Numerical Simulation and Analysis of the Diffusion Combustion Flowfield in Hybrid Rocket Motor
- Paper number
IAC-08.C4.2.8
- Author
Prof. Dechuan Sun, China
- Coauthor
Prof. Guoqiang He, Northwestern Polytechnical University, China
- Year
2008
- Abstract
In hybrid rocket motor, diffusion combustion is the main combustion type, which makes the lower regression rate of the solid fuel. For steady flow, the regression rate equals to its pyrolysis rate at the burning surface that related with the surface temperature. Which means higher heat flow to the solid fuel can cause higher regression rate. Unfortunately, more pyrolysis gas leaves from surface will decrease the heat transfer to the solid. This is the main reason of the low regression rate in hybrid rocket motors.
In this paper, a simplified heat transfer model was provided and used to treat with the boundary condition of the burning surface. This model is similar to the erosion method and can be used for steady flow and no need to couple with the heat transfer in solid fuel. In the model, regression rate is calculated by Arrhenius equation related with surface temperature and pyrolysis parameters that can be obtained from experiments.
Based on the treatment method at burning surface, some numerical simulation was done for a two-dimensional test model to study the parameters affecting diffusion combustion and fuel regression rate. Calculations were done by FLUENT software. And the heat transfer model was programmed as UDF that was called at the burning surface boundary. It will output the local regression rate when calculating.
The two-dimensional model has three geometric types. One is planar, one has variable turn angle, and the other has arcs with different radius. The oxidant is 85% H2O2 and the fuel is low density polyethylene (LDPE). For these models, mass flow rate of the oxidant at inlet boundary was changed and finally about fifty results were gotten.
From the results, it was obvious that to strength the diffusion combustion near fuel surface will increase regression rate. Along the direction of main flow, combustion domain becomes larger and more reactants combust. So the regression rate slowly increases. Increasing the mass flow rate or inlet velocity of the oxidant makes the combustion domain close to burning surface and thus to increase the regression rate. Large turn angle of the main flow will strengthen the diffusion combustion. When main flow turns parallel with burning surface, regression rate maintains higher level. The results show that circular flow is much complex than others. Near the beginning of combustion, small radius reduce the regression rate locally and after turn the same angle, all circular flow gain higher rate.
- Abstract document
- Manuscript document
(absent)