Computation Of Combustion Chamber And Nozzle Flow In N2O_HTPB Hybrid Rocket Motors

Paper number

IAC-07-C4.I.01

Author

Dr. Hui Tian, Beijing University of Aeronautics and Astronautics, China

Coauthor

Prof. Guobiao Cai, Beijing University of Aeronautics and Astronautics, China

Year

2007

Abstract

A hybrid rocket motor stores propellant in two different states —liquid and solid. In a typical hybrid, the fuel is a solid and the oxidizer is a liquid. Hybrid rocket propulsion offers a number of advantages over traditional liquid and solid rocket systems particularly in the areas of safety, throttling, environmental cleanliness, grain robustness, low temperature sensitivity and low cost. Hybrid rocket systems can be used in sounding rocket, target missile and tactical missile. Study of hybrid rocket was developed increasingly since 1990s. 
The saturated vapor pressure of nitrous oxide(N2O) is higher and is about 50atm. It can be transported by itself, so separate pressure unit had no use for the nitrous oxide propellant feed system.. The temperature of nitrous oxide by catalytic decomposition is near 1900K and can reaction with HTPB under the temperature. The igniter had no need of the N2O/HTPB motor. Because of the advantages, the hybrid motor use the nitrous oxide is developed rapidly recently. 
A combustion characteristic of a N2O/HTPB hybrid rocket is different from a traditional liquid and solid rocket, so making research on operation of a hybrid is necessary. Computation of combustion chamber and nozzle flow of a hybrid rocket motor used N2O/HTPB is presented in this paper.
Inject, atomization and evaporation of liquid oxygen and pyrolysis process of solid fuel are quite complicated. All processes are simplified in computation. We suppose that HTPB changes into 1,3 butadiene(C4H6) by pyrolysis and N2O changes into mixture of gas oxygen(O2) and nitrogen gas(N2) .Nitrogen gas is inert and is not reaction with C4H6.Then, C4H6 reacts with O2. Two chemistry models are adopted in computation.
The control equation used in this paper is the axial symmetry, unsteady, compressible, nonequilibrium, turbulent, Reynolds average N-S equations while the force and thermal radiation is ignored. The B-L turbulence model is used. Lower-Upper decomposition scheme and MUSCL-type and VanLeer approach were used.
From the results, Oxidizer concentration at solid fuel surface is zero and increases along the radial direction. On the contrary, fuel concentration at solid fuel surface is equal to 1 and decreases along the radial direction, so combustion occurs in the flame zone. The temperature at the flame zone is higher and the density is lower. The temperature distribution of combustion chamber is very nonuniform. The flame zone thickened along with the combustion process. Combustion efficiency improves through using the aft chamber, which will be useful for the hybrid rocket motor design.

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