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The Return of No. 83, a Hot Air Engine
vtsteam:
I think experiments with hot air engines often lose sight of the fact that they have an advantage over IC and steam in that they can use any form of heat (unlike IC engines) and don't require the danger, operational watchfulness, and expense of boilers (unlike steam engines). Most experimenters seem to have in mind an ultimate goal of fueled transportation, and use gas fossil fuels to experiment with in hot air engines. They search for efficiencies with engine configurations that favor these fuels.
Hot air engines can run on non-fossil biological solid fuels, including waste like sawdust, nut shells, rice husks, mulch hay, leaves, pine cones, branches, chips and waste wood, and they can run on solar heat, and waste heat from industrial processes.
Stationary uses where some fuel or heat source is inexpensive and available is a niche use that they seem eminently suitable for to me, rather than transportation, which is better suited to fluid fuels and electricity.
I don't believe hot air engines will ever be able to replace high power density fossil fueled IC engines. But as stationary engines they can utilize high availability local fuels that IC types absolutely can not. And so provide a low cost power source, and a different definition for the concept of fuel efficiency. That's been my interest all along.
nickle:
They are fascinating things... I still have not built one despite them being the main reason for buying my first lathe 20 years ago! I have the beginnings of a fizgig on the shelf in my shed. The surface area for heat exchange thing is an interesting aspect of Stirling Engine design... I wonder if some sort of ribbed displacer cylinder would help... but then you get more drag from a larger surface area and the thermal mass of the cylinder can become an issue. As you say, there are so many variables. Aside from the ability to use low energy density fuel, I think one of the most interesting aspects of these engines is the ability to use waste heat. there are endless industrial and domestic processes that have heat disposal as a problem... including a Stirling cycle in that process allows some energy extraction to happen. It wont always be optimal temperature differentials between the hot and cold sides, but its waste heat so efficiency doesn't have to be the main driver. Have you got a copy of Edgar Westbury's "A Practical Treatise on Hot Air Engines"?
vtsteam:
Hi Nickle! :beer: I do have Westbury's treatise, also a lot of old Model Engineers, which I've collected over the years. Coincidentally I have just been reading yesterday about Westbury's last engine, a Robinson type, published a couple months before he passed away. And a then an editor's note, about a year later:,
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I find this not only a little sad, but also somewhat mysterious, and it makes me want to build that engine just to see for myself whether this is true, or not.
nickle:
Isn't that design in the book? that would be a shame as i was eying that build off for a some day project.
vtsteam:
I'm not convinced that it doesn't work as drawn. But if it doesn't, it would be instructive to make the changes to get it running. Part of the fun actually, and a place to learn things.
I will give one interesting side note (clue). Robinson engines used a perforated displacer with regenerative material inside. The Westbury design does not, and E.T.W. seems not to have realized this, and had drawn a sealed hollow conventional displacer.
Still, I believe it should work that way, as well.
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