The critical enabling technologies which have been identified to fully realize the potential of Autonomous Underwater Vehicles (AUVs) are: long endurance propulsion/energy systems; geodetic and relative navigation; underwater communications; mission management and control; sensors and signal processing; and vehicle design. However, perhaps the most critical technology for almost every AUV application, and often the operational limiting factor, is the availability of adequate onboard energy/power. Given the specialist nature of the AUV market, research and development into new AUV-Specific power systems is inevitably limited by resources. At the present, the relative merits and disadvantages of the competing Air-Independent Power Systems (AIPS) are fairly well known. However, the greatest need of advice is with the "total system" and its integration, i.e., how the AIPS is affected by, and affects the overall vehicle design. Hence, with the numerous design considerations of an AUVs, full knowledge and understanding of the total AIPS integration is essential, if a technically and operationally successful vehicle design is to be achievedhis paper examines the conceptual design of an AUV with specific emphasis on the integration of an air-independent powered diesel engine with respect to the power system options and subsystem equipment selection.

Thermodynamically and mechanically ideal Stirling machines offer the greatest potentia I of any heat engine in terms of perform an ce quality. This great potential has not been fully realised in practical designs but high performing Stirling machines have found a market in cryogenic and underwater power generation applications. In the latter case, over the last two decades, Stirling systems have been used, in a small 500 ton civilian manned research submarine and in medium-sized operational Nacken and Gotland class naval submarines of the Royal Swedish Navy, as auxiliary power units called Air Independent Propulsion systems (AIPs). Stirling systems have also been investigated for use as the main power units in smaller manned and unmanned autonomous underwater vehicles (AUVs) as well as diver propulsion devices/vehicles (DPD/Vs) and swimmer delivery vehicles (SDVs). In the post-Cold War environment the latter types of underwater vehicles are attracting increasing interest, particularly in the United States, as navies strive to develop the brown-water or littoral warfare capabilities necessary to prosecute operations in hostile coastal waters. Moreover, with offshore commercial oil and gas production moving into increasing deeper waters and other commercial and scientific ventures requiring AUVs of increasing endurance and under-ice capabilities there is a global interest in developing improved power systems for the new generation of underwater vehicles. The Stirling machine, with its proven record in the underwater environment, is an obvious candidate for such applications.When their cycle of operations is reversed Stirling machines can be used not only to produce power but also to provide cooling, i.e. they can be refrigeration machines and excellent cryocoolers. Many of the emerging underwater technologies such as magnetohydrodynamics' (MHD) and superconducting machinery require cryogenic cooling facilities to operate effectively - as do many sensor systems and the Stirling cooling machines may have a role to play in such systems. The non-naval uses of the oceans have also lead to the need to provide fixed sea-bed installations and habitats with their associated life-support and environmental condition equipment. Stirling machines used as coolers, heat-pumps or in total engine systems could be used in these applications. However, in the main this paper is principally concerned with underwater power systems which produce rather than use electrical power and are used with vehicles that are autonomous, independent and operate wholly submerged.

To operate in a nonair environment, a diesel engine must be supplied with a synthetic atmosphere which mimics the role of normally aspirated air. To determine the optimum synthetic atmosphere mixture, an intensive experimental investigation has been carried out by the authors using a specially developed test rig. Provision has been made on the test rig so that a number of different composition synthetic atmospheres can be produced. In this way, it has been possible to measure the effects of carbon dioxide ratios on the performance of the diesel engine. In addition to the shaft performance, power and fuel efficiency, exhaust gas emissions and combustion noise have also been measured. This paper details the operational principle of an underwater diesel engine and reports on the performance of such an engine whilst operating with high intake carbon dioxide levels

Ships at sea produce waste and in recent years great efforts have been made to manage this waste in accordance with national and international standards such as MARPOL. There are various categories of waste, such as 'blackwater', which includes infectious liquids such as human waste or sewage. At the present time, sewage generated at sea by ocean-going vessels is discharged raw or after minimal treatment. Some warships and other vessels which operate, almost exclusively, in coastal waters have been fitted with biological sewage treatment plants, but despite the best efforts of the IMO and shore authorities, coastal waters are under increasing threat from pollution. Efforts to develop effective sewage and nonorganic solid waste treatment plants have come a long way over the last 10 years, in order to protect the ocean environment. Advanced techniques such as plasma arc, gasification, etc may provide solutions to the problems, but not in the immediate future. However, the use of heat engines, such as the diesel engine and the Stirling, could provide a near term solution for the thermal destruction of sewage waste streams. In this paper, the environmental effects of the sewage stream are discussed and the future technology destruction concepts are briefly considered. The case for considering both the diesel engine and the Stirling cycle machine to act as sewage thermal destruction devises is presented.

Over the last ten years or so there has been a renewal of interest in the use of small autonomous unmanned and untethered underwater vehicles (AUVs) for naval and commercial tasks. One of the principal problems encountered in the evolution of such vehicles has been the development of suitable power systems. The onboard power and energy storage requirements are almost entirely dependent on vehicular performance. In many applications, to be cost and mission effective such vehicles must be able to transit large distances (hundreds of kilometres) and stay submerged for tens of hours, maybe several days. These needs represent a challenging task to the power system designer. The powering of an AUV is largely determined by the shape, size and desired speed of the vessel. However, contemporary underwater power systems may take up to a half of the internal space of the vehicle. Thus the size of the power systems is one of the most important factors in the determination of the vehicle's size. This situation represents an iterative loop in the design process. The propulsive power requirements are dependent upon the speed and drag resistance of the vehicle. In turn, the drag is dependent upon the interrelated parameters speed, shape and the nature of the flow over the vehicle. To reduce the drag, but maintain the design speed, the designer can then try to alter the flow regime over the vehicle or the vehicle shape. The latter tactic is the subject of this paper. For the concept reported here it was envisaged that the overall length of an AUV could be changed during its mission by discarding the empty energy storage sections and hence reducing the drag. Preliminary calculations indicate that the endurance of such an AUV could be increased by 15%.

The Stirling heat engine was first patented in 1816 [1]. It was a form of closed-cycle hot air engine, which, in itself, was not a new concept, even in the early nineteenth century. However, in Stirling's version there was a crucial innovation that made the engine unique-a regenerative heat exchanger. This was a remarkable invention, considering the state of knowledge of thermodynamics and heat transfer at the time. Moreover, Stirling, in his original patent document, foresaw the many future uses the regenerative principle could be put to in iron, steel, and glassmaking processes. The inventor of the regenerator-he called it an economizer-worked with his brother James to perfect the device, and by 1845 their experimental investigations had clearly identified the complexities of balancing the conflicting requirements for enhancing heat transfer and reducing gas dynamic drag [2]. Their contributions to the field of regenerative heat transfer have never been universally acknowledged. It is hoped that this article will help to redress this situation.

The authors detail the results of a study to develop and evaluate a knowledge-based aid for the selection of autonomous underwater vehicle (AUV) energy systems. The Royal Naval Engineering College and the University of Calgary have developed a model that allows detailed comparisons of candidate energy systems to be made once a mission profile has been specified. This model, termed ENCALC, is intended to act as an aid in identifying systems worthy of further detailed analysis. The initial phase of the project was intended to validate the operation of the ENCALC model against known data. Subsequently, a Stirling/liquid metal heat source combination was chosen. The initial results, from ENCALC, based on conservative energy, power and heat transfer efficiencies indicated that an 8-m-long AUV with a usable power plant section of 4-m would result in approximately 900 kWh of available stored energy. Considering the propulsive energy requirements of the given mission profile, this resulted in an attainable engine efficiency of 23.5%

To maintain its invulnerability the submarine must have a power plant capable of long periods of energy efficient operation so it can stay submerged, patrol silently and, when necessary, move at sustained high speeds. To do this the vessel must have a sufficient energy storage capability. The ubiquitous lead-acid submarine battery has a relatively poor energy storage capacity. Nuclear submarines, however, have access to almost limitless power, but their technology is only available to a few navies and they have displacements in excess of 3000t. The paper reviews the efforts, especially those developments taking place with the current leading candidate power plants including, the Synthetic Atmosphere Diesel, the Stirling, the Fuel Cell and advanced electrochemical batteries.