Detonation wuz Things not to wear when welding

[haygood at myway.com (Brian Haygood)]

There is also some engine related stuff in the last half of this! Lol.

That original myth is just that.  I've done a good bit of research over the last few months on combustions, detonations and explosions.  A plastic lighter, even though pressurized, shouldn't do any more than burn dramatically.  It would not explode for a few reasons.  Inside a lighter there shouldn't be any considerable amount of oxygen (if there were, you might be at risk for the thing igniting internally during use), so a flame would not burn inside the lighter body to explode the lighter.   If a flame did occur in the lighter, it would be deflagration, which is a slowly moving flame, like lighting a pool of gasoline.  It's cool, but you don't get anywhere near the "stick of dynamite" force until you get a detonation.  A deflagration becomes a detonation when the flamefront reaches the speed of sound.  There you get a sonic shockwave that concussively ignites a large amount of fuel mix all at once, resulting in dramatically higher pressures.  Enclosed deflagrations typically result in pressures 6 to ten fold that of the original pressure.  Detonations are way way beyond that.  Assuming there were a flame inside the lighter (which there couldn't be b/c of lack of oxygen), a flamefront requires a certain distance to accelerate and progress up to the speed of sound, determined by the type of fuel, pressure and container/flamefront geometries.  Suffice it to say there isn't enough room in a lighter for a detonation to occur in propane or whatever else is in those things.

Given the actual case, that there is no oxygen to burn inside a lighter (or hardly any, to be sure), the worst that could happen would be something perforating the plastic shell of the lighter, igniting it simultaneously, and guess what you get.  A flame.  You know, like you always get when you light a lighter.  No torso removing action here.   Maybe it could spew lighter fluid a bit and get a decent fire going, and I can see that being pretty bad.

So I promised something "on topic", right?   If you have a combustion in a combustion chamber of an engine, hopefully you have a deflagration.  If you have a really fast burning fuel, or if you have a really large diameter piston, then the distance from the end of the spark plug to the ends of the cylinder might exceed the minimum detonation-to-deflagration distance for the given fuel mix and pressures.  If that happens, you get detonation in your engine. The rapid combustion creates a big pressure spike that is audible.  The sound is called "knock" and a knock sensor is basically a microphone used to listen for it. Detonation became a problem in WWII aircraft engines as piston sizes grew dramatically.  The solution was to use two sparkplugs, effectively cutting the distance the flame front travels across the piston in half, and keeping this below the deflagration-to-detonation transition (DDT) distance.  Modern piston planes still have twin spark, and it is kept around as part of a redundant spark system that is supposed to save your butt if one magneto system fails.  While it will do that, that was not it's original purpose.  Personally, I don't think its worth keeping because I've never heard of someone no warning of electrical trouble (batt. light) long before their engine dies from lack of electricity, but then I'm not the FAA.

Octane is added to fuel because it doesn't burn as quickly as gasoline.  This slows the reaction rate, which increases the distance to the deflagration-to-detonation transition (DDT).  This keeps your engine from experiencing detonation.  With the reaction rate slowed, you are free to run higher compression.  The slower reaction provided by octane can also lead to a more even burn throughout the ignition cycle, which often leads to a more efficient running engine (slightly, and I know a lot less about that end of things).  

So detonation, or knock, is also completely separate from pre-ignintion.  That's when a poorly timed spark, or a hot ember on top of a piston (or such) ignites the mixture before it's time, and the flame front whacks into the top of the piston while the piston isn't free to move out of its way.  It's actually usually less violent than detonation (unless it happens so early that is causes a backfire and fries a turbo or something).  I think octane helps with that by slowing the reaction rate, allowing (and also requiring) more spark advance to get the flame and piston well synchronized.

Hope that was long and rambling enough for everyone!!! If I have missed or flubbed up some of this, you are all welcome to have a field day correcting me.  I'd want nothing less!  

Cheers,
Brian in Texas (not Pittsburgh)




 --- On Sun 04/11, David Utley < mr.utility@highstream.net > wrote:
From: David Utley [mailto: mr.utility@highstream.net]
To: ats@longcoeur.com, smithma7@yahoo.com, scirocco-l@scirocco.org
Date: Sun, 11 Apr 2004 11:39:55 -0500
Subject: RE: Things not to wear when welding

That reminds me of that Darwin award winner, that used a 22 unused shell as<br>a fuse in the fuseblock of his ford pickup (for the lights)...  Teseticular<br>removal at high speed, which then hearly killed his passenger as he wrecked<br>the truck...!<br><br>I hate that when -that-- happens...<br><br>David<br><br>-----Original Message-----<br>From: scirocco-l-bounces@scirocco.org<br>[mailto:scirocco-l-bounces@scirocco.org]On Behalf Of Patrick Bureau<br>Sent: Sunday, April 11, 2004 7:55 AM<br>To: 'Mike Smith'; 'car'<br>Subject: RE: Things not to wear when welding<br><br>Don't throw ammo in a fire, unless you don't value your life.<br><br>I know your joking around, but hundred of children and young men, each year<br>end up in hospitals and sometimes die in accidents, from people tossing<br>ammunition into fire camps or bond fires because "its cool to hear the<br>"BANG", and this list should not let such a comment go without a warning<br>(there are younger folks on this list that may get ideas from your words),<br>not to mention the risk of the live round flying through the camping ground<br>with nothing more than "tents" as barriers, you can definitely hurt a lot of<br>people with such a prank. Sorry if I am preaching here, but I think someone<br>had to speak up on that subject.<br><br>DO not put ANY ammunition in a fire period.<br><br>-<br>ATS - Patrick Bureau - http://ats.longcoeur.com -<br>A1 eBay Sales: http://tinyurl.com/22e5b<br><br><br>->-----Original Message-----<br>->From: scirocco-l-bounces@scirocco.org<br>->[mailto:scirocco-l-bounces@scirocco.org] On Behalf Of Mike Smith<br>->Sent: Sunday, April 11, 2004 1:00 AM<br>->To: car<br>->Subject: Re: Things not to wear when welding<br>-><br>->For the camping folks (me included) do we want to be invited<br>->back to Cowen?  This sounds like fun... <evil laugh>I can<br>->bring ammo</evil laugh><br>-><br>->Mike<br>->sshh!  There's liberals afoot!<br>->Scourge <scourge@cogeco.ca> wrote:<br>->lol, I've done that.....one of my freinds threw a full can of<br>->wd40 into a campfire...almost burnt down a few trees.<br>->I always liked cans of stew best......lol<br>-><br>-><br>->-George<br>-><br>->----- Original Message -----<br>->From: "C Boyko"<br>->To:<br>->Sent: Saturday, April 10, 2004 7:48 PM<br>->Subject: Re: Things not to wear when welding<br>-><br>-><br>->> If you want kablooey, toss an unopened Coke can into the<br>->old campfire.<br>->> Ask me how I know about this, oh yeah, I'm a mother of an<br>->idiot. Does<br>->> a really good job on the tents too, all that hot carmelized<br>->liquid and<br>->> shards of aluminum. DON'T try this, okay? It's a wonder soft drink<br>->> manufacturers<br>->don't<br>->> have a warning about it actually.<br>->> Cathy<br>->><br>->><br>->> >From: Dan Smith<br>->> >To: scirocco-l@scirocco.org<br>->> >Subject: Re: Things not to wear when welding<br>->> >Date: Sat, 10 Apr 2004 16:02:25 -0700 (PDT)<br>->> ><br>->> >Entirely different situation. When tossing lighters, it<br>->works by the<br>->> >top metal part breaking and sparking, causing the fluid to<br>->both pour<br>->> >out and light. It's about the same as pouring lighter fluid on the<br>->> >ground and lighting it. Remember lighters are pressurized and when<br>->> >you put a small piece of glowing hot metal into them, then<br>->they can<br>->> >explode. Think of it this way. Imagine shoving a red hot<br>->nail into a can of hairspray.<br>->Kablooey!<br>->> >Take a hairspray can and break the top off so the gas can freely<br>->> >escape<br>->and<br>->> >light it on fire. Not much happens besides a firely blaze.<br>->> ><br>->> >Dan<br>->> ><br>->> >chris gonzalez wrote:<br>->> >I call BS on that myth. I used to explode plastic lighters<br>->when I was<br>->> >a<br>->kid<br>->> >by throwing them at the ground. Just a big flame out, like<br>->when you<br>->> >pour lighter fluid on a BBQ. Absolutely no concussive force. You<br>->> >could definitely get burned, but doubt you'd get killed.<br>->Let's call<br>->> >Mythbusters....<br>->> ><br>->> >John Klun wrote:Dan and y'all:<br>->> ><br>->> 
 >The story below is quite true. In 1966 when the first BIC plastic<br>->> >lighters came out, lots of sailors bought them because they were<br>->> >cheaper than Zippos. A Naval Safety Bulletin was issued to<br>->the entire<br>->> >Navy in late 1967 early 1968 forbidding any one who was<br>->welding from<br>->> >keeping the plastic lighters in their breast pocket. The Bulletin<br>->> >referred to an accident that occurred to a sailor who was welding<br>->> >ashore. (At that time, the welding 'leathers' were more<br>->like butchers<br>->> >aprons- covered most of the body but did leave the breast pockets<br>->> >unprotected.) A spark from the sailor's welding torch struck his<br>->> >breast pocket, burned through to the lighter and it caused the<br>->> >lighter to explode. The bulleting referred to the<br>->resulting explosion<br>->> >as equivalent to the explosive force of a stick of<br>->dynamite resulting<br>->> >in the sailor's death. I do know that on our ship, any sailor<br>->> >assigned to welding and repair had to be 'inspected' by<br>->his leading<br>->> >P.O. or his Division Officer before being let loose with a<br>->welding torch....<br>->> ><br>->> >Dan Smith wrote:<br>->> ><br>->> > > He also knew of people (or stories of said people) who<br>->always kept<br>->their<br>->> >lighter in their breast pocket while welding and an errant piece of<br>->molten<br>->> >metal would land on/near the lighter, melt through it and blow off<br>->> >the person's torso.<br>->> > ><br>->> > >Dan<br>->> > ><br>->> > ><br>->> ><br>->> ><br>->> >_______________________________________________<br>->> >Scirocco-l mailing list<br>->> >Scirocco-l@scirocco.org<br>->> >http://neubayern.net/mailman/listinfo/scirocco-l<br>->> ><br>->> ><br>->> >---------------------------------<br>->> >Do you Yahoo!?<br>->> >Yahoo! Tax Center - File online by April 15th<br>->> >_______________________________________________<br>->> >Scirocco-l mailing list<br>->> >Scirocco-l@scirocco.org<br>->> >http://neubayern.net/mailman/listinfo/scirocco-l<br>->> ><br>->> >---------------------------------<br>->> >Do you Yahoo!?<br>->> >Yahoo! Tax Center - File online by April 15th<br>->> >_______________________________________________<br>->> >Scirocco-l mailing list<br>->> >Scirocco-l@scirocco.org<br>->> >http://neubayern.net/mailman/listinfo/scirocco-l<br>->><br>->> _________________________________________________________________<br>->><br>->http://join.msn.com/?pgmarket=en-ca&page=byoa/prem&xAPID=1994&;<br>->DI=1034&SU=htt<br>->p://hotmail.com/enca&HL=Market_MSNIS_Taglines<br>->><br>->><br>->> _______________________________________________<br>->> Scirocco-l mailing list<br>->> Scirocco-l@scirocco.org<br>->> http://neubayern.net/mailman/listinfo/scirocco-l<br>->><br>-><br>-><br>-><br>->_______________________________________________<br>->Scirocco-l mailing list<br>->Scirocco-l@scirocco.org<br>->http://neubayern.net/mailman/listinfo/scirocco-l<br>-><br>->word (w{rd)<br>->interj. Slang. Used to express approval or an affirmative<br>->response to something. Sometimes used with up. Source<br>-><br>->---------------------------------<br>->Do you Yahoo!?<br>->Yahoo! Tax Center - File online by April 15th<br>->_______________________________________________<br>->Scirocco-l mailing list<br>->Scirocco-l@scirocco.org<br>->http://neubayern.net/mailman/listinfo/scirocco-l<br>-><br>-><br><br><br><br>_______________________________________________<br>Scirocco-l mailing list<br>Scirocco-l@scirocco.org<br>http://neubayern.net/mailman/listinfo/scirocco-l<br><br><br>_______________________________________________<br>Scirocco-l mailing list<br>Scirocco-l@scirocco.org<br>http://neubayern.net/mailman/listinfo/scirocco-l<br>

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