Fuel Oxygen Effects on Soot Formation in Counterflow Diffusion Flames

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Abstract
The effect on the soot formation processes of the addition of small quantities of oxygen to the fuel has been studied by making velocity, temperature, soot volume fraction, particle number density, and fluorescence measurements along the frontal stagnation streamline of counterflow diffusion flames established around a porous cylindrical burner. Flames of five fuels with and without oxygen in the fuel stream were studied. In ethene flames, addition of 10 percent oxygen resulted in an increase in the final soot volume fraction (near the stagnation point) of more than 100 percent. For the other fuels, namely propene, propane, isobutane, and n-butane, little change was observed. The difference between ethene and the other fuels is explained on the basis of the H radical concentrations. Oxygen addition decreased the fluorescence signal levels in all the flames, except ethene where an increase was measured.