Phase Change Characteristics of Impinging Hydrocarbon Mixture Jet with Critical Properties

Supercritical combustion occurs in the high-pressure environment of a rocket engine where supercritical atomization is required. In this experiment, a kerosene surrogate, the primary fuel of a liquid rocket, is selected and injected into a high-temperature, high-pressure chamber above the critical point. The experiment is conducted to analyze the jet penetration sprayed from the subcritical state to the supercritical environment and to confirm the phase change at the jet-ambient gas interface. The atomized jet is generated by impinging a hydrocarbon mixture propellant, and this experiment examines the phase change in a supercritical environment. A mixture of n-decane and methylcyclohexane is used as the surrogate propellant. The propellant is injected into the chamber of the sub/supercritical environment, and the jet core and penetration are visualized using a shadowgraph method. The ambient pressure exhibits two conditions: 2.6 MPa ( $${P}_{r}$$  = 1.00) and 3.6 MPa ( $${P}_{r}$$  = 1.38). These conditions have different pseudo-critical points, and the experiment is carried out while increasing the ambient temperature from 599 K ( $${T}_{r}$$  = 1.00) to 700 K ( $${T}_{r}$$  = 1.17). At 2.6 MPa, the density of the propellant decreases drastically near the critical temperature of the mixture, 602 K. At 3.6 MPa, the density decreases near 630 K, a pseudo-critical temperature. Consequently, it is confirmed through the visualization that the length of the liquidlike core of the jet is shorter at 2.6 MPa than at 3.6 MPa, all else being equal.