Flame stabilization in cryogenic propellant combustion

Abstract

Cryogenic combustion is of considerable technological interest in propulsion applications. Cryogenic propellants used in rocket engines provide the high performance needed for spacecraft launching and have operated safely for a number of years, but the processes that control combustion in such devices are still not well understood. Among the many important issues, flame stabilization constitutes one basic problem. This question is investigated in this article by imaging the flame originating from a single, coaxial injector fed with liquid oxygen and gaseous hydrogen. Results of experiments carried out on a facility for cryogenic propellant combustion research operated by ONERA are used to characterize the mechanisms that control the flame-holding process at atmospheric pressure, 5, and 10 bars. Data acquired correspond to elastic scattering by the spray, emission of OH radicals, and planar laser-induced fluorescence of these radicals. Fluorescence is obtained by pumping the X2II (v″=0)→A2Σ(v′=1) band of OH, and off-resonance light radiation is observed. This database provides the general structure of the flame in the injector near-field, and may be used to determine the position of the flame stabilization region. Simultaneous acquisition of laser-induced fluorescence and elastic scattering was used to locate the flame in respect to the liquid. It is shown that in all cases investigated the flame is initiated at a close distance from the injector exhaust plane.