Wake flame dynamics in a freely falling burning droplet

The moving burning droplet is an interesting area of fundamental research that gives insight into spray combustion. A freely falling burning droplet was experimentally investigated in a drop tower facility. After the droplet is ignited and is allowed to fall freely, the droplet flame transitions to a wake configuration due to forward extinction. The different wake flame behavior regimes have been identified, and the various flame transitions exhibited have been investigated. The wake flame showed similar characteristics as a laminar lifted triple-flame, and the flame stand-off increases continuously as the droplet falls. Wake flame topology changed in two regimes corresponding to different droplet diameters. The flame transitioned between premixed and diffusion due to the alteration of the fuel availability. A theoretical formulation has been proposed based on the momentum diffusion into fuel stream, which has satisfactorily estimated the flame behavior and transitions in different regimes. Furthermore, at very high Re >150, the flame stretching/shedding is observed, which is caused due to the asymmetric vortex shedding from the droplet induced by the BVK instability.