Analysis of Flame Patterns in Cryogenic Propellant Combustion

Abstract

Design and optimization of high performance rocket engines may be improved by detailed studies of the basic combustion mechanisms. Much detailed information exists on elementary processes such as atomization, multiple jet interactions, vaporization of single droplets, structure of spray flames, ignition of nonpremixed systems etc. It is however important to approach the real conditions existing in rocket motors and to this purpose several facilities for cryogenic propellant combustion research have been designed and constructed. One experimental set-up designated as “Mascotte” is operated by ONERA and used for fundamental research as well as technical studies. This article describes results of experiments conducted in this facility by our laboratory. Two series of tests carried out during the last two years have provided a large set of images of combustion in a liquid oxygen/gaseous hydrogen coaxial injection geometry operating at atmospheric pressure and at 5 and 10 bars. The data correspond to laser elastic scattering of the spray, spontaneous emission of OH radicals and planar laser induced fluorescence of these radicals. Fluorescence is obtained by pumping the EQUATION band of OH. Off-resonance light radiation is observed with an intensified CCD camera. The large data base of images collected in these experiments provide the general flame structure in the injector nearfield, and may be used to determine the position of flame stabilization. Effects of global injection parameters (momentum flux ratio, Weber number, mixture ratio) and operating pressure are described. It is shown that the conditions prevailing in the liquid and gaseous jets influence the flame stabilization process, the instantaneous combustion patterns and the mean flame shape.