Asymmetric methane/air flames in narrow channels

Document Type

Conference Proceeding

Publication Date

1-1-2013

Abstract

Lean premixed laminar combustion in narrow channels is known to display a range of different flame behaviors: periodic ignition/extinction, symmetric flat/V-shaped, asymmetric, oscillating between two asymmetric flames and axially pulsating asymmetric flames. The specific combustion mode depends on the operating conditions, where inlet velocity, equivalence ratio, channel height and wall temperatures play important roles. This work investigates structure and characteristics of asymmetric premixed methane/air in the presence of preheating. 2-d numerical simulations with detailed chemistry are performed for different inlet conditions in a long narrow channel. Within the channel, the incoming mixture is gradually preheated by a prescribed temperature ramp that is imposed on the walls. Despite symmetric boundary conditions, numerical results confirm that a range of asymmetric flame shapes including periodic non-stationary fronts are observed. Comparing results obtained from different conditions, the impact of varying operating conditions (equivalence ratio/channel height) is observed and analyzed. Asymmetric flames occur at elevated inlet velocities, where typical flame shapes display strong curvature at the channel center, and elongated oblique reaction layers close to channel walls. Due to flow redirection, the mass flux across the flame sheet is highly non-uniform. The pronounced two-dimensional effects give insights on curved two-dimensional flame structures, which can be analyzed in a small computational domain. Simulations with detailed chemistry allow for a detailed investigation of reaction zone characteristics. Within the reaction zone, major species and radical concentrations as well as temperature profiles are discussed, where the variation of enthalpy, equivalence ratio, carbon-hydrogen ratio and the estimated adiabatic temperature based on local state properties are considered.

Publication Source (Journal or Book title)

Fall Technical Meeting of the Western States Section of the Combustion Institute, WSS/CI 2013 Fall Meeting

First Page

506

Last Page

523

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