The annular flow, electrothermal plug ramjet

Abstract

The annular flow, electrothermal plug ramjet is examined as a possible means of achieving rapid projectile acceleration for applications such as direct space payload launches. Electrothermal plug ramjet performance is examined for cases when hydrogen propellant is treated 1) as a perfect gas and 2) as a gas that can dissociate and ionize and then recombine at finite rates in the nozzle. Performance results for these cases are compared to the performance of a conventional ramjet operating with a perfect gas hydrogen propellant. Models describing electrothermal plug ramjet and conventional ramjet operation are presented and it is shown that, for a given flight velocity, there is an optimum rate of heat addition per unit mass of propellant. Propellant dissociation and ionization losses are found to be small and the nozzle flow is shown to be near chemical equilibrium rather than in a chemically frozen state. Diffuser shock losses are found not to degrade performance to unacceptably low levels. Fluid particle residence times are found to be small compared with those required for significant flowfield changes and it is argued that assuming quasisteady flow does not introduce significant errors. Thermal efficiencies over selected launch cycles are between 30 and 40% and pressure, temperature, and power requirements are demonstrated to be reasonable.