Abstract
Hydrogen combustion is attracting attentions because of zero CO2 emission. Recently, a gas turbine which uses hydrogen-rich fuel is being developed. In this study, we examined the influence of hydrogen-containing ratio on combustion oscillation for fuel mixtures of hydrogen and town gas (13A) experimentally and analytically. In the experiment, pressure oscillations were measured by a sensor which is installed at the bottom of the combustor. It is found that two oscillation frequencies near 200 Hz and 400 Hz were simultaneously detected in the case of hydrogen-containing fuels, whereas single oscillation frequency around 350 Hz was observed in the case of only 13A fuel. To understand this difference of oscillating frequencies, we conducted acoustic analysis considering the 𝑛 − τ model as the heat release model; this model has time delay τ. However, the simplest model, one-dimensional different diameter model, could not reproduce three types of oscillating frequencies obtained by the experiment. Besides, we used acoustic impedance measured with the experimental setup as the acoustic boundary condition of the bottom of the chamber. Time delay, flame position and temperature used for the correction of the acoustic impedance and the mean temperature in the chamber were calculated by the CFD analysis. As a result, it is found that hydrogen makes the natural frequencies a little higher, because temperature becomes higher and delay time becomes shorter.
