Proposed Design - Straight Pipe 'Henri' Valveless Pulsejet

[larry cottrill]

Still more photos from the initial phase. Forming the intake slots and tail end flare.

L Cottrill

[Mark]

I should say on my larger 1.25 inch diameter Logan, (as opposed to my tiny .75 inch diameter Logan), it also revs up quite nicely with methanol and a lighting of the tail. But sometimes it produces a distinct bang first off and then just as instantaneouly a loud rev with a mere coating of methanol misted inside it. Somehow the flame front rockets up the tail end and makes this startling starting concussive wave ahead of the near instantaneous loud reving, a Pow-Rev sound that is very strange. It's a fairly short Logan and if I get it to run constantly via the tip fuel feed, I will post a picture.
I often do bang starts using a plug, it's unusual to get a bang start from a tail light.

Mark

[larry cottrill]

All right, we'll try it this way then (my bandwidth, not Kenneth's ;-) - the final Henri construction photos:

Tacking the front plate to the tube with four very small tack
welds. The bolt and nuts are used as weight, as well as protection
for the threads of the plug mount. Note that the steel washer is
slightly larger in OD than the engine tube:

Copyright 2005 Larry Cottrill

Finish welding is just a matter of melting the edge and blending it
into the tube - no filler rod required:

Copyright 2005 Larry Cottrill

The front plate, fully welded, after cleaning up with the wire
brush:

Copyright 2005 Larry Cottrill

The copper fuel line is carefully bent and wrapped around the engine just
ahead of the intake ports. Here's what it looks like fully installed:

Copyright 2005 Larry Cottrill

The Henri prototype, all finished, fresh out of the bench vise.
I got a haircut from Wal-Mart on the same day. What this research
proved is that I could have built two complete Henri engines for
the cost of a Wal-Mart haircut [including a reasonable tip]:

Copyright 2005 Larry Cottrill

L Cottrill

[larry cottrill]

Initial tests showed that an external blower was NOT the way to drive
air into this engine, as described in an earlier post. An air pipe assembly
was made from an old tire valve extension [core removed] and a small
length of 1/4-inch brake line. The simple hose link allows different ends
to be tried with very easy substitution. The flattened nozzle was bent so
it would hook into the intake slot:

Copyright 2005 Larry Cottrill

Lean running with staccato explosions was quickly achieved,
although the fuel and air flows were fairly touchy to establish
and the air pressure setting was much higher than expected,
about 30 PSIG. Here's a pretty low-level "run" with the air
pipe on the near side - maybe 10 or 15 explosions/second:

Copyright 2005 Larry Cottrill

The best combustion was actually obtained by moving the
air pipe to the opposite side from the fuel line, so the fuel and
air flows apparently blend farther forward in the chamber.
This was at least 20 explosions/second when the photo was
taken:

Copyright 2005 Larry Cottrill

My conclusion from these tests is that the air volume from the pipe and/or the intake slots is not yet adequate. A more wide-open nozzled pipe end has been prepared for further testing.

L Cottrill

[Mark]

Hmmm, looks like a maybe. The jet aesthetically looks fine. I like the flare on the tail. You are starting to approach a straight tube design. Speaking of which, just that very length and size of pipe without anything more than a hand over one end and some methanol misted in will bark if lit from the tail. I wish someone would try that just to humor me. Feedback builds instantly and the strange sharp bark is keen.
Anyway Larry, best of luck, it's always enjoyable to read and see your posts.
Mark

[Bruno Ogorelec]

Great photos, Larry! You should be doing how-to books.

I like the engine enormously. But, my liking it won't make it self-sustain.

Given that it's so cheap to build, would you be willing to try either a longer tube (with longer combustion chamber and tailpipe sections) or a pipe with a somewhat greater diameter? It seems to be so close to taking up and self-sustaining it's almost painful. Maybe a little additional volume would kick it over the threshold.

If it works, it's going to be a boys' dream come true. You can cut thread into the pipe end and screw the end cap in -- and have a true no-weld valveless pulsejet. Figure out a way to use a lighter fluid bottle as a fuel tank and you have a winner on your hands.

The design is actually quite similar in spirit to my no-weld engine concept (the one with the cut and pinched tube side), but your layout is sounder, I think. It provides a kind of intake pipe, which makes it closer to successful conventional pulsejets. Mine is closer to a pure Reynst pot but perhaps oversimplified. It would probably be trickier to make work than yours.

I am really pleased with 'Henri' and it has not even worked properly yet.

[Mark]

For another fun idea, it might be simple enough to fashion a depression/groove/channel in the side of a pipe similar in size to Larry's for a smaller tube or side port rather to rest in which could merely be TLARed in a hole and held in place by a hose clamp.
Mike, could you get right on that? Also you could flare one end of your side port tube and slink it in from the inside of the main pipe like loading a rifle bullet. The indented channel along the outside wall of the main pipe would allow the side port to fit flush and again, the hose clamp would hold it snug.
Mark

[larry cottrill]

You can cut thread into the pipe end and screw the end cap in -- and have a true no-weld valveless pulsejet. Figure out a way to use a lighter fluid bottle as a fuel tank and you have a winner on your hands.

The pipe is awfully thin walled for a threaded connection. Alternatives might be:

- Lathe turn a steel end plug that would be a tight press fit and press it in [or hammer all around until it's in] - will this stay tight when things heat up?
- Extend the front end of the chamber just a hair and deform it in with your vise to make a pointed nose that closes around the plug nut. This sounds a lot more difficult than it is, esp. with such thin walled tubing. You would finish up with welding, but it would be simple and minimal.

L Cottrill

[Bruno Ogorelec]

Here's another alternative -- homemade cryogenics!

Machine a steel plug for a fit so tight you cannot press it in without a mallet. Put the plug into deep freeze. Take out, hammer it in (it will be smaller and easier to push in), let it thaw. Presto! A fit so tight you won't take it out very easily anymore. Pulsejet operation will only make it tighter still.

[mk]

Very nice photos, Larry.

[...] Given that it's so cheap to build, would you be willing to try either a longer tube (with longer combustion chamber and tailpipe sections) or a pipe with a somewhat greater diameter? It seems to be so close to taking up and self-sustaining it's almost painful. Maybe a little additional volume would kick it over the threshold. [...]

Ditto.

[...] The best combustion was actually obtained by moving the
air pipe to the opposite side from the fuel line, so the fuel and
air flows apparently blend farther forward in the chamber. [...]

Thus I'd go for setting up fuel and air supply at both inlet ports.
Maybe some kind of fuel stinger protruding further into the comb. chamber part or slightly outside the inlet ports might help. Hmmm...

[Mark]

I use to put plugs in my rocket tubes and then hammer tap the rim of the pipe all around until it folded over forming a neat flat/flush 90 degree lip perhaps 3/16ths all around the edge. This was plenty strong.
I've noticed that my stainless steel strapping that I snug down to hold my Dynajet is loose after a run and I have had expansion/cooling problems in the past by mere snug fitting. Heating and cooling different substances of different composition in intimate contact seems to create looseness.
I'm sure there are a lot of neat ways to seal or plug the end. Wouldn't it be funny to just flatten the end with a hammer or vise and fold it over?
And then sell it on eBay.
Mark

[mk]

[...] And then sell it on eBay. [...]

...with the attached explanation, of course. 100 percent serious...hehehe...

Safed my day again. Thanks Mark.

[larry cottrill]

Illustration resembles ...

I about laughed right off my chair!

L Cottrill

[hagent]

Hey Larry,

Nice job. It's great that you uploaded pictures of your work. It's nice to see how poeple make their stuff and the little helpful building secrets.

Was wondering what you think of the following changes to your design.

If you could flare the intake inward and extend the metal into the chamber so that exhaust couldn't sneak around the sides of the flare, and If the intake was just behind the pinch near the CC.

With a detonation the pressure maysuck air in through the air intake because of the ventura effect and into the pinched area. With the following vaccum cycle, the air intake would provide fresh air first to the CC because it's closer than the exaust outlet.

Thanks,

Hagen Tannberg

[Bruno Ogorelec]

Hagen, in other words you would like to make it more like the conventional Reynst. The order or stations would be chamber-exhaust, with the non-resonant intake just a slit in between the two.

Larry's layout is chamber-intake-exhaust. It is unconventional but may have the benefit of a resonant intake. Could be easier to make work than the usual Reynst pot.

I have proposed something similar to your idea with my pinched tube (see the picture), but I do have a feeling that Larry's layout could be more successful. We'll see what the development brings.

On the picture, the chamber is to the right. Indentations are where the air slips into the tube through slits (which are not visible in this projection).