Transport and Reignition of Unburnt n-Dodecane Fuel Droplets in a Transverse Jet in Supersonic Crossflow

Le résumé fourni par la source

The canonical "jet in a crossflow" (JICF) problem is of significant recent interest in divert thrusters (used in hypersonic missiles, interceptors, and re-entry vehicles), as well as in scramjets and detonation engines. This study presents detailed 3D numerical simulations of a jet comprising gaseous burnt products and unburnt fuel particles in a supersonic crossflow using an Euler-Lagrange algorithm. Our objective is to explore droplet breakup and evaporation characteristics, and the possibility of evaporated fuel reignition. The jet comprises a preheated carrier gas of burnt products, laden with mono-dispersed 20μm, n-Dodecane droplets, representative of partially burnt exhaust from an engine/thruster carrying unburnt (residual) liquid fuel. As the high-pressure jet enters the crossflow, it expands and forms a diamond shock structure, while the droplets reach a local Weber number of ~300, initiating breakup. Observations indicate that greater than ~ 90% of the droplets break up into child droplets with diameters < 3 μm within a downstream distance of 6 jet diameters. The child droplets achieve a velocity close to the gas flow velocity, with a Weber number below the critical Weber number (We_cri=12 ) preventing further breakup. Heat transfer from the hot carrier gas enhances droplet evaporation, with nearly all the total injected liquid mass observed to be evaporated by the time the droplets reach a distance of 10 jet diameters. The crossflow consisting of pure O2 was observed to entrain significantly into the jet mixture, initiating reignition of the evaporated fuel, which can damage the external surface of the vehicle to which the thruster is attached.

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