Expansion and mixing processes of underexpanded supercritical fuel jets injected into superheated conditions

Abstract

Theexpansionandmixingprocessesofunderexpandedsupercriticalfueljetsinjectedintosuperheatedconditions were experimentally studied. Ethylene was used as the fuel, and nitrogen was the ambient gas. The near-e eld jet plume structure was characterized by the location and size of the Mach disk and the expansion angle. The Mach disk location of the supercritical ethylene jet matches that of an ideal-gas jet. The size of the Mach disk and the expansion angle, however, increase as the injection temperatureapproaches the critical value. Thefar-e eld mixing processes were characterized by measuring fuel mole fraction and temperature distributions using spontaneous Raman scattering. Fuel mole fraction distributions follow a Gaussian function, whereas temperature distributions exhibit a dee cit inside the jet plume because of the expansion and acceleration of the fuel jet. As the injection condition approached the critical point, the following observations were made: 1 ) the ethylene centerline mole fraction increased, 2 ) the jet width at the stoichiometric level increased, 3 ) the jet width at half the maximum concentration remained the same, and 4 ) the temperature dee cit became more signie cant. These results were attributed to the larger injected fuel mass e ow and fuel condensation when the jet injection conditions approach the critical point.