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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.

Long range, extended endurance, variable speed autonomous underwater vehicles (AUVs) appear to be an attractive solution to problems of environmental monitoring, geophysical exploration and military surveillance. To undertake their intended autonomous missions these vehicles require reliable and cost-effective power systems. Although there is presently an extensive interest in untethered AUVs, with far reaching efforts being made in a variety of activities, only limited headway has been made in the development of power systems which could be readily integrated into these vessels. The majority of current research is focusing on increasing the underwater endurance and hence cost effectiveness of the vehicle by developing compact, lightweight high energy density power systems for vessel propulsion. Subsequently, a number of different power systems have been investigated proposed, designed and developed.

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.

EGR diesel engines are used in an underwater environment, or in terrestrial applications that demand low exhaust emissions. In the underwater mode the intake mixture may contain up to 30% CO2 whereas with land-based EGR diesels the percentage will be much lower. In both applications noise is an important emission parameter for not only is it a pollutant but in the underwater environment a primary means of detection. Thus, in the research reported here the combustion noise levels and spectra have been measured for a diesel engine using a variety of precisely proscribed intake mixtures containing levels of CO2. It has been found that the presence of CO2 alters both the sound level and frequency spectra of the combustion noise and that in general, although not in all circumstances, the sound pressure levels are increased.