MULTIDIMENSIONAL NUMERICAL SIMULATION OF KEROSENE SPRAY FRAGMENTATION, VAPORIZATION, AND SELF-IGNITION IN AIR

Abstract

The physical and mathematical models of droplet breakup [1] and evaporation [2] are thoroughly tested for single-component physical surrogates (n-decane and n-dodecane) of aviation kerosene. Also, the overall kinetic mechanisms of self-ignition and combustion of singlecomponent and 9-component chemical surrogates of aviation kerosene vapors are developed and thoroughly validated against available experimental data. The tested models, chosen surrogates, and validated kinetic mechanisms are then applied to the solution of the multidimensional problem of kerosene spray self-ignition in a con¦ned volume. For the droplet breakup model [1], the values of empirical coef- ¦cients inherent in transverse injection of kerosene spray into a hot air stream are determined. The evaporation model [2] is shown to be well applicable at gas pressures lower than the liquid critical pressure, while at supercritical pressures, the use of a real-gas equation of state is required. As chemical surrogates of kerosene vapors, a singlecomponent surrogate based on n-dodecane and a 9-component surrogate based on the blend of normal alkanes with the number of carbon atoms from 8 to 16 are selected. The volume fractions of n-alkanes in the blend are chosen in accordance with the amplitudes of carbon peaks in the chromatogram. The overall kinetic mechanisms of selfignition and combustion of the selected chemical surrogates are based on the ¦xed set of reactions, namely, the rate-limiting irreversible reaction of n-alkanes oxidation to CO and H2O followed by reversible water gas shift and water dissociation reactions and irreversible reactions of CO and H2 oxidation. Despite the set of reactions is ¦xed, the values of the kinetic parameters of the rate-limiting reaction for self-ignition and combustion are di¨erent because in self-ignition, the main role is played by chain branching reactions in the absence of external heat and mass sources, while in combustion, such sources exist due to huge gradients of temperature and active species concentrations. Comparison with available experimental data shows that the overall kinetic mechanisms are well applicable to the problems of selfignition and combustion of kerosene in wide ranges of temperature, pressure, and composition of kerosene air mixtures. The results of multidimensional calculations are compared with experimental data on self-ignition delays and spatial evolution of the reaction zone [3]. Calculations are shown to be in satisfactory agreement with the experimental data despite somewhat conditional de¦nitions of the selfignition delays and spatial domains occupied by the reaction zone.