hot air engines

[brickyParticipant @bricky]

Having received a book on Stirling engines, I am becoming interested in building one.I can't find an explanation of whether air in the hot cylinder is contained or needs replenishing by a valve.I can't see one on any of the engines in the book,or dose the air enter with the piston rod.Until I have got my head around this I can't read on.I know there are experts in this field amongs members and I need your input.

Frank

[brickyParticipant @bricky]

[SillyOldDufferModerator @sillyoldduffer]

They're contained.

I've built a Jan Ridders' Coffee Mug engine and the design has no valves. Also have looked at a variety of other designs and none of them had valves either. In theory the same air is used over and over again; it's expanding and contacting within a closed cycle that works the piston.

Possibly a full size engine would need a valve to stop a vacuum forming as it cooled down due to some air having leaked out whilst hot. I think small engines leak enough on their own to equalise pressures without needing a valve.

The engines work more efficiently if the working fluid is pressurised but I've not seen a model engine going to those lengths. That type would need a valve to keep the engine charged, I don't suppose a well-made engine would leak much – the operating pressures are low.

Dave

[Ian S CParticipant @iansc]

Hi Frank, welcome to the world of Stirling Engines/hot air engines. As Dave says the engines are sealed (as well as you can), the main thing that limits success is friction, with a motor with B***** all power, there is no use taking up 1/2 of B***** all with friction.

Some motors have a snifter valve to make up pressure from the small amount that leaks out, I have not found that necessary in any of my little motors. Other types such as the Robinson use an air valve to govern the speed.

This is my smallest motor, power piston 3/8" bore x 1/2" stroke, made from bits and pieces found in the workshop.

Ian S C

[JasonBModerator @jasonb]

Just to clarify the "air valve" Ian mentions that is used to govern the speed of the Robinson engines does not draw in new air it is simply sucked into the path of the contained air as it moves from one cylinder to the other restricting the flow rate and therefore speed.

[brickyParticipant @bricky]

Thanks for replying and clarifying my question.When I have finished the i/c Rockerblock engine I will have a go at making a starter engine .

Frank

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