The Stirling EngineRobert Stirling invented the Stirlingengine in 1816. At the time he was a Scottish minister. Stirling engineswere the safest engines made during that time period that would not explodelike a steam engine could.
The Stirling engine would not explode becausethe pressures could not be elevated to that to such a high level. The machinesimply stopped when the heater section failed from thermal stress or imperfectionsin the material or manufacturing process. So from that day on there wasa better, safer way to produce power, far superior than that of a steamengine. A Stirling Engine is a mechanical device,which operates on a closed looping thermodynamic cycle. Different temperaturelevels cause compression and expansion of the air or steam, which causesthe piston arms to move back and forth keeping up with the changes in theinternal pressure. The flow of the steam is controlled by changes in thevolume of the hot and cold spaces, without the use of valves.
The Stirling cycle can be is still appliedto day in common appliances such as a refrigerator. The heat cycle whenapplied to a heat cycle can produce cool air. This will occur when workis done on the Stirling device, and the heat energy is discarded into theroom. The heat energy that came from the Stirling cycle would be take fromthe inside of the refrigerator therefore making it cooler on the inside. In 1876 Rev. Stirling wrote in a letterabout his brother James, who had just died, “.
. . These imperfections havebeen in great measure removed by time and especially by the genius of thedistinguished Bessemer. If Bessemer iron or steel had been known thirtyfive or forty years ago there is scarce a doubt that the air engine wouldhave been a great success. . .
It remains for some skilled and ambitious mechanistin a future age to repeat it under favorable circumstances and with completesuccess. . . . ” Rev. Dr.
Robert Stirling (1790-1878) from “Stirling Engines”by G. Walker. Robert Stirling applied for his first patentsfor this engine and the economizer in 1816, only after a few months ofgetting nominated as a minister at the Church of Scotland. Sir George Caleyhad devised air engines previous to this time and other devices calledair engines were known as early as 1699. Steam engines began to carry abad name along with it because they were so dangerous. Air engines wereso safe and they operated on completely different principles.
The”economizer” or regenerator has come to be recognized as a most importantpart of the patent that Robert Stirling received. This patent was so outstandingbecause of the fact that it predated much of the study of thermodynamics. Some historians believe that the reason for Robert Stirling’s efforts atsuch a device were driven by his concern for the working people of hisparishes as steam engines were being used extensively in that area andtime period. Because of the lack of strength in the materials availableto construct, they would frequently explode sending shrapnel, boiling water,and steam at the people working nearby. After the years the gasoline internalcombustion engine has taken over.
The reason this occurred was becauseof the time it takes for a Stirling engine to heat up enough to get moving. Lately with all of the problems with the environment a need for automobileengines with low emission of toxic gases has revived interest in the Stirlingengine. Some Stirling engines have been built with up to 500 horsepowerand with efficiencies of 30 to 45 percent. The common internal-combustionengine would have efficiency in the range of 20 to 25 percent. One of the fastest moving technologiesis that of composites. These materials have a type of plastic make up alongwith other properties.
The strength of this type of material is superiorin nature and for the purposes of a Sterling engine, I feel that it wouldbe perfectly suited. They have already begun to experimentally replacecertain motor parts in the internal combustion engine, such as the pistons. The advantages of this would be that the weight of internal parts wouldbe significantly lighter and therefore able to run at higher speeds. Anotheradvantage would be that the heat developed inside the engine would haveless affect on the components because composites react, (shrink and expand)less that a metal would. Lubrication also plays a huge part in engineperformance. If all parts slide together easy than the total force putinto overcoming friction would be reduced.
Bearings and other parts wouldalso play a large part in reducing friction. The design technology of sterling enginesover the years has changed very slowly. Over the years the materials haveslowly began to change, what was once a wood wheel is now machined outof steal. The main theory of the Sterling cycle has remained the same,but because of its incapability to be convenient when placed into a car,the Sterling engine has never become a huge success. This probably explainswhy the manufacturing process has never moved into a mass production orand assembly line operation of larger sized engines.
The model industrythat produces them, as toy is probable the only type of company that doesmass-produce them. Because the parts for the Stirling engine are fairlyeasy to machine, the materials are common, and fairly inexpensive, an assemblyline type of production would be fairly easy and inexpensive to set up. These are the 2 basic design types; thetwo-piston type Stirling engine is shown to the left. A space above a hotpiston is always heated and the space above a cold piston is always cooled. The displacer type Stirling engine (the one to the right) has a space abovea displacer piston, and it is always heated by a heat source. A space belowthe displacer piston is cooled always.
The displacer piston displaces hotair and cold air. The 1900’s brought on a time of industrializationand few things were still made by hand. In this age Stirling engines couldbe built bye assembly lines but Henry Ford had already began productionof his model T Ford, which used an internal combustion engine. This prettymuch killed the need for the Stirling engine. During this these old timesprototypes were almost non-existent except for that of a seldom made model. The reason this occurred is if a “prototype” was made it was probably putinto use not just set aside whit the actual models were getting manufactured.
Before this time if somebody wanted something they had to build it forhim or her self, or they would have to find someone to build it for them. This explains why there were very few Sterling engines that were similarback then. Most parts were built by hand which explains the wooden flywheel. Because the cost of the part presently used to make it are so cheep andthe parts are adequate to the demands of this engine.
If I was the designer of the Stirlingengine and I had the technology of today to help me in my work I wouldhave to make it out of composite products or at least a good portion ofit. The Sterling engine in itself if very safe and the simple facts thata cleaner fuel that is being burned will also reduce emissions making ita better engine for the environment. To increase power and make it runfaster I would add piston rings to the piston to give it a tighter seal. To reduce friction in the flywheel I would make sure bearings were placeron the axle and make sure they were oiled properly.
Another was to makethe engine move faster would be to add some wings or flattened metal sheetsto the cool piston case in order to increase surface area allowing it tocool even faster.
