In order to extend the operation regime of existing gas turbine combustion systems to lower the minimum loads, the applicability of matrix burners (arrays of jet flames) as an alternative to conventional swirl stabilized burners has been considered. In comparison to well-studied single jet flame systems, the effects of geometry and thermodynamic parameters on characteristics of matrix burner systems have not been studied in detail. Information, which is essential for design processes e.g. scaling of matrix burners, is not yet available in public domain. This work involves a systematic investigation of a matrix burner system operating at highly turbulent flow conditions (Reynolds Number ≈ 20000) prevailing in gas turbine combustion systems.
In order to understand the effects of geometrical scaling, three variants of jet diameter have been investigated. A detailed test campaign including lean blow out limits detection, velocity field measurement and hydroxyl radical (OH*) chemiluminescence recording has been conducted. Influence of variation in stoichiometry and exit velocity of fuel-air mixture has been captured. The results show that it is possible to generalize the scaling of the matrix burner using the well-known Peclet criterion.
To ensure compliance with stricter regulations on exhaust gas emissions, new industrial burner concepts are being investigated. One of these concepts is the matrix burner, consisting of an array of premixed, non-swirling jet flames. For the design of such burners, the prediction of fundamental burner properties is mandatory. One of these essential quantities is the lean blowout limit (LBO), which has already been investigated experimentally. This study investigates the possibility of numerical LBO prediction using a tabulated chemistry approach in combination with Large-Eddy-Simulation turbulence modeling. In contrast to conventional swirl burners, the numerical description of blowout events of multi jet flames has not yet been studied in detail. Lean blowout simulations have therefore been conducted for multiple nozzle variants, varying in their diameter and global dump ratio for a variety of operating conditions, showing their general applicability. A procedure to induce LBO is introduced where a stepwise increase in total mass flow is applied. LBO is determined based on the temporal progress of the mean reaction rate. A comparison with measurements shows good agreement and demonstrates that the procedure developed here is an efficient way to predict LBO values. Further investigations focused on the flame behavior when approaching LBO. The flame shape shows a drastic change from single jet flames (stable conditions) to a joint conical flame approaching LBO, which increases in length for increasing inlet velocity, showing the importance of jet interaction at LBO.
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