Stirling Engines

Project description The Stirling engine is the most flexible of all known heat engines but despite this remains the least developed concept. Unfortunately, because of design problems, this type of motor remains somewhat neglected. However, the use of modern materials and design methods has recently brought new life to the Stirling engine. Stirling engines can use any form of heat source because their working medium (in most cases gas) is sealed in the engine and does not change. The working medium is heated at one end of a cylinder while the other end of the cylinder is cooled (usually by water). A displacer piston pushes the medium periodically into each end of the cylinder, so that the medium expands and compresses in the same manner. Movement of another piston in the same cylinder is caused by the resulting difference in pressure which in turn generates work. Both pistons are connected to a crankshaft which drives them with a phase shift of approximately 90 degrees. Owing to the nature of its design, the displacer piston in conventional Sterling engines moves sinusoidally which means that during the majority of the time the cylinder is simultaneously occupied by both warm and cold gases. The maximum and the minimum pressures, which both determines the output power and efficiency of the engine, are reached only at the end points where the piston changes its direction. Should it be possible to drive the piston in a non-linear manner (for example by a square wave) - in order to exploit the points of maximum power - then both the energy density and the efficiency will be increased. Based on the invention of such a non-linear technique a prototype has been built in order to prove the concept. The following photo shows the first prototype: Within the framework of this project several such prototypes have been built in order to prove the viability of this new principle. At the same time further research in improving the necessary mechanical and electrical configurations is being carried out. This project was carried ou by Daniel Dragoi of the Mechatronics Research Unit in conjunction with Prof. Elsner of the Mechanical Engineering Fakulty of the Fachhochschule Regensburg.

 

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