Natural convection turbulent diffusion flame near a vertical surface

The structure and dynamics of a natural convection 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 ensures a sufficient spatial resolution of the boundary layer structure. It is shown that the computed value of the total heat flux on the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of completely gasifiable thermal plastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction shows that the heater-igniter parameters determine the duration of the transitional period, but weakly affect the growth rate of the heat release intensity and the height of the pyrolysis region at the stage of developed combustion. Significant effects of the heater shape, size, and temperature, as well as lateral entrainment of air on the velocity of flame propagation upward over the plate surface and on the shape of the pyrolysis front. The existence of critical parameters of the heater separating flame decay from developed combustion is demonstrated. Three regimes of flame propagation with different pyrolysis front shapes are identified.