vapour carburetor

What risk of flash back explosion might exist by adopting a glass jar petrol vapour carburetor? The engine in question is 1 inch bore, 4 stroke, with Hall effect ignition operated at crank speed. Petrol vapor will be drawn to the air inlet of a Nemett designed barrel throttle carb through a clear plastic tube. Of concern is possible leaky valves, valve overlap period, valve timing events in general, and also the extra spark in the valve overlap period. Thanks in advance for any comments. Patrick Cubbon

Have you seen the carbs made by Jan Ridders? They are glass cylinders or glass end plates.

**LINK**

http://ridders.nu/Webpaginas/pagina_1-cilinder_glas_4takt/1cil_glas_frameset.htm

I've run a couple of my engines on quickly knocked up vapour carbs when I was having flooding problems did not even think of blowback. Seen plenty of other engines running with them and all seem OK. The propane ones are more likely to singe your eyebrows!

Thanks to Brian Sweeting and JasonB who suggest experience with this form of carburation presents little risk. The problem engine was given part finished as a challenge to complete. Numerous adjustments to the carb and ignition timing failed. However, the plug needs deepening to ensure the spark is within the chamber, then, combined with petrol vapour success may be the prize? If not it is back under the bench! Thanks for the mention of Jan Ridders and his web link.. Patrick Cubbon

I have run a Hit and Miss (RLE) engine on a vapour carb and like Jason never gave blowback a thought, the engine ran OK with the setup, a air bleed in the intake line helps with the running. Mike.

If really concerned, a short section of fairly large diameter pipe stuffed loosely with wire ought to serve as a flash arrestor, it would both cool and slow a flame front.

There should be no real problem as a surface carb is not a pressure vessel and has a pretty much unrestricted airflow through it so I imagine the worst case would be a loud >pop<

Neil

I supose potential is there if the fluid level gets really low. Back in my RC Heli flying days we carried ot an experiment with a used up 4L 30% nitromethane fuel bottle... obvious dregs tipped out, sat bottle on ground and applied a lit match on the end of a pole - instant huge flame out of the neck of thing 2-3 feet long. Self evidently more dramatic due to the nitro.

pgk

Puny!

As a teenager I fitted a meccano gear wheel to the end of a butane canister and improvised a flame thrower capable of 10-foot flames. Probably was NOT a good idea to ry bit out in the kitchen...

In these days of paranoia I won't detail my other teenage misdeeds, but there were some big bangs

Neil

I knew some large girls too...

pgk

Presumably, the concern is that in the event of a"backfire" there would be an explosion closely followed by flying glass particles.

(In a former life, I exposed a glass filter/agglomerator bowl, used for 5 -10 psi, to 60 -70 psi as an air bell to reduce fuel pressure fluctuations, and lived to tell the tale! )

Does the chamber have to be glass, other than to view the level? Metal would be stronger, and less likely to become shrapnel.

Neil's suggestion of steel wool as a flashback arrester is a good one, also it might serve to revapourise any fuel that condenses en route to the engine. Possibly just a little copper gauze would suffice for both functions?

Howard

MichaelR - air bleed in the intake - a sensible idea

Neil Wyatt - wire mesh as a flash arrestor, a good suggestion thanks, reminder not a pressure vessel. Flame thrower! I am older than you, in the 50's gunpowder ingredients could be purchased from the chemist - my friend was able to fire ball bearings from a small brass canon, me - lit some powder in the fireplace (Father not aware).

PGK - 2 to 3ft flame out thanks for the warning.

Hi Howard - Yes, I have a copper tank that could be used though I like to see what is going on with petrol levels. Wished to add a picture of the problem engine for general inteterest but did not succeed. I see MichaelR managed with his photo.

I've just plumbed an RC "klunk" tank the opposite way round when needed but a nice little jam jar does look mor ethe part for display.

Have a look at this for how to add a photo of your engine

And in the 70s, along with other useful products.

Neil

My RLE Running on Vapour. Mike. https://youtu.be/bNx0TpJKulk

Edited By JasonB on 16/08/2018 19:25:44

Hi Jason, Many thanks for sorting my video out, much appreciated. Mike.

That's a poor way to treat a cleric

Problem engine, thanks JasonB for photo guide input, quite a bit of time for the result to appear.

David standing - canon/cannon that really provoked more than a smile a real laugh!

Will be pressing on with a vapour bottle, the photo shows petrol supply to a Nemett carb. on the other side.

Patrick Cubbon.

It might help some readers to know that a vapour carburettor is also known (historically) as a surface carburettor. As distinct, in pre WW1 days, from a spray carburettor. Several early cars had them, including Lanchester, and a few motorcycles. But the latter have not survived well as a minor spill usually meant a major fire. Especially if the ignition was by hot tube.

Cheers, Tim

That sure does 'cut the mustard'

MichaelG.

Being a surface carburretor, how about following the prototype ones and drawing the petrol vapour from above a felt pad that was moistened by the petrol?

Also lessens the risk of mixture variations caused by vibration disturbing the actual surface of the fuel.

Howard