OCTANE----PRE-IGNITION
Thread Starter
Teching In
Joined: Feb 2002
Posts: 25
Likes: 0
From: College Station, TX
OCTANE----PRE-IGNITION so me and my buddy are having issues.
lets suppose im driving home in my above average WS6 when behold, the heat from my header fries only one of my spark plug wires (assume no spark). the other 7 cylinders are pumping like champs. meanwhile, the cylinder with no spark is still being pumped full of air and fuel. what happens here? does the mixture combust completely due to the pressure of the piston and heat from the head and adjacent cylinders? does it combust only partially, leaving your hometown full of crap? or does it not combust at all, and exit through the exhaust valve? assume normal atmospheric conditions standard ls1 or lt1 CR, and premium fuel ( i dunno...91?)
i say the mixture combusts partially (not clean).
my friend says in his words "nothing will happen. fuel will just come out."
so...i know compression ratio, air density, octane, temperature, and a couple other things determine the rate of burn. make a few assumptions.
who's right?
<small>[ November 04, 2002, 11:18 PM: Message edited by: Cobalt ]</small>
lets suppose im driving home in my above average WS6 when behold, the heat from my header fries only one of my spark plug wires (assume no spark). the other 7 cylinders are pumping like champs. meanwhile, the cylinder with no spark is still being pumped full of air and fuel. what happens here? does the mixture combust completely due to the pressure of the piston and heat from the head and adjacent cylinders? does it combust only partially, leaving your hometown full of crap? or does it not combust at all, and exit through the exhaust valve? assume normal atmospheric conditions standard ls1 or lt1 CR, and premium fuel ( i dunno...91?)
i say the mixture combusts partially (not clean).
my friend says in his words "nothing will happen. fuel will just come out."
so...i know compression ratio, air density, octane, temperature, and a couple other things determine the rate of burn. make a few assumptions.
who's right?
<small>[ November 04, 2002, 11:18 PM: Message edited by: Cobalt ]</small>
Re: OCTANE----PRE-IGNITION </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">It just comes out...</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">IOW: (I believe) the mixture does not partially burn up on a well running (no heat spots) above average WS6, such as yours, in this scenario. If it did I believe pre-ignition would be a bigger problem than it is. I think you are about to get owned by your friend.
Just a guess!
<small>[ November 04, 2002, 11:37 PM: Message edited by: 96-speed ]</small>
Just a guess!
<small>[ November 04, 2002, 11:37 PM: Message edited by: 96-speed ]</small>
Re: OCTANE----PRE-IGNITION </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Cobalt:
<strong>ALERT: 96-speed is the friend.
cheater.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Haha
I am no expert by any means. But assuming there is 0 and I stress 0 spark in the chamber along with the rest of your conditions I would say the A/F charge is just along for the ride through the head and out the exhaust wothout combusting. You would probably throw a misfire code as well. If there really was no spark and you had ignition in that cylinder that means problems like pre-gnition or hot spots, bad gas, etc.
Most of my experiences with something similiar to this though have almost always had a partial spark making its way to the plug...and giving partial combustion of some type.
<strong>ALERT: 96-speed is the friend.
cheater.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Haha
I am no expert by any means. But assuming there is 0 and I stress 0 spark in the chamber along with the rest of your conditions I would say the A/F charge is just along for the ride through the head and out the exhaust wothout combusting. You would probably throw a misfire code as well. If there really was no spark and you had ignition in that cylinder that means problems like pre-gnition or hot spots, bad gas, etc.
Most of my experiences with something similiar to this though have almost always had a partial spark making its way to the plug...and giving partial combustion of some type.
TECH Fanatic
Joined: Aug 2002
Posts: 1,566
Likes: 0
From: Objects in mirror no longer matter.
Re: OCTANE----PRE-IGNITION </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Cobalt:
<strong>does anyone know the amount of CR and heat to combust 93 octane gas, with no spark?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Its definately not enough to cause combustion without ignition. Put your hand on the header primary after a few minutes and you can see how it stays cool.
<strong>does anyone know the amount of CR and heat to combust 93 octane gas, with no spark?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Its definately not enough to cause combustion without ignition. Put your hand on the header primary after a few minutes and you can see how it stays cool.
Re: OCTANE----PRE-IGNITION If it did come out i think it would throw your whole A/F ratio off because the computer is giving the engine gas for 8 cylenders but only 7 are working. when it gets to the 02's its gona tell the computer that the engine is running rich therefore putting less gas in the engine and causing the other cylenders to run lean and then knock then it retards the ignition and tries to give it more gas to stop the knock and messes everything up. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Trending Topics
Re: OCTANE----PRE-IGNITION And then making it go through the cycle of making it lean knocking then retarding the ingnition and givvin it more gas then running rich and keeps going and going and going and I think it causes a crap idle. So whoes car did this happen to, you or your friend <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Launching!
Joined: Dec 2001
Posts: 206
Likes: 0
From: N. Carolina
Re: OCTANE----PRE-IGNITION Trust me....
With no spark at all, raw gas will be pumped out of the cylinder into the exhaust system washing oil off the rings and cylinders as it goes. You would need diesel type compression (16:1 or higher) to burn the fuel mixture with no spark in a gas motor. At such high compression, the gas mixture will not 'burn' as it should, but will simply EXPLODE, and the results will not be pretty. In addition, you'll throw some sort of SES code from such things as spark knock, O2 sensor, etc.....
With no spark at all, raw gas will be pumped out of the cylinder into the exhaust system washing oil off the rings and cylinders as it goes. You would need diesel type compression (16:1 or higher) to burn the fuel mixture with no spark in a gas motor. At such high compression, the gas mixture will not 'burn' as it should, but will simply EXPLODE, and the results will not be pretty. In addition, you'll throw some sort of SES code from such things as spark knock, O2 sensor, etc.....
Thread Starter
Teching In
Joined: Feb 2002
Posts: 25
Likes: 0
From: College Station, TX
Re: OCTANE----PRE-IGNITION well, everything people are saying makes sense.
i am curious though NC Guy, where did you come up with a 16:1 CR in order for the fuel to ignite with no spark? not saying your wrong, so please dont take it that way. it just seems like an assumption? <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />
i am curious though NC Guy, where did you come up with a 16:1 CR in order for the fuel to ignite with no spark? not saying your wrong, so please dont take it that way. it just seems like an assumption? <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />
Re: OCTANE----PRE-IGNITION Diesel engines work by having the CR so high that the compression burns the fuel, not a spark. So in order to make the fuel burn they have to use more compression, to make more heat, to make the A/F mixture burn. Something else that help diesel engines work is the heat from the turbo. You know how if you run too much bost how your engine knocks, pings, detonates, and all the other stuff. Thats what a diesel engine lives off of. Thats why the internals or diesel engines are made of iorn. and because of the parts being so heavy they cant spin that high of an rpm, and theyre gear ratios are numericly low, but they make so much TQ that it can pull thoes gears. Someone correct me if im wrong.
Thread Starter
Teching In
Joined: Feb 2002
Posts: 25
Likes: 0
From: College Station, TX
Re: OCTANE----PRE-IGNITION stang killer....ive got a good grip on the theory behind diesel engines. btw, they also use glow plugs to heat the cylinder up before starting to help combustion.
theres got to be a static CR that is needed in order to ignite 93 octane fuel. right?
theres got to be a static CR that is needed in order to ignite 93 octane fuel. right?
Re: OCTANE----PRE-IGNITION yes,
When there is no spark you have a dead hole, you could touch the header tube when you are done with it, it will be cold. The air/fuel with head right to the exhaust and prolly throw a code because you will be rich and the computer can't fix it.
Gas in an engine never explodes, it burns. Explosions by definition are at a high rate of speed like 2000mph rather than the 6-7mph of BURN that happens in a engine. The pre-ignion, or knock is caused when the charge starts to burn some place else and the two flame fronts meet and "knock" into each other. A octane rating is the ability for it to resist doing this without the introduction of a spark into the system.
The dynamic compression ratio is more important to induce a burn on gas when it is ignited, but I don't really think there is a minimum, but yes it will be more inefficent.
I don't want to support another forum, especially one I don't sponsor, but the CamaroZ28 Advanced Tech Forum has this same question in it right now and it gets even more indepth.
Bret
<small>[ November 06, 2002, 12:01 AM: Message edited by: SStrokerAce ]</small>
When there is no spark you have a dead hole, you could touch the header tube when you are done with it, it will be cold. The air/fuel with head right to the exhaust and prolly throw a code because you will be rich and the computer can't fix it.
Gas in an engine never explodes, it burns. Explosions by definition are at a high rate of speed like 2000mph rather than the 6-7mph of BURN that happens in a engine. The pre-ignion, or knock is caused when the charge starts to burn some place else and the two flame fronts meet and "knock" into each other. A octane rating is the ability for it to resist doing this without the introduction of a spark into the system.
The dynamic compression ratio is more important to induce a burn on gas when it is ignited, but I don't really think there is a minimum, but yes it will be more inefficent.
I don't want to support another forum, especially one I don't sponsor, but the CamaroZ28 Advanced Tech Forum has this same question in it right now and it gets even more indepth.
Bret
<small>[ November 06, 2002, 12:01 AM: Message edited by: SStrokerAce ]</small>
Re: OCTANE----PRE-IGNITION Cobalt, the theory of CR igniting fuel is slid. The important part is that diesel burns slower than high octane gas. If you put diesel in your car you get a very poor running if it all engine. On the other hand you put high octane in a diesel, you get an explosion, an uncontrolled release of atomic energy that simply cannot be tolerated in an engine. So, how can the dragsters get away with it. I believe timing is set, compression is just under volitile levels and all that shant. So, it is clear that 96-speed does in fact got ya. Good point about the glow plugs, but you can crank the engine long enough the internal temps will raise to a suitable level to ignite the fuel- I used to do this to the Army HMMWV's-in time of need of course <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> . Later.
Charlie.
Charlie.
