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Free piston engine


The Old Guy
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Without more specifics I'm afraid I can't help you out. Have you tried a search of the web?<P>"Free" piston engine can mean a number of things but I'm assuming your talking about an engine that used adiabatic expansion of a gas sealed with a piston separating the two "expansion" ends. These engines were basically low speed and relied on thermal expansion of the gas heated by an outside source to effect piston movement.<P>The process is theoretically very efficient but problems with heat transfer plagues the cycle. This same cycle (I think) is used successfully in space for pumping liquids etc. The cycle is attractive because of the sealed nature of the system and the reliability of the simple components involved.<P>If you can imagine a cylinder sealed at both ends with a piston floating in between, a pressurized gas is the working fluid and is moved from end to end through a piping system and associated valving actuated by the piston. You basically heat one chamber and then the other to get reciprocation. <P>This can be accomplished in space for no cost by spinning the engine so that each side alternates facing the sun (free power!). <P>There might be other members here with more engineering knowledge of this type of cycle than I. I think that it's fair to say the major manufacturers have tried every type of cycle including the compressed avocado engine (just kidding!!). If for no other reason than to patent whatever they might find useful.

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The free piston engines that I have any knowledge of are used to generate hot exhaust gases which are then used to drive the blades of a turbine. In this way you don't have the power loss of the compressor stage of a turbine engine. These free piston engines use a sealed end on one side of the piston which provides the "rebound" to cause the piston to move back towards the opposite end of the cylinder after combustion has taken place. A series of check valves allows charging of the cylinder and escape of the gases after combustion. I think they are still used in ships, and are sometimes called gasifiers. The ones GMC was working on were for a turbine engine in a state of the art semi truck.

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Mr. Chuck, Thanks for those interesting websites, really enjoyed them.<P>I'm a little surprised no one has mentioned the original 19th cent. free piston engines as manufactured by Otto & co.and others for a brief space which were the first reliable gas stationary motors.<BR> These were atmospheric non-compressing engines, I.E. the heavy vertical piston was attached to a long toothed rack which engaged a gear coupled to the flywheel with a one way sprag clutch, the cycle began by turning the flywheels which, depending on the position of the half speed cam would lift the piston sufficiently to admit a charge of gas and air thru a slide valve, near the end of this short travel another slide valve opened communicating with an open flame which ignited the mixture,said expansion forcing the piston and rack skywards until the rapidly cooling gases caused atmospheric pressure to draw the piston downwards engaging the flywheel clutch and thus transferring impulse and spinning the flywheels happily, this was the "power" stroke.<BR>I have restored one and the operation is really smooth although it's very wasteful of gas and does not produces much more heat than power.<P>Remember,the first Duryea wagon used a similar free piston engine until it's lack of power made J Frank discard it for a 4 cycle type. Carleton shocked.gif" border="0

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Old Guy,<P>Have you ever heard of the K Cycle engine, the engine itself was designed by an engineering professor at the University of Manitoba by the name of Christensen.<P>The engine had one running prototype produced installed in a (yuk) K car, I think that was supposed to be funny. The engine itself looked much like a six gun rotating barrel with a rhombic plate translating the piston movement into rotary motion. <P>The key feature of the engine was that it had an extremely long stroke with a very slow compression stroke. It was said that with this design the exhaust left the cylinder at 15 psi which meant it needed no muffler. <P>Torque was completely flat from 0 rpm to power peak, much like an electric motor. The engine itself put out about 20% more power per cubic inch of displacement than a comparable conventional 4 stroke engine in 1985.<P>The only problem with the design was the sealing of the rhombic plate (cam) at the rear of the engine as the large dia. made it difficult to seal. One prototype actually ran but as soon as power was applied it would blow the seals out.<P>When the patent ran out and the chief investigator died a small portable compressor/vacuum pump using the design was produced for use in remote areas. This design got around the sealing problem by placing two engines back to back, you could run either side for vacuum or pressure.<P>I worked with a number of Tool@Die makers who worked on the project and they all said it was a great idea waiting for technology to solve the seal problem. I've contacted the University to see what literature is available so I might write an article on it's conception.<P>Has anyone heard of this engine?

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Chuck, was this some kind of swash plate engine?<BR>they have been around since the late 19th cent. and were developed in the steam age.<BR>Get ahold of a book called "knights mechanical dictionary" a fairly common volume from 1872 that has been reissued, you'll be amazed at some of the"modern" engines and other devices that folks are constantly claiming as the "latest" developement.

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Stellite, your right the design is not that new or revolutionary. They were trying to get one mass produced on a large scale and revive the idea, to bad they had to shoot for the moon by trying to build a production engine. I'll try to get some photos when the Dean of engineering gets back to me, might have to hit the University library for more info. What I remember was from one article in the local newspaper.

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Chuck, I think I have a ratty old Popular Science mag with an article on the motor you describe along with news of a "freon"expansion motor, I'll go up to the attic later and look.

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Just got an e-mail back from the Dean of engineering at the University, it was as follows;<P>"We recently obtained some memorabilia from the K-Cycle. We now have <BR>one of the prototypes and some promotional descriptions. I seem <BR>to recall that Brian Lanoway, now with Standard Aero, was involved at <BR>one time. Another person was Don Fisher but I have lost track of him. <BR>Don Alexander, a former prof, was also involved. He is retired but <BR>still active. Another contact may be Ray Chant who still lives <BR>part-time in Winnipeg.<P>Personally I know very little about the project, although it was <BR>going on while I was at the University. My only recollection is <BR>when one of the test vehicles was propelled down the ME labs to the <BR>cheers of all involved.<P>All the best"<P>The test prototype apparently still exists so I'm going to go down to the University and get some digital photos just for fun.<P>If you could find the article that would be great Stellite, the project I believe took place around 82-85 I think.

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