Stochastic Equilibrium Analysis to Optimize Solid Propellant Combustion Gas Composition

Abstract

Solid fuel ducted rockets operate with two-stage combustion. The first stage generates burnt products from the combustion of a fuel-rich solid propellant. In the second stage, those combustion products react with air and are ejected through a nozzle to produce thrust. The combustion efficiency of such a device strongly influences its performance and depends on the composition of the rich-fuel-burnt pyrolysis products. This study investigates the sensitivity of carbon, hydrogen, oxygen, and nitrogen (CHON) solid fuels’ burnt product composition to the fuel properties, composition, and heat of formation. The calculations are performed assuming adiabatic, isobaric chemical equilibrium on synthetic species. Existing species’ properties constrain the properties of the synthetic species. The trends of formation of the main species observed in gas generators, i.e., H2, CH4, CO, N2, CO2, H2O, and solid carbon, are presented. The sensitivity of the molar concentration ratio ξ of H2 to CH4 to the oxygen balance and propulsive properties is compared with an example of gas generator propellants. Recommendations for the possible optimization of fuel composition are formulated. For blends of the existing CHON species reported in the literature, it is shown that improving ξ is only possible by degrading the specific impulse.