Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface

Abstract

The structure and dynamics of a natural buoyant turbulent diffusion flame near a vertical surface with combustible gas exhaustion are numerically studied by using the FDS model and computer code. The flame is considered near the surface through which gaseous propylene is injected with a prescribed flow rate. Requirements are determined for the grid cell size in the near-wall region, which ensure sufficient spatial resolution of the boundary layer structure. It is shown that the predicted value of the total heat flux at the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor parameters determine the duration of the transient period, but weakly affect the growth of the heat release rate and the height of the pyrolysis region at the stage of developed burning. Significant effects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the velocity of the upward flame spread rate over the plate surface and on the shape of the pyrolysis front are revealed. The existence of critical parameters of the ignitor separating flame decay from developed burning is demonstrated. Three flame spread regimes with different pyrolysis front shapes are identified.