The Invention Of Stirling Engine

An engine is a machine that converts energy into useful work.

For example burning coal to turn the drive shaft of a power plant generator. The most common engine in production today is the gasoline-powered automobile engine. Other common engines are the diesel engine used in heavy trucks and some passengers cars, the steam turbine that generates electricity in power plants, the jet engine used to propel aircraft, and the two-stroke gasoline engine used to power smaller appliances like lawnmowers. Each of these engines converts heat generated by burning a fossil into useful work.

The science that studies how heat is cycled in an engine to create work is called thermodynamics, from the Greek therme (heat) and dynamics (power). A cycle that converts heat into work is known as a Thermodynamics Cycle. A gasoline-fueled automobile engine uses the Otto Cycle. A diesel-fueled engines uses Diesel Cycle. A steam turbine engine, or steam power plant, uses the Rankine Cycle. None of these cycles can be used to completely convert energy to work.

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This is because all of them have to reject heat into the environment. A power plant or steam engine has to condense steam in order to send the water back to the boiler (losing energy). An automobile engine must reject the hot exhaust gases, containing a considerable amount of energy, out the tailpipe. The most thermally-efficient practical cycle for converting heat into work is the Stirling Engine. The Stirling Cycle is the most thermally-efficient engine because it wastes (or reject) the amount of heat to the environment for the amount of work it produces of any engine.

A Stirling Cycle engine can be used to power a car, truck, or airplane, or to generate electricity. It will do this work for less energy input than a comparable Otto, Diesel, or Rankine Cycle engine could.

The resulting loss of life was the motivating factors that led the Reverend Robert Stirling (in addition to being one of the foremost engineers of his day, he was also an ordained minister of the Church of Scotland) to develop an engine was much more thermally-efficient than Watt’s engine, principally because it did not require that steam be condensed during the cycle. Although Stirling’s engine was much safer, the technology of the time did not allow for the manufacturing of Stirling Engines of more than a few horsepower.

Stirling’s engine never caught on the nineteenth century. Fossil fuels plentiful and metallurgy improves to the point where steam engine was no longer quite as hazardous. Thus, the inherent thermal-efficiency advantage of the Stirling Cycle was not enough of a motivator to overcome the significant design challenges that faced engineers wishing to build more powerful Stirling Cycle engine. Today, Stirling Cycle engine are used to produce most of the liquefied air made in research laboratories. They are also used in weather and spy satellites and by the Swedish Navy to power some of its submarines.

The quest for increased submerged endurance in small submarines led to the development of Stirling engines in Marine use. The Stirling Cycle engine forms the basis of the Air Independent Propulsion system to enter naval service in recent times. The Swedish builders, Kockums Naval Systems, tested a prototype plant at sea in 1989, and today, three Swedish Gotland-class boats are each fitted with two adjunct, 75 kilowatt Stirling Cycle propulsion units that burn liquid oxygen and diesel fuel to generate electricity for either propulsion or charging batteries within a conventional diesel-electric plant. The resulting underwater endurance of the 1500- ton boat reported to be up to 14 days at 5 knots. Large power Stirling Engines are difficult to develop as the sizes required for effective heat transfer from heat source to the working fluid become very large. Hirata Et.al have shown that a 20000 Kw equivalent Stirling Engine for propulsion needs of a large cargo ships needs to be at least twice the length of a comparative Diesel Engine which makes its application prohibitive for propulsion applications at present. However in the range of 2-5 KW its compactness and ease of operation makes it attractive for use as a WHR unit to charge batteries in small ships, which can later be used to supply power during harbor thereby eliminating the release of exhaust emissions in harbor areas.