Gallery, Projects and General > The Design Shop
Flame eater questions
NickG:
No problem Geoff,
Always try to offer advice on these as I know how frustrating it can be getting them to run! The only other obersvations I can think of at the moment are:
Try not bothering with any water in the hopper .... sometimes these engines (which you may think is contradictary to how they work!) need to get quite hot before they'll run! It's possible to get a quenching effect where the gases are cooled too quickly before the valve has closed!
Bearings and friction reduction measures seem good.
Aluminium on aluminium for piston / cylinder wouldn't be my first choice, because they tend to scratch easily giving a high coefficient of friction. However, if they are a very good fit and the friction is minimal there is no reason it shouldn't work, at least initially. I have to use oil on my Jan Ridders flame eater or it doesn't run. The oil helps both seal and prevent combustion products from adhering to the parts increasing friction massively. I use engine oil as it can cope with the high temperatures and is very thin when hot.
The port, now I have seen it looks about the right size to me.
The only other thing is, as I mentioned before, your valve is being forcibly opened rather than closed, it is good that your valve slides upwards away from the flame, but it may be better if the belcrank operated from the top of the cam, closing the valve for the required time and position rather than opening it. Also, make sure the elastic band isn't too strong, I suspect the farting noise is the valve lifting off its face which is desirable anyway, like a sort of automatic relief valve when the pressures equalise ... but you want this to happen very easily.
I don't think it's far off, other than above, what fuel are you using? I use denatured alcohol or industrial meths - a cleaner burning methylated spirits. Make sure your flame covers the entire port, if you draw in cold air it can scupper the whole thing!
Nick
geoff_p:
Thanks, Nick.
In no particular order:
I haven't been putting water in the hopper except when the whole thing gets too hot to handle.
Having tried 'nightlight' candles, gas cigarette-lighter, blowtorch and all else in between, I now have a source of Gel Fire in tin-can packages similar to nightlights. The carton lists the fuel as 'Alcohol Fuel' and 22gms each. At 2 Baht (4 pence) each, they are cheap enough for experimenting, though the flame is quite massive - it certainly covers the port.
Last night, in the dark, I was able to observe that the flame is blown away from the port by the exhaust air and because of the lump-of-graphite (AKA 'valve') above the port deflecting it, that often also blows the flame out. Watching a few YouTube videos I noted that many open the valve downwards so the exhaust air goes up-and-away from the flame.
So this morning I'm lowering the valve - it will now open downwards and close upwards. Which will, by coincidence cover your point about the cam forcing it closed. Checking the cam-lift, it looks as though the timing can be adjusted to suit. I hope!
Mind you, I may have to wait till after dark to see the blooming flame.
Geoff
NickG:
Geoff,
Good point there ... but, the valve might get in the way of the flame being sucked in this way around ... worth a try though and if it solves the other issue with the cam closing the valve rather than opening it, it may work,
Your flame sounds good.
With regards to blowing the flame around, they can be very sensitive to that ... on poppin, if you put the flame directly in front of the port it runs very fast, but then gets so fast it blows the flame out! On the Jan Ridders engine, Jan did lots of work to find the optimum flame position ... which is actually not in front of the port but to one side ... bit different as it's a side port on that though. It will not run at all with the flame in front of the port though. Try experimenting moving the flame around to many different positions if you can easily do so.
All of that said, if the engine in sucking the flame / hot gases in properly and the valve is closing at the right time, the engine should actually exhale (if that's the right word!) much air, only right near the top of its stroke with internal and external pressures equalise.
Nick
geoff_p:
I wish I had your analytical mind, Nick.
You are dead right about the 'lump' getting in the way of the flame. It looks as if there is only a tiny amount 'bending in' to the port, and that only sometimes. Mind you, when it does, there is a definite vacuum lock - as soon as the valve closes (turning the engine with my finger in the flywheel-spokes) it becomes very hard to continue through to Bottom Dead Centre.
Aha! Retard the valve-closing. Nada! Zilch! Nothing at all. not even a 'fart'.
Try something radical: I turned the engine 90 degrees and held the wood base in the vice so the hopper faced me and the port was vertical. With a candle's yellow flame I could see the flame sucking into the port quite strongly, so I swapped for a blowtorch (turned down to a very low flame) and suddenly I had power. A lot! But not for long as it threw/blew the valve off the engine after a few revolutions. But it had definitely accelerated away from my fingers.
So now I will rotate the cylinder-head 90 degrees and am rebuilding the valve gear to move sideways. Pictures to follow when I have made a bit more progress.
Geoff
NickG:
Geoff,
as soon as I read the bit about the vacuum lock I thought ... retard the valve closing ... then read your next sentence!
It sounds like it's almost there then, it's surprising how sensitive to things like flame position a lot of them are and I always thought a vertical cylinder would be better too. Poppin seems to run just sucking a little flame in, it runs best with the flame at a slight angle so as not to get disturbed by the residual air exhaling, but the other won't even try if there's the slights mis placement of flame or a flicker.
Nick
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