Dynamic pressure characteristics of multi-mode combustion instability in a model gas turbine combustor under simulated hydrogen–methane co-firing conditions

The adoption of H 2 fuel in gas turbine systems is steadily increasing as part of the transition toward cleaner energy sources. However, its unique combustion characteristics pose significant challenges in managing combustion instability. This study examines the acoustic behavior of H 2 -CH 4 mixed-fuel combustion instability using a model gas turbine combustor. To simulate instability situation of mixed fuel, multi-mode acoustic excitation experiments are performed with the fixed fundamental forcing at the combustor’s resonance frequency (∼160 Hz), together with additional variable forcing at 250 Hz and 1,000 Hz, which are the representative instability modes of CH 4 and H 2 flames, respectively. In some cases, highly risky signal amplification is observed. For example, when the amplitude ratios of forcing at 160, 250 and 1000 Hz are 1:9:0, the response reaches up to 106.15 kPa at the other frequency of 1,750 Hz. This phenomenon is confirmed by attribution of the interaction of the overlapping mode frequencies and the node and antinode position of standing wave, with no such amplification observed at other experimental conditions. Consequently, the optimal sensor location is expected to vary with changes in the co-firing ratio and conditions, and identifying these optimal positions is essential for reliable monitoring and successful implementation of H 2 co-firing technology. ● Multi-mode acoustic experiment replicates H 2 –CH 4 co-firing combustion instability. ● Combined modes reflecting fundamental, low CH 4 and high H 2 instability are forced. ● Overlapping acoustic modes induce high-amplitude resonances at unforced frequencies. ● Pressure sensor placement significantly affects combustion instability detection. ● Delicate tuning and proper sensor location are needed to avoid unexpected failure.