Big Linear FWE for a Paying Client

[larry cottrill]

... all the best with it I hope it rocks your world :)

Thanks, James. I'll be lucky if it doesn't rattle windows till they crack, rattle dishes out of cupboards, etc. The world will come later. Ha.

L Cottrill

[Ghrey]

I have been occupied elsewhere as well.....

I hope this endeavor does well for you, the work looks top notch.

[larry cottrill]

Thanks, Ghrey. Yes, Jim and Matt Russell do a fine job of quality construction in metals, especially stainless. It's hard to believe that much metal will be running red hot in a matter of seconds. If I actually ever get to test it ...

The weather has been hideous for several days. Some days, all the time I didn't spend mucking out horse stalls has been spent shoveling paths and the driveway. This morning it was -4 degF and snowing, but amazingly it came up 33 degrees by 1 PM or so, with (relatively) warm wind and sunshine. I went in for lunch and by the time I got back out it was clouded over again and so cold and windy it was almost "blizzard conditions" (except that snow wasn't actually falling, just blowing around). So, still no test. Sounds like Thursday might be decent; tomorrow is supposed to be clear, cold and windy.

I talked to a guy today who has propane-powered forklifts (where I get horse bedding), who might be able to provide a cylinder of propane -- if the valve fitting matches the barb on my regulator. He says they use a small "hose" fitting, but I bet I'll find that's just some kind of adapter added to the valve or some such. I should be able to get over there and check it out tomorrow, since I need a bunch of shavings before the weekend, anyway.

L Cottrill

[Ghrey]

Our current temp is 42F and we expect 33F over night, with a little more rain showing on radar. It has been wet. Sad thing is, it is coming your way....

Except for fixing leaking roofs, I have been shut down...

Hope you find a good window in the weather for testing.

Cheers

[larry cottrill]

Well, the forklift cylinder I looked at was a pretty good size but wouldn't have worked. The valve connection was completely different, and not an adapter to the "regular" fuel valve. Apparently standard for forklifts, though. We learn something each day, but not always to our liking.

Does anyone know if the larger cylinders used on RVs and trailers have the flow restrictor? That was another suggestion from an older gentlemen, but then it occurred to him that these might have the restricted valve too, since they're basically supplying cooking gas.

Tomorrow's supposed to offer good weather, for a while. Maybe I should just give her a try with a 20 pounder if the weather gives me a couple of hours. The best I could hope for is that I'd know that she will start and run, even if the power turns out to be very limited. At least that would be something more than I have now. Everything else is ready; the fuel supply is the only remaining glitch that I know of. I wish I had thought of this potential problem much earlier on, so I'd be prepared now. It's tough working within the framework of an Iowa winter.

L Cottrill

[larry cottrill]

All right, I went ahead with a test using the 20 lb tank, since the weather this afternoon was wonderful. The 20 lb tank was not, as just about everyone would have predicted. I will try to find something better tomorrow, somehow.

I set it up with the high turbulence fuel pipe (the one with half the ball ground away). The engine managed a few lapses into a kind of low, apparently resonant growl -- I wish the sound of this would have come through better on the video. This makes me about 95 percent sure of two important things:
The engine WILL run, if adequate fuel can be supplied.
The engine WILL start without compressed air or blower, at least when the higher turbulence stinger is used.

I tried a few different settings of the fuel spout position. Nothing worked as well as the initial position; however, this could be because the vapor pressure in the cylinder was falling off by the time I tried the alternatives. So, nothing really proven, in my opinion. The cylinder was covered with a thin layer of frost after the testing.

An important observation was that as the throttle was advanced from low to full, the regulator gauge pressure DROPPED from 20 to about 3 or 4 PSIG. This indicates SEVERE restriction upstream of the regulator. As if you didn't know.

L Cottrill

[larry cottrill]

I spent all morning calling and finally driving to a town about an hour away to get a 50 lb propane cylinder. The full weight is a mere 90 POUNDS, which is about all I can handle. Fortunately, there is a lot of packed snow here, so I was able to mostly slide it down into the back yard alongside the engine and set it up solidly. Unfortunately, there wasn't adequate time to set up for the next test. Today was close to freezing with a short period of sunlight; a little windy, though.

The valve on this cylinder is termed (in the vernacular of the propane trade) a "torch valve". This means a valve without the OPD and flow restrictor. I was severely cautioned that opening that valve without anything screwed into it would release a LOT of gas. As if I didn't know. It is visibly simpler than the valve bodies on the 20 pounders, but has the same internal LH thread that will fit the regulator barb perfectly. So, we're go for launch. I won't test on Sunday, so it will probably be sometime Monday at 20 degF with snow flying and 3 or 4 more inches on the ground. Ha. The cylinder is in brand new condition, about 24 inches high and maybe just a little larger OD than the 20s, with a MUCH larger and more substantial steel support ring with generous rolled rim at the bottom.

This simpler type of valve is standard on this size cylinder. The propane cost a hair over $30 (including sales tax) and I think he said the cylinder would be $142 if I decide to buy it instead of returning it. Though heavy, it's not that bad since most of the time you can just roll it on that heavy duty bottom rim instead of lifting and carrying it.

L Cottrill

[larry cottrill]

First test session using the 50 lb tank. Still nothing better than some pretty loud growling. See video clip attached.

I was actually able to experiment with the other fuel pipe a little, and I was able to do a LOT of playing around with the spouting location. The "low turbulence" fuel pipe was useless -- never got anything like rumbling out of it, no matter how I tried to position it in the intake (though admittedly I only varied it about an inch from the theoretical location).

With the "high turbulence" pipe I was able to determine that my theoretical spouting point is virtually correct: At about 1 inch (25 mm) forward of the intake-to-chamber transition out to maybe 1.25 inches (32 mm) I get some good episodes of growling operation. Positions outside this range do nothing but give me a thrustless burner.

However, no loud explosive pulsation at any time. Also, even with the 50 lb tank, the pressure still drops off pretty fast. Ambient temps today were somewhere around 22 degF, and that may be a lot of the problem. There was frost on the cylinder in a few minutes of testing. Still, the growling was impressive enough that I think she's awfully close to taking off and running. I'm wondering if I might have to double up on the fuel pipes or something.

L Cottrill

[BenJet]

That is one big flame thrower.

[larry cottrill]

Testing has been a rocky road. To start out, I was testing for a couple of weeks in February, but was hampered by terrible weather and got almost nothing accomplished. The client understandably became weary of this and insisted that I ship it down to Louisiana for them to test. It turned out that because of noise concerns, they could only test on weekends. Their main advantage besides warm weather was that they have BIG propane tanks manifolded together. Their main disadvantage was lack of experience testing unproven prototype designs, with all the interesting amusements that entails. And of course, all this was while working with the only fairly large engine I've ever designed and built. They managed some growling operation and some impressive bangs, but nothing resembling real power running, even though they tried multiple fuel pipe designs and many different pressure and flow scenarios. So a couple of weeks ago, the engine was shipped back to me.

My first job was to build a reasonable test stand to replace the snow-studded 2x6 plank used in the winter. What I came up with can be seen below -- basically a frame of two 4x4 rails with four 2x6 cross ties embedded in a crushed rock leveling bed. A couple more 2x6 pieces were added to the top at the rear. The engine is bolted to these with three 3/8-inch bolts in oversize holes, with heavy rubber pads to allow vibrational motion. Static thrust of the engine is not large because of its "linear" design (tailpipe and intake in opposition).

Using a high flow "high pressure" regulator (0-75 PSIG) and a high restriction fuel pipe, I was able to get resonant running within ten minutes. However, this produced low noise and low power. Examination of the fuel pipe showed its outlet was severely restricted. I made a new pipe of the "trilobite" design (squeezed into three lobes using a 3-jaw Jacobs chuck). I ran various tests, gradually squeezing it down until a really good velocity was obtained at around 60 PSIG delivery pressure. I was able to get good power runs early last week, but they lasted for only a few seconds. Hmmm ...

I finally tried adding a crude tailpipe extension. At an extension of a single inch, I was able to get arbitrarily long runs, but getting weak because of failing propane pressure at the tank. Even a 50 lb tank chills quickly once you've used up half or more of it, of course. I finally found a local RV place that would refill it by weight, and was back in business. However, the next few days were all some variation of cold, wet, thunderstorms, or extremely windy. We were under a tornado watch Wednesday this week for most of the day, with lots of large hail in various parts of the state.

Finally today I was able to get back to it, with the engine fitted with the original prototype of my ProTuner tuning sleeve. I tried a few different extensions, but 1 inch (25mm) still appears to be the best. I was able to get a run of about one minute when suddenly the propane hose burned through near the engine and dropped away. I was able to immediately shut off the propane with my SportThrottle valve (attached to the output of the regulator) with no damage to the test stand, even though there was a very impressive fireball briefly enveloping the area below the engine for just a brief instant.

In high pressure running, the spouting point of the fuel pipe is just outside the start of the intake throat, within the intake flare. The engine is perfectly self-starting in this configuration, without any need for auxiliary air.

I believe I now have the right setup for high pressure running, except for the need to re-design the fuel delivery setup so the hose will be farther from the intake flame. Once that is firmly established, I'll go back to the low pressure regulator and a low speed fuel pipe at what I call the "carburetion point" near the rear of the intake. I want to have a handle on both operational modes before I send this back to the client.

At this point, the client has over $3500 US invested in his pulsejet. I have assured him he will have a running engine without further expense.

L Cottrill

[Mark]

"An unfolded FWE, not for propulsion. The client wanted high tail flame temps AND velocities. Exact usage is proprietary." If you ever find out or can say in the future, I'd be curious what he's planning to use it for.

[larry cottrill]

"An unfolded FWE, not for propulsion. The client wanted high tail flame temps AND velocities. Exact usage is proprietary." If you ever find out or can say in the future, I'd be curious what he's planning to use it for.

I'll be able to reveal it after his patent is granted. In the meantime, I have lots of ideas for a straight-tail engine this size, although most of them involve re-folding it into the "standard" FWE configuration. Of course, in many cases, a "bustle tail" would be an improvement. Custom-built cones in these sizes are expensive, though, and I have a LOT of that 4-inch OD stainless tubing left. I used to be able to order custom cuts, but now they only sell you 20 ft lengths of it (at a mere $18 per foot). Aargh.

Now that I've found the (apparently) correct length, I can reveal the dimensions. I'll work up an "as-built" drawing (without the removable section in the middle) and post it here sometime soon. Obviously, there's nothing "proprietary" about the engine itself.

L Cottrill

[larry cottrill]

I added a 5 ft section of 3/8 inch OD brake line to completely isolate the fuel hose from engine heat and flame. I reduced the hose length from 8 ft to 4 ft so it's just a short link to the rigid steel line. I put three bends in the line so that it's stable on the ground, not just dependent on the fuel pipe at the engine for support. I believe this is long enough that engine vibration won't be an issue. The connection to the engine fuel pipe is now a flared tubing fitting, which is the standard method for fuel gases in rigid tubing; very tight and safe.

Hoping for another test run or two later today. Overcast and looking like it could rain any time, but not windy and very comfortable temps.

L Cottrill

[larry cottrill]

Well, the rigid line worked great. However, my testing was finished almost immediately because I had under 20 lb of propane left -- in a matter of minutes the bottom few inches of the cylinder was frosted up, and the regulator would no longer respond to demand. So yesterday, I got the 50 pounder re-filled, but then couldn't try anything because of high gusty winds from the south (i.e. right up the tailpipe). Same today, nice and warm but gusty all day.

The only drawback to the rigid pipe section is that it is somewhat awkward when making slight depth adjustments to the fuel pipe in the intake. But I quickly got used to doing it, and the inconvenience is certainly more than offset by the increased safety of the work. Only a few inches of the grey line got hot in the few minutes I tried it.

You really don't want to test an engine like this in windy conditions -- I'm probably driving the pipe with better than a half pound of propane per minute. That is a LOT of flame when she doesn't catch and resonate, or you flame her out.

L Cottrill

[larry cottrill]

Got a brief run Saturday with the low speed fuel pipe. However, even with that pipe it took 60 PSI on the gauge to get the volume needed! When I tried to duplicate it today, I couldn't get anywhere with it. The low speed pipe seems very sensitive to the slightest variation in position and/or procedure. There was a little light gusty wind today that may have affected it. It was about 70 degF when I was trying it. I finally gave up on this pipe and had to let the propane warm back up for a couple of hours. This pipe DOES need starting air added in - which of course means yet another set of variables to mess with.

Finally I got back to it, but with the high speed pipe I made the other day (the trilobite nozzle end). Got her started with no problem, and of course without auxiliary air to start -- didn't even bother to mount the starting air tube. I started with the regulator set at 65 PSIG. She ran for almost a minute before flaming out - when I closed off the throttle, the gauge was down to 45 PSI, so that seems to be about the lower limit. The short time span is because, once again, I'm down to about 10-15 lb of propane in the tank. I will get re-filled again tomorrow. If I can get a 5-minute run, I'll cell phone the client for a demo run. It looks to me like the high speed pipe is the right way to go. That brief run today was the first time I've been able to see the chamber running red hot in daylight!

The thing is, I need to get a good 5-minute red hot run under our belts, and THEN do a careful inspection of the welds between the mounting plate and the chamber wall. If all looks good after that, I'll be ready to ship her back to the client. I'll send him the high-pressure regulator, of course -- just like the earlier one, except for a 0-100 PSI gauge with no "red range". It is clearly labeled not to be used for acetylene. The throttle valve is like before but significantly larger, equipped with the same nice throttle lever and knob. Super smooth action.

All you have to do to start this thing is hook up the fuel system and spark wires, set the reg for 65 PSI, start the spark and smartly open the throttle until she catches and roars. Then, pull the spark wires. Once she warms up you should be able to throttle up and down over a small range and get some practice making her run just the way you want. There's nothing to starting her up with the fast fuel pipe once you get used to it.

Tomorrow is supposed to be just like today all over again -- about 70 deg and light winds. With a re-filled cylinder, a 5-minute test run should be doable. I'd love to get some night run photos, but I don't know if the neighbors will tolerate too much more.

L Cottrill