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Unread postPosted: Sat May 16, 2009 10:33 am
Author: SPG
How big a hybrid are you thinking of building? Or to be more precise how much meths are you going to need to put into your chamber? I've got a vague idea involving spool valves, but if it's a small amount then a 3 way ball-valve could work and be much simpler, so because I'm feeling lazy I thought I'd ask before I hit Paint.

Unread postPosted: Sat May 16, 2009 3:20 pm
Author: daccel
I don't have any concrete plans yet, but probably .375-.75" barrel, with a small high mix chamber, if it's possible to do high mixes with methanol. Not more than a few cu in if possible, just to make life difficult :wink:.

Out of curiosity, I tried using starter fluid (ethyl ether, aliphatic naptha, co2... but doesn't give proportions) without any real measurement in my mini piston hybrid. Just sprayed a bit on the end of the schrader until it looked like there was a few drops sitting in it, put on the pump and forced the fuel through the valve with the air.

At first nothing, but after flushing a few pumps of air through, it fired. Then the interesting part, added a few fresh pumps of air without more fuel and it was able to fire again.

I think I tried the same before with methanol with no ignition, but I'll double check it later today to make sure.

So perhaps the starter fluid is a viable option for micro chambers which are hard to meter. Or I should stop trying to be different and shell out for one of those expensive pressure gauges and use propane :roll:.


Edit: Tried methanol again in the mini hybrid, but no variances in fuel/air could get it to ignite.

Tried starter fluid again and filmed it for your viewing pleasure. Valve has an opening pressure of ~50 psi, which I filled it to. The pressure returns to this after the combustion spike. Each pump after is basically flushing the chamber. Looks promising if it can fire that consistently, because it means it's vapourizing rapidly and under pressure. I suppose the chamber warming after each shot would help with this.

[youtube]http://www.youtube.com/watch?v=xVp-HWpSO3s[/youtube]

Unread postPosted: Mon May 18, 2009 11:16 pm
Author: daccel
Well, I think I'm going to pursue ether as a fuel, given the promise it shows.

Eventually a hybrid version of Rambo's auto combustion, perhaps?

But since my complex projects don't seem to get far off the ground, I'd like to throw something simpler together for now to experiment with the fuel. Enter the picture, below.

It's really just your basic piston hybrid, likely made out of 3/4" copper. But for fueling you would unscrew the cap on the bottom and spray in the starter fluid to saturate the fiberglass. The fuel would then wick up the fiberglass into each arm of the chamber to enhance vapourization. But would the addition of fiberglass possibly be overkill, and lead to a rich mix out of flammability range?

Unread postPosted: Mon May 18, 2009 11:21 pm
Author: Technician1002
daccel wrote:Well, I think I'm going to pursue ether as a fuel, given the promise it shows.

Eventually a hybrid version of Rambo's auto combustion, perhaps?

The fuel would then wick up the fiberglass into each arm of the chamber to enhance vapourization. But would the addition of fiberglass possibly be overkill, and lead to a rich mix out of flammability range?


A wick provides a huge variable to the metering of fuel. How much evaporates? How much resudial is remaining to make the next shot too rich, etc.. Is the chamber warmer after a couple shots? It would be a liquid spray and pray.

It's best to have a fresh dry chamber for each shot and a metered amount of fuel fully evaporated for consistant shots.

The multiple shots indicate the mix is too rich as you have unburned fuel left over.

Unread postPosted: Mon May 18, 2009 11:58 pm
Author: daccel
Well it would be easy enough to do some trial and error with and without a wick, I suppose.

Forgot to show it in the diagram, but the idea is to have a small pool of fuel at the bottom to allow multiple shots without manually re-fueling.

Agreed, that is what you'd ideally want. But I'm willing to sacrifice some efficiency/power/accuracy for ease of construction/use, if I can make it fire reliably.

While it is likely, the multiple shots don't necessarily indicate a rich mix, because the mix could be accurate in terms of vapourized fuel, but with liquid fuel sitting in the chamber that subsequently vapourizes and mixes with the next batch of air. Optimistic, perhaps, but in theory... :D.