Energetic Fuel Droplet Gasification with Liquid-Phase Reaction.
Final rept. 1 Nov 93-30 Jun 97,
CALIFORNIA UNIV IRVINE DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
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An analytical and computational study of the gasification and oxidation of an energetic liquid fuel droplet is presented. Single-step, finite-rate, Arrhenius reaction rate expressions are used for exothermic liquid-phase decomposition and gas-phase oxidation. The liquid fuel is assumed to decompose to a gaseous product at a fixed number of bubble sites per unit mass specified a priori within the droplet. Decomposed gas escapes the droplet surface by 1 decomposition gasification of the droplet surface, 2 decomposition at the surface of bubbles that connect with the droplet surface, and 3 escape of gas inside bubbles due to droplet surface regression. Without oxidation, 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 right arrow 1. The transient, two-phase, governing equations are solved numerically for various values of the nondimensional reaction rate coefficients for both decomposition and oxidation, heats of decomposition and oxidation, number of bubbles per unit mass Nm, and ambient temperature and pressure. Consistent with simplified scaling for the limit of chemical rate control, the droplet lifetime eta d is strongly dependent on the nondimensional decomposition rate 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 d slightly.
- Physical Chemistry