To reduce the amount of carbon dioxide, it has been examined to fuel hydrogen to conventional fuel such as natural gas for gas turbine combustors in thermal power plants. However, it is insufficient to investigate combustion oscillation phenomena in the case of hydrogen-containing fuel. Then, our research group performed a combustion oscillation experiment fueling a mixture of hydrogen and town gas whose composition corresponds to natural gas. As a result, oscillating frequencies of around 350 Hz were observed in the case of town gas only, whereas oscillating frequencies of around 200 and 400 Hz were observed in hydrogen-containing fuel case. The former frequency around 350 Hz could be obtained by the calculation assuming a one-dimensional pipe with different diameters with acoustical boundary conditions of upstream-end closed and downstream-end open, however, the latter frequencies of around 200 and 400 Hz could not be obtained by the calculation under the same acoustical boundary conditions. Then, we hypothesized that the shift of oscillating frequencies may occur by changing temperature-distribution inside the tube, which was caused by different combustion conditions with fuel mixture in the hydrogen-containing fuel case. Therefore, we examined the oscillating frequencies based on the one-dimensional acoustic network model. In our previous study, the acoustic impedance as the acoustic boundary condition was employed to only two regions, that is, unburned and burned regions, the temperatures of which were determined based on the result from the CFD simulations. 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 detail temperature distributions, that is, the location of the steep temperature gradient corresponding to the location of the flame surface, the magnitude of the temperature gradient, and the maximum flame temperature, should be considered to clarify the effect of the change of 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 detail temperature distributions, the acoustic network model was divided into enough number of thin 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. As a result, the location of the steep temperature gradient has a large influence on the possible oscillating frequencies which implies that changing the location of the flame surface in a combustion tube in the hydrogen-containing fuel case affect the oscillating frequencies.


Examination of Oscillating Frequencies Generated by Combustion Oscillation Considering Temperature Distribution in a Combustor Tube Fueled by Natural Gas and Hydrogen Mixture

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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