Another Simple Hot Air Engine

Coming along nicely ...... it looks like a piece of modern art which should be in the window of an expensive London gallery! 

Hopefully it won't end up as just an ornament!

Made the little block to go at the top of the displacer rod, there will be two flat rods either side going up to the crank pin with the piston rod sitting between.

Made a piston from some reclaimed cast iron but somehow managed to take too much off - it would probably be fine for a compressor powered engine but not good enough for a hot air jobbie. Also as it would be difficult to get the small cross hole properly centred afterwards, I made another one from some aluminium rectangular bar which I drilled first for the wrist pin then turn down very carefully. The fit is rather good.

Next I made the aluminium piston rod from some recycled garden furniture (I could probably make a thousand of those from the masses of square tube I salvaged). Drilled the holes at the right distance then filed it to shape using filing buttons for the larger end.

Made some more bits, just a pair of simple link rods and a flywheel needed and that'll be the engine itself finished. Other than that I need to make some legs with a way to hold the 'heat shield' and probably another burner as the others I have are too weedy.

I'm still thinking there are too many places for a bad seal to stop this from working at all. But if that does happen, I can bypass those issues fairly easily by soldering a tube between the (un)plugged hole and the back of the power cylinder but it'll mean the bits can't then be disassembled.

That's most of the bits done, just need to connect them together with some proper fasteners and make a crank pin etc.

Ah, now I get it! Came together quickly, looking forward to the chugging ....

Quote from: Sanjay FAh, now I get it! Came together quickly, looking forward to the chugging ....

I certainly hope not Sanjay.

This is the sound Paul should be aiming for!

https://youtu.be/_3qiYZRrE6g?is=co_bS6ADz0Wtbv8D

  Graham.

I can't hear anything on your video.........must be that silent chugging 

Nice whispering engine Graham.

Made the little spacers and the crankpin today - what a ridiculously fiddly design I came up with  I put a meths flame under it but despite being pretty free-running there was no hint of life. While there could be a leak somewhere, once again I get the feeling that cooling is the issue and probably worse now that the engine is all above the flame. I put a few small lumps of brass on the bedplate and in no time they were too hot to touch. Even the flywheel was starting to get hot  . Maybe I should make a firebox for a burner and put some heat resistant mill board on top.

I also noticed (well heard really) that the block at the top of the displacer rod is just about tapping the brass bush whereas it was supposed to be about 0.5mm clear at its lowest point. That's easily fixed but it looks like lots of experimentation ahead elsewhere...

Can you hold it sideways to stop the heat getting to the engine so much? It would help test that there are no leaks and confirm the problem is the engine getting too hot.

Quote from: JasonbCan you hold it sideways to stop the heat getting to the engine so much? It would help test that there are no leaks and confirm the problem is the engine getting too hot.

Cheers Jason, yes that did occur to me as I burnt my fingers for the nth time - will give it a blast tomorrow.

An insulator block between the hot and cold end would help, I use Linen Phenolic on mine with a thin gasket on each side. You would need to adjust the thickness of the cold end block to accommodate the thickness of the insulator. You could  also cut fins into the block, I think that it has way too much thermal mass to ever work the way you have it.

Dave

Another thought is to add a deflector so the heat of the flame does not get to the frame etc. You see this on some of the full size engines where there is a plate to deflect the heat out the chimney and stop it going right up to the underside of the engine. Lid of a bean tin drilled to fit over the hot cylinder and clearance holes for the screws would do it, use the screws to hold it in place

The flat disc is for my Raab, the conical one for the Heinrici.

Quote from: Dave OttoAn insulator block between the hot and cold end would help, I use Linen Phenolic on mine with a thin gasket on each side. You would need to adjust the thickness of the cold end block to accommodate the thickness of the insulator. You could  also cut fins into the block, I think that it has way too much thermal mass to ever work the way you have it.

I was planning on putting a heat resistant sheet around the displacer near the upper end but hadn't worked out the means to hold it there. Re the thermal mass I figured that although heat would still spread throughout the engine it would radiate away and never get as hot as the hot end. Seems there's not enough difference as it stands though.

Quote from: JasonbAnother thought is to add a deflector so the heat of the flame does not get to the frame etc. You see this on some of the full size engines where there is a plate to deflect the heat out the chimney and stop it going right up to the underside of the engine. Lid of a bean tin drilled to fit over the hot cylinder and clearance holes for the screws would do it, use the screws to hold it in place

I don't claim a great mind but we were thinking alike... at 10 o'clock last night I was head down in the recycling bin rooting around for a suitable tin! Plum tomatoes trumped 'Chappie' and spent the night having a good soak. If I put the heat resistant sheet on top of the tin that might work even better...

Made a simple tin can furnace and put a sheet of heat resistant board on top (just covered one side as it wasn't drilled to fir the displacer. It made quite a difference to the amount of heat getting to the engine but there was still no sign of life.

Turned the engine on its side and tried again (also with a little heat protection) but it was still dead. I'll start looking into where it might be leaking and also want to eliminate some other bits of potential friction.