Crack of the Snorkelers

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Mark
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Re: Crack of the Snorkelers

Post by Mark » Tue May 11, 2010 2:09 pm

Another thing I was thinking is that there might be a region or eddy where there is a near constant negative pressure in the snorkeler or jam jar. Probably there is some ideal solution without the need to take pressure off the engine to fuel it. I was just throwing out some half-baked ideas in a free association state of mind and being so very tired yesterday.
It might be best to get the feed more inside the engine for with my Logan some of the fuel was sacrificed for the simplicity of a primitive design.
Last edited by Mark on Tue May 11, 2010 2:51 pm, edited 1 time in total.
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PyroJoe
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Re: Crack of the Snorkelers

Post by PyroJoe » Tue May 11, 2010 2:34 pm

Ha, my kitchen thrives off the half baked, we're in good company. :wink:

There is much to be gained by fighting the hysteresis. At times the fuel air mix would be correct, and the results are astonishing.

The more I think about it, I should try to make a fuel pipe that catches less of the outflow exhaust, as it may be pushing the fuel far back into the fuel pipe. That may account for some lag.

There is somewhat a "catch 22" in shortening the intake path, It brings the fuel source closer to the combustion zone, but loses velocity needed for rectification. Also because the positive pulse has a higher peak pressure, the fuel system will start working against a higher average positive pressure.... not good.

It is time to dismiss most of what I learned about carburetion, as no piston engine (i know of) has a high outflow velocity from the intake manifold. Guess its time to get creative.

"there might be a region or eddy where there is a near constant negative pressure"
Haven't found this region, I think Larry mentioned a node where this should happen (within VPJ). Have been trying to artificially create a area using the half flare on the snorkel. The boundary conditions may serve some usefullness, as my best results have been when the fuel pipe is lined up with the inner surface of the snorkel below the flare.

(one thing not readily seen in the photos, is the snorkel edge opposite the flare has been ground to a sharpish edge to resist inflow on that side/edge)
Last edited by PyroJoe on Tue May 11, 2010 5:41 pm, edited 4 times in total.

Mark
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Re: Crack of the Snorkelers

Post by Mark » Tue May 11, 2010 2:48 pm

Well I guess as with Reynst's quasi "cone snorkeler" he got good mixing introducing the fuel at the transition point near where the cone meets the combustion chamber. But if there were a way to get a feed even on the bottom of the tank in such a way as to keep just enough fuel to splash about, then maybe that would produce an acceptable performance. I really hate it on extended runs with my jam jars when the fuel becomes watery or too hot and the balance goes off and the engine stops. If there were an effortless way to introduce new fuel at a rate to kept the conditions steady ...
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PyroJoe
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Re: Crack of the Snorkelers

Post by PyroJoe » Thu May 13, 2010 2:05 pm

Tested a perpendicular cut fuel pipe last night,
completely flooded the snorkel volume with a fuel cloud, the outflow picked up the fuel flow and made a fair size mist cloud that descended for several seconds after the last chuff. I would say it is the highest fuel flow rate thus far.

Previously thought a mist cloud like that would ignite at some point, but it didn't. Had not weighed in the exhaust plume that travels with the mist, probably robs the cloud of the oxygen needed for ignition.

Will do some rough calcs by combustion volume to try to find a reasonable fuel pipe diameter. This CC appears to be running at a good fill volume, dead reckoning, it is probably filling near 60% or more on a good cycle.

Need to start modification of a fuel tank that is tapped at the bottom of the tank. Have several of these LM tanks on hand. They hold right at 24oz. or two bottles of HEET.

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Re: Crack of the Snorkelers

Post by PyroJoe » Thu May 13, 2010 2:41 pm

I'll share my method for sizing the diameter of the fuel pipes, for my own use constructed this ratio chart from several valved PJ engines that sip fuel, it is not whole cloth but gives a ballpark figure to help guess.

The chart is based on tailpipe diameter, which is of little use in jars unless a similar combustor volume is substituted. Which is the path I chose here, using 60% of the jar CC volume gives a corresponding tailpipe diameter of approx. .....oops original volume was off, recalculating.....

(note to self: rescaling solid object by .60 will not yield a 60% in volume per CAD)

ok, 286.49cu.in. is volume of jar, 60% of jar volume represents 171.89cu.in.
Corresponding tailpipe diameter for 171.89cu.in. combustor is approx. 2.53"dia.
Using alcohol in the ratio chart gives 2.53"/22= 0.115" fuel pipe diameter..almost 1/8" diameter


existing fuel pipe is approx. 0.20" diameter.
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Re: Crack of the Snorkelers

Post by PyroJoe » Tue May 18, 2010 5:56 pm

After attempting to weld the smaller tank for a few dozen minutes, watching the thin steel disappear with each struck arc, figured it would be as fast to custom build a tank with thicker material.

Found a piece of 4x4" square tubing, and cut it 7" in length. welded a 3/8" coupler to the bottom, and a 1" nipple with fill cap, enclosed by welding both endcaps. Painted, added some fittings to the lower tap. Pressure tested, she held 25-30 psi without fail.
Must say the on-off ball valve was a little fancy, but a guy has to splurge on occasion.

Drilled 3 small vent holes in the fill cap. Next up, finding a way to secure the small 1/8" I.D. fuel line in the snorkel cradle.
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Re: Crack of the Snorkelers

Post by PyroJoe » Tue Jun 01, 2010 3:08 pm

Not much luck with the side flare on the snorkel.
Continuing work with snorkels sliced at an angle. The outflow is proving more
a problem as I think the outflow time is longer than anticipated. Looking at the you-tube Schlieren video with a stopwatch, shows the intake flow cycle is nearly equal to the outflow at times, but inflow can have a much shorter duration on some cycles, maybe as brief as half of the outflow cycle time.

It appears on average the outflow has higher pressure for a longer duration. This is probably why jars have been difficult to fuel from the snorkel area.

There may be a solution not in tapping the flow characteristics as with the side flare, but tapping into the brief low pressure swing at the base of the snorkel. With the snorkel cut at an angle I hope to create enough bias to one side to tap the useful low pressure. Some indications show this is already bearing fruit but will take time to develop into something robust and reliable.

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Re: Crack of the Snorkelers

Post by PyroJoe » Mon Jun 14, 2010 2:22 pm

Into about the fourth snorkel design, not much progress.

Have tested several 3/4" nipples snorkels that provide a extra strong cycle on the 6" dia. jar.

Setup a test that was only supposed to last a few seconds, then I would snuff the jar with a fire brick over the snorkel. Ignited the jar and the cycle was robust, then went to snuff it with the brick over the snorkel, it would blow the brick away just long enough to pull a intake charge. To my astonishment it ran several seconds until the cycle finally weakend enough to cease.

Will continue to work at it, maybe it would be useful to apply a pressure and vacuum gauge.

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Re: Crack of the Snorkelers

Post by PyroJoe » Mon Jul 12, 2010 2:24 pm

Here are a few snorkels that have been tested, I would prefer to continue testing liquid fueling with the draft engines.
The potential of the jar continues to looks good, and one day may make another go at it with pressurized fuel.
IMO lip/snorkel fuel feeding may not be the best arrangement.
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Re: Crack of the Snorkelers

Post by Mike Everman » Wed Jul 14, 2010 4:10 am

Coool. Makes me want to go out to the garage and dig out some jar stuff! Good times, man. I had some fun with a disc of cloth in the bottom of one pot to hold fuel without sloshing. Off subject, I know, just wanted to stop in. Made it run on it's side, though.
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PyroJoe
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Re: Crack of the Snorkelers

Post by PyroJoe » Wed Jul 14, 2010 2:23 pm

Thanks Mike,
It's tempting to hook up a automotive fuel injector to the sidewall of the jar with some heat shielding. That would be to much like cheating. :D

May return to this when I have time to snoop around with pressure/vacuum gauges.

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