Comparisons have been made between the ignition delay and combustion performance of sunflower oil and diesel fuel. The experimental results have been obtained in a naturally aspirated direct injection diesel engine, and particular attention has been given to the heat release analysis, ignition delay, combustion noise and lubricant degradation. The anomalous behaviour of sunflower oil is explained by reference to its physical properties and ignition quality, as reported in the literature from bomb tests.It is concluded that the power output and brake efficiency are largely unaffected by the use of the sunflower oil, and that lubricant degradation is not likely to be significant. However, the build up of combustion deposits already widely reported in the literature was observed. Suggestions are made as to how this might be ameliorated through modifications to the injection system.