Does Oil Viscosity Impact Low Temperature Stirling Engine Performance?

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Discussion Overview

The discussion centers around the impact of oil viscosity on the performance of low temperature Stirling engines. Participants explore various design considerations, specifically addressing whether or not to lubricate the working piston, and the implications of oil viscosity on engine efficiency and functionality.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses concern about a recommendation against oiling the working piston, suggesting that while oil is viscous, it may not be detrimental enough to warrant running the engine dry.
  • Another participant notes that the RPM of the Stirling engine is low, indicating that it may not be intended for serious applications, but rather as a toy for educational purposes.
  • A different viewpoint highlights that oil can significantly affect mechanical performance, mentioning that even light oils can thicken over time and attract dust, which could hinder performance in precision applications.
  • There is a mention of conflicting advice between different designs regarding the use of oil, with one design recommending a thin coat while another advises against it.

Areas of Agreement / Disagreement

Participants express differing opinions on the use of oil in Stirling engines, with no consensus reached on whether oiling is beneficial or detrimental to performance.

Contextual Notes

Participants note that the effects of oil viscosity may vary based on environmental factors such as humidity and dust, and there is an acknowledgment of the potential for conflicting recommendations in different engine designs.

Who May Find This Useful

Individuals interested in building Stirling engines, those studying mechanical performance in low temperature applications, and hobbyists exploring the intricacies of engine design may find this discussion relevant.

MacLaddy
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I have been doing a bit of research on building a low temperature Stirling engine, and I came across this website,

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_koffiekop_jan/koffiejan_frameset.htm

The design on this website looks nice, and I would like to give it a go (after I build a simpler model), but I have my doubts about the following statement within the instructions.

Never oil the working piston in the cylinder! Even very thin oil is more or less viscous and increases the friction. Mind that the power of this type of Stirling models is very low so little friction can be fatal.

Any thoughts on this? I understand oil could be a bit viscous, but it wouldn't seem to be so dramatic that you would want to run this engine dry.

*EDIT* Be sure to hit the "English" button at the very top of the webpage.
 
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It looks cute, but the RPM is unimpressive, to say the least, as those props want to turn around 5-6 thousand rpm to generate any appreciable thrust.
 
Cyrus said:
It looks cute, but the RPM is unimpressive, to say the least, as those props want to turn around 5-6 thousand rpm to generate any appreciable thrust.

Well, I don't believe it's designed to be anything more than a toy. I personally want to build it just so I can get a better understand of the inner workings of a Stirling. Plus, it runs on a coffee cup. I mean how cool is that?

I will be starting to build this one in a day or so,

http://www.physics.sfasu.edu/astro/courses/egr112/StirlingEngine/stirling.html

but I am still curious about the "To oil, or not to oil" situation. This one calls for a thin coat of oil, whereas the other one says not to use it.
 
Last edited by a moderator:
oil can have a significant effect on mechanical performance. even a very light oil will slowly thicken over time, grab dust from the air, and change with humidity. Thats why most dial gauges, watches, and other precision mechanicals use no oil. In some of our precision pneumatic equipment, just the residual oil from a finger will prevent its function.
nice links, but the english conversion didn't change the main text
(I was bummed...looks interesting...must learn dutch now...lol)

dr
 

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