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This study concerns flame speeds during the ignition and combustion processes in a spark-ignition engine. These have been analysed from both combustion images in the early stages of the flame kernel development, and from the pressure time history. Simultaneous measurements of engine operating conditions, pressure traces and sequences of combustion images have been made in a single-cylinder four-stroke engine. The early stages of the combustion have been analyzed using stochastic image analysis techniques. These techniques can measure the total kernel growth, the local translational velocity of the centroid, the stretching of the flame kernel surface and its roughness. In addition, the fraction of the flame surface area supporting propagation has been determined from the directional variation of flame propagation between successive image frames.

Closed and recycle diesel engine systems have been developed for use on board conventional manned military and commercial submarines. This type of power system is now being considered for unmanned Autonomous Underwater Vehicle (AUV) applications. However, with a simple recycle system, the recirculated carbon dioxide rich combustion products can be expected to have an adverse effect on engine performance. Recent developments in this field have been concerned with producing synthetic atmospheres whose properties match those of free air so enabling the non air performance at least to match that of the normally aspirated unit. This philosophy has resulted in bulky and complicated exhaust gas management systems. The possibility of a diesel engine operating on a carbon dioxide/oxygen atmosphere whilst still retaining acceptable engine operating performance would therefore seem to require further examination.