Stable circular and double-cell lean hydrogen-air premixed flames in quasi two-dimensional channels

In this work, a computational study on nearly two-dimensional reacting fronts under canonical configurations is proposed. Specifically, a quasi-2D description of the conservation equations with a one-step irreversible Arrhenius chemical model is used to simulate ultra-lean hydrogen-air premixed flames that slowly propagate over streams of reactants that are confined between plates and are subject to conductive heat losses. Under these conditions, recent previous experiments identified two unprecedented stable flame configurations: two-headed and circular isolated flames. This study identified buoyancy and the relative importance of conductive heat losses as the two parameters controlling the formation of these isolated flames. The numerical evaluation of the different terms ascertains the physical mechanisms that drive the formation of two-headed or circular flames. Additionally, the systematic variation of the controlling parameters depicts the maps of stable solutions that determine the capability of the two flame configurations to emerge. In particular, the existence of a range of parametric values in which both flame configurations are stable proves, also, that initial conditions are crucial to determine which of the two configurations prevails.