Investigation of Cryogenic Propellant Flames Using Computerized Tomography of Emission Images

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Cryogenic propellant combustion is investigated in this paper. It is shown that the mean e ame structure may be obtained by applying computerized tomography principles to oxygen‐ hydrogen (OH) emission images obtained from experiments on a shear coaxial injector. The data correspond to injection conditions typical of those found in rocket motors, but to lower operating pressures of 1, 5, and 10 bar. The transformed emission images yield the mean volumetric OH emission distribution. This quantity may be roughly interpreted as the mean volumetric rate of reaction. The data provide the location of the mean e ame zone and cone rm that stabilization takes place in the immediate vicinity of the injection plane. I. Introduction L IQUID oxygen ‐ gaseous hydrogen rocket engines have been used for a number of years because they yield the high specie c-impulse values needed in space propulsion applications. Cryogenic propellants thus diminish the cost per mass of payload in orbit, but pose specie c storage, handling, and operating problems. Current rocket motor design relies on extensive experience and technological expertise. The detailed processes involved in cyrogenic combustion are, however, not yet fully documented. An improved understanding of the mode of e ame stabilization and of the e ame structure in the near e eld of the injector head would be quite valuable. This information could be used to improve design methodologies and enhance reliability of operation. Such information would be useful for more accurate predictions of heat transfer rates to the engine walls. In this context, knowledge about whether the e ame is stabilized right on the injector lip or at a distance as a lifted e ame is of considerable interest. The stabilization region is specie cally investigated in this paper on the basis of experiments carried out on a cryogenic model scale combustor designated as Mascotte. This facility, operated by ONERA, is dedicated to basic research and technological studies. Data gathered at this facility include planar laser-induced e uorescence (LIF), planar laser light scattering, and emission imaging. Simultaneous recording of light elastic scattering and hydroxyl radical (OH) e uorescence images has allowed identie cation of the e ame stabilization. When the liquid oxygen (LOX) is injected by a central tube and is surrounded by an annulus of high-speed gaseous hydrogen, it is shown 1 that the e ame is established in the outer boundary of the LOX jet, where the hydrogen stream velocity is low. It is also found that the laser-induced OH ‐ e uorescence signal level remains in the same range over the zone visualized, with little change in the signal amplitude as a function of the axial distance. However, the emission images of the excited OH radical appear to yield a different picture of the e ame stabilization region. The emission amplitude is low close to the injector and increases rapidly at a distance. From these specie c features