Model Reduction of Rich Premixed Hydrogen/air Oscillatory Flames by Global Quasi-Linearization (GQL)

The Global Quasi-Linearization (GQL) method for model reduction of chemical kinetics is applied to describe the very sensitive regime of the onset of the thermal-diffusion oscillations of the rich hydrogen-air flames. This type of flame propagation is characterized by a complex interaction of chemical reaction, ordinary diffusion, as well as thermal diffusion. It represents a very challenging phenomenon with respect to both modeling and computation. Therefore, it is chosen as a test case for the GQL model reduction method. We show that the GQL matrix obtained for the auto-ignition problem can be applied to study the diffusive-thermal instabilities of premixed combustion systems. In order to demonstrate that the method is generic, the invariance of the GQL basis is tested on a number of well-known and established mechanisms. The results show that the GQL basis-based low-dimensional (4D) manifolds of slow motions can successfully describe rich hydrogen-air flames and reproduce all important characteristics for both the onset of pulsations and the properties of oscillatory regimes of the flame propagation. Moreover, estimations of critical parameters, e.g., critical pressure for the onset of pulsations, based on the GQL reduced models, show significantly better performance if compared to the differences between detailed mechanisms of chemical kinetics.