Relaxational oscillations of burner-stabilized premixed methane–air flames

Abstract

In this paper, the dynamics of diffusion-thermal oscillations of burner-stabilized methane–air flames are numerically and experimentally investigated. High speed imaging and laser induced fluorescence of OH radicals are used as experimental techniques, while a hierarchy of models is employed in numerical simulations: a system of ordinary differential equations describing dynamics of flame location and temperature, models with one-step and detailed reaction mechanisms. It is demonstrated that for small (near the neutral stability boundary) and moderately relaxational oscillations, all three approaches are able to describe the flame dynamics however with different levels of detailization. This is due to the fact that in these regimes the flame front structure remains similar, although perturbed, to that observed in freely propagating combustion waves. However, this flame structure breaks in the regime of highly relaxational oscillations, which can only be described within the detailed reaction mechanisms. The combustion front splits into the high and low-temperature reaction zones, which are shown to be highly and weakly sensitive to the diffusive-thermal pulsations. The high temperature reaction zone is blown away and extinguishes in the course of flame pulsation, and the low temperature zone remains near the burner surface and causes re-ignition of the combustion front. Prospects of further investigations are discussed.