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One of the many advantages perpetually claimed for the external combustion Stirling engine over it's internal combustion (IC) contemporaries is that it produces lower exhaust pollutants. However, this claim was made before carbon dioxide (CO2) was identified as one of the most important contributors to the undesirable greenhouse effect. Unfortunately, the more efficient combustion of a Stirling system results in proportionately more CO2 being produced than with an equivalent IC engine. Therefore, if the Stirling is to maintain it's position as an environmentally friendly engine, then some efficient means of removing the exhaust CO2 must be found. Of the many techniques available for removing this gas, the cryo-process appears to be well suited for use with the Stirling. However, a rudimentary analysis, presented in this paper, of such a system has indicated that the performance penalties imposed by making provision for CO2 removal would probably be unacceptable.

Non-air-breathing diesel engine systems have, and continue to be developed for underwater applications. When the engine is operated in such an environment the intake oxidant mixture consists of a combination of oxygen and recycled exhaust gas. The latter will contain combustion gaseous products and may also include additional inert diluents. Since its initial conception in the late nineteenth century, a major problem encountered in the operation of the recycle diesel engine has been the detrimental effect of the recirculated exhaust carbon dioxide upon the engine's performance. To avoid this problem exhaust gas scrubbing systems have been developed to remove the carbon dioxide from the exhaust gases. In addition, inert gases such as argon and helium have been added to the non-air mixture to improve its thermodynamic and transport properties and hence engine performance.

This paper describes work aimed at developing an underwater power system and an environmental control EGR system based on the recycle and closed-cycle operations of conventional diesel engines. Particular emphasis is placed on one of the key problems associated with the recycling some of carbon dioxide in closed-cycle diesel engine (CCDE). A quasi-dimensional model has been developed to investigate the effects of different intake compositions on engine performances. The paper also introduces the development of instrumentaion for measurement and control combustion conditions in CCDE. With the objective of improving fuel ignitability and reducing the ignition delay, the paper experimentally investigates the effects of heated fuel on fuel injection characteristics, engine performance and exhaust emissions in DI and IDI diesel engines.