Maybe, the problem with vacuum, flame eater, atmospheric engines?

[John Hill]

Maybe, the problem with vacuum, flame eater, atmospheric engines?

Atmospheric engines under various names and configuration are popular home shop projects and many seem to be a real challenge to get to run.

One of the popular types is the 'flame licker' where a port opens and hot gases are drawn into a cylinder then the port closes, the gases cool and while contracting atmospheric pressure pushes the piston down.

So lets look at this for a moment, the port opens at or near bottom dead centre and hot gases are drawn in as the piston goes 'up', the port closes near the top of stroke and the gases cool to produce the 'power' stroke.

But hangonaminute! As soon as those gases start to get drawn in they contact the cool cylinder walls they start to contract, ditto for the gases that contact the piston head. Therefore by the time the piston gets to top of stroke we have cold, contracted, gases all around the cylinder and near the piston, around the cylinder head too if it is cooled. Obviously a large proportion of the gases in the cylinder are already cool and take no part in the power stroke. If the engine was turning slow enough presumably all the gas would be cool at top of stroke and there would be no power to be had at all.

So how to fix this? Maybe a partial fix would be an insulating sleeve or liner to the cylinder geared to move and cover or uncover the cylinder walls according to crank position.

Bottom of stroke, sleeve right down, gases are starting to be drawn in.
Near top of stroke, most of the gas is still hot, sleeve moves up to expose cool cylinder walls, gases contact cool cylinder walls and contract for the power stroke.
Near bottom of stroke, sleeve moves down.

Now it might appear that this scheme would have a few drawbacks, and I can see a few.

For example the piston crown and cylinder head are not shielded, maybe it would be better if they had insulated surfaces and take no part in the cooling at all?

Friction, there would be an unavoidable increase in friction.

Something to think about?

 

[fcheslop]

Hi,definitely some thing to think about but as you say friction is a killer for these engines.It maybe an idea to use stainless steel for the cylinder as its a very poor heat conductor and expands very little and graphite/ceramic for the piston for the same reason but also keep the flame path as short as possible and also use a valve to exhaust as the piston comes back to T.D.C to reduce any compression.These are the ideas I'm playing with on a boxer build i intend on doing but you can also see them on many other designs.
The port on my engines open just after TDC and closes after 120 degrees of crank movement in a clockwise direction.
Another problem area is the that the flame needs to be bushy to prevent cold air been drawn in with the hot so the flame really needs to cover the complete port.
Theres some good info on Jan Ridders site just my two bobs worth
cheers Frazer

 

[John Hill]

Hi Frazer, as I see it what is needed idealy is highly conductive cylinder walls, piston crown and cylinder head, for the power stroke but insulated for the induction stroke! :-\

 

[fcheslop]

Hi John, I am no expert on these engines and agree with the idea but think that friction will be the problem as they produce very little power .Its nice to think things out are you planning on building one.
kind regards frazer

 

[John Hill]

Thanks, I have a feeling they produce too little power because so much of the gas is cold before the port closes.