Comparison of Methods for Calculating Turbine Work in the Air Turborocket

Abstract

The air turborocket (ATR) is an airbreathing propulsion system that utilizes a turbine-drive gas source, which also providesfuelforthemain combustor.Bymakingsomesimplifying assumptions, ATRspecie cimpulsebecomes largely a function of turbine specie c work and main-combustor gas total temperature. Turbine specie c work is the major driver of ATR specie c impulse because it also determines the main-combustor fuel-to-air ratio. Turbine specie cworkcanbecalculatedassumingtheturbine-drivegasisanequilibriumgasmixture,whichexpandswithout reaction, a nonreacting gas mixture, or an equilibrium gas mixture, which expands with reaction. Turbine work, main-combustor gas total temperature, and specie c impulsebased on theseassumptionsare compared. Signie cant errors in specie c impulse result if an equilibrium, nonreacting gas mixture is assumed. This assumption can also lead to the mistaken conclusion that there are two maximum specie c-impulse values at signie cantly different gas-generator oxidizer-to-fuel ratios. By assuming a reacting gas mixture, it is shown that the maximum specie cimpulse of an O 2/H2 driven ATR occurs at a gas-generatoroxidizer-to-fuel ratio of about 4. There aretwo possible maximum specie c-impulsevalues forthe O 2/propane-driven ATR at gas-generator oxidizer-to-fuel ratios of about 1 and 2.