Hydrodynamic and thermodiffusive instability effects on the evolution of laminar planar lean premixed hydrogen flames

Abstract

Numerical simulations with single-step chemistry and detailed transport are used to study premixed hydrogen/air flames in two-dimensional channel-like domains with periodic boundary conditions along the horizontal boundaries as a function of the domain height. Both unity Lewis number, where only hydrodynamic instability appears, and subunity Lewis number, where the flame propagation is strongly affected by the combined effect of hydrodynamic and thermodiffusive instabilities are considered. The simulations aim at studying the initial linear growth of perturbations superimposed on the planar flame front as well as the long-term nonlinear evolution. The dispersion relation between the growth rate and the wavelength of the perturbation characterizing the linear regime is extracted from the simulations and compared with linear stability theory. The dynamics observed during the nonlinear evolution depend strongly on the domain size and on the Lewis number. As predicted by the theory, unity Lewis number flames are found to form a single cusp structure which propagates unchanged with constant speed. The long-term dynamics of the subunity Lewis number flames include steady cell propagation, lateral flame movement, oscillations and regular as well as chaotic cell splitting and merging.

Linear and weakly nonlinear instability of a premixed curved flame under the influence of its spontaneous acoustic field

“…A general hydrodynamic theory of flames pertaining to low-Mach-number flows was presented by Matalon & Matkowsky (1982). As the resulting system, consisting of the Euler equations governing the flow coupled with a flame-front equation, is highly nonlinear, numerical solutions appeared only recently (Helenbrook & Law 1999;Rastigejev & Matalon 2006;Creta & Matalon 2011;Altantzis et al 2012). It has been found that a slightly perturbed flat flame develops wrinkles owing to DL instability.…”

Asymmetric hydrogen flame in a heated micro-channel: Role of Darrieus–Landau and thermal-diffusive instabilities

“…[10] and [11]). The other 77 method is to use non-unity Lewis number (e.g., [12]). Altantzis et al [12] investigated the effect 78 of hydrodynamic and diffusive-thermal instabilities in lean premixed hydrogen/air planar 79 flames using DNS and utilizing a one-step global reaction model.…”

“…To 95 exclude the effects of thermal-diffusive instability, they assumed the Lewis number is unity. [12]. The governing equations are solved using detailed transport to investigate the effects of …”

“…In order to better understand the process of evolution a symmetric flame into the on the previous works (e.g., [11], [12], [30]- [32]) in order to isolate the effects of Darrieus-…”

“…With this assumption the effects of diffusive-thermal instability are dropped [12]. Hence, in our 270 computation for all time steps for having a unity Lewis number, the mass diffusivity is 271 considered to be a fixed coefficient of thermal diffusivity (i.e.…”