This paper presents data obtained from a single-cylinder direct injection diesel research engine (121mm bore × 139mm stroke) fitted with a deep torroidal piston cavity but which was fitted with a detachable-port cylinder head and could be operated both with and without swirl. Tests were carried out with a number of different fuel injection pump plunger sizes (which yielded significant changes in injection rate patterns) and the results have been analysed with the aid of a computer program (INJECT) which can be used to determine instantaneous rates of fuel injection, based on data acquired from a firing engine. The results indicate that observed changes in emissions levels can be explained in terms of variations in the instantaneous injection rates.In particular, for a given engine speed, a strong correlation has been shown to exist between NOx emissions and the volume of fuel injected during the ignition delay period, particularly at high engine loads. Also, a clear correlation is demonstrated between exhaust smoke emissions and the mean injection kinetic energy (M.I.K.E.). The latter correlation is evident at different engine loads and for a number of engine configurations and illustrates that, in general, an increase in calculated M.I.K.E. correlates with a decrease in exhaust smoke It is also shown, not withstanding the importance of the mean kinetic energy of the fuel spray, that the distribution of the kinetic energy levels in the spray can also play an important role in determining levels of exhaust smoke.