INJECTION OF FLUIDS INTO SUPERCRITICAL ENVIRONMENTS

ABSTRACT This paper summarizes and compares the results of systematic research programs at two independent laboratories regarding the injection of cryogenic liquids at subcritical and supercritical pressures, with application to liquid rocket engines. Both single jets and coaxial jets have been studied. Cold flow studies provided valuable information without introducing the complexities of combustion. Initial studies utilized a single jet of cryogenic nitrogen injected into a quiescent room temperature nitrogen environment with pressures below and above the thermodynamic critical pressure of the nitrogen. Later, the work was extended to investigate the effects of a co-flowing gas. Parallel to this work, combustion studies with cryogenic propellants were introduced to understand high pressure coaxial injection phenomena with the influence of chemical reaction. Shadowgraphy and spontaneous Raman scattering were used to measure quantities such as growth rates, core lengths, turbulent length scales, fractal dimensions, and jet breakup regimes. It is found that jets injected at supercritical pressures do not atomize as they do at subcritical pressures. Rather, they behave in many respects like variable density turbulent gas jets. Keywords: propellant injectionsprayssupercritical pressure The DLR would like to acknowledge all those who have been involved in the research programs. These people include colleagues at the test bench and technicians who have helped make these studies possible. The last two authors would like to thank Mr. Mike Griggs and Mr. Earl Thomas, and Mr. Mark Wilson for their assistance in machining, setup, and operation of the AFRL facility. Ms. Jennie Paton is also thanked for making literature available in a timely manner. The AFRL part of the work is sponsored by the Air Force Office of Scientific Research under Dr. Mitat Birkan, program Manager.