Flashing flow of superheated jet fuel

Abstract

Fuel stabilization technologies make it possible to utilize jet fuel to meet the heat sink capability demanded by the high performance jet engines in development. The resultant high fuel temperature creates the danger of vapor lock in the fuel line but also the possibility of utilizing the flash boiling to enhance the spray and mixing characteristics of an aero-engine combustor. To incorporate this new technology into the next generation aero-combustors, we need a quantitative understanding of the effects of this non-equilibrium, or flash vaporization of fuel in the Jet-A family on both the internal flow and the spray. We present the first attempt in simulating the flashing flow of a superheated JP8 fuel using a multi-dimensional transient code which incorporates a multi-component surrogate model to predict the JP8 properties in the superheated regime and resolves the finite flash vaporization rate under realistic flight conditions. Our numerical code was validated against available flashing flow data for water. Our simulations with superheated JP8 showed that, with respect to flow control and risk mitigation, flashing induced choking can occur even when the flow is subsonic – a consequence of the significant and rapid expansion of the two-phase fluid during the flashing process. This restriction on the flow rate, however, can be effectively controlled by adjusting the up-stream pressure. Our simulations also provided the initial conditions for the spray model. It showed that the spray core at the exit of the injector is non-uniform and is in the superheated state of varying degrees. A preliminary analysis of the flash vaporization time scale and the spray core breakup time indicated that the flashing phenomenon will play an important role in the spray breakup processes which will constitute our further works.