Although hydrogen combustion has been extensively investigated in recent years, several challenges remain in accurately assessing jet flame transfer functions (FTFs) under intermediate thermal load conditions with a thermal power over ( P th ≥ 100 kW ). The well-established multi-microphone technique, commonly used for swirl-stabilized methane flames, faces several difficulties when applied to jet hydrogen combustion. These challenges are connected to the non-acoustically compact extension of the mixing tube in hydrogen jet burners and to significant changes in the gas properties under non-reactive (air) and reactive (air-hydrogen) conditions. In previous studies, the impact of changes in fuel properties on the multi-microphone method and burner transfer matrix (BTM) reconstruction was demonstrated. However, this approach was limited to well-mixed configurations. In the present work, we extend the methodology to technically premixed single-jet burner systems by introducing an array of four microphones within the mixing tube. This configuration significantly reduces the complexity of the BTM. We demonstrate this experimentally on a technically premixed hydrogen jet burner. Using low-order acoustic modeling of the BTM, we show through sensitivity analysis that the relocated microphone array enables a more robust assessment of the flame transfer matrix for the considered jet–burner configuration, and thus the FTF. Finally, a distributed time-delay model is fitted to the measured FTF to analyze flame dynamics across the relevant frequency range.
Nedden et al. (Mon,) studied this question.