Review of atomization mechanism and spray characteristics of a liquid jet in supersonic crossflow

The injection and atomization process of a liquid fuel jet is critical for an ignition start of a scramjet engine. Airwall-mounted crossflow injection strategy is widely used in scramjet combustors, avoiding high total pressure loss and allowing the liquid fuel to rapidly undergo atomization, mixing, and evaporation. In this review, research progress on a liquid jet in supersonic crossflow was evaluated from aspects of atomization mechanism and spray characteristics. When a liquid jet is injected into a supersonic crossflow, primary and secondary breakups occur successively. The surface instability of liquid can significantly affect the breakup process. This review discusses the current understanding of the breakup process and spray characteristics of a liquid jet in supersonic crossflow including the mechanism of atomization and the characteristics of distribution and atomization. The development of windward Rayleigh-Taylor (R-T) unstable waves is the main factor in column breakup. The development of Kelvin-Helmholtz (K-H) unstable waves along the circumferential direction of the jet or droplets is the main factor of surface and droplet breakups. The liquid–gas momentum ratio is the most important factor affecting the penetration depth. The span width of the liquid jet is affected by the windward area. Breakup and coalescence lead to a transformation of the size distribution of droplets from S- or C-shaped to I-shaped, and the velocity distribution of the droplets on the central symmetry plane has a mirrored S-shape. The droplet distribution on the spanwise cross-section retains a structure similar to an "Ω" shape. At last, some promising recommendations have been proposed, namely a theoretical predictive model which can describe the breakup mechanism of a liquid jet, the distribution characteristics and droplets size distribution of a liquid jet under a cavity combustion chamber, especially for enthalpy flows with complex wave structures.