21-05-2014, 04:56 PM
Stirling Engine
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ABSTRACT
The quest of human beings to develop engines with high power, high torque, less vibration and most essentially with no pollution is on since the discovery and development of engine. Stirling engine is just one step forward towards the creation of a noise free and pollution less engine.
The Stirling engine is the engine, which uses a fixed amount of gas sealed inside a cylinder. The expansion and contraction of the gas, using heat from external source, creates the useful work. The main advantage of this engine is its capability to use any type of fuel and the emission of no exhaust gases.
Due to this pollution free and use of any type of fuel characteristics the Stirling engine shows a greater potential over any other type of engine existing today. To consolidate this claim an effort has been made to develop a working model of Stirling engine.
INTRODUCTION
All of us including the lamest of laymen would have at one time or another experienced problems with our vehicles engine and most of the time after moaning and cursing finally in line with the universe and accepting our doom we would have coughed up the cash for repairs and parts and insistently taken old parts home, disregarding the fact that no descent human would have wanted them and during this exercise in existence it is doubtful that anybody would have chance to miss seeing a piston or two, this ubiquitous creatures that scurry up and down in an enclosed cylindrical space, getting their crowns slammed regularly and unceremoniously…eventually to be thrown aside and replaced by a marginally wider chap. Doubtful that any of us would be able to imagine modern travel without an internal combustion cycle. Hell if we ask our mechanic if he has ever seen a vehicle without any exhaust then he is probably going to refer to you to the nearest shrink.
STIRLING ENGINE
The Stirling engine is a heat engine that is vastly different from an internal combustion engine. Stirling engines have two pistons that create a 90-degree phase angle and two different temperature spaces. The working gas in the engine is perfectly sealed, and doesn't go in and out to the atmosphere. The Stirling engine uses a Stirling cycle, which is unlike the cycles used in normal internal combustion engines.
OPERATION
Since the Stirling engine is a closed cycle, it contains a fixed mass of gas called the "working fluid", most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. No valves are required, unlike other types of piston engines.
The Stirling engine, like most heat engines, cycles through four main processes: cooling, compression, heating and expansion. This is accomplished by moving the gas back and forth between hot and cold heat exchangers, often with a regenerator between the heater and cooler.
The hot heat exchanger is in thermal contact with an external heat source, such as a fuel burner, and the cold heat exchanger being in thermal contact with an external heat sink, such as air fins. A change in gas temperature will cause a corresponding change in gas pressure, while the motion of the piston causes the gas to be alternately expanded and compressed.
The gas follows the behaviour described by the gas laws which describe how a gas' pressure, temperature and volumeare related. When the gas is heated, because it is in a sealed chamber, the pressure rises and this then acts on the power piston to produce a power stroke. When the gas is cooled the pressure drops and this means that less work needs to be done by the piston to compress the gas on the return stroke, thus yielding a net power output.
The ideal Stirling cycle is unattainable in the real world, and the actual Striling cycle is inherently less efficient than the Otto cycle of internal combustion engines.
The efficiency of Stirling machines is linked to the environmental temperature; a higher efficiency is obtained when the weather is cooler, thus making this type of engine less interesting in places with warmer climates.
As with other external combustion engines, Stirling engines can use heat sources other than from combustion of fuels.
When one side of the piston is open to the atmosphere, the operation is slightly different. As the sealed volume of working gas comes in contact with the hot side, it expands, doing work on both the piston and on the atmosphere.