Hydrogen co-firing combustion technology has been developed for gas turbines to suppress carbon dioxide emissions from thermal power generation. Our research group has conducted experiments using a mocked gas turbine combustor. As a result, we confirmed two types of combustion oscillations: around 350 Hz under the condition fueled by only natural gas and around 200 Hz and 400 Hz under the condition fueled by hydrogen and natural gas mixture. Based on these results, we are trying to develop a model that can predict the oscillating frequency of combustion oscillation generated under the various conditions fueled by a hydrogen-containing mixture. In the previous study, we measured the temperature distribution inside the combustor by the combination of CFD calculations and experiments and successfully created the axial representative temperature distribution. In the model, we modeled only the combustor element, and the combustor's upstream end and downstream end were treated as the closed-end the open-end, respectively. However, this model could not predict the oscillating frequency accurately. Therefore, in this study, we propose an acoustic network model using the transfer matrix method, which is often applied to study pressure pulsation of the pipeline system, and we re-examined the resonance frequency.First, we represented only the combustor and constructed the acoustic network model considering the axial representative temperature distributions under the following two conditions, one is fueled by only natural gas and the other is fueled by the hydrogen-natural gas mixture. In this model, we modeled the combustor temperature in two regions, i.e. unburned and burned regions, which is named the two-regions model. As a result, the resonance frequency obtained by calculation in the condition fueled by only natural gas was found to be consistent with the range of frequencies obtained in the experiment. On the other hand, the model could not reproduce the experimental values obtained for the condition fueled by the hydrogen-natural gas mixture. Next, we constructed a different-diameter tube model, adding a swirler installed upstream of the combustor to match the actual combustor's geometry more closely, which is named the swirler-combustor model. However, the swirler-combustor model could not calculate the resonance frequency under the condition fueled by hydrogen-natural gas mixture as in the case of the two-region model.Therefore, we considered the piping elements and acoustic boundary conditions of the upstream of the swirler to affect the oscillation frequency, which is named the upstream pipe-combustor model. The piping elements considered were the combustor, swirler, casing, and air supply piping. Here, we defined the acoustic boundary condition between these piping elements as acoustic impedance. The calculation results by the combustor model including the upstream piping elements proposed in this study show the frequency of generated combustion oscillation not only in the case of natural gas dedicated combustion but also in the case of hydrogen natural gas co-firing measured in past experiments. Therefore, the resonant frequency calculated by this model can estimate candidate frequency for the observed combustion oscillation frequency. In summary, these results indicate that the acoustic network model, which includes the combustor and its upstream piping elements, can predict the oscillation frequency of combustion oscillations under hydrogen-mixing conditions.

Examination of Resonant Frequencies Generated by Combustion Oscillation in a Combustor Fueled by a Hydrogen-Natural Gas of Resonant Frequencies Generated by Combustion Oscillation in a Combustor Fueled by Hydrogen-Natural Gas Mixture and the Upstream Pipe

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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