Hydrogen enriched confined methane flame behavior and flashback modeling

Most gas fueled power generation units presently operate on natural gas and many of them would need to tackle the challenges due to a fuel switch towards syngas in the near future. Operating regime of a gas turbine combustor is sensitive to the changes in the fuel composition. Behavior of a premixed enclosed methane-hydrogen flame is studied with regard to thermo-acoustic instability induced flame flashback, emissions, flammability limits and acoustics over a wide range of operating conditions. Hydrogen addition extends the lean flammability limits and enables lower NOx emissions levels to be achieved. However increased RMS pressure fluctuation levels and higher susceptibility to flashback is observed with increasing hydrogen volume fraction. This is associated with higher burning speeds of hydrogen in comparison to methane. Furthermore flashback in the experimental facility is triggered by thermo-acoustic oscillations. Therefore, an analytical model has been developed to capture the flame holding and thermo-acoustically induced flashback dynamics for a pre-mixed gas turbine combustor. A simple linearized acoustic model is derived from the basic conservation laws, and a front-tracking algorithm based on the Markstein's G-equation is coupled to combustor acoustics it in order to track the flame-front which yields in an understanding of dynamic flame holding and flashback behavior. Due to the non-linear nature of the coupling between acoustic velocity and heat release a limit cycle behavior in the flame front movement is observed during simulations. Sets of experiments including phase locked CH radical imaging have been performed in order to time resolve the flame initiation front behavior. Numerical simulations are performed to study flashback and combustor acoustics together and it is found that these are in good qualitative agreement with the experiments.