Large-Eddy Simulation of a Dry Low-Emission Gas Turbine Combustor: Impact of Hydrogen Addition on Thermoacoustic Instability

Abstract

Hydrogen is a promising alternative fuel for decarbonising stationary gas turbines. However, increased hydrogen content in lean premixed fuel blends may increase susceptibility to thermoacoustic instabilities (TAI), which arise from a feedback loop between flame dynamics and acoustic waves. These instabilities can lead to damaging pressure oscillations, often not identified until engine tests are conducted, resulting in costly redesigns and development delays. In this regard, high-fidelity simulations are important in guiding combustion system development, if they can be demonstrated to reproduce the flame-acoustic coupling physics. The present study uses large-eddy simulation (LES) to analyze a complete, dry low-emission (DLE) gas turbine combustion system and predict thermoacoustic stability limits as hydrogen is added to the fuel. A stable baseline case using pure methane is first validated with measured noise data from the engine. Hydrogen is then incrementally introduced to predict its impact on flame-acoustic interaction. High-amplitude, high-frequency pressure fluctuations are observed at 15 and 25 vol.% hydrogen in the mixture, indicating TAI, whereas the system remains stable up to 10 vol.% hydrogen. These findings suggest that the thermoacoustic stability threshold of this engine lies between 10 and 15 vol.% hydrogen, with the onset of instability closely linked to a flame shape transition from V-shaped to M-shaped. This study provides a predictive framework to support the combustor design process and facilitate a safe and efficient integration of hydrogen into gas turbine systems.