Experimental study on sooting propensities of ternary blends of n-dodecane, isododecane, and C8 oxygenates at high pressures

Abstract

The use of liquid fuels in internal combustion engines is still prevalent in society because of their high energy density, ease of handling, and matured engine technology. Along with other power generation sectors, the transport sector faces the need to reduce emissions such as soot. One option to address this is to use oxygen-bearing fuels. The presence of oxygenated compounds in fuels have the potential to reduce soot emissions in heavy duty diesel engines and various power generation sectors. Understanding the fundamental combustion and sooting characteristics of oxygenated compounds at high pressures is essential for the development of future low sooting fuels. In this work, four oxygenated compounds belonging to the C8 functional group were deployed along with normal dodecane and isododecane to form ternary blends having the same oxygen content, of 2.5% by mass, and a matching cetane number of 52. The blends were injected at a high pressure into controlled high pressure, high temperature conditions in a constant volume chamber. The flame and the soot natural luminosity were investigated with high-speed diagnostics. The results revealed that the blends delayed the onset of the first appearance of soot. The presence of oxygenates increased the soot lift-off length by 40%, hindered the formation of soot by up to 55%, and enhanced the oxidation by up to 10%, all relative to diesel. The sooting tendency of the oxygenated blends increased in the order of ketone ≈ alcohol < ester < aldehyde < diesel. The difference between the sooting tendencies of the oxygenates was smaller than those between the oxygenates and diesel, showing that soot reduction was mostly due to oxygen content and dilution effects. However, the small differences observed between the oxygenates indicates that the moiety does have an effect on soot reduction—but to a lesser extent than dilution and oxygen effects.