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

Abstract

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.