Research on the Combustion Mechanism of Hybrid Rockets

Investigations of the turbulent boundary layer with heat transfer, mass transfer, and chemical reactions are reviewed, with emphasis on recent studies motivated by the hybrid combustion problem. Relatively high mass injection rates and rapidly changing composition and enthalpy boundary conditions along the boundary layer edge are inherent to the hybrid problem, and earlier treatments are somewhat inconsistent with this situation. To account for these aspects, a more recent analysis reviewed here differs from earlier ones in the way the mass transfer number B, or thermochemical driving force, is related to the thermodynamic parameters of the propellants and flow and in the treatment of the heat transfer blocking effect caused by wall mass injection. It is shown that the present boundary layer analysis is applicable up to B 100, while the maximum thermochemical driving force available from any possible combination of propellants is less than 40. This analysis is used to predict the regression rate performance of several typical propellant combinations with good accuracy.