High regression rate hybrid rocket propellants

#The present invention relates generally to the field of propellants suitable for use in hybrid rockets, and more particularly to propellants and a method of selecting propellants that exhibit high regression rates.

#Two basic types of chemical rocket propulsion systems are widely used in the rocket industry; namely, liquid systems and solid propellant systems. In a liquid system, liquid oxidizer and liquid fuel are fed at high pressure to a combustion chamber where they mix and react producing high temperature, high pressure gases which exhaust through a converging-diverging nozzle producing thrust. The mixing of reactants requires a high performance pressurization system for the fuel and oxidizer which must often operate in a cryogenic environment at extreme pressures and mass flow rates. The injection system and combustion chamber require exotic materials, complex systems for cooling, and very high precision manufacturing techniques. All of these factors contribute to a high cost.

#Solid propellant systems do not require the complex and expensive machinery of liquid systems. Nevertheless, solid systems are complicated, and are subject to the difficulties of producing crack-free, repeatable, fuel grains, and by the need to transport and handle explosive materials. In a manufacturing process that requires extreme safety precautions, solid fuel and oxidizer are intimately mixed and allowed to cure inside the rocket case producing an explosive fuel with roughly the consistency of plastic or hard rubber. Fuel grains which contain cracks present a risk of explosive failure of the vehicle and must be rejected, driving up the cost of manufacture. Upon ignition the solid fuel burns uninterrupted until all the fuel is exhausted.

#Additional objects and advantages of the invention will become apparent in reading the detailed description of the invention and the claims and with reference to the figures, in which:

#FIG. 1 is a schematic diagram of a hybrid rocket which may be employed with the present invention.

#FIG. 2 is a schematic diagram of the combustion configuration in a single port hybrid rocket motor.

#The invention is now described in more detail. The following terms used throughout the description herein are defined below as:

#ah Liquid layer thickness parameter, m2/sec acl Classical regression rate parameter, m2.6/kg0.8 − sec0.2 aonset Entrainment onset parameter, kg1.45/m2.3 − sec1.45 aent Entrainment regression rate parameter, m2.6/kg0.8 − sec0.2 B Blowing parameter CB1 Blowing correction coefficient Cf Friction coefficient Cfref Reference friction coefficient Cl Liquid specific heat, J/kg-K Cs Solid specific heat, J/kg-K G Port average mass flux, kg/m2 − sec h Melt layer thickness, m hv Effective heat of gasification, J/kg hvcl Classical effective heat of gasification, J/kg Lm Latent heat of melting, J/kg Lv Latent heat of vaporization, J/kg Lgrain Length of the port, m Mwg Mean molecular weight of the port gas, kg/kmole Pg Port mean pressure (chamber pressure), N/m2 (Pascal) Pd Dynamic pressure in the port, N/m2 {dot over (Q)}r Radiative heat flux, J/m2 − sec {dot over (Q)}c Convective heat flux, J/m2 − sec Rl Thermal to radiation thickness ratio Rez Reynolds number based on distance along the port Ru Universal gas constant, J/kmole − K {dot over (r)} Surface regression rate, m/sec {dot over (r)}cl Local regression rate predicted by classical theory, m/sec {dot over (r)}e Regression rate component due to entrainment, m/sec Ta Ambient fuel temperature, K Tg Port mean temperature, K Tm Melting temperature, K Tb Boiling temperature, K Tinterface Liquid-gas interface temperature, K Tsolid Characteristic temperature for the solid, K Tliquid Characteristic temperature for the liquid, K ΔT1 Temperature difference Tinterface − Tm, K ΔT2 Temperature difference Tm − Ta, K Ug Port average gas velocity, m/sec z Axial distance along the port, m Liquid thermal conductivity, J/m − sec − K μl Liquid viscosity, kg/m − sec μg Port mean gas viscosity, kg/m − sec τinterface Shear stress at the liquid-gas interface, N/m2 ρs Solid density, kg/m3 ρl Liquid density, kg/m3 ρg Port average gas density, kg/m3 a Surface tension, N/m

#The theory which underlies the present invention indicates that propellant surface tension and especially liquid layer viscosity at the combustion chamber conditions are the key physical properties that determine whether or not the propellant will entrain.