Chemical heating of the working gas in a short-duration high-enthalpy facility

Abstract

Operation of a short-duration high-enthalpy facility with products of reactions of propane, hydrogen, and nitrous oxide with air and oxygen is studied. The mixtures are ignited either by an electric arc or by an igniter with a “chamber-plume” principle of operation, which involves local ignition of the mixture from one spot located at the center of the settling chamber. It is confirmed that the use of a combined (electrical and chemical) heating of the working gas completely resolves the problem of reproduction of real values of stagnation pressure and enthalpy for flight conditions of a vehicle with Mach numbers of 4 to 7. The lean flammability limits of ignition by an electric arc turn out to be lower than the data reported in the literature for standard conditions. Combustion of three-species (fuel + oxygen + air) mixtures with hydrogen (mole fraction of hydrogen $$r_{H_2 } > 0.1$$ ) and mixtures with propane $$(r_{C_3 H_8 } > 0.027)$$ is completed in 5–8 msec with combustion efficiency close to unity. The time needed for chemical reactions initiated by an igniter to be completed is significantly greater than that with ignition by an electric arc. The time of combustion with the use of an igniter can be substantially reduced by increasing the number of ignition spots, by using mixtures with a greater fraction of the fuel than that required for reproduction of natural enthalpy, or by replacing a certain part of the fuel in the original mixture by nitrous oxide.