Thermoacoustic Stability Analysis of Methane and Hydrogen Laminar Systems: Sensitivity to Combustor Transversal Dimension at a Constant Heat Release Rate

The use of hydrogen to enrich or replace hydrocarbon-based flames represents an appealing perspective to reduce pollutant emissions in gas turbine combustors, but it involves significant issues related to their combustion stability. This paper investigates the linear stability of a Rijke tube fueled by two different conical, laminar, perfectly premixed flames: one based on a pure methane–air mixture and the other based on a pure hydrogen–air mixture. In both cases, the heat release rate was kept constant, while the other characteristics of the system were varied. Through the constant heat release rate, the inlet velocities of the mixtures, their Reynolds numbers and the flame aspect ratios were related to the radius of the chamber, which was limited within a realistic range in order to avoid both flashbacks and turbulent transition of the flow. A Flame Transfer Function was derived by means of a linearized Level Set Method approach, highlighting a neat disparity in the flame dynamics of the two mixtures. Linear stability of the system was assessed in order to understand its sensitivity to changes in the transversal dimension of the chamber, revealing clear differences in the behavior of hydrogen and methane mixtures, motivated by the dissimilarities in their gain response, and thus demonstrating a reduction in design flexibility of hydrogen-based combustion chambers.