When sunflower oil (or plant oil, in general) was used as diesel engine fuel, the ignitability at low temperatures was much poorer than for No. 2 diesel oil. In addition, unburned carbon accumulated in the combustion chamber when the engine was idling. The research reported in this paper was conducted to investigate the causes of these problems.
A single fuel droplet set at the tip of a combustion thread was inserted into an electric furnace and ignited. The behavior of the combustion was observed and analyzed by a high speed rotary video camera. The fuels studied were sunflower oil, No. 2 diesel oil, sunflower oil methyl ester and fish oil methyl ester.
As a result, even if the droplet size of sunflower oil was the sane as that of No. 2 diesel oil, its ignition delay was much longer than No. 2 diesel oil. This may be the main cause of poor ignitability of sunflower oil at low temperatures.
When the temperature in the electric furnace was low, sunflower oil did not ignite but formed a cenosphere (a net structure). This may be the cause of carbon deposits during idling.