Secondary combustion in a staged hybrid rocket engine

The staged Hybrid rocket engine (HRE) is a relatively new concept that minimizes a loss of combustion performance with an oxidizer to fuel ratio shifting, while maintaining the key advantages of HREs. Knowing that a key component of the staged HRE is the secondary combustion, in this study a reacting flow Computational fluid dynamics (CFD) based tool was developed to analyze and to predict the performance of staged HRE secondary combustion. Using an equilibrium-chemistry one stream Probability density function (PDF) combustion model, the reacting flow CFD modelling has been done under eight different test conditions. After extensive validations both with non-reacting flow experimental and numerical data and with combustion experiments, this study finds that the CFD-based tool provides satisfactory predictions about the combustion efficiency of staged HRE secondary combustion. The results of both the CFD-based tool and combustion experiments showed a very similar tendency to combustion efficiency under the same test conditions, with an exception that the CFD-based tool seems to overestimate the combustion performance by 11-25 % compared to the combustion experiment. These differences are likely due to overestimation of the one-stream PDF model and oversimplification of the CFD modeling as well as measurement uncertainty in the experiments.