Experimental investigation of the interaction between swirl stabilized pressurized flames and effusion cooled walls related to thermochemical states, reaction rates and pollutant formation
Final Report Abstract
Combustion chamber wall cooling plays a crucial role in the safe and long-term operability of aircraft propulsion systems. The occurring temperatures in the combustor core typically exceed the operating limits of metallic materials, requiring active cooling of the combustor liner. The advancement from traditional Rich-Quench-Lean combustors to Lean-Premixed systems to reduce nitric oxide emissions leads to an even increased importance by two means: the reaction zones inside the core is shifted more towards the walls and due to premixing, less cooling air is available. Thus, developing efficient cooling strategies is of high relevance. One of these strategies is effusion cooling, where cooling air is supplied through an array of slanted holes in the liner. During passage through the liner, heat is removed by forced convection and a cooling film is generated at the inside of the liner, which is supposed to shield it from the hot combustion products. Even though effusion cooling has been widely studied in the past decades, the focus was mainly on cooling efficiency and mostly neglected the mutual interaction between cooling air and reacting main flow. Gaining a deeper insight into the fundamental processes of flame-cooling air interaction is the aim of this project. Typically, experimental investigations are carried out with reduced complexity compared to real systems. One approach involves placing an effusion cooling plate downstream of a hot gas source, which provides good experimental accessibility and high reproducibility of boundary conditions. However, interaction mechanisms between the cooling air and the reacting mainstream flow cannot be studied in these configurations due to their inherent design limitations. Alternative approaches reduce complexity on the measurement side, such as conducting exhaust gas analysis on realistic systems. However, these approaches do not allow inferences about the underlying mechanisms since measurements are not spatially or temporally resolved within the combustor. In this study, an effusion cooling plate is used as a wall segment in a generic combustion test rig featuring a swirl-stabilized turbulent flame at elevated inlet temperature and pressure. This setup enables the representation of influences from unsteady heat release, convection, radiation, and chemical reactions. Quantitative and semi-quantitative laser-based measurement techniques with high spatial and temporal resolution were employed to identify the sensitivity of flame-cooling air interactions to important boundary conditions related to flow and temperature fields, as well as the cooling process itself. Mixing processes between the reacting mainstream flow and the effusion cooling air were investigated using a combination of quantitative laser-induced fluorescence of hydroxyl radicals (OH) and nitrogen monoxide, which is used as a tracer for the cooling air. The collected data provided insights into how often mixing of the gas streams occurs before, during, or after the chemical conversion of the fuel. Measurements of the thermochemical state, represented by local carbon monoxide (CO) mole fraction and gas-phase temperature, were performed using a combination of CO laser-induced fluorescence (LIF) and rotation-vibration coherent anti-Stokes Raman spectroscopy with nitrogen as the resonant species. Simultaneous measurements of OH, CO, and formaldehyde LIF allowed for investigating sensitivities to CO production and oxidation processes with respect to the studied variations in boundary conditions. The obtained data revealed that interactions between the flame and the effusion cooling air locally affect the structure of the premixed flame within the preheat zone, the main reaction zone, and the exhaust gas. These effects are not limited spatially to the region near the effusion-cooled wall but extend through recirculation into the primary zone.
Publications
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Influence of effusion cooling air on the thermochemical state of combustion in a pressurized model single sector gas turbine combustor. Combustion and Flame, 226, 455-466.
Greifenstein, Max & Dreizler, Andreas
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Investigation of mixing processes of effusion cooling air and main flow in a single sector model gas turbine combustor at elevated pressure. International Journal of Heat and Fluid Flow, 88, 108768.
Greifenstein, Max & Dreizler, Andreas
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MARSFT: Efficient fitting of CARS spectra using a library‐based genetic algorithm. Journal of Raman Spectroscopy, 52(3), 655-663.
Greifenstein, M. & Dreizler, A.
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Mischungsprozesse und Einfluss von Effusionskühlung auf den thermochemischen Zustand in einem generischen Druckbrennkammerprüfstand, Poster and Speaker. 30. Deutscher Flammentag (2021)
M. Greifenstein & A. Dreizler
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CARS.jl: Efficient fitting of dual‐pump multi‐species CARS spectra using compressed libraries. Journal of Raman Spectroscopy, 55(4), 459-472.
Greifenstein, M. & Dreizler, A.
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Influence of effusion cooling air on the CO production in the primary zone of a pressurized single sector model gas turbine combustor. Combustion and Flame, 248, 112511.
Greifenstein, Max & Dreizler, Andreas
