Combustion Science and Technology, Vol.114, 471-491, 1996
Energetic fuel droplet gasification with liquid-phase reaction
An exploratory analytical and computational study of gasifying energetic liquid fuel droplets is presented. The liquid-fuel reaction, heating, and breakup are modelled and characterized. A spherically-symmetric geometry is considered, and the problem is described by considering a general formulation capable of resolving the solution domain consisting of a liquid-phase region, a bubbly two-phase region, and a gas-phase region. The transient, two-phase, governing equations are solved numerically for various values of the nondimensional rate constant, heat of decomposition, activation energy, number of bubbles per unit mass, and ratio of gas-phase to liquid-phase thermal conductivities. Results are compared between one model wherein gaseous fuel leaves the droplet due to decomposition of the droplet surface and bubbles that connect with the droplet surface when the void fraction exceeds a critical value (phi(c)), and another model wherein the droplet mass decreases due to discontinuous bubble bursting at the droplet surface. The models agree well (with the exception of oscillations in the droplet radius predicted by the latter model) in the limit of phi c --> 1. Consistent with simplified scaling for the limit of chemical rate control, the droplet lifetime eta* is strongly dependent on the nondimensional decomposition rare constant and activation energy, and less strongly on the number of bubbles per unit mass, ambient pressure, and heat of decomposition. Increasing the ratio of gas-phase to liquid-phase thermal conductivities increases eta* slightly. The droplet lifetime is a monotonically increasing function of initial droplet radius but too weak for diffusion rate control; the results are closer to the chemical rate control limit.