Soot formation and burnout were studied at atmospheric pressure in co-¯owing, axisymmetric,
buoyant laminar diusion ¯ames and double ¯ames of lique®ed petroleum gases (LPG)±air mixtures. In
diusion ¯ames, two dierent fuel ¯ow rates were examined. In double ¯ames, three dierent primary
air ¯ow rates were examined. A soot sampling probe and a thermocouple were used to measure the
local soot mass concentration and ¯ame temperature, respectively. Flame residence time was predicted
using a uniformly accelerated motion model as a function of axial distance of the ¯ame. The increase of
primary air ¯ow rate was found to suppress the energy transfer from the annular region, at which the
soot is produced, to the ¯ame axis. The time required to initiate soot formation at the ¯ame axis
becomes longer as the primary air is increased. The trend rate of soot formation was found to be similar
along the ¯ame axis in all tested diusion ¯ames. The increase of primary air by 10% of the
stoichiometric air requirement of the fuel results in a 70% reduction in maximum soot concentration.
The ®nal exhaust of soot, which is determined by the net eect of soot formation and burnout, is much
lower in double ¯ames than that in diusion ¯ames