Are piston rings absolutely necessary?
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Posted by: D.Taggert

04/18/2006, 19:48:27

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I am requested to evaluate a conventional piston engine design that claims "no piston rings." I say it's impossible, but wondered if anyone has ever heard of this being done successfully or if it is remotely possible. Your expert insights will be invaluable to me. Thanks.







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Re: Are piston rings absolutely necessary?
Re: Are piston rings absolutely necessary? -- D.Taggert Post Reply Top of thread Forum
Posted by: james25

04/19/2006, 08:33:55

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yes it is plausible but piston rings are there to keep a tight seal between the piston and the cylinder wall therefore increasing horsepower and fuel efficientcy but i have seen a motor with a special type of piston with a little groove poking out of the piston to replace the piston ring







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Re: Are piston rings absolutely necessary?
Re: Are piston rings absolutely necessary? -- D.Taggert Post Reply Top of thread Forum
Posted by: Kelly_Bramble Administrator

04/19/2006, 08:29:12

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Interesting question, I am aware of a miniature compressor which does not use piston rings. The compressor is used in a tiny refrigeration unit used to cool electronic components. I don't know what the materials where, however I do know that the tolerances where very tight. Clearance between the piston and sleeve was .0002" nominal.

The answer is "yes" it is possible. The question you should realy ask is "is the design adequate for the intended application?

In any evaluation of a technology you should test, test and then test some more.







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Re: Are piston rings absolutely necessary?
Re: Re: Are piston rings absolutely necessary? -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: randykimball
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04/19/2006, 23:23:52

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"model" airplane engines (that I have experienced) do not have rings. However, as diameter of the piston increases the thermo expansion ration begins to make it necessary to fill the compression gap between the piston and the cylinder with some device as this gap size increases to prevent interference fits at idle through overheated temperatures.

To truly (to me) design a reasonable sized internal combustion engine without some sort of compression rings one would need to design a piston and cylinder with nearly identical thermal expansion. This is tricky if the piston has a rod bearing and a solid crown with support ribs. Also, many modern pistons are usually designed not round (because of the above different thermo masses) until they are at operating temperature.





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Modified by randykimball at Wed, Apr 19, 2006, 23:26:30


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