Simple Conduit Engine

[vturbine]

Our local fair started today and runs through tomorrow. Yesterday my wife readied her entry in the contest, a chocolate cake with mocha icing, and my three year old daughter asked me to pick two of her pumpkins for the junior produce contest entry. "What about you, Daddy? she asked me."

I don't know, I said. I don't have anything for the fair. My wife handed me the fair booklet and looking through the contests, I noticed a metalworking category for welded entries. Hmmmmmm, I thought. How much time have I got? "Three hours," she said. Okay, I said, and ran down to the workshop.

Gotta be simple, I thought, I found a rusty pile of bent salvaged electrical conduit in back of the shed -- 1/2" and 3/4" EMT. Remembering I'd printed out the rules Mike Everman had posted in the pipewood thread for the all pipe engine, I found the sheet, did a quick mental calculation and looked around for something 1-1/2" in diameter for the CC. I found a piece of galvanized tube that also looked like conduit, just the right diameter.

I had a hole saw that made about a 2" disk, and cut out some thin sheet steel into two disks. Luckily I also had a 1" and a 3/4" hole saw so I turned the cutouts into washers with holes that size.

I cut the smaller conduit to approximate length and I used Grim's flaring tool to flare the CC ends of the tubes. I then slipped the intake and tailpipe into the washers and they slipped down until the flares caught in the washers. I then gas welded the flares to the washers, and ground down the welds -- luckily my welding skills have improved and there was very little to grind.

I then placed the CC on top of the tailpipe washer and aimed the torch in to push the excess metal of the washer in toward the cc for a tack weld in a few places. Then I welded all around pushing the extra 1/8" rim of washer in to fuse with the CC. I repeated this for the intake end. Suddenly, the engine was whole, but pretty ugly, with white paint and rust all over the used conduit, and scale, etc. I also didn't have a sparkplug, or injector, and no display stand.

At this point my wife and daughter stopped by and said it was 20 minutes until all entries must be in. I knew I couldn't do any more on the engine, so I put it aside, and went with my family to the fair, holding two small pie pumpkins.

Today my daughter won a red ribbon, and my wife a blue. There was only one entry in the metalworking contest -- a rusty pig made out of some discarded pieces of farm equipment. It had a spring for a tail. We had a great time at the fair. And there was also one other great thing that happened today, too. When I got home I had a new pulsejet to clean up and finish off. I'd probably never have built it otherwise.

Any excuse will do.

[Rossco]

hahaha, classic, "3 hours spare... what can i do? PULSEJET!"

I'm sorry to say my friend, you have the bug and its incurable.
It will mellow with time, although there is nothing that can be done for short term relief.
Just be warned, compulsive sporadic pipe creation assembling activity can be a concern for outsiders, especially at odd times of the night or during otherwise unconnected events.
In my case, family get-togethers, parties, other peoples parties, with "strange people met over the internet" , work (we were slow, and the boss was sick of me talking about something he had never seen, had one built in 1/2 hour very similar to yours) just to name a few.

Seriously, very cool. This is what these play engines are about and keeping with the simplicity of the concept.
Big bonus of this engine for a demonstration unit, it looks "too basic to work" and you can look right on through it, even when running. "and you have nothing in that pipe there?"
Please give a "****cojector" and cig lighter a go, best demo engine you can have then, keep it simple. I guarantee with some tweaking and "knack" you will be able to start and run this engine with a handheld, no air, no spark.

Rossco

[vturbine]

Hey Rossco! Cig lighter? you mean for ignition .... or some kind of fueling or something else...? Sorry for dumb questions at this point!

Will do with the rosscojector -- I found that one earlier.

I must really have the bug -- I mean I'm a totally sick individual now, because I'm already thinking about how I would put a turbine on it. Nuts! Stark raving. I haven't even tried to get the damn thing to run and I'm trying to drive a shaft off of it in my head...

But I really do have a VERY cool idea about that. Assuming I get the rosscojector and cigarette lighter working, of course

I've also got it in my head running as a pulsejet on top of a 1 meter model boat -- tethered like I mentioned .

I'm done for, doc.

[Rossco]

Yep, cig lighter for ignition.
There is a certain knack to it, easy when you know what your listening for.
My SLI vid on youtube shows me doing it (i think that one is a good example of cig lighter starting)

Another thing that engine in the vid had was a slide on tail couple, which is where the smoke is coming from, easy for tail experiments.
I had a hellitail for that one. two 90* elbows on a "T". good fun.
i "held" the engine by the stationary injector and let the whole thing spin. surprising amount of torque (probably not surprising if i calculated it, but i didnt).
Very hard to keep control of for two reasons, it was not balanced and had no bearings to run in, and it was hard to hold still or see when laughing manicly.

Rossco

[vturbine]

What's the youtube link Rossco -- or what's your youtube nick there?

Sounds like a pulsejet Hero engine!

[Rossco]

http://www.youtube.com/watch?v=Zq-Ofp3Oci8

[vturbine]

Thanks Rossco. That's a really interesting engine.

Do you have a vid of the helio tail thing?

[vturbine]

Spent an hour today trying to get it going w/out compressed air or spark ignition, but no go. Tried rosscojector, then 3/32" tubing in L bend per the Ugly stick. The main problem was, when it was bent in an L, It was hard to keep lit as I pushed it into the inlet. When done rosscojector style, it stayed lit but I coldn't get much pulse action -- except very near the mouth of the inlet.

I had a feeling I could get it going if I could keep it lit with the L bend.

I'm thinking about coming in through a hole drilled through the front corner of the CC -- like it is on the draft engine. That would give a cross flow orientation, yet allow pushing the lit injector straight in to keep it lit.

The other thing is, just visually, the inlet looks small and long, the CC looks small, and the tailpipe looks large in diameter. Just visual reactions, but I'll keep trying with what I have before trying a different geometry.

[vturbine]

Looks like I goofed on this one. I measured the true ID of the "3/4" EMT tailpipe, and it's quite a bit larger than .75" (like .82").

Likewise the CC is wrong -- it's actually 1.5" OD. Not ID. So it's small by quite a bit in relation to the tail pipe.

Finally, the inlet is larger in ID than the nominal 1/2". It's .62"

So it looks like the CC should be made of 1-3/4" ID stuff, not 1.5" OD stuff, to match the tailpipe.

Guess I'll look around for something with that ID and try to save the ends.

Another possibility would be to keep the CC, and sort of consider it a stepped cone by adding a wider section of tube closer to the front -- this would lengthen the CC as well as making it effectively wider at the front.

Anyway, the goof up explains why the tailpipe looked so large in comparison with the CC to me.


EDIT:
Looks like what I used was "1-1/4" EMT, which has an actual OD of 1.51". If I had used true "1-1/2" EMT, it would have had an OD of 1.74. Even that is a little small by the time you subtract the wall thickness, but a lot better than what I have.

I'll have to work on this more.....

[tufty]

You might get some mileage by applying "kazoo" techniques to the tailpipe to bring it down in size a bit. A more modern version of the the old engineer's approach of "if it doesn't work, bash it with a hammer"

[vturbine]

Thanks Tufty,
Reading some more things in the forum, including Pyrojoe's recommendation not to go 1.5" or below in CC diameter for propane, I have rethought the EMT engine.

I think of the second version of the Simple Conduit Engine will be:

inlet 3/4" EMT (.82" ID) .......3-3/4" long
CC 1-1/2" EMT (1.6" ID) ........4-1/2" long
tailpipe 3/4" EMT (.82" ID) ........18" long

It will be a little simpler than the first one since it only requires 2 sizes of EMT instead of 3 and the CC ends (washers) are identical.

[PyroJoe]

Didn't have much luck with anything below 1.75" CC diameter with propane. The 1.5" & 1.6" ones would run for just fractions of a second.

It is hard to say where the cusp is for propane sustaining. If there was enough air flow and the mixture remained lean, one may be able to go below 1.75" or even 1.5"

I noticed the flame front would advance out the intake, but if I increased the flow to push it further back it would go rich and flame out. (observed during 3 weeks of tinkering with 5 different 1.5" CC engines in a multitude of setups, really was hoping one would run)

This was somewhat of a eye opener about flame speeds. Methanol will burn fast enough to stay up with the flow required to sustain a 1" chamber and below. The Craftjet is a good example(although valved), even the J-draft sings along with a 1" CC.

Acetylene is also a fast fuel, as seen running Marks Logan and many other tiny engines.

The 2.3" diameter pipe has made many good propane runners when used for the CC. The 1.75" ones were not nearly as stable as the 2.3" and would often drift out of lock in.


As a side note, it is not assured the the propane sold here in the south is of a good grade, they could be mixing some butanes or lower grade stuff that would perform poorly in the north regions. Often have suspicions. ha

Apologize for the ramblings

[vturbine]

ramblings both valuable and interesting!

I might just try it anyway, to sort of reinvent the flat tire, I guess.

[PyroJoe]

Have a go at it. Everyones setup is a little different, and she may just fire up and be a good engine for you. If she gives you to much heartburn, may hunt for some acetylene. I usually don't like the smell and the soot involved or would be using it more often.

[vturbine]

Have a go at it. Everyones setup is a little different, and she may just fire up and be a good engine for you. If she gives you to much heartburn, may hunt for some acetylene. I usually don't like the smell and the soot involved or would be using it more often.

Thanks Joe -- no, not interested in acetylene as a fuel -- expensive enough as it is for welding.

I did get curious about the flame speed theory you mentioned, so I looked up propane and methanol online. I found that the stoichiometric flame speed of methanol in air is 0.43 m/sec and the the same for propane in air is 0.45 m/sec. So it looks like propane's flame speed is actually a little higher than methanol. (Acetylene is listed as ranging from 1.6 to 2.7 m/sec). So there must be another reason why methanol works in a 1" diameter CC and the other doesn't. Mixture tolerance has been mentioned a lot in these forums -- methanol requires much less air than propane does to burn, and has a much broader mixture range:

Propane 2.1 to 9.5%
Methanol 6.7 to 36%

My guess is therefore that better and more accurate mixing of propane would help in smaller CCs. The injector precision and mixing ability would be critical. Also good intake breathing since it needs a lot of air.

You mentioned that your preference is for a smaller inlet diameter than tailpipe diameter. I decided to try an inlet the same diameter as the tailpipe -- maybe that will help?

I also sometimes wonder if premixing with some air before injection would help -- as is done on a cook stove burner with an orifice jet and air venturi/mixing tube. If there was insufficient air for combustion and sufficient gas speed it couldn't ignite until injected into the secondary air mass of the combustion inlet -- but premixing would help the speed and completeness of the whole mixing process, I think. And that might look a little like "higher flame speed" in behavior. In other words, the necessary higher frequency of a smaller engine would be sustainable, because mixing speed increased.

I notice Reynst used a premixing chamber of sorts outside the annular slit. I believe even Mr. Ogorelec questioned the reason for this.