Experimental study on the combustion characteristics of high-pressure octanal spray flames

In view of the stringent emission regulations, oxygenated fuels are growing in popularity owing to their potential to reduce emissions in diesel vehicles and off-road applications. It is important to explore the combustion characteristics of oxygenates that can match the energy content and density of diesel whilst reducing the formation of pollutants. Furthermore, having similar thermo-physical properties to diesel could yield them as drop-in fuel candidates. In this work, the combustion characteristics of a long carbon chain oxygenate, octanal (C8H16O), and diesel, were investigated using the two-colour pyrometry method to study the temperature and soot distributions in the spray flames. This investigation was done by injecting the fuels at high pressures in an optically accessible constant volume chamber under a diesel engine-like environment, at high ambient pressures and temperatures. The soot lift-off length for octanal was longer than for diesel, which reduced the amount of time available for soot to grow. For the same injected mass of diesel and octanal, the combustion of octanal was faster due to the presence of fuel-bound oxygen. The two-colour pyrometry results revealed that the spatial distribution of soot for octanal was slightly different from that of diesel. The chemical structure of octanal, consisting of a long chain alkane with an aldehyde functional group at the end and without the presence of any aromatic structures, hindered the soot formation significantly throughout the combustion process when compared to diesel.