Proposed Combined Fuel Tube / Starting Air Tube for FWE

[larry cottrill]

Here's how I made my combined fuel/air tube, as now attached to the Elektra II. The tube was positioned with an ordinary C-clamp and a single tack weld applied; then, the aim of the top end was carefully adjusted, two more tack welds added, alignment checked and welds built up a bit to full strength. The outer tube is 1/4-inch brake line, the fuel pipe is 1/8-inch copper tubing.

Comments?

L Cottrill

[larry cottrill]

Did it work?

Just finished it Thursday night, and haven't had a chance to try it out yet. I'll post results when I mess with it enough the find the just-right air pressure to use, etc. I need a little hose link [or some neat method] to hook up the air portion of it, since it doesn't happen to have a tire valve on the end of it!

L Cottrill

[steve]

that is a pretty slick looking setup you have got there- I have no doubts that it will work.

The only thing I would have done differently is wraped the end of the copper tubing around the tailpipe a few times to preheat the fuel (like you did with the last fuel setup)

There is just something about a coiled fuel line that gives an engine a real professional look to it- just look at the gluey!

[Mark]

I once pondered sort of the same thing , but with the spark tacked on. Perhaps if the fuel/air line were insulated from the engine you could arc a spark from the tip of the injector into the engine.
I remember awhile back there were some exotic spark plugs that were made hollow down the center for some special purpose and I posted the corporation that made them. I don't remember where now. But you could feed in all three elements that way, fuel, starting air, and spark. The spark plugs had a core like any spark plug, but the core electrode was also hollow.
Mark

[larry cottrill]

I remember awhile back there were some exotic spark plugs that were made hollow down the center for some special purpose and I posted the corporation that made them. I don't remember where now. But you could feed in all three elements that way, fuel, starting air, and spark. The spark plugs had a core like any spark plug, but the core electrode was also hollow.

Mark, why didn't you get some of those? You could have made a tiny Logan with a single Steve-and-a-half plug as the intake pipe! ;-)

L Cottrill

[Mark]

Believe me if it were possible I'd try that. My little stainless steel teapot cream pitchers arrived yesterday with those quirky side port spouts I was hoping to Loganize with some sort of pipe length added on. The weld where the spouts are fused to the body are very nice, as smooth as glass inside and out.
Where to begin ... what kind of spark plug goes with a creamer?
Mark

[larry cottrill]

Did it work?

Yes - it works beautifully. It took a few tries to get the air pressure right. As shown on my Elektra II photos above, the exit face of the air pipe is precisely 1.5 inches aft of the intake flare rim, and the regulator pressure that works is 30 PSI - about 4 or 5 times what I guessed, but it happens to be exactly what I set up for my Dynajet, so it will be easy to remember. Presumably, less pressure would be needed for delivery if the pipe were spouting closer to the intake.

This thing does for our rear-breathing vapor fueled engines exactly what the Flowjector does for the Dynajet: It gives you a properly set up, fixed geometry that will work every time. Once I had the pressure set right, all I did was start the spark, push the air valve button and open up the fuel until it started pulsing. When I let go of the air button, the strength of running diminished slightly but it was sustaining! I got the ignition voltage out of there and cranked up the propane to full grease and let her run while I disconnected the air pipe [a simple friction-fit hose link]. Nothing to it.

Steve, since I know you use compressed air for starting anyway, you've absolutely GOT to try one of these on your old FWE! Yes, it's kind of a hassle to put together, but once you've got it, it works wonderfully! Sure starts in seconds ...

L Cottrill

[Mark]

In some way the little metering jet fitting on the Dynajet works kind of like your fuel/air feeder. And too, it also reminds me a little of the Bunsen burner or Reynst mixing technique. Of course my obscure anologies are probably very remotely similar. It's just something that came to mind when I saw your fuel/air feed. One thing nice about your design is that it standardizes starting, no fussing with the right angle for the air injection starts.
Mark

[larry cottrill]

I also noticed how pronounced the heating pattern was and came to the same conclusion that it corresponded to your your original prediction.

Starting it now is comparable to starting the original FWE.

Steve -

When I got my good run of the Elektra II last night, I was careful to observe the heating of the chamber in order to compare it to your shot of the Elektra I.

They are nothing at all alike. The E II chamber is almost uniformly red, with a slightly duller red at the front end of the pipe [note that this is 1.25-inch antenna mast, NOT conduit like the E I]. The red hot zone, as seen at night, extends perhaps 8-10 inches aft of the rear of the chamber.

The air intake pipe stays totally dark, of course, and there is absolutely no flame ejection in a 'full grease' run. I don't know if this has anything to do with squashing the pipe flat, better chamber geometry, or just good vibes, or what.

I just realized today that I don't have a single picture of the Elektra II running. Now that I can always start it reliably [without hauling the shop vac out to the test pad], I need to get that accomplished! I kind of wish you would build one sometime, so I could get another perception of the similarities and differences in the two engines. Not nearly as exciting anymore as your FWE projects, of course, but cheap and easy.

L Cottrill

[steve]

my guess is that the flow of air into the cc is much smoother due in large part to the long straight intake. since this results in low turbulence, it takes longer for the air and fuel to mix adequately and therefore the intake air swirls around the CC (creating the cold spots around the foward perimeter) for awhile before burning near the front of the tailpipe.

In elektra2 the squash and the very sharp turn in the intake are definately creating a great deal of turbulence, contributing to better mixing, and therefore quicker burning. also once the intake air has left the intake it is free to flow in all directions creating more turbulence and more even distribution of the burn. In Elektra1 the bottom of the intake is in close proximity with the floor of the CC. this is forcing the air to flow only in one direction even after entering the CC. this probably stabilizes the flow somwhat and therefore there is less turbulence which means bad mixing.

This all makes perfect sense to me, but as allways I am probably wrong.


Interestingly enough the elektra1 is the seccond most expensive pulsejet I have ever built (the most expensive is Mark's mini logan made from pipe fittings- $20) Since I get all my sheet metal from the school and live off of donations and stuff scravenged from the trash, I have only spent about $50 total to support my pulsejet habbit for the last two years, including the cost of the methanol I have burned!

I may try Elektra2 sometime this summer when I am again left with nothing to do and nothing with which to form sheet metal with.

;-)

[larry cottrill]

OK, here's a simpler form of the same thing, for those who don't want the hassle of feeding one curved tube through another.

L Cottrill

[steve]

can you imagine what he could do with a good CAD program?!

it boggles the mind!

[mk]

Your drawings get better and better, Larry.

The historical factor ("Since 19...") and the art-factor that counts for Larry to do everything in Paint and in b/w. Then these two factors sum up in the "Cottrill Criteria"...hehe.

Note: Larry, of course the drawings are nice and getting better.

[larry cottrill]

As shown in my Henri thread, a tire stem extension, with core removed,
is useful to get air into a starting air nozzle. This is a heavy brass one
I found lying around on the ground beside a recycling bin. I just use a
length of large automotive vacuum hose to connect it to the desired
starting nozzle, as shown here:

Copyright 2005 Larry Cottrill

Here it is as used on my Elektra II combined fuel tube / starting air tube.
This works wonderfully for sure starts, as described earlier:
Description

Copyright 2005 Larry Cottrill

L Cottrill

[steve]

any particular reason you bent it towards the CC? I yould think the air line might get a bit charred, but beter the air line then the fuel line, right?

;-)