Structure and Dynamics of Cryogenic Flames at Supercritical Pressure

Abstract

A detailed understanding of liquid propellant combustion is necessary for the development of improved and more reliable propulsion systems. This article describes experimental investigations aimed at providing such a fundamental basis for design and engineering of combustion components. It reports recent applications of imaging techniques to cryogenic combustion at high pressure. The flame structure is investigated in the transcritical range where the pressure exceeds the critical pressure of oxygen ðp > p c ðO 2 ¼ 5:04 MPaÞÞ but the temperature of the injected liquid oxygen is below its critical value ðT O2 < T c ðO 2 Þ ¼ 154 KÞ. Data obtained from imaging of OH Ã radicals emission, CH Ã radicals emission in the case of LOx=GCH 4 flames and backlighting provide a detailed view of the flame structure for a set of injection conditions. The data may be used to guide numerical modelling of transcritical flames and the theoretical and numerical analysis of the stabilization process. Calculations of the flame edge are used to illustrate this aspect. Results obtained may also be employed to devise engineering modelling tools and We wish to thank CNES, Snecma and CNRS for their continuous support of our work in rocket propulsion. The assistance of the ''Mascotte'' team of Onera under the leadership of Lucien Vingert and Mohamed Habiballah is gratefully acknowledged.

Simulation of supercritical flows in rocket-motor engines: application to cooling channel and injection system

“…Generally, the chamber pressure is above the critical pressure of the fuel (p > p c ) while the injection temperature is subcritical (T < T c ). For example, the critical properties of decane which is commonly used to simulate kerosene, are p c = 2.1 MPa and T c = 617.7 K. Such a state is called compressed §uids (or transcritical state [2]). After injection, the fuel heats up and its temperature exceeds its critical value (T > T c ).…”

Supercritical Mixing and Combustion of Liquid-Oxygen/ Kerosene Bi-Swirl Injectors

“…Substantial experimental [8][9][10][11][12] and numerical [13][14][15] efforts on the characterization of propellant injection, mixing, and combustion processes at near-and supercritical conditions have recently led to improved understanding of the mechanisms involved. Most of these studies, however, have focused on shear coaxial injectors with light fluids, such as hydrogen and methane, as fuel.…”

Ignition of a gaseous methane/oxygen coaxial jet

“…Previous studies have shown that for higher chamber pressures, methane/oxygen §ames stabilize attached to the injector [4,7]. For lower pressures, the anchoring of the methane §ame seems to be much more dependent on injection parameters [3,5,8].…”

“…While with hydrogen fuel, the §ame anchors properly at the injector lips in most cases [3 6], the use of methane fuel induces di¨erences in §ame stabilization. The §ame behavior appears to be highly dependent on injection and combustion chamber conditions: for supercritical injected propellants, the LOX/CH 4 §ame stabilizes near the injector [4,7]; however, for subcritical condition, the methane §ame can stabilize either anchored or detached [3,5,8]. Even though the laminar §ame velocity for methane oxygen mixture is about a factor of 2.7 lower than that for hydrogen oxygen mixture [9], the reasons explaining the §ame behavior di¨erence are up to now not clear and further investigations are still going on to better understand the mechanisms of methane §ame stabilization.…”

“…inner diameter, outer diameter fps frames per second GO 2 gaseous oxygen GCH 4 gaseous methane J momentum §ux ratio, J = (ρu 2 ) CH 4 /(ρu 2 ) O2 ' m mass §ow rate p, P pressure R of mixture ratio, R of = ' m O2 / ' m CH 4 T temperature u injection velocity V ratio velocity ratio, V ratio = u CH4 /u O2 ρ density equivalence ratio…”