Examination of oscillating frequencies generated by combustion oscillation considering temperature distribution in a combustor tube fueled by natural gas and hydrogen mixture

A combustion oscillation experiment fueling a mixture of hydrogen and natural gas was performed. The results showed oscillating frequencies of around 350 Hz in the case of the town gas only, whereas oscillating frequencies of around 200 and 400 Hz were observed in the hydrogen-containing fuel case. We hypothesized that the oscillating frequencies shift may occur by changing the temperature-distribution inside the tube, which was caused by different combustion conditions with the fuel mixture. As a result, the possible oscillating frequencies of not only around 350 Hz but also around 200 and 400 Hz were obtained. Although three types of possible oscillating frequencies were obtained in our previous study, more detailed temperature distributions should be considered to clarify the effect of the changing fuel mixture composition. In this paper, representative one-dimensional temperature distributions were formed by the combination of measured and calculated temperature distributions in the combustion tube for the corresponding fuel mixture. To include the detailed temperature distributions, the acoustic network model was divided into enough small elements to express the temperature distributions, where each element was connected by the transfer matrix. Then, the possible oscillating frequencies were calculated, taking account of the influence of the temperature distributions.