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Soot particles are noxious emissions that are associated with global warming and are known to be harmful to humans. They are partly produced from the combustion processes in diesel engines, and can be reduced by altering the fuel structure. For this, adding an oxygen moiety becomes an attractive solution to reduce soot formation and enhance its oxidation. Nonetheless, the oxygenated fuel must meet several criteria to be a candidate for blending with, or replacing, diesel in current engine infrastructures. For example, it must have similar physical properties and a similar energy content to diesel. A promising fuel that could meet these criteria is octanal. However data on its spraying and combustion characteristics is lacking, and neither fundamental studies nor studies under engine-like conditions are available in the literature, to characterise the spray combustion of octanal.
To fully characterise the potential of an oxygenated fuel and its sooting propensity, both its spray and spray combustion characteristics must be understood. In this work, the latter is addressed to build up on the knowledge about this fuel and gauge its potential as an alternative to diesel. In order to study the combustion properties of octanal, we studied the soot and temperature distribution by using a two colour pyrometry system coupled with a high speed camera. The same amount of mass for diesel and octanal was injected neat into an engine-like; high temperature, high pressure environment, using a multi hole injector. This allowed for a relative comparison of the combustion of each fuel's spray. It was discovered that diesel and octanal's sooting characteristics were fundamentally different, owing to octanals thermochemical properties. For a similar flame temperature it was observed that octanal produced less than half of the amount of soot than diesel and that its formation and oxidation rate differed. In addition to the above, we proved that the physical similarity between both fuels makes it possible to inject octanal using a standard common-rail system.
The novel findings from this work revealed that octanal could be a viable oxygenated fuel for implementing in Diesel engines for both its similar thermophysical properties and that its soot reduction potential.
