Propagation of Nonequidiffusive Premixed Flames in Channels with Open Ends

Abstract

Combustion in micro-channels has numerous fundamental and practical applications, with oscillations and acceleration representing the two distinct modes of premixed flame propagation in “fully-open” channels (both ends of the channel are open). The type of propagation encountered is determined by such factors as the internal condition of the channel, the width of the channel, the thermal expansion ratio, the thermal-to-mass diffusivity ratio (defined as the Lewis number, Le), and their interplays. We have therefore investigated the impact of these factors, especially, the role of the Lewis number and its coupling to other parameters, on the dynamics and morphology of premixed flames in fully-open channels. We have computationally solved the set of reacting flow equations, including the balance of mass, momentum, energy and species, with fully-compressible fluid dynamics and Arrhenius chemical kinetics. Specifically, the Lewis numbers in the range  are considered. Other factors varied in the parametric study include the thermal expansion ratio ; the channel half-width , scaled by the flame thickness , in the range ; the blockage ratio , as well as the spacing between the neighboring obstacles  scaled by  such that  are considered. It is shown that the Lewis number provides both quantitative and qualitative effects on the flame dynamics. In some cases of the channels filled with obstacles, the flames show an oscillatory propagation about a steady value, while in other cases, sudden transition to acceleration after an initial period of oscillations is seen. Without obstacles ( ), the flames are only found to exhibit oscillatory motion through the channel. All flame propagation parameters, such as the oscillation frequency, amplitude, and the time of initial propagation before transition to acceleration occurs, are found to be affected by Lewis number and other factors.