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978-3-8439-1715-5, Reihe Thermodynamik
Jiby Jacob Vellaramkalayil
Experimental and Numerical Investigations of Different Injection Schemes in a Supersonic Combustion Chamber
197 Seiten, Dissertation Universität Stuttgart (2014), Softcover, A5
One of the major challenges to overcome in achieving a high readiness level for SCRamjet-powered vehicles is to maximize the heat release and to minimize the total pressure losses in the combustion chamber of such an engine in order for the propulsive unit to generate sufficient thrust. Staged injection of fuel has been identified to be a promising approach to enhance mixing as well as to avoid steep pressure gradients, thus allowing higher heat release and avoiding boundary layer separation.
The main objective of this thesis was to validate and to quantify the performance gain of a model combustor with a staged injection scheme compared to a single stage design. This objective was met by initially obtaining an experimental database for the non-reactive flow field, the single stage and staged combustion scheme with different wall-bound and strut-based injector configurations for a variation of combustion chamber parameters. Different combustion modes were observed and characterized. However, the harsh thermal conditions within the combustion chamber made it difficult to obtain measurement data, which would have made it possible to perform a satisfying performance analysis. Therefore, in the next step, 3D numerical CFD simulations were conducted and the results were validated with the experimental data. The possibilities and the shortcomings of the applied commercial simulation tool are described. In the last step, a performance analysis was carried out with the help of the numerical simulations for the different single stage and staged injection configurations and their performance concerning mixing, heat release and total pressure loss were compared.
The results indicated that staging of fuel bears the possibility to increase the total amount of fuel mixed and combusted within the combustion chamber by simultaneously avoiding large pressure gradients. The assessment of different staged injector configurations revealed that the combination of a strut and a wall-bound injection scheme proved to be the most effective considering heat release. The validation of the numerical simulations exhibited that the general agreement to the conducted experiments is well. Discrepancies were found in the prediction of boundary layer separation, which was identified to play a major role in the formation of the combustion modes. A detailed analysis of the connection between boundary layer separation and the transition of combustion modes is part of this thesis.