Effect of a homogeneous combustion catalyst on combustion characteristics of single droplets of diesel and biodiesel

Abstract

Combustion characteristics of single droplets of diesel and biodiesel in air at temperatures between 923K and 1073K, with and without being dosed with a ferrous picrate based homogenous combustion catalyst, were studied. The time-resolved ignition and burnout behaviour of the droplets were observed with the aid of a CCD camera, which enabled the determination of the ignition delay period, the burnout time and the flame temperature using the thermal imaging taken by the CCD camera. A flame emission spectrometer was used for identification of the presence of iron ions in the flame and TGA experiments were carried out to study the thermal decomposition behaviour of pure ferrous picrate. It was found that the catalyst shortened the burnout time, increased the burning rate and the flame temperature of the droplets of both diesel and biodiesel. At the catalyst dosing ratio of 1:10,000 (by volume) in the diesel and biodiesel, the flame temperatures of the catalyst dosed droplets were about 40–50K higher than those of the droplets without the catalyst while the burning rate was 0.05–0.1mm2s−1 higher. It was also found that the biodiesel droplets had longer ignition delay period but shorter burnout times, higher burning rates and flame temperatures than those of the diesel droplets. Iron ions were detected to present in the flame of the combustion of the catalyst droplet alone and it was found that the pure ferrous picrate decomposed at 523K. This low decomposition temperature of the picrate ensured the release of the iron ions into the flame, which in turn promoted the combustion rate of the fuel vapour.