Supercritical droplet vaporization and combustion in quiescent and forced-convective environments.

摘要

Vaporization and combustion of liquid droplets in both subcritical and supercritical environments have been studied systematically. A varieties of liquid propellants and propellant simulants, including hydrocarbon and cryogenic fluids, in both steady and oscillatory environments, are treated. The formulation is based on the full conservation equations for both gas and liquid phases and accommodates variable properties and finite-rate chemical kinetics. Full account is taken of thermodynamic non-idealities and transport anomalies at high pressures as well as liquid/vapor phase equilibrium for multi-component mixtures. Because the model allows solutions from first principles, a systematic examination of the droplet behavior over wide ranges of pressure, temperature, and ambient flow velocity is made possible. Results can not only enhance the basic understanding of the problem, but also serve as a basis for establishing droplet vaporization and combustion correlations for the study of liquid rocket engine combustion, performance, and stability.;A series of calculations have been performed to understand the effects of ambient flow conditions on droplet gasification behavior. Results indicate that the velocity and thermodynamic state of the ambient flow have strong influences on the mass, momentum, and energy transport in the droplet gasification and burning processes. The droplet gasification rate increases progressively with pressure and ambient Reynolds number. The amplitude of pressure-coupled droplet vaporization response increases with increasing pressure owing to the susceptibility of enthalpy of vaporization to ambient flow oscillations at high pressures. However, the effect of mean pressure on the phase angle of the droplet vaporization response appears quite limited.;Detailed flow structures and thermodynamic property variations are examined to reveal underlying mechanisms for droplet gasification and burning as well as deformation and breakup dynamics at supercritical pressures. Correlations of droplet lifetime and aerodynamic drag coefficient are developed as functions of fluid thermodynamic state, Reynolds number, and vaporization transfer number.