Measurement of smoke point in velocity-matched coflow laminar diffusion flames with pure fuels at elevated pressures

Using a coflow burner, a quartz chimney, and a pressure vessel with good optical access, smoke points of pure fuels were measured in a laminar jet diffusion flame. The smoke point is a fundamental kinetic parameter, as this is the point where production of soot is exactly offset by its oxidation. Ethylene and methane, burning in a velocity-matched, overventilated coflow of air, were tested over a range of pressures from 1 to 16 atm. Fuel flow rate and air coflow rate were iteratively increased, keeping the exit velocity equal, until the smoke point was reached. The volumetric fuel flow and flame height were measured as a function of pressure to determine the functional relationship between these parameters and pressure. The volumetric fuel flow at the smoke point is observed to scale as a power law with pressure, while the smoke point height is best described by a log law with pressure. The residence time, based on flame height and exit velocity, was also calculated as a function of pressure and found to have a nonmonotonic behavior, with a peak at lower pressures.