Gel fuels are non-Newtonian fluids with a yield stress. In the absence of sufficient shear stress, the gel has a solid-like behavior. Under shear stress the viscosity decreases to allow the atomization and subsequent vaporization and combustion, not much unlike the vaporization and combustion of liquid fuels.
In terms of safety, gel fuels exceed both solid and liquid propellants. Moreover, gel fuels have significant advantages in terms of performance. As in the case of liquid fuels, the flow rate of a gel fuel to the combustion chamber is controllable. In addition, gel fuels are ideal for energetic additives. Energetic additives, such as metal particles, compensate for the loss in energy content due to the addition of the gellant.
The present work deals with the mathematical modeling and numerical simulation of the combustion of a single droplet of gel fuel based on organic gellant. Organic-gellant-based gel fuel drops exhibit a cyclic combustion mechanism. The process begins with a traditional combustion, followed by the formation of an elastic impermeable film of gellant around the droplet. As a result, vapor fuel bubbles form and expand inside the droplet until the fuel vapors burst through the film. This process repeats itself until complete depletion of the fuel and gellant. This behavior occurs because the gel fuel is basically a mixture of species with very different volatilities: the gellant on one hand and the parent liquid fuel on the other.
