Compressibility effects of unreacted propellant on thermally choked ram accelerator performance

Abstract

Thrust calculations of the thermally choked ram accelerator propulsive mode based on quasi-steady, one-dimensional modeling of the flow process have been quite successful in predicting the experimental velocity-distance profile when real gas corrections are applied to the combustion products of propellants at initial fill pressures up to 8 MPa. A further refinement of the modeling takes into account real gas corrections for the initial state at higher fill pressures. It turns out that the Redlich-Kwong equation of state accurately determines the thermodynamic properties of the unreacted propellant for fill pressures up to at least 20 MPa. Using this equation of state for the calculation of the sound speed for a typical propellant provides a 15% higher value at 20 MPa than that predicted for an ideal gas; this increase significantly affects the operating characteristics of the ram accelerator at a given velocity. The corresponding thrust maximum increases by 30%. This corrected theory is most appropriate under conditions of high pressure operation at relatively low acceleration levels; i.e. , less than 10 000 g. The corrections to the aerothermodynamic equations that are discussed in this paper are fully generalized and can be applied using any equation of state.