On the Soot Formation in the Diffusion Flames

(Experimental Investigation on the Measuring Methods)

Abstract

There have been many new developments in the studies on the formation of soot. The soot formation of hydrocarbons with air in a diffusion flame, however, is a very complicated process, from the viewpoints of both the kinetics of reaction and the effects of the mixing processes.
But, little has been published on the soot formation process and measuring methods of soot particles in the flame.
At the same time the intermediate products for soot formation have not been investigated.
In this paper, three different fuels have been used: C₃H₈, C₃H₈/N₂ (70/30, vol.%) and C₂H₂. The soot particles are obtained through the profiles of both the relative value and absolute quantity in which they are collected on a filter paper and a glass wool at the end of a cooled probe.
The concentration in flames of methane, progressively less-saturated straight-chain hydrocarbons and polycyclic aromatic hydrocarbons (p.c.a.h) as intermediate products for the soot formation has been analysed by chromatography and ultraviolet spectrocopy.
To sum up the results of our experiments, the most important points are as follows:
1) The soot particles collected on the glass wools are shown by absolute quantity as mass fraction.
The distribution of soot concentration along the flame axis, regardless of the fuel, is demonstrated by the normal distribution over the flame.
2) The intermediate species for soot formation can be regarded not only as the less-saturated straightchain hydrocarbons, but also as the important role on the formation of polycyclic aromatic hydrocarbons.
The relative values of p.c.a.h can be availably detected by ultraviolet absorption spectrogram.
Finally, it is necessary to ensure the higher precision of soot quantity and intermediate products.