Heat release diagrams derived from measured cylinder pressure data are presented for a Ricardo E16 single cylinder naturally aspirated direct injection diesel research engine (121mm bore × 140mm stroke). The data covers a wide range of engine builds and operating conditions and shows the effects of varying swirl, injection rate and piston cavity shape. Also, the effects of varying engine speed at ‘zero’ swirl are investigated and discussed.The results show the effects of swirl and of chamber shape to be somewhat smaller than those of injection rate. Also, engine speed-related effects are shown to have a very major influence on rates of combustion.Trends in calculated heat release patterns did not always appear to be consistent with measured BSFC and ISFC trends. This gave rise to some doubts about accuracy, arrising in particular from the in-cylinder heat transfer calculations. The latter were based on well known equations which are widely used elsewhere.