Big Linear FWE for a Paying Client

[metiz]

Hey Larry

Looks like things are shaping up. good work!
Any chance you could videotape your 5 minute attempt?

[PyroJoe]

Hi Larry,
Looking good,
May want to bring a second tank online halfway through the run, 5 minutes is a long time to pull from one tank.
Joe

[larry cottrill]

Hey Larry
Looks like things are shaping up. good work!
Any chance you could videotape your 5 minute attempt?

Thanks! Yes, I should get back to video this time. My latest problem is, I can't get my video capture to work well. Playback on the camera appears OK, but my capture card and/or software keeps dropping frames, big time. I've tried different cables, no improvement. So even if I tape it, I don't know if/when I'll be able to post it.

May want to bring a second tank online halfway through the run, 5 minutes is a long time to pull from one tank.

Remember, I'm working from a 50 lb tank. Seems to me that on a warm day starting with a newly filled tank, I surely ought to be able to get 5 minutes before that much cool-down. We'll see, I guess.

L Cottrill

[Bruce Simpson]

Remember, I'm working from a 50 lb tank. Seems to me that on a warm day starting with a newly filled tank, I surely ought to be able to get 5 minutes before that much cool-down. We'll see, I guess.

You might want to consider drawing liquid propane and building an evaporator.

I did this for one particular test session.

The liquid propane was run through an automotive oil-cooler which was kept 'warm" with a constant flow of water (from a garden hose). The huge specific heat of the water meant that the evaporator (ie: the oil cooler) did a very good job of converting the liquid propane into gas and so long as I had sufficient water-flow, it didn't ice-up at all. The cylinder won't ice-up when you're drawing liquid because there's only a tiny amount of vaporization going on there.

If your draw is lower than mine you might get by using forced air (perhaps a leaf-blower) on the evaporator instead of water.

[larry cottrill]

You might want to consider drawing liquid propane and building an evaporator.
. . .
The cylinder won't ice-up when you're drawing liquid because there's only a tiny amount of vaporization going on there.

Bruce -

I hypothesized that this would be a good method a year or so ago, but never tried it. I was interested in it for flying small engines with a hand-torch size cylinder on board, and using a length of 1/2-inch tubing as an evaporator (of course, we're talking about very small flows in the case of a model aircraft size engine). Apparently your experience bears out the value of this method.

It just made sense to me that if most of the evaporation happened outside the cylinder, the pressure there would be much more stable over the time of a reasonable engine run.

I didn't try this on this big one, though. With a full 50 lb cylinder, I was able to get a couple of 2-minute runs, which was good enough to prove the engine would run continuously. It is now back in the hands of the client.

Thanks for suggesting this. It always seemed to me like a really good method, and it's good to know you've actually seen it work as predicted!

L Cottrill

[larry cottrill]

Grim PM'd me suggesting I try one of his "three point" fuel pipes -- the ones made by pinching a tube with a big 3-jaw Jacobs chuck. By the time I got his message, I had already made one this way and it worked excellently! I pinched mine with a 1/2-inch chuck and 3/8-inch steel brake line. I finished with a little hand work with Vise Grips (TM) pliers, just to make the central part of the pattern as small as possible and to ensure that the pinched wings had nice parallel sides. The three open slots in the spout pattern were just under 1 mm in width.

This pipe resulted in successful starting (WITHOUT starting air!) when 60 PSIG propane was supplied by the regulator. This is pretty high pressure, so the fuel spout had to be located out in the middle of the intake flare. I got a couple of nice two-minute runs with this method, proving that the engine can be started easily and run continuously.

This fuel pipe design is well worth trying, if you haven't already; I believe he presented this a while back in the 'Tools and Construction' forum. The design is simple, but making them (at least, big ones like mine) is NOT an effortless process. But in this case, I certainly found it well worth trying.

Anyway, thanks to Grim for this design. For my purposes, it worked out really well.

L Cottrill

[GRIM]

Hey Larry , glad to hear your engine worked out ,
I need to clarify one thing , I guess it was misleading in my pm , I do indeed have several different sizes of these injectors ,but i was not suggesting that i want to make or sell them , getting into the pulsejet market is not one of my goals

[metiz]

Ha the GRIMjectors are quickly turning in the new Rosscojectors, and with a catchier name to boot!
Larry, do you have a video of your test run?

[Mike Everman]

I'm not around much these days, but just wanted to drop by and say "neeto"! That's a mighty big one for a guy that likes little ones so much.

[metiz]

That's a mighty big one for a guy that likes little ones so much.

Must....resist....making "that's what she said"....joke...!

[Mike Everman]

Ha ha ha. I have two teenage boys in my house, so everything possibly sexual is "that's what she said", until last night when there was an actual thing that "she" actually said. We all stopped everything. I think there was a tremor in the force that you must have felt...

[metiz]

Puberty: the longest 30 years of your life

[larry cottrill]

Hey Larry , glad to hear your engine worked out ,
I need to clarify one thing , I guess it was misleading in my pm , I do indeed have several different sizes of these injectors ,but i was not suggesting that i want to make or sell them , getting into the pulsejet market is not one of my goals :lol:

You probably were not misleading, the PM was a few days ago and I am undoubtedly mis-remembering. I find that I am no longer competent to do much of anything from memory. I'll edit out the misleading part of my comment.

All the best, sir.

L Cottrill

[larry cottrill]

I'm not around much these days, but just wanted to drop by and say "neeto"! That's a mighty big one for a guy that likes little ones so much.

Mike, let me tell you, there are some surprises when you build your first big engine.

I started grass fires about four times out behind my test stand. I burned through the propane hose because of having it come up to the fuel pipe too near the intake outflow. That one was exciting for a second or two! I couldn't believe that I couldn't get the low pressure fuel pipes to work at all (although with plenty of starting air, I seemed to be getting close). Apparently, you just can't move enough propane through a 3/8-inch OD tube at 25 or 30 PSIG to get the job done. I couldn't believe where I had to put the spouting point with high pressure fueling.

However, I did finally get it to run. It's amazing what a difference it makes when you finally get the picture and set up everything right. Last Tuesday I got two good two-minute runs and then called up the client on my cell phone to try to demonstrate it. Almost got a really good run for him, but was interrupted by one of the grass fires that I had to stamp out before resuming. They then wanted it shipped on Wednesday so they could get it on Friday for some traveling; fortunately it got there in good shape. They then worked with it under hot and dry conditions from Sunday through Tuesday without much luck, and had just about decided to throw it back to me to use as a paperweight. However, they had been trying several different fuel pipes, and the guy I normally talk to said, "Hey, let's go back to the pipe Larry sent with it." This would be the GRIMjector described above. It gave a good bang and started running fine, and so they've decided to keep it. They find they can now start it instantly even from cold metal and run it as long as they want, with fuel pressures ranging from the 60 PSIG that I was using up to 150 or so. That's the good news.

The bad news is that (naturally) it is The Gas Hog Of The Western World. At 60 PSIG, I estimated that I had to be doing at least a half pound of propane per minute. At the high end, it must be unbelievable. The radiated heat is just staggering. But here's the worst part, and I'm going to have to do something about this because it's just awfully dangerous: The front end of this engine projects a sort of "death ray". Invisible in daylight, naturally. Ha. I have been informed that in full bore operation, you cannot safely stand closer than FIFTEEN FEET directly in front of the intake! They must be getting Mach 2 or 3 or something out of her at the front end. This is a nice example of The Law Of Unintended Consequences at work: the relatively small intake area combined with that front transition cone makes for some mighty fine exit velocity. If the engine were a U-shaped propulsion config, it would be a perfect fit for a nice augmentor at the intake. I may have to provide a U-shaped diverter (recuperator) just to make it safe to work around.

Thus ends the lesson for this day.

Let me tell you Mike, even at 60 PSI fueling, the noise is something to behold.

L Cottrill

[metiz]

I haven't made engines quite as big as this but the dreadnought came pretty close. The noise and vibration comming from that thing was something else. It wasn't just loud but it physically hurts your head and body when running it. In the last run of my smaller M40 I tried to be funny and roast a potato in front of the exhaust (it's in the vid). I did not anticipate my head nearly exploding from the sound energy. I held on for a couple of seconds but then had to retreat. Standing near the exhaust is a very bad idea indeed.

Of course these engines are way smaller then yours but I know the feeling