Effect of oxygenates addition on the flame characteristics and soot formation during combustion of single droplets of a petroleum diesel in air

• Effect of oxygenates on diesel droplet combustion and soot formation was studied.
• Oxygenates addition reduced soot emission, burning rate and flame temperature.
• Soot reduction correlated well with the oxygen content of the fuel mix.
• Ethanol was more effective than methyl oleate in reducing the soot emission.

The effect of methyl oleate and ethanol addition on the combustion characteristics and soot emission of single droplets of diesel was studied by means of experimentation and kinetic modelling. The experiments were performed using a high-temperature tube furnace operating at 973 K and the soot intensity indicated by the soot KLKL factor, and flame temperature were simultaneously measured using a two-colour pyrometry technique and a colour CCD camera. A detailed chemical kinetic calculation was performed using CHEMKIN-Pro. The experimental results showed that adding methyl oleate to diesel significantly suppressed the soot formation. The burning rate and flame temperature of the droplets decreased with increasing methyl oleate addition up to 20 vol% and slowly increased again at methyl oleate addition exceeding 20 vol%. Ethanol addition up to 10 vol% in the diesel also led to less soot formation, lower flame temperature and burning rate. Kinetic modelling showed satisfactory agreement with the experimental results: the effectiveness of ethanol and methyl oleate in soot abatement was linear with the oxygen content in the fuel mixtures with ethanol being more effective than methyl oleate. The kinetic analysis also showed that ethanol utilised its oxygen atoms more efficiently than methyl oleate in suppressing the formation of soot precursors.