Multiphase and Non-Equilibrium Effects in Highly Fuel-Rich Solid Fuel Gas Generators

Solid fuel gas generators (SFGGs) allow compact storage of fuel for flight vehicle combustors. Design of propellants for SFGGs requires optimization for secondary combustion properties, making oxygen balance (OB) a primary performance parameter due to its influence on specific impulse and SFGG product composition. In this work, a class of three propellants of varying OB are developed, with ammonium perchlorate, hydroxyl-terminated polybutadiene, and polyethylene as primary ingredients. Equilibrium combustion predictions are calculated, showing that exhaust composition is expected to change significantly with oxygen balance. Propellant burn rate is measured between 1.5 and 9.25 MPa, and equilibrium pressure measurements are made in an SFGG combustor. Burn rate is shown to decrease with decreased OB, while pressure sensitivity is shown to increase. Propellant performance metrics for SFGGs are developed, and it is shown that SFGG sizing parameters are only slightly sensitive to OB for this propellant class. Finally, it is shown that equilibrium composition calculations with first-order multiphase corrections are insufficient for predicting the equilibrium pressure in an SFGG.