New APC Motor #1

[hinote]

This is to announce the successful first test of my latest valveless pulsejet--the M41E "toy motor".

Attached is a photo of it on the test stand, running at about 90% or so.

This motor was to fulfill my desire to build a "small" motor (by my standards), and to use existing materials in my inventory.

The combustion chamber is 54 mm ID stainless exhaust tubing; the intake is 1" EMT; the u-bend/throat tube is a 1.25-inch nominal exhaust tubing size (29.26 mm ID). The sheet metal for the transition cone and meg is 20-gauge stainless (0.8 mm). The "bustle" is a piece of exhaust tubing, 66.5 mm ID.

Acoustic length is 1297 mm (.3D end correction).

Results:

The first tests have revealed a max thrust of 5.25 lbf, and a TSFC of 2.4 on gaseous propane at 3.75 lbf.

The max possible appears to be about 6 lbf. Note: I made an educated guess on the injector orifice port size--and didn't have the correct drill to create it. So, I chose the next size down, and sacrificed about 12% flow as a result. I believe I can easily achieve the 6 lbf level with the correct orifice diameter.

The operating frequency is 222 Hz; this corresponds to an acoustic temp of 824 K.

This motor was quite difficult to build well; I spent about 6 hours forming the megaphone to the desired degree of accuracy. The mild steel ubend will be replaced with a good SS unit--and this motor will make an excellent demonstrator, with long life.

With injector design improvements it should be easy to break into the sub-2.0 TSFC numbers.

This motor weighs 4.48 lb--quite heavy, but not bad when the material usage is considered. To get a sense of scale--the fuel tube in the photo is 1/4-inch diameter.

[Dave_G]

Bill,

Very nice test report! It's nice to read such a concise yet detailed account of a motor test.

Also, very nice execution of the motor itself. I especially like your use of reinforcing rings to help form and support the tapered sections. The motor itself looks very well built.

Congratulations on fine work!

Dave

[mk]

Everything OT aside, the engine mounting has been done very properly. Especially the central intake-tailpipe support.
Only personally I would have made the other supports somewhat different in a few details.
One of rarely spread good examples like, for instance, it can be done.

[Mike Everman]

I have cleaned up this thread. Blame me. At the risk of being heavy-handed, I and others off line are sick to death of flame posts. Done with it. Don't waste your breath.

[Jonny69]

Looks great Bill and must be a lot smaller than it looks in the picture, this is obviously a very effective layout judging by the numbers from you and others using it. What sort of injector are you using on that?

Mike thanks for cleaning the thread up, I was going to post some grief but thought better of it.

[hinote]

Looks great Bill and must be a lot smaller than it looks in the picture, this is obviously a very effective layout judging by the numbers from you and others using it. What sort of injector are you using on that?

This motor owes its heritage to the IAME Escopeta, from the late '50's and early sixties. I have optimized its dimensions using my current skill level in UFlow. BTW this consists primarily of observing operating parameters --and excludes wave actions. This statement is to inform those disbelievers in my method.

Here's a photo of yrs trly holding the little thing, before mounting. For perspective.

The injector is ultimately simple--just a piece of 3/16" OD brake line tubing with the end pinched off and 2 opposing holes drilled near the pinched end. Mount it so the pinch is presenting minimum disruption to the airflow. The holes should spray the propane into the airstream, just behind the head plate.

[Mike Everman]

Surely those two pictures aren't of the same motor??

[mk]

Surely those two pictures aren't of the same motor??

Hmmm...maybe only the trailer shrinked somewhat?

[hinote]

Surely those two pictures aren't of the same motor??

They are!

You should hear this thing scream at 222 Hz. A very smooth, strong runner.

[Mark]

How long is the jet if you were to make it a straight duct?
Thanks,
Mark

[El-Kablooey]

Thanks Mike! You aren't heavy-handed at all, just the opposite actually.


Nice engine Bill!

[hinote]

How long is the jet if you were to make it a straight duct?
Thanks,
Mark

Mark:

Please look at the first post:

quote: Acoustic length is 1297 mm (.3D end correction).

From this and the other supplied data (diameters of intake and exhaust final) we can derive the actual "duct length". This is the length of the motor, as if it were one continuous length. This number is 1269 mm (physical length).

Calculate the length with the end-correction factors subtracted from the acoustic length.