MIXING AND COMBUSTION OF CRYOGENIC OXYGEN-HYDROGEN SHEAR-COAXIAL JET FLAMES AT SUPERCRITICAL PRESSURE

ABSTRACT

This paper extends past analyses of liquid-oxygen-hydrogen flames at supercritical pressure by providing quantitative results that characterize multicomponent diffusion processes in the flame zone of a shear-coaxial injector element. High-fidelity simulations, using both the large-eddy-simulation and direct-numerical-simulation techniques, have been performed using detailed treatments of thermodynamic, transport and chemical kinetics. Results are presented for a condition where oxygen is injected in a cryogenic state, at a subcritical temperature and supercritical pressure, and hydrogen is injected in a supercritical state. This condition has significant technical relevance in liquid-rocket engines but is not well understood. For this situation a diffusion dominated mode of combustion occurs in the presence of exceedingly large thermophysical property gradients. The flame anchors itself in the interfacial region of high shear that exists between the liquid-oxygen core and the annular hydrogen jet. Intense property gradients approach the behavior of a contact discontinuity in this region. Significant real-gas effects and transport anomalies coexist locally in colder regions of the flow, with ideal gas and transport processes occurring within the flame zone. The current work provides a detailed analysis focused on the effects and relative contributions of various diffusion mechanisms and the net coupled effect of these processes on the observed mode of combustion.

Keywords:

• cryogenic propellants
• supercritical pressure
• flame structure
• Liquid-rocket propulsion

Notes

Critical properties of O₂: p _c  = 5.04 MPa (49.7 atm) and T _c  = 155 K.

Critical properties of H₂: p _c  = 1.30 MPa (12.8 atm) and T _c  = 33.2 K.

Portions of this work have been funded by the United States Department of Energy, Office of Basic Energy Sciences and the NASA Marshall Space Flight Center. The support provided is gratefully acknowledged.

The U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences supported this work. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94-AL 85000.