Engineering Senior Design Project 2011

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pulsejetgroup
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Engineering Senior Design Project 2011

Post by pulsejetgroup » Wed Oct 19, 2011 1:38 am

We’re working on a mechanical engineering senior design project. Our plan is to build a valveless pulsejet, get it running, instrument and measure it, and then improve it. Been browsing the forum and we’re looking at Lockwoods and the 40lb Chinese engine. Something that’s easy to get going would help speed up the process of measuring and improving. Any experience with these engine’s ease of starting? Also, about how long will carbon steel hold up under normal working conditions on a static stand? Stainless is looking expensive. Thanks for the help. Thank you everyone for sharing your designs.

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Re: Engineering Senior Design Project 2011

Post by Viv » Wed Oct 19, 2011 3:08 pm

Hi,

For an engine pick a smaller engine that has more forum posts, that way you will tap in to more experience, very few people bother with big Lockwoods now as the bend is to expensive or hard to come by, they also have a tendency to "suck flat" the exhaust cone when built from carbon steel (it softens (it runs red hot) and the vacuum during the intake cycle does the rest;-) look at an FWE or similar.

Instrumenting an engine, I have built and designed five data acquisition systems for various engines now, my advice is start with a blank peace of paper and write down what it is you want to learn first, every thing else comes from this first step, honestly this is the hardest step to get right so focus on it ;-)

After that you can start to put together a plan

A small engine running on a test stand is as noisy as a large engine in real terms but the fuel flow problem is cut to a fraction, by that I mean maybe one BBQ bottle per 20 or 30 minute run (yes really) you will still need to make sure the bottle does not freeze and you will need to take steps to keep a constant fuel flow or it will affect your results, falling gas pressure will read as falling thrust/heat output during your test runs, expect to run flat out for 5 minutes minimum to heat soak the engine and stabilize it before you start to record results.

Carbon steel? forget it! it wont last at the run times you need to do for your results, imagine how an oxyacetylene torch works and what it does to steel, that is a good analogy of what a running pulse jet looks like to steel, its red hot or hotter with lots of air and oxygen being pulled past it, ordinary steel ether dissolves or suffers from so much oxide growth and flaking it becomes paper thin and fails very quickly.

Use stainless steel, get friendly with an exhaust shop for scrap tubing, try scrap yards 304 is ok (exhausts) 316L is common (dairy/food)

Hope that helps

Viv
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pulsejetgroup
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Re: Engineering Senior Design Project 2011

Post by pulsejetgroup » Wed Oct 19, 2011 8:28 pm

One of our constraints with this design is that we specified a 25 pound thrust engine or better in our proposal to the school. I should have mentioned that earlier. We're planning on having an engine built by Christmas, and the next semester will consist of running and instrumenting the engine. As far as the instrumentation goes we're mostly looking at measuring internal pressures and thrust. Maybe more if we can find the money. I guess we expected that with the materials though, stainless it is. Should be able to get a good deal from the technical college here. Thanks for the advice Viv. What kind of data were you collecting with your systems?

Right now we're pretty set on the M-40.

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Re: Engineering Senior Design Project 2011

Post by luc » Thu Oct 20, 2011 1:17 pm

304 is ok (exhausts) 316L is common (dairy/food)
Sorry ... But just so material, $$$ and time is not waisted ... It's the otherway around ...

304 = Dairy / Food
316 or 316L ("L" stands for "Low carbon") = Chamber / Exhaust (If we can say so, but I would not use it even) ...
Because here's what happen when you use 316 or 316L for a combustion chamber (See the image).

321 (Or higher grades) = Chamber & Exhaust

Hope that helps
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Combustion Chamber Deformation.JPG
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Re: Engineering Senior Design Project 2011

Post by Viv » Thu Oct 20, 2011 3:20 pm

The pictures show distortion in a section of a nose cone made by the metal spinning process, the uneven metal thickness results in the distinct bands of distortion you can see, it has nothing to do with the materiel or grade used, the heat from combustion causes the rippling effect as the different thicknesses of materiel work against each other as they expand and contract.

If you use plain sheet materiel then you should be fine ;-)

Hope that helps

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Re: Engineering Senior Design Project 2011

Post by Viv » Thu Oct 20, 2011 3:27 pm

Here is a better photo of that same engines failure mode, you can clearly see were the metal has been thinned down too far due to the metal spinning and how it has distorted in relation to the thicker section behind it.

Viv
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Re: Engineering Senior Design Project 2011

Post by Viv » Thu Oct 20, 2011 3:39 pm

pulsejetgroup wrote:One of our constraints with this design is that we specified a 25 pound thrust engine or better in our proposal to the school. I should have mentioned that earlier. We're planning on having an engine built by Christmas, and the next semester will consist of running and instrumenting the engine. As far as the instrumentation goes we're mostly looking at measuring internal pressures and thrust. Maybe more if we can find the money. I guess we expected that with the materials though, stainless it is. Should be able to get a good deal from the technical college here. Thanks for the advice Viv. What kind of data were you collecting with your systems?

Right now we're pretty set on the M-40.
Hi

Ok knowing the thrust target changes things, I would still have gone for a smaller more manageable engine though but that's water under the bridge now.

You said you wanted to measure and then improve, that is a good, so what do you want to measure? thrust is what every one aims for but it does not tell you much about how good your combustion or volumetric efficiency is, these are after all the two factors that add up to thrust.

My own targets in the past were for as much dynamic information on what was happening during the cycle and then improving those cycles so they added up to a better running engine or burner, that worked very well for me.

Pressure: is dynamic as the engine is constantly changing, good waveforms would be fun to have for comparison to sound pressure recordings outside the engine.

Temperature: normally just an average of the cycle temperature due to the speed of measurement, after all cheap thermocouples don't work at 150 Hz engine speed.

Air mass flow: that would be nice if you could work it out.

Fuel mass flow: again nice if you have have it calibrated some how and compare it to air flow?

Combustion products: can you borrow a chimney stack gas analyzer? Co2 Co Nox will tell you a lot about your combustion process/fuel/air mix

I am sure some of the more experienced members like Mike or Bruno can add to this list with ease

Viv
Last edited by Viv on Thu Oct 20, 2011 3:53 pm, edited 2 times in total.
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Re: Engineering Senior Design Project 2011

Post by luc » Thu Oct 20, 2011 3:40 pm

Viv wrote:The pictures show distortion in a section of a nose cone made by the metal spinning process
Sorry ... But that's the chamber right at the 3rd stage level. The nose cone is 3.5 inches further down ...
The steel bar on the left side is the coil attachment ...
Then ... You have the area for the 3rd stage (Apprx. 3.5 inches wide) ...
THEN ... the cone ...

Think I should know since I designed and built the darn thing ... :wink:

Anyway ... And still ...
304 = Dairy / Food
316 or 316L = Chamber / Exhaust (But not if you plan for long runs).
321 is better ... :wink:

P.S : Chamber is not spun since it's a cylinder ... :wink:
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Re: Engineering Senior Design Project 2011

Post by Viv » Thu Oct 20, 2011 3:52 pm

Mike, would you sort that out please.

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Re: Engineering Senior Design Project 2011

Post by luc » Thu Oct 20, 2011 5:16 pm

pulsejetgroup wrote:As far as the instrumentation goes we're mostly looking at measuring internal pressures and thrust.
A Little advice here ...

Be careful when selecting your thrust reading device. Regular "Strain" loadcells make poor thrust reading system as their reading cycle is for most of them, to slow for these engine's "Pulsed" thrust.

Better off with a "Dynamic" or "Quarts" loadcell like the DLC101-50 and here's a place where you can find or read about it ... http://www.omega.com/pptst/DLC101.html

Good day,
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Re: Engineering Senior Design Project 2011

Post by luc » Mon Oct 24, 2011 2:19 pm

Here's another usefull trick ...

This forum being so vaste, full of infos and/or other stuff ... Often hard to find back when needed ... You know :wink:
Do "Screenshots" of the pages or postings you find usefull to your project and save them as images so you can build your self an archive in reference of your "Interest" and use it so you don't have to spend time searching. A book sort of thing ...

You will find this very usefull when time comes ... :wink:

Did I say ... I LOVE "Screenshots"???? ... Frozen in Time and Unchangeable they are ... :wink:

I love fishing too ... :wink:

Good day and best of luck with your project ... :wink:
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Re: Engineering Senior Design Project 2011

Post by Viv » Mon Oct 24, 2011 7:30 pm

My apologies to you pulsejetgroup but some one is making a mess of this thread for you and that I do not think is very fair, I will not bother answering now in the hopes you can get the discussion back on topic and find some one else to help you with your project.

Good luck, hope your project goes well

Viv
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Re: Engineering Senior Design Project 2011

Post by metiz » Mon Oct 24, 2011 9:21 pm

Hello pulsejetgroup.

Have you started the build yet? If you need help with some construction details, let me know. you'd be amazed what you can do with a broomstick and hammer.

I would realy like to see a build of the M40 (please film a good run!) but if you're having cost issues (you shouldn't, scrap stainless is piss cheap) you can consider building the M25 instead. That engine will push 26.4 pounds at maximum throttle, but is a bit harder to start/ has tighter tollerances. Good luck with your project!
Last edited by metiz on Tue Oct 25, 2011 4:00 pm, edited 1 time in total.
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pulsejetgroup
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Re: Engineering Senior Design Project 2011

Post by pulsejetgroup » Tue Oct 25, 2011 2:39 pm

Good advice on the tubing inconsistencies, we’ll be checking that out for sure. As for the pressure, we’re looking for a transducer that is fast enough to measure the cycle. We’ll be measuring a few areas for pressure. Still deciding where the areas are going to be. The only load cells we have at school are strain types so we’ll need to get some new ones. Exhaust gas analysis sounds like a good idea too but we'll see what money and time allow. I’ll try to get the rest of the group going on this forum as well so they can put in their thoughts as well.

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Re: Engineering Senior Design Project 2011

Post by luc » Tue Oct 25, 2011 7:08 pm

As for the pressure, we’re looking for a transducer that is fast enough to measure the cycle.
Indeed ... You will have to consider the transducer and meter reading or sampling rate per second, as both must have reading capabilities exceeding the engine's normal pulsating frequency if you want to see peek pressures. You will probably have to "Trigger" the reading using a small DAS program. The dynamic loadcell can help you in that regards ... Or maybe a microphone if you have this linked to a very fast PC.
The only load cells we have at school are strain types so we’ll need to get some new ones.
"Strain" loadcell are good too if only they have a high reading sampling rate, but they usually don't and why my advice goes with a small dynamic one.

One big note here ... Be very carefull when building you test stand, and as you don't want this thing too flimsy. Weak, soft or flexy test stand have a way of screwing up accurate "Pulse-Jets" thrust readings. You don't want this stand to oscilate either way with your engine's pulsating thrust. ALL metals have a "Yield" and "Flex" momentum, even if 1 inch thick and that flex can really mislead you reading your engine's thrust.

PDE research programs have learn this the hard way. So true, that often for PDE engines, they limit them self reading only the first detonation, knowing the following ones are not accurate ... What ever bed rigidity they have.

But again, it all depends on "How accurate" you want to be ... But better knowing then not :wink:

Good day,
Luc
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