ANALYSIS OF FLAME PATTERNS IN CRYOGENIC PROPELLANT COMBUSTION

Design and optimization of high performance rocket engines may be impr oved by detailed studies of the basic combustion mechanisms. Much deta iled information exists on elementary processes such as atomization, m ultiple jet interactions, vaporization of single droplets, structure o f spray flames, ignition of nonpremixed systems etc. It is however imp ortant to approach the real conditions existing in rocket motors and t o this purpose several facilities for cryogenic propellant combustion research have been designed and constructed. One experimental set-up d esignated as ''Mascotte'' is operated by ONERA and used for fundamenta l research as well as technical studies. This article describes result s of experiments conducted in this facility by our laboratory. Two ser ies of tests carried out during the last two years have provided a lar ge set of images of combustion in a liquid oxygen/gaseous hydrogen coa xial 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 fluores cence of these radicals. Fluorescence is obtained by pumping the X-2 P i(upsilon '' = 0) --> A(2) Sigma(upsilon' = 1) band of OH. Off-resonan ce light radiation is observed with an intensified CCD camera. The lar ge data base of images collected in these experiments provide the gene ral flame structure in the injector nearfield, and may be used to dete rmine the position of flame stabilization. Effects of global injection parameters (momentum flux ratio, Weber number, mixture ratio) and ope rating pressure are described. It is shown that the conditions prevail ing in the liquid and gaseous jets influence the flame stabilization p rocess, the instantaneous combustion patterns and the mean flame shape .