音響的境界条件を考慮した燃焼振動発振周波数の検討

抄録

Hydrogen combustion is attracting attentions because of zero CO₂ emission. Recently, a gas turbine which uses hydrogen-rich fuel is being developed. In our previous study, we examined the influence of hydrogen-containing ratio on combustion oscillation for fuel mixtures of hydrogen and town gas (13A) experimentally. 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 using one-dimensional different diameter acoustic model. However, this simplest model could not reproduce three types of oscillating frequencies obtained by the experiment. Besides, we used an acoustic impedance of the bottom of the combustion chamber as an acoustic boundary condition. The acoustic impedance is measured experimentally under the noncombustion (cold) condition and corrected by combustion temperature obtained by equilibrium calculation. As a result of applying the corrected acoustic impedance, the three types of oscillating frequencies could be reproduced by acoustic analysis. Furthermore, to express the difference among fuel mixtures, delay times, flame positions, and the mean temperature in the chamber were calculated by the CFD simulation. Consequently, it is found that the acoustic analysis result could reproduced the difference among fuel mixtures; hydrogen makes the oscillating frequencies a little higher, because temperature becomes higher and delay time becomes shorter.