New project, semi internal combustion atmospheric engine!

[John Hill]

Yep, that's right, semi internal combustion atmospheric engine!

The idea is a basic 'flame licker' atmospheric engine but in lieu of a big flame there will be just a small pilot light while just inside the valve port there will be a wick fed with a volatile fuel (petrol maybe).

The theory is that the valve will open at the top of stroke in the normal way and the pilot light flame will be drawn in to ignite the volatile fuel  resulting in a  flame right inside the cylinder.  As the piston nears the end of the down stroke the valve will close and the flame will be snuffed out.  The gases will then contract and the piston will be driven upwards by atmospheric pressure in the normal way.

The cylinder will have a pressure release valve which will open as the piston comes up and the exhaust gases will be pushed out.

Hopefully the engine will be more powerful as all combustion will take place within the cylinder and it will use less fuel as combustion will not be continuous.


But will it work?    Time will tell!

Sorry, no drawings.

[Arbalist]

I'm not even qualified to guess whether it will work or not but it sounds good!
Not sure about the petrol though, would alcohol work instead?

Many folks have problems getting their flame lickers to run so if it works this could be a viable alternative. Look forward to see what other folks think of your idea John.

[John Hill]

Maybe not petrol but it has to be something that ignite really easily and wont get blown out by the incoming air.

[vtsteam]

I like it John! Always want to see alternative stuff tried. Makes life interesting!

But you'll need excess air after the pilot light to give enough oxygen to burn your volatile fuel. The pilot will use a lot of it up.

Prior to spark plugs, wasn't there something similar for ignition?

[vtsteam]

Also if you increase the temperature inside the engine you need a corresponding increase in cooling rate to utilize it, otherwise the engine will mostly just run at a hotter average temperature. The trick is to increase running differential -- which can be done either by more heat, or faster cooling. But they must be matched, or the average only changes and the power output doesn't increase as much as expected.

[vtsteam]

I was trying to think why flame lickers run best once heated up, then.

Maybe, it's the usual air cooling -- the hotter the engine the more differential of the fins to the air -- the faster the cooling heat exchange rate.

Or, could be the opposite, in a very weak engine -- so little heat available that air cooling is overkill. I guess it depends on the engine which it is.

[S. Heslop]

I was trying to think why flame lickers run best once heated up, then.

Maybe, it's the usual air cooling -- the hotter the engine the more differential of the fins to the air -- the faster the cooling heat exchange rate.

Or, could be the opposite, in a very weak engine -- so little heat available that air cooling is overkill. I guess it depends on the engine which it is.

I think I read once it's that when cold the water in the flame gasses can condense on the cylinder walls more.

[Stilldrillin]

I like your way of thinking John! 

David D

[fcheslop]

A similar set up was used on old gas as in town gas engines
Some flame gulpers need pre heating because condensation on the port face prevents them venting well
Polly enginering do a set of castings and a brief description is there catalogue page 23/24
http://www.pollymodelengineering.co.uk/sections/bruce-engineering/docs/Catalogue-oct-2013.pdf
cheers

[John Hill]

Thanks for the comments!

The cylinder will be water jacketed and I have toyed with ideas for cooling the piston.  I will probably pour in boiling water before starting.


Vtsteam, I did some experiments with a tea light candle under a glass tumbler to judge the rate that a single flame used up oxygen and I concluded that that particular wont be a major problem.

It will be interesting to learn what happens when air (including pilot light flame) is drawn at high velocity over the main fuel wick.  Perhaps I should design in a variable size inlet port.  Finding the best fuel may take some time.


I have not chosen a material for the wick and when thinking about it I came up with another idea.
If the wick was of suitable material it might stay alight for the entire cycle dying down to a smoulder when the valve closes and the oxygen is exhausted but flaring into full flame when the valve reopens and fresh air rushes in.  Hmmmmm

[vtsteam]

It's going to be an interesting project, to say the least! Looking forward to it 

[John Hill]

Someone tell me about glow plugs? What sort of glow plug would I need that would light the fuel air mixture being drawn into the cylinder?  As far as I know the model aircraft engine glow plugs operate on some principle involving catalytic processes and pressure but there is no pressure in an atmospheric engine.

(I actually glow plug is not what I want but someone did suggest it to me.)

[S. Heslop]

Sounds like it could be similar to how I imagine this engine works.

I'd love to find more information on this engine though, but what I think it's doing is igniting the fuel and then using the vacuum drawing the piston back in to turn the flywheels.

[Jasonb]

Thats probably a Crossley which was an Otto Langen made under licence. It does indeed use a small flame that is drawn into the cylinder to ignite the gas and gravity plays a big part in helping the piston drop back down to start it all off agian. Speed is controlled by a valve on the exhaust which adjusts how quickly the piston decends, there is a ratchet arrangement on the gear that engages with the rack that forms the piston rod so the crankshaft is onlt driven on the power stroke.

This is a video of first Otto which shows the pilot light being lit about 35 secs in.

Its been modeled in several scales, all but one have resorted to a spark plug hidden under the engine. The one that worked correctly was 3/4 scale and about 7ft tall. Its on my list to build some time but I'm not in a hurry to do it, drawings are available from the states but mine will be a bit larger.

J

[Stilldrillin]

Simon.

That engine is in the Museum of Science and Industry, Manchester.

I chatted to the guy, as he prepared and started up. Then, I was so mesmerised, I almost forgot to film it! 

Thanks for the better vid, Jason. 

David D

[vtsteam]

John, it's been awhile since I flew with IC glow engines -- all electric now. But as I remember it glow plugs were just a coil of very fine platinum wire the glowed when you put 1.5V through them, and once the engine started would continue to fire the engine without current.

I don't actually know if it's caused by catalytic combustion, or just the tendency of a fine wire to keep glowing when heated. But I imagine most other metals would have oxidized quickly. Don't know if they needed pressure to work. Sorry. Anyway, they worked, and are still available to try.

[John Hill]

Thanks vtsteam,  I dont really like the idea of using a glow plug but it is something that came to mind when I realised that the engine might run with a constant ignition source.

[Jasonb]

You would be better off looking towards a "hot bulb" than a glow plug. These are basically a heated element sometimes using a small blowlamp if using liquid fuel others take a feed from a engines gas supply wich would work if running the model on propane or butane. Unlike a model glow plug these will stay hot enough to ignite your fuel when exposed to it. These were used on a lot of early gas engines.

Take a look at the models Finds builds, you can see the miniature lamp that heats the element.

http://www.findsminimodelhotbulbengines.dk

[John Hill]

Jasonb,  yeabut, hot bulb, glow plugs, hot tube and such ignition systems operate when the mixture is compressed.  In the proposed atmospheric engine the fuel air mix will not be under pressure.  The old very low pressure gas engines used a pilot light behind a sliding valve,  that is not exactly what I am contemplating but it will be a pilot light at least to the stage when I get the engine running.

[Arbalist]

Glass fibre is good for a wick when you get to that point John.

[John Hill]

Thanks,  real glass fibre or the chopped strand mat?  I am not sure where I would get real glass fibre from..

[Stilldrillin]

John.

Look for stove rope, on Ebay.......

David D

[DMIOM]

Thanks,  real glass fibre or the chopped strand mat?  I am not sure where I would get real glass fibre from..

I guess its a bit like copra, so maybe from a tree?

[John Hill]

David, stove rope, thanks!

DMION, I know a shopping mall that has fibreglass palm trees in the public areas, perhaps they would have the correct type of coconuts for glass fibre copra!

[Arbalist]

Nice range of sizes:

http://www.wickstore.com/Departments/Fiberglass-Wick.aspx?sortorder=1&page=2