Sooting tendency of paraffin components of diesel and gasoline in diffusion flames

The influence of the chemical structure on the sooting characteristics of some paraffin class hydrocarbons which are found in gasoline and diesel fuel is studied experimentally. The experiment involves the combustion of the paraffin in a wick-fed burner. Differential mobility spectrometry is used to measure the particle size distribution (PSD) at different flame heights. The wick-fed laminar diffusion flame is sampled at the tip; the flame height is modified systematically from small heights to large heights. Normal, iso and cyclo paraffins PSDs evolve in a similar way with flame height. At very low flame heights the PSD is unimodal, but rapidly evolves into a multi-modal one. The total number of particles peaks at small heights, and then decreases as flame height increase until it approaches constant values for all considered fuels. The mean soot particle diameter increases with flame height until a height where a maximum is achieved and sustained. Among each type of fuel, a systematic decrease in the maximum mean soot particle diameter was observed as the number of carbon atoms in the molecule increased. At all flame heights, comparing fuels with the same carbon number, cyclic paraffins presented the largest mean soot particles sizes, followed by iso-paraffins and the smallest particles for normal paraffins.