Effect of n-butanol addition on the burning rate and soot characteristics during combustion of single droplets of diesel–biodiesel blends

The effect of n-butanol addition on the burning rate and soot characteristics of single droplets of diesel–biodiesel blends was systematically studied. A single droplet of a diesel–biodiesel-n-butanol mixture of approximately 1 mm in diameter was suspended on a silicon carbide fibre and burned in air at 973 K in an electrically heated tube furnace. The droplet size during combustion was continuously recorded using a colour CCD camera and the burning rate based on the d² law was determined. The soot intensity as indicated by theKLfactor and flame temperature were estimated from the CCD camera spectrum data using a two-colour pyrometry technique. Soot particles were also sampled using a thermophoreric deposition probe and characterised using a high resolution transmission electron microscope (TEM) for particle size and morphology. The results showed that n-butanol addition increased the burning rate of diesel–biodiesel blends, reduced the KL factor, being more profound with increasing n-butanol addition. The temperatures of the flames surrounding the fuel droplets with and without n-butanol addition showed little differences. The mean diameter of primary soot particles decreased and the particle size distribution shifted towards a smaller size range with n-butanol addition. At low levels of n-butanol addition the soot particles consisted of predominantly amorphous carbon, however, became progressively more graphitic in the inner structure with increasing n-butanol addition.