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Low temperature-difference Stirling engines, while of limited perceived applicability, offer excellent opportunities to challenge the existing state of theoretical knowledge with low-cost yet revealing experimentation. The general availability of a well-performing low-cost Ringbom-Stirling engine provides an excellent basis for widespread experimentation based upon a common platform. Whereas some broad characteristics of this engine have already been presented this paper addresses in particular a number of aspects in regard to displacer springing. Most particularly, the gravitational effects on a vertically-oriented free displacer may be inferred with reference to a spring-suspended displacer. At the same time, theoretical predictions regarding sprung-displacer performance can be tested.

Stirling cryocoolers with a single stage of expansion routinely achieve cryogenic refrigeration temperatures of 70 K. Lower temperatures can be achieved with multiple expansion stages arranged ‘in series’, 20 K with two stages, and less than 10 K with three or four stages. Multiple expansion Stirling power systems are also in prospect particularly for exhaust heat recovery systems using different stages of progressively lower temperatures. Two or more stages can be combined in a single cylinder. Multiple expansion Stirling machines have been a topic of interest at The University of Calgary for some years. Recently a second-order computer simulation program with integral graphics package for Stirling cryocoolers with up to four stages of expansion were developed and made available to the Stirling community. Adaptation of the program to multiple expansion Stirling power systems is anticipated. This paper briefly introduces the program and presents a specimen result.

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.

Many non-renewable land-based resources are becoming depleted and the search for alternative sources of raw materials is intensifying. This situation has lead to the involvement of a number of countries, especially those of the European Community, in heavily funded ‘Wealth from the Oceans’ projects. A significant element of the research being conducted under the auspices of these projects is concerned with the development of small unmanned and untethered autonomous underwater vehicles (AUVs). To carry out their intended autonomous missions these vehicles will need reliable power systems which have high energy densities. However, although research into navigation, control and command systems has progressed considerably under this development effort, only limited headway has been made in the development of power systems which could be readily integrated into these vessels.

In pipeline compressor stations natural gas fuelled aircraft derivative gas turbines are frequently used in conjunction with a power turbine to drive the large centrifugal compressors for ‘boosting’ the pipeline pressure. Typically two thirds of the energy provided to drive the turbine is carried off as heat in the exhaust stream. These hot exhaust streams, typically at temperatures around 500 K contain very substantial energies, 50 MW being not uncommon. This paper summarises recent studies carried out to assess the feasibility and worth of applying Stirling power systems to generate electric power from these ‘waste’ streams. Both ‘bottoming’ and topping cycles are of interest and are briefly considered in this paper. An elementary, but realistic, performance analysis indicates the possibility of recovering as much as 9 MW power from the exhaust of a gas compressor equipped with a Rolls-Royce RB 211 aircraft derivative gas turbine.

The Fluidyne, or liquid piston stirling engine, has many characteristics which make its use in developing nations particularly attractive. Besides being compatible with the use of lowgrade heat sources, the machine is simple to manufacture using a variety of low cost materials and is exceedingly reliable. This paper uses a summary of fluidyne experience to evaluate applications of the fluidyne to water pumping requirements in developing countries for purposes including domestic, livestock, and irrigating uses for water pumping. Possible sources of energy are evaluated in the light of availability and needs. Environmental, economic, and social benefits are also examined. Particular applications of the fluidyne to existing situations in China are evaluated in detail.

Stirling refrigerators are well established in the cryogenic temperature range and the system of choice in the miniature closed cycle versions used for cooling the infrared detectors of night vision and missile guidance systems. They are rarely used at the higher ‘near ambient’ temperatures of air conditioning plants and domestic or commercial refrigerating systems. However, increasing public concern at the impact of ‘Freon’ refrigerants on the ozone layer of the Earth has focussed attention on the need for alternatives to the present vapor-compression refrigerating systems. This social concern provides unparalleled opportunities for the development and application of ‘near-ambient’ temperature refrigerating systems. This paper briefly reviews the previous work and presents recent innovative concepts and designs for compact Stirling refrigerators that could be the basis for alternatives for Freon-free refrigeration.

Large rear end dump trucks are used for downhaul operations in mountain mines. On these trucks mechanical service brakes are provided on both front and rear wheel sets. They may be either disc or drum brakes actuated by a hydraulic/pneumatic system. On some trucks provision is made for the brake effort on the front wheel sets to be reduced at the discretion of the driver. This proportional braking is intended to minimise the possibility of front wheel skidding on icy roads with consequent loss of steering. However, this voluntary reduction in front wheel braking seriously impairs the braking capacity of the truck. A study was made of the braking requirements of heavy vehicles on inclined surfaces. It was found for typical loaded truck geometries in present use that the rear wheels will always slip first.

This paper is supplementary to an earlier presentation of a generalized theoretical analysis of the Stirling engine cycle developed by Finkelstein. The theory is complex and the final equations do not have closed solutions. Only one numerical result was given with the original presentation of the theory. Now, with the aid of a digital computer a study has been made of the effect of the four principal design parameters on the performance of an engine assumed to be operating with adiabatic processes of compression and expansion. Typical values of heat exchanger thermal loading, net engine output, and thermal efficiency are presented for a defined reference engine configuration, showing the effect of variation in the temperature ratio, phase angle, swept volume ratio, and dead volume ratio.