Lean-premixed hydrogen combustion technology is expected to play a crucial role in reducing anthropogenic greenhouse gas emissions, ultimately in achieving energy system decarbonization in the near future. However, the use of hydrogen fuels in gas turbine engines raises a host of combustion-related problems such as flashback and combustion instabilities. The probability of flashback events is substantially increased due to ultra-fast premixed hydrogen flames. Another major issue is the resonant coupling between unsteady flame’s heat release rate and combustion chamber acoustics, referred to as combustion instability, resulting in high-intensity pressure perturbations. The resulting combustion-acoustic interaction phenomena are extremely difficult to predict without experimental data due to inherent highly nonlinear characteristics.
In our laboratory, we are currently studying self-excited instabilities of lean-premixed pure hydrogen flame ensembles. Our recent data demonstrate that pure hydrogen flames generate high-amplitude pressure oscillations over a broad range of frequencies between 400 and 1800 Hz. We use OH planar laser-induced fluorescence imaging technique to measure local contours and unsteady flame surface dynamics during limit cycles. Our measurement reveal that low-frequency flame dynamics involve a complex balance among several coexisting phenomena, including strong vortex interactions and periodic extinction-reignition processes. By contrast, high-frequency instabilities are not influenced by such structurally complex flame dynamics, but by exceptionally simple flame surface motions. The current experimental investigations provide insights into our physical understanding of pure hydrogen combustion dynamics, and suggest wide-ranging implications for future carbon-free energy generation in heavy-duty gas turbine engines.