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whats wits everyone saying that DDT will blow up steel pipe

A place to ask general spud cannon related questions.
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Unread postAuthor: paaiyan » Mon Sep 03, 2007 10:16 am

pyro86 wrote:ALL THE INFORMATION BELOW CAME FROM WIKIPEDIA AND IS 100% FACT


Yea... Try that in any respectable college, and then tell me if you fail the paper or not...
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Unread postAuthor: turbohacker » Mon Sep 03, 2007 11:13 am

I have one problom with this.

Have you ever seen how thick cylinder walls are on a diesel engine? Everything that you have pictured are piston sleeves, which are not designed to harness all the stresses of the cumustion process, they are just a smooth surfuse for the piston rings to seal aganst.
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Cylinder_Block_for_Deutz_F6L913.jpg
Notice at least an inch between cylender walls.
Cylinder_Block_for_Deutz_F6L913.jpg (15.71 KiB) Viewed 358 times
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If it walks like a dog, sratches like a dog, and barks like a dog, than its probobly a...-TURTLE, it's a TURTLE!!! Cant you see?!!!

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Unread postAuthor: SpudBlaster15 » Mon Sep 03, 2007 11:58 am

It is unlikely that a detonation will damage an engine block, which is at least an inch thick at it's thinnest point, but detonation is well known in the automotive world to cause severe damage to the much thinner piston.

Also, pyro, your comparison is invalidated by the fact that almost all engine blocks are made from aluminum, which responds differently to detonation forces than steel.
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Unread postAuthor: CannonBall » Mon Sep 03, 2007 12:13 pm

well..
I would say sch 40 cant hold the 30x mix pressure...
But how do you guys prove that DDT will happen..
Commonly everybody say ddt will happen at 5x or 6x mix...
Well im shooting my cannon at 7.5 x.... did it burst nope !
My chamber is now regular plumbing pipe rated at 150psi.
cause the sch80 was to heavy..

Its hard to say if sch40 will blow it can certainly hold a 8 x .. we dont know when DDT occurs at wich pressure..
I only know that a sch40 wont held a 30x
A cilinder from a moped is at least 0.8 cm thick.. that is alot more than sch40.
ehmm an engine block aluminium... isnt aluminium less strong than steel

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Unread postAuthor: spud yeti » Mon Sep 03, 2007 12:31 pm

pyro86, your poll only allows for[quoted] "half retarded american's" to disagree with your (half retarded) statement. Now I'm a South African, and pretty much disagree... Oh dear, whatever can I do? [/sarcasm]
Please accomodate for all next time
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really good quote/phrase here
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Unread postAuthor: noname » Mon Sep 03, 2007 12:46 pm

A 10" long 2" Sch 40 steel chamber will hold an 8x mixture just fine, as long as you have the fittings screwed in with at least 5 or 6 threads.
I would have kept the 1/2" pipe as a souvenoir type thing, but I deemed it useless after it almost blew up. :? I definitely should have taken pictures of it first.
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Unread postAuthor: PCGUY » Mon Sep 03, 2007 12:49 pm

Pyro you are welcome to disagree with anything and argue a point, however screaming in your posts and making a poll and saying Americans are stupid is not welcome.

This thread is on it's last leg. Anymore outbursts should be reported to me, and Pyro you will have to be delt with.

Poll edited.
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Unread postAuthor: jimmy101 » Mon Sep 03, 2007 12:54 pm

I believe most people have a major misunderstanding of what DDT is and how it relates to engine predetonation (pining, knocking etc.).

I don't believe a gasoline engine ever does a DDT. Predetonation, pinking etc. is not the same as DDT. In an engine the "DDT" events are small local events, they do not involve the entire volume of unburned fuel.

In a normal combustion cycle the pressure versus time curve looks similar to what you get in a spud gun. A fairly fast rise in pressure, the rate at which this occurs varies somewhat with conditions.

In test engines that can measure the pressure versus time curve to a high degree of accuracy (in both the pressure and time domains) "pinging" is not a rapid spike in the pressure representing essentially instantaneous combustion of the remaining fuel. Instead, and this is key, predetonation is a series of fairly small detonation events, each involving only a very small amount of the remaining fuel. On a pressure versus time graph there are many of these events, not just one.

Each of these events releases a fair amount of energy but not nearly enough to do any damage to an engine. The main mechanical problem is that these events resonate in the engine. Under certain circumstances this resonation can do damage to parts of the engine that aren't even in the cylinder (like rods, bearings etc.)

I'll see if I can rumage up a nice pressure versus time graph of a gasoline engine undergoing significant pinging.
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Unread postAuthor: boilingleadbath » Mon Sep 03, 2007 1:03 pm

"Try quoting wikipedia in a college-level research paper"
...quoting <i>any</i> encyclopedia in a college-level research paper is a bad idea.

That said:
1) It is my understanding that diesel engines first compress the air until it's hot, and THEN inject the fuel. This prevents detonation, as there is no large mass of pre-mixed gases.

2) As others have said, your pictured items are piston sleeves... if they where not supported by the engine block, they'd rupture in the same manner an unsupported case wall would rupture in a firearm. (what, you thought .01" thick brass held 60,000 psi?)

3) DDT isn't a very pressure-dependent phenomenon.
A 1x mix can detonate. A 30x mix can burn.
Rather, it is dependent upon:
a - oxygen concentration
b - temperature
c - pipe diameter
d - run-up distance
(high oxygen concentrations, elevated temperatures, and small pipe diameters REDUCE the distance require for a combustion to transition to a detonation.)

Either way, you shouldn't be running 20x mixes in your typical sch 40 steel pipe; I don't think it's rated to 2000 psi.
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Unread postAuthor: spud yeti » Mon Sep 03, 2007 1:04 pm

Poll edited.

Thank you PCguy, you officially made my day with that one :D
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really good quote/phrase here
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Unread postAuthor: noname » Mon Sep 03, 2007 1:11 pm

I've often heard DDT and lean mix detonation; are they linked or the same thing? As in, having a leaner mixture increases chance of detonation?
A 2" x 10" chamber is like a 1/2" x 2.5" chamber. Having a 5 foot x 1/2" chamber (DDT occured) would be like a 40 foot 2" chamber. Using a larger diameter and shorter overall length chamber will decrease the chance of detonatin by quite a bit, because it doesn't give the flame front time to further compress and ignite the gases in front of the flame front.
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Unread postAuthor: pyro86 » Mon Sep 03, 2007 2:51 pm

I'm baaaaaaaaaaaaack
pyro: the shockwave would only act on the walls of the cylinder and the cylinder itself won't burst because that would require enough force to blast open the engine block, which CAN NOT be generated because the detonation moves the piston and releases the excess gas at the end of the stroke.

try to picture the piston as a potato and the potato releases the excess gas when it leaves the barrel

but detonation is well known in the automotive world to cause severe damage to the much thinner piston.

ya it melts it

I've often heard DDT and lean mix detonation; are they linked or the same thing? As in, having a leaner mixture increases chance of detonation?
A 2" x 10" chamber is like a 1/2" x 2.5" chamber. Having a 5 foot x 1/2" chamber (DDT occured) would be like a 40 foot 2" chamber. Using a larger diameter and shorter overall length chamber will decrease the chance of detonatin by quite a bit, because it doesn't give the flame front time to further compress and ignite the gases in front of the flame front.

you got the right idea heres what causes detonation: advanced spark timing , high compression with crappy gas, and running lean

Try quoting wikipedia in a college-level research paper"
...quoting any encyclopedia in a college-level research paper is a bad idea


i put the wikipedia stuff for you, i got my understanding from real world experience, like when i advanced the timing on my lawnmower motor and ran it on 13 to 1 mixture of alcohol and i got rid of the head gasket \

it ran and sounded like pieces were smashing (DETONATION) and MELTED a couple minutes later
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Attachments
ns_cylinder_1.jpg
a 2 stroke cylinder that runs a 6 to1 compression ratio and can detonate without problems
ns_cylinder_1.jpg (15.54 KiB) Viewed 281 times
ns_cylinder_1.jpg
6 to 1 compession can handle repeated detonations until it melts

WHY DO PEOPLE WORRY ABOUT 6X IN STEEL PIPE?
ns_cylinder_1.jpg (15.54 KiB) Viewed 275 times
Last edited by pyro86 on Mon Sep 03, 2007 3:11 pm, edited 2 times in total.
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Unread postAuthor: SpudBlaster15 » Mon Sep 03, 2007 3:00 pm

Jimmy raises an interesting point.

In test engines that can measure the pressure versus time curve to a high degree of accuracy (in both the pressure and time domains) "pinging" is not a rapid spike in the pressure representing essentially instantaneous combustion of the remaining fuel. Instead, and this is key, predetonation is a series of fairly small detonation events, each involving only a very small amount of the remaining fuel.


Pyro86, the detonation you are describing that occurs in engines is NOT the same as the detonation of a large percentage of the fuel in a combustion cannon's chamber. As jimmy said, detonation in a car engine does NOT involve a large percentage of the fuel, and is thus nowhere close to the same level as a detonation that occurs when say, 75% of the fuel mixture is left in the chamber of a combustion cannon.
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Unread postAuthor: turbohacker » Mon Sep 03, 2007 3:10 pm

Sch 40 galvanised pipe is not even designed for heat, I do not belive that this pipe will handle a 30x mixture.


SpudBlaster15 wrote:Also, pyro, your comparison is invalidated by the fact that almost all engine blocks are made from aluminum, which responds differently to detonation forces than steel.


Sorry, most engine blocks are cast steel or iron. I pit drag race in the outlaw series and run an all aluminum big block which cost the guy well over $2000 just for the bare block. 95% of all V8 enines on the road are not aluminum. (maybe aluminum heads)
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If it walks like a dog, sratches like a dog, and barks like a dog, than its probobly a...-TURTLE, it's a TURTLE!!! Cant you see?!!!

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Unread postAuthor: Pete Zaria » Mon Sep 03, 2007 3:12 pm

@pyro86,

Sir, your arrogance continues to baffle me.

Two moderators and the owner of this site told you that you were being arrogant and spewing bullshit - we edited your thread at least twice, PM'ed you at least twice...

And here you are, STILL defending your argument which several senior members have already proven to be inaccurate, and you have not offered an apology whatsoever, not even an "ok, sorry, I'll try not to do it again".

I don't know much about you, but I can tell that you're an angry young lad with some self confidence issues. Otherwise, you wouldn't be aggressively defending a point that's already had holes shot in it, and refusing to acknowledge that you might be wrong, or that you've pissed people off. I hope you find a way to deflate your ego a bit before college, otherwise you're going to have a real hard time.

Peace,
Pete Zaria.
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