previously. Furthermore, the formation of strong shock waves, inducing a large loss of total pressure, can be avoided. The new injector has the potential of a much higher combustion performance than standard flame stabilization methods and extends the operating range of scramjet engines to low flight Mach numbers.