Oscillating Frequencies Generated by Combustion Oscillation in a Combustor Tube Fueled by Natural Gas and a Hydrogen Mixture

From previous combustion oscillation experiments using a simulated gas turbine combustor, oscillation frequencies around 350 Hz were measured in only natural gas-fired, and around 200 and 400 Hz were measured in the case of hydrogen-containing fuel. In this study, the axial gas column vibration mode was assumed, and the method to reproduce the change of oscillating frequency due to the difference of fuel was investigated. In the previous study, the temperature distribution in the combustor was divided into only two regions, and there were problems in terms of parameter estimation for modeling the flame dynamics. Therefore, the transfer matric method that incorporates a linear temperature gradient was employed. Also, the temperature distributions obtained from computational fluid dynamics, and experiments were reduced to one dimension to reproduce the difference in combustion characteristics due to the difference in fuel composition; four methods were proposed, the axial representative temperatures. The Nyquist plot method was used to calculate up to 10 combinations of resonant frequency and growth rate simultaneously. Furthermore, the oscillation frequency was determined in which the resonance frequency with the growth rate was maximum. As a result, the value of the oscillating frequency obtained differed depending on creating the representative temperature distribution.

Automated summary

This study investigated the method to reproduce the change of oscillating frequency due to the difference of fuel. The transfer matric method that incorporates a linear temperature gradient was employed to model flame dynamics. Four methods for axial representative temperatures were proposed and the Nyquist plot method was used to calculate resonant frequency and growth rate.