Study on combustor in mini jet engine

• Main Author: Gao, Xuan
• Other Authors: Fei Duan
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Motors, engines and turbines
• Online Access: http://hdl.handle.net/10356/54552
• Institution: Nanyang Technological University

Mini turbojet engines can be widely used for unmanned aerial vehicles due to their main advantages of small size and relatively high propulsion. This study focuses on the reverse flow combustor in the mini jet engine. It mainly includes the experiments and numerical simulation. The experiments have been conducted in the test rig of jet engine and pressure, temperature, and emission gas concentration were measured by the probes at several key positions: compressor inlet, combustor inlet, turbine inlet and outlet, and exhaust nozzle outlet. These experimental data allow us to validate simulation results, thus helping to improve the current combustor modeling. To understand the effects of turbulence models and combustion models on gas diffusion mixing process, the simulation of non-premixed flames has been conducted, based on the published experimental data. The results indicated that the Realizable k-ϵ turbulence model and Probability Density Function (PDF) model fitted the experimental data. Considering the importance of controlling NOx formation in gas turbine combustor, NOx formation mechanisms were investigated for methane and hydrogen mixture under the moderate or intense low-oxygen dilution (MILD) conditions. It was found Dinitrogen monohydride (NNH) and prompt routes dominated NOx formation process. Two-dimensional numerical simulation has been performed, showing that the Realizable k-ϵ model and the PDF model could predict temperature distribution more accurately than other models. In the three-dimensional computational domain, the combustion modeling coupled with Discrete Phase Model (DPM) was built up to analyze the detailed flow field inside the combustion chamber, in the light of temperature and pressure distribution, the liner wall temperature as well as pollutant emission. The simulation results show the main flaws in the current combustor: uneven temperature distribution at outlet combustor, large pressure drop, hot spots in the inner liner wall, and large pollutant emission. Based on the flaws found in the original SR-30 combustor, the new combustor has been designed to solve these problems to the greatest extent. By the modification of the size and distribution of dilution holes, the new design can satisfy the requirements of the combustor under the new operating conditions. In future work, Large Eddy Simulations (LES) of gaseous flames in gas turbine combustion chambers is suggested. Moreover, more efforts will be put on study of fuel swirl nozzle, improving the performance of fuel and air mixing.