A morphological study of supercritical fuel flash-boiling spray. (15th February 2022) - Xu, Qinglin
Highlights: The formation of shockwave affected the transient process of supercritical spray. The supercritical flash-boiling spray feature approximates highly underexpanded jet. The minimum heat for complete vaporization dominates the spray steady penetration. Isentropic expansion ratio dominates the spray radial expansion. Mach disk location correlates with expansion ratio similar to the underexpanded jet. Abstract: The optimization of fuel injection is one of the key technologies to achieve cleaner and more efficient engines. Extensive studies have demonstrated that the flash-boiling of superheated fuel would dramatically improve the atomization, mixing and combustion process. Further increasing the fuel temperature can make the fuel at a supercritical state, the flash-boiling spray of which has rarely been noticed in existing studies. The relevant data and analysis of the behavior and characteristics of supercritical fuel flash-boiling spray are still lacking. In this study, the supercritical flash-boiling injection was achieved by heating the fuel inside the injector, and its spray behavior was examined by high-speed backlit imaging. This study found that the supercritical fuel flash-boiling spray has a transient formation process different from common sprays due to the supersonic effect during the initial injection. The spray structure was carefully analyzed based on its thermodynamic state and hydrodynamic state. The spray penetration, radial expansion, location of Mach disk was also systematically investigated. The characteristics of the supercritical fuel flash-boiling spray are very similar to that of the highly under-expanded jet.