Measurements of self-excited instabilities and nitrogen oxides emissions in a multi-element lean-premixed hydrogen/methane/air flame ensemble |
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| Institution: | 1. Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea;2. Department of Mechanical Engineering, Hanbat National University, 125 Dongseodae-ro, Yuseong-gu, Daejeon 34158, Republic of Korea;1. Lehrstuhl für Thermodynamik, Technische Universität München, Garching, Germany;2. Institute for Advanced Study, Technische Universität München, Garching, Germany;3. Institute of Energy Systems and Fluid-Engineering, Zürich Univerity of Applied Sciences, Winterthur, Switzerland;1. CORIA UMR 6614 CNRS, Site Universitaire du Madrillet, Saint Etienne du Rouvray 76801, France;2. EM2C lab, CNRS and CentraleSupélec, University Paris-Saclay, Gif-sur-Yvette 91192, France;1. Universidad Carlos III de Madrid, Av. de la Universidad 30, Leganés 28911, Madrid, Spain;2. Institut Pprime, UPR 3346 CNRS, ISAE–ENSMA, BP 40109, Futuroscope-Chasseneuil Cedex 86961, France;3. ETSIAE, Universidad Politécnica de Madrid, Madrid 28040, Spain;1. Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim N-7491, Norway;2. Key Lab of Education Ministry for Power Machinery and Engineering, School of Mechanical Engineering Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, China;1. Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, Darmstadt 64287, Germany;2. Barlow Combustion Research, Livermore, USA;1. Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong;2. Guangdong–Hong Kong–Macao Joint Laboratory for Data-Driven Fluid Mechanics and Engineering Applications, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong;3. Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea |
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| Abstract: | Understanding the distinguishing physical properties of multi-element lean-premixed high hydrogen content flames is expected to be integral to the development of carbon-neutral, and ultimately carbon-free, gas turbine combustion systems. Despite their fundamental importance, the thermoacoustic and emission-related characteristics of such small-scale flame ensembles are not thoroughly understood, particularly for the full range of 0 to 100% hydrogen content blended with methane fuel. Here we investigate the structure and collective behavior of a multi-element lean-premixed hydrogen/methane/air flame ensemble using measurements of nitrogen oxides emissions and self-excited instability, combined with OH* and OH PLIF flame visualizations. Our results indicate that the system's responses can be classified into several distinctive stages according to their static and dynamic stability, including flame blowoff and thermoacoustically stable regions under relatively low hydrogen concentration conditions, low-frequency self-excited instabilities in intermediate hydrogen concentration, and triggering of intense pressure perturbations at about 1.7 kHz under high- or pure hydrogen combustion conditions. While the low-frequency combustion dynamics are dominated by axisymmetric translational movements of parallel flame fronts, the higher frequency response originates from significant lateral modulations accompanied by small-scale vortical rollup and flame surface annihilation due to front merging and pinch-off. Longitudinal-to-transverse dynamic transition is observed to play a mechanistic role in kinematically accommodating higher-frequency heat release rate fluctuations, and this newly identified mechanism suggests the possibility of high-frequency transverse modes, if such lateral motions are strong enough to induce inter-element flame interactions. In contrast to the substantial differences in thermoacoustic properties for different fuel compositions, the total nitrogen oxides emissions are found to depend primarily on adiabatic flame temperature; the influence of fuel composition is limited to approximately 20% under the inlet conditions considered. |
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