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

The expansion and mixing processes of underexpanded supercritical fuel jets injected Into superheated conditions were experimentally studied. Ethylene was used as the fuel, and nitrogen was the ambient gas. The near-held 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 ethyl ene jet matches that of an ideal-gas jet. The size of the Mach disk and the expansion angle, however, increase as the injection temperature approaches the critical value. The far-field mixing processes were characterized by m easuring fuel mole fraction and temperature distributions using spontaneous Raman scattering. Fuel mole fraction distributions follow a Gaussian funct ion, whereas temperature distributions exhibit a deficit inside the jet plu me because of the expansion and acceleration of the fuel jet. As the inject ion condition approached the critical point, the following observations wer e made: 1) the ethylene centerline mole fraction increased, 2) the jet widt h at the stoichiometric level increased, 3) the jet width at half the maxim um concentration remained the same, and 4) the temperature deficit became m ore significant. These results were attributed to the larger Infected fuel mass flow and fuel condensation when the jet injection conditions approach the critical point.