Published online by Cambridge University Press: 11 December 2002
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 ${\rm CH}_4/{\rm O}_2/{\rm N}_2$ 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.