Acoustic Wave Interaction with Counterflow Methane-Air Premixed Flames

Abstract

Under certain operating conditions, many combustion systems exhibit large amplitude pressure oscillations coupled with unsteadiness in the combustion processes (thermoacoustic instabilities). Model-based active control approaches are being pursued to suppress the potentially destructive instabilities, where a fundamental understanding of the flame-acoustics coupling mechanisms is critical. The formulation of a detailed numerical model for the investigation of the spontaneous resonant interaction of longitudinal acoustic waves with planar counterflow flames is presented, with the inclusion of compressibility and finite-rate chemistry effects. For well-resolved simulations, the occurrence of self-sustained thermo-acoustic instabilities in methane-air premixed counterflow flames is analyzed for a range of flow strain rates, employing both detailed and global one-step chemical kinetic models. It is shown that the response of the flame to acoustic perturbations is dependent on the flow strain rate as well as on the reaction mechanism employed. In particular, unlike their non-premixed counterpart, premixed counterflow flames modeled with detailed chemical kinetics show the potential for flame-acoustics coupling. The sensitivity of chemical kinetic parameters on the acoustic response is investigated for several one-step models.