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For far to many years now I have had the germ of an idea for possibly a new variation of Hot Air Engine. I say possibly new, as I’ve looked and not seen anything similar, but that could just be me not knowing where to look. Now the thing is, I don’t have the engineering knowledge to even know if it will work, which is why I was wondering if you would like to cast your eye over it, or even have a go building one.

Like I say, it may not work, but it is an idea I have had since I fell in love with Hot Air Engines at a model show I was attending with friends back in the 1990s. My only attempt at making one to test the idea was an absolute failure. Not surprising really considering I was using my brothers MakerBot to build the parts. Way to much slope and bad joins for it ever to be a real working model.
The 3D Plastic Engine was going to be powered by Hot & Cold Water running through the two insulated sections of the engine. Without a well engineered piston it was never going to work. I think I made it more out of hope than anything.

I’m not looking for anything, it’s just a bit of fun.

The simple idea behind my engine is to do away with the crank arms and combine the piston and displacer. Like I say, not sure if it’s been done before.
Anyhow, in this version the piston is part of the top of the displacer. The piston gets its air pressure from another chamber with a displacer at the right place in the cycle to drive it. Now I was looking at four chambers, but maybe an odd number like three would be better.
By running feed pipes between different chambers and pistons the best order can be found. The Displacers are hollow to save weight and help them with inertia as they change/reverse direction.

I have attached some screen grabs from the old SketchUp design I did a couple of years back. It might explain things better than me. :)

Anyone out there interested in casting an eye over it? Maybe make it a Forum Build.

Regards
Helen x

Some more screen grabs...

So. Instead of using a displacer, you move the chamber between hot and cold. I don't see why not. Just that the temperature difference between hot and cold water is not going to make you any useful power. On top of that moving the entire chamber requires more energy than moving a displacer.

Aviator168 wrote:So. Instead of using a displacer, you move the chamber between hot and cold. I don't see why not. Just that the temperature difference between hot and cold water is not going to make you any useful power. On top of that moving the entire chamber requires more energy than moving a displacer.

Hi,
I wasn't sure about the water, it was going to be boiling in the top and ice cold in the bottom.
Looks like I left a bit of detail off, sorry.

The Chambers are the cream coloured tubes and are in two halves, as they are part of the two insulated (also cream coloured) water tanks.
The Green Tubes are the Displacers and are hollow to make moving them easier, although filling them with a mesh might be better. In the top of them is a hollow that is in effect the Engine Cylinder.
The Red Tubes are attached to the water tank roof and do not move, they are in effect the Piston Head. There is a thin tube down the middle of this that the hot/cold air from another chamber passes down through into the cylinder at the top of the displacer. The expanding and contracting gasses move the displacer.

Hope that helps.
Thanks for the reply!

Helen, the nearest I can come to something similar is the Ringbom engine (famous example in the modelling world is Tapper), in this type of motor the power piston is attached to a crankshaft, the displacer is not attached to the crank. The displacer has a thick rod that is actually a piston that operates the displacer as the pressure changes in the cylinder, I'v got three of this type of motor, and another that goes a stage further, in that it dispenses with the crankshaft, making it a free piston motor, using the like poles of two magnets as a spring for the power piston.
Ian S C

Hi, Thanks for the replies.
I have found one of the old sketches I did from many years ago, with that in mind I've made a Sketchup drawing that I hope will make things a little clearer.