Shane Pomeroy engine

[Tom Booth]

I'm no expert but shouldn't a dynamometer be applied to the shaft rather than the outer rim of the flywheel?

I have a feeling he may be underestimating the actual output as it is much more difficult to break at the shaft than at the outer diameter, I think, isn't it?

A quite impressive engine in any case IMO. I especially like the wheelbarrow-like maneuverability.


https://youtu.be/-izeccWHhuI

[VincentG]

Shane seems like a clever guy I think he worked that out in his calculations.

Very cool design that I think would work far better with much less regenerator mass as Stephenz has shown us.

[stephenz]

I was tempted to ship some of the ceramic I picked up in exchange for him taking thermocouple measurements in 3 different areas of the regenerator (left, middle, right).

[Stroller]

Shane posted up another episode on his Mk4 engine recently. He achieved 87W, which is around half of what he thought it could do with some refinement. It's not a huge amount, but it doesn't use much woody fuel to achieve it, and it's a very quiet engine, which to my way of thinking, are the two biggest reasons to struggle with power production Stirling engines instead of just buying a Honda suitcase generator.

https://www.youtube.com/watch?v=GB0cd3ZzF3w

[VincentG]

He has an incredible talent for designing and assembling large engines with those cnc cut plates. I wish he would drop in on this forum to discuss the thermodynamics and kinematics of his engines. The current engine for example uses a common crank pin like an alpha, but with opposed cylinders. So unless I'm missing something, the cycle is severely limited.

[Stroller]

I think you can tell from the stretching/contracting of the spring and the more-than-90-degrees angle of the con-rods in the 'slow motion' section of the video from 3:33 to 3:42 that it's not so simple to work out the phasing. The way this engine is laid out is not so different from the Essex engine you posted about. The innovation is using diaphragms instead of pistons, which enables the much greater surface area of the heating/cooling chamber manifold.

By the way Vincent, maybe you could add a cooling fan to your Essex engine to overcome the heat saturation issue, like on this original:

https://www.youtube.com/watch?v=rN1cLc17U6I

Shane built a cooling paddle fan into his engine too.

[Stroller]

This Essex twin also uses a common crank pin for both ends.

https://www.youtube.com/watch?v=9_dRBNi28kw

[VincentG]

Totally different linkages for the Essex single and twin that maintain correct phasing, and it's a Beta with more flexibility in phasing too.

I've watched his engine run for a while in slow motion and the piston movement is very strange. The high pressure blow occurs too soon BTDC but unfortunately there's no easy way to fix it without major rethink to linkages.

[VincentG]

I mean no disrespect to Shane at all btw. He is putting in alot of effort with these engines and has a very entertaining presentation. It would be great to have Shane on the forum.

[Tom Booth]

Totally different linkages for the Essex ...

Maybe off topic here, but since the video of the Essex was posted here, it provides a good view of the "negative dead space" as both power piston and displacer piston move to the left together during heating/compression.

I slowed down the video and tried to mark the starting point where the two pistons move to the left together, the power piston "following" the displacer for what looks like possibly 3/4" more or less?

https://youtu.be/X0XDTmcnrRg?si=fv8JoocN473Db4Hl

[Stroller]

a good view of the "negative dead space" as both power piston and displacer piston move to the left together during heating/compression... the power piston "following" the displacer for what looks like possibly 3/4" more or less?
https://youtu.be/X0XDTmcnrRg?si=fv8JoocN473Db4Hl

Nice work with the video Tom. Maybe this is why the Essex single makes around 745/45 = 16.55W while Shane Pomeroy's engine makes around 5 x more with a bit more calorific input.

On the other hand, the Essex twin makes comparable power with maybe slightly more input. Hard to tell really. Graceful antiques versus new prototype design and build: take your pick.

[matt brown]

I've watched his engine run for a while in slow motion and the piston movement is very strange. The high pressure blow occurs too soon BTDC but unfortunately there's no easy way to fix it without major rethink to linkages.

Anyone know if Shane has a video describing how he arrived at this design ?

Indeed, strange motion and diaphragm bell cranks are placed wrong (see video comments). However, there's something sweet about his crank configuration that probably slipped by everyone, except Vincent.

[matt brown]

slingshot.JPG (368.5 KiB) Viewed 105 times

Here's the basic cat and mouse piston chase that I've posted before. This is the alpha flavor (not to scale for clarity) and there's various ways to game this concept. Essex design has displacer in lieu of cold piston (this graphic) which results in a rather unique hot end gamma. I always wondered how the Essex works, now I know.

[Stroller]

I'm obviously missing something because I don't understand the problem with the phasing on Shane's engine. The cold end diaphram leads the hot end diaphragm by around 90 degrees as far as I can tell from a rough reckoning.

[VincentG]

Near as I can tell, the angle between the long connecting rods and the bell crank causes a folding and unfolding that loses motion so the actual stroke is shorter than the crank throw. It does add dwell that can be useful.

I think the issue is compounded by the piston's crank arm being shorter than the input crank arm. This means the actual stroke is shorter than the crank throw, in this case exaggerating any issues further upstream.

Maybe I'm way off base here but thats How I see it. If you look at the movement of a traditional 90 degree v twin it seems very different from that.