Burning characteristics of non-spread diffusion flames of liquid fuel soaked in porous beds

An experimental study was conducted to investigate the effects of sand size and sand layer depth on the burning characteristics of non-spread diffusion flames of liquid fuel soaked in porous beds. Sand beds with sand sizes from 0.12 to 3.18 mm and sand layer depths from 50 to 80 mm were chosen as the porous beds. Pure methanol was used as the liquid fuel. The flame appearances and effects of sand sizes and sand layer depths on flame temperature profiles, locations of vapor/liquid interface, vapor region moving speed, combustion duration time, fuel consumption and amount of fuel residues in the porous beds were studied in the experiments. An approximate analytical model based on the assumption of a two-phase Stefan problem was employed to predict the fuel consumption rate and the interface location. This model can quantitatively predict the interface position of combustion of the liquid fuel in the porous bed. The predicted results can also confirm that heat transfer in the bed is the controlling mode at the beginning stage of the combustion. After that, capillary force acts as the dominant role for diffusion of the vapor upward.