Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multi-stage combustion to lower nitric oxide emissions and enhance turndown ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet lift-off depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K) and jet momentum ratio (6–210). The differences to existing lift-off studies are the high cross flow temperature and applying a premixed jet. The lift-off height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the lift-off height for similar staged combustion systems. A main outcome of this work is that the lift-off height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz number. Furthermore, the ignition delay time scale τign also misses part of the lift-off height mechanism. The presented model uses turbulent time scales, the ignition delay and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.
A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow
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Kolb, M, Ahrens, D, Hirsch, C, & Sattelmayer, T. "A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow." Proceedings of the ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. Volume 4A: Combustion, Fuels and Emissions. Montreal, Quebec, Canada. June 15–19, 2015. V04AT04A023. ASME. https://doi.org/10.1115/GT2015-42225
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