Mixing Dynamics of Supercritical Droplets and Jets

Abstract : This report summarizes a research program to understand the mixing dynamics of supercritical droplets and jets. The research was motivated by the recognition that pressures in modern liquid rocket engine combustion chambers tend to be higher than the critical pressure of one or more of the propellants. Prior to the beginning of this research, combustion processes were largely modeled using low pressure, subcritical spray combustion concepts. At supercritical pressures, however, a distinct difference between "gaseous" and "liquid" phases no longer exists, surface tension and the enthalpy of vaporization vanish, and "gas" phase density can approach that of the "liquid" with correspondingly significantly enhanced aerodynamic forces relative to the "liquid." These and other effects are discussed in detail in the references contained in the report. Under such conditions, questions such as whether droplets can even exist or what "spray combustion" would look like lacked even qualitative answers at the beginning. As a result of the research conducted under this program, most of the qualitative questions have now been answered, and significant progress has been made in determining quantitative mechanisms.