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It has been known for nearly a century that by recycling the exhaust gas and adding renewal oxygen for combustion, it is possible to operate a standard diesel engine in air restricted conditions. However in order to operate under these conditions, such as found in underwater vessels, exhaust gas management systems are required to process the combustion products. The characteristics of recycled working fluids and the effective disposal of the exhaust gases leads to conflicting system operational requirements. In order to operate the whole system as a compact and efficient power unit, a compromise needs to be found between the performance of the engine with the recycled exhaust and the physical size and efficiency of the exhaust processing system. Previous research using non-conventional or contaminated atmospheres for underwater vehicles power systems, pollution control and mine engineering has mainly used three methods of supplying the intake atmosphere.

Synthetic atmosphere diesel (SAD) engines have been and are still being developed as air-independent power systems for use in naval and commercial underwater vehicles. Although the basic concept of such a system is relatively simple, its practical implementation is somewhat complicated and normally involves expensive and time consuming prototype development. If an analytical method existed which could be used to compare the overall performance of different configurations or highlight essential control aspects, system optimization could be attempted more readily and a close-to-optimum design produced prior to any subsequent practical development. Consequently, a thermodynamic simulation model has been formulated so that the performance and/or design of such systems can be investigated, and the effects of the various system variables can be identified. In this paper the development of the model and the associated experimental investigation is described.