PREDATOR - valveless PDE build blog
Moderator: Mike Everman
PREDATOR - valveless PDE build blog
Some months ago I started creating a valveless PDE , fueled by stoichiometric propane/air mixture. The already manufactured pieces are lying around and waiting for completion. Now I hope to speed up my efforts.
what has been done until now?
- applied PDE function principle: propane / air injector tube provides intermitted detonable gas mixture, that is pushed into DDT tube, where intermitted ignition is done by spark plug. Propane gas solenoid valve and ignition will be triggered by AVR ECU (timer programming)
- spreadsheet calculation of supersonic propane nozzle , air-gas injector (stoichiometry) and DDT tube dimensions has been done already.
- intake flare, injector tube and DDT tube are welded together (welding is not one of my favorite skills )
-- propane nozzle throat d = 1.15mm
-- injector tube d_i = 27mm ; L = 350mm ; high alloy stainless steel 2.8mm thickness
-- DDT tube d_i = 76mm (=minimum DDT cell size) ; L = ca 1600mm ; high alloy stainless steel 2.5mm thickness
-- 10mm thick steel Shchelkin spiral for advanced DDT (deflagration to detonation transition)
- recent gas and spark trigger technology is very crude : manual switch and piezo agitator. (AVR ECU will be completed next time)
no test run yet ! (but soon....)
what has been done until now?
- applied PDE function principle: propane / air injector tube provides intermitted detonable gas mixture, that is pushed into DDT tube, where intermitted ignition is done by spark plug. Propane gas solenoid valve and ignition will be triggered by AVR ECU (timer programming)
- spreadsheet calculation of supersonic propane nozzle , air-gas injector (stoichiometry) and DDT tube dimensions has been done already.
- intake flare, injector tube and DDT tube are welded together (welding is not one of my favorite skills )
-- propane nozzle throat d = 1.15mm
-- injector tube d_i = 27mm ; L = 350mm ; high alloy stainless steel 2.8mm thickness
-- DDT tube d_i = 76mm (=minimum DDT cell size) ; L = ca 1600mm ; high alloy stainless steel 2.5mm thickness
-- 10mm thick steel Shchelkin spiral for advanced DDT (deflagration to detonation transition)
- recent gas and spark trigger technology is very crude : manual switch and piezo agitator. (AVR ECU will be completed next time)
no test run yet ! (but soon....)
___________________________
zono - the thruster buster
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zono - the thruster buster
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Re: PREDATOR - valveless PDE build blog
Not only an actual attempt but also a build log! I realy hope you make me swallow my words
Any estimation when you will have this engine done? Also, on topic more or less, what exactly is a Shchelkin spiral; what is its exact function? It's very hard to get any good info on the thing.
Good work so far!
Any estimation when you will have this engine done? Also, on topic more or less, what exactly is a Shchelkin spiral; what is its exact function? It's very hard to get any good info on the thing.
Good work so far!
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Re: PREDATOR - valveless PDE build blog
I am very covered by my job, so I can't do an estimation, when we will hear the first BANG- BANGs . But I will speed-up
Shchelkin spiral helps speed-up DDT by causing turbulences, so detonation tube can be shortened. Normally DDT minimum lenth of propane/air mix is (cant remember exactly) ca 1.8 ... 2.5 meters. Good starting point on literature:
http://en.wikipedia.org/wiki/Shchelkin_spiral
Instead of Shchelkin spirals many other obstacles has been tried by research institutes. Orifices, wedges, cavities....all objects, that can cause turbulence are principally applicable.
Shchelkin spiral helps speed-up DDT by causing turbulences, so detonation tube can be shortened. Normally DDT minimum lenth of propane/air mix is (cant remember exactly) ca 1.8 ... 2.5 meters. Good starting point on literature:
http://en.wikipedia.org/wiki/Shchelkin_spiral
Instead of Shchelkin spirals many other obstacles has been tried by research institutes. Orifices, wedges, cavities....all objects, that can cause turbulence are principally applicable.
___________________________
zono - the thruster buster
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zono - the thruster buster
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Re: PREDATOR - valveless PDE build blog
Ok thanks for the info. Do you know what a Tesla valveless conduit is? It constantly reverses flow back onto itself. Maybe if that same principle was incorporated inside a ddt engine tailpipe it would cause sufficient pressure build-up to do the same thing, maybe even quicker...hmm food for thought
Last edited by metiz on Sun Oct 10, 2010 10:15 pm, edited 2 times in total.
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Re: PREDATOR - valveless PDE build blog
Btw reading your description, am I right in asuming this engine does not breath on its own or auto-ignites?
Quantify the world.
Re: PREDATOR - valveless PDE build blog
yes, I know the Tesla valve, but I don't make use of in on PDE construction. My PDE is quite simple: intermitting self-breathing by supersonic propane-injection (jet-pump principle = air suction by propane-jet). No auto-ignition. Ignition spark is triggered at end of propane injection. See the sketch of valveless PDE.
- Attachments
-
- Predator-PDE.png
- (9.72 KiB) Downloaded 216 times
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zono - the thruster buster
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zono - the thruster buster
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Re: PREDATOR - valveless PDE build blog
Ok thanks for the info. very professional build so far, excellent work
Is your knowledge on the subject purely self taught i.e for hobby purposes or does your job have something to do with propulsion/ acoustics as well?
Is your knowledge on the subject purely self taught i.e for hobby purposes or does your job have something to do with propulsion/ acoustics as well?
Quantify the world.
Re: PREDATOR - valveless PDE build blog
Yes, its an own development for non-commercial purposes, but I have some background knowledge as I am a chemical process engineer. So far fluid dynamics and thermodynamics and propulsion touches my job in general.
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zono - the thruster buster
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zono - the thruster buster
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Re: PREDATOR - valveless PDE build blog
Good work, and it is good to see a build log here.
Be safe, this is a high risk area with little payout for Do It Yourself folk.
Attaching the internal objects should be done with care, in the past they have been shot out the tube in bullet fashion.
In short, don't have anything of value down or up range. Secure the engine well.
Survivability is often relative to proximity, best to give some distance.
Thanks for sharing, Joe
Be safe, this is a high risk area with little payout for Do It Yourself folk.
Attaching the internal objects should be done with care, in the past they have been shot out the tube in bullet fashion.
In short, don't have anything of value down or up range. Secure the engine well.
Survivability is often relative to proximity, best to give some distance.
Thanks for sharing, Joe
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Re: PREDATOR - valveless PDE build blog
Hi Zono
Looks nice to me, I like your simpler approach to getting some thing to go bang but I did wonder about your tube sizing as its pretty much on the minimum cell size for propane, my question is this, does the shchelkin coil occupy some of the space in your DDT tube that the shock cell needs to occupy? so 75mm for the cell plus the shchelkin coil = the inner DDT size?
Viv
Looks nice to me, I like your simpler approach to getting some thing to go bang but I did wonder about your tube sizing as its pretty much on the minimum cell size for propane, my question is this, does the shchelkin coil occupy some of the space in your DDT tube that the shock cell needs to occupy? so 75mm for the cell plus the shchelkin coil = the inner DDT size?
Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke
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Monsieur le commentaire
Viv's blog
Monsieur le commentaire
Re: PREDATOR - valveless PDE build blog
Hi friends,
I am very glad, that you like this build ! Hopefully you get satisfying answers from myself.
Ok, I am aware, that 76mm dia and blockage by Shchelkin spiral affecting or concerning a possible run. The good news is that (on literature I read) obstacles lower the necessary cell size, so we wait and see....The simple reason is, I got this tube very cheap out of scrap metal. If it doesn't work, I will take 100mm dia.
Safety: the maximum detonation pressure of propane-air mix is by Chapman–Jouguet-condition only 18 bars, so most bicycle tires could withstand this load --- really dangerous is hydrogen or acetylene with oxygen
Now i am on travel for some days, and will continue after that. so long, guys...
I am very glad, that you like this build ! Hopefully you get satisfying answers from myself.
Ok, I am aware, that 76mm dia and blockage by Shchelkin spiral affecting or concerning a possible run. The good news is that (on literature I read) obstacles lower the necessary cell size, so we wait and see....The simple reason is, I got this tube very cheap out of scrap metal. If it doesn't work, I will take 100mm dia.
Safety: the maximum detonation pressure of propane-air mix is by Chapman–Jouguet-condition only 18 bars, so most bicycle tires could withstand this load --- really dangerous is hydrogen or acetylene with oxygen
Now i am on travel for some days, and will continue after that. so long, guys...
___________________________
zono - the thruster buster
--------------------------------------
zono - the thruster buster
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-
- Posts: 2158
- Joined: Sat Oct 04, 2003 2:35 pm
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- Contact:
Re: PREDATOR - valveless PDE build blog
Hi Zonozono wrote:Hi friends,
I am very glad, that you like this build ! Hopefully you get satisfying answers from myself.
Ok, I am aware, that 76mm dia and blockage by Shchelkin spiral affecting or concerning a possible run. The good news is that (on literature I read) obstacles lower the necessary cell size, so we wait and see....The simple reason is, I got this tube very cheap out of scrap metal. If it doesn't work, I will take 100mm dia.
Safety: the maximum detonation pressure of propane-air mix is by Chapman–Jouguet-condition only 18 bars, so most bicycle tires could withstand this load --- really dangerous is hydrogen or acetylene with oxygen
Now i am on travel for some days, and will continue after that. so long, guys...
Thanks for the answer, I would be interested to read the reference on cell size reduction if you can post it when you get back
Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke
Viv's blog
Monsieur le commentaire
Viv's blog
Monsieur le commentaire
Re: PREDATOR - valveless PDE build blog
Hi All !
See some useful literature regarding cell size and other dimensioning parameters (answer to Viv's question)
here "quasi-detonation" is explained for tube diameters smaller than cell-size
http://www.iwr.uni-heidelberg.de/groups ... 00/231.pdf
other useful stuff :
http://www.dtic.mil/cgi-bin/GetTRDoc?Lo ... =ADA411011
http://conference.ing.unipi.it/ichs2007 ... 1.3.40.pdf
http://www.gexcon.com/handbook/GEXHBcontents.htm
here is a good explanation of "cell size" (tube diameter may have minimum cellsize/3 ) :
http://www.gexcon.com/handbook/GEXHBchap6.htm
See some useful literature regarding cell size and other dimensioning parameters (answer to Viv's question)
here "quasi-detonation" is explained for tube diameters smaller than cell-size
http://www.iwr.uni-heidelberg.de/groups ... 00/231.pdf
other useful stuff :
http://www.dtic.mil/cgi-bin/GetTRDoc?Lo ... =ADA411011
http://conference.ing.unipi.it/ichs2007 ... 1.3.40.pdf
http://www.gexcon.com/handbook/GEXHBcontents.htm
here is a good explanation of "cell size" (tube diameter may have minimum cellsize/3 ) :
http://www.gexcon.com/handbook/GEXHBchap6.htm
___________________________
zono - the thruster buster
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zono - the thruster buster
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Re: PREDATOR - valveless PDE build blog
announcement:
in the next days I hope to start first static tests with single-shot
in the next days I hope to start first static tests with single-shot
___________________________
zono - the thruster buster
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zono - the thruster buster
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successful run !!!!
Hi All,
end of May I had some successful runs of valveless PDE "Predator" !
This videos don't look or sound very spectacular (bright daylight, microphone overblow...), but believe me: detonations blastwaves give a nice massage of your intestins!
So, consider these details : wiggling and trembling frame and concrete plate (weight) ; and echo of detonations. The surging sound is made by the propane injector, which provides the stoichiometric mix with air. Sometimes you can hear some self-ignition pulsations like in a normal valveless pulsejet.
http://www.youtube.com/watch?v=j7av5ae7dDI
http://www.youtube.com/watch?v=yAnFORosMPs
end of May I had some successful runs of valveless PDE "Predator" !
This videos don't look or sound very spectacular (bright daylight, microphone overblow...), but believe me: detonations blastwaves give a nice massage of your intestins!
So, consider these details : wiggling and trembling frame and concrete plate (weight) ; and echo of detonations. The surging sound is made by the propane injector, which provides the stoichiometric mix with air. Sometimes you can hear some self-ignition pulsations like in a normal valveless pulsejet.
http://www.youtube.com/watch?v=j7av5ae7dDI
http://www.youtube.com/watch?v=yAnFORosMPs
___________________________
zono - the thruster buster
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zono - the thruster buster
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