This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
I deleted this para: "Knock is detonation within the cylinder. Uncontrolled combustion. It is not the same as pinging/pinking which is pre-ignition.". As far as I'm aware (25 years of experience with engines aware, that is), this is wrong - preignition and pinking ARE the same thing. It's also pinKing, not pinGing, though perhaps in some parts of the world it's called that? - I suppose the sound is a sort of ping GRAHAMUK 06:35, 3 August 2003 (UTC)
I saw the suggestion on merging this article with Engine Knocking. If to merge means also move, ie the original article willo ceases to exist then I am against this. Detonation is not unique to engine knocking at all. The Detonation process is also core to the Pulse Detonation Engine [no cylinders] among many other things which is why I found it. Had it been merged with Engine Knocking I doubtfully would have come across it. I would suggest keeping the original article and continue to add to it from the detonation science theoretical point of view but additionally incorporate whatever is needed in the Engine Knocking Article.
Just my 2 cents ? Any thoughts ? Steve Mew Sunday, 5 February 2006, 07:07:19 GMT
detonation occurs when the flame fronts pressure wave ignites the air fuel mixture instead of the heat of the front itself causing the burn to advance at the local speed of sound rather than the relatively benign rate of 50-100 feet per second these multiple pockets and colliding flame fronts you speak of are fictional —Preceding unsigned comment added by 99.164.52.146 ( talk) 04:26, 16 October 2007 (UTC)
As I have been taught, knock and ping are actually two different things. Although they are somewhat related in this topic they do occur at different stages of the cycle.
Knocking can occur under pre-ignition due to poor quality fuel, carbon deposits, etc. or due to improper timing (advanced), many reasons have been mentioned earlier in this discussion. The 'knock' comes from the piston being forced down on its up-stroke by the pre-ignition or the spark firing too soon, banging the piston down while it's trying to move up and against the cylinder wall, rattling the works all the way to the crank. This opposition of forces is what makes it louder and more pronounced.
Pinging occurs from post ignition, after the piston reaches TDC and begins its down-stroke. Caused by poorly ignited fuel resulting in an extended or delayed ignition, too much fuel resulting in an extended combustion cycle or improper timing (retarded), Etc.. Basically anything that could cause an undesirable ignition after TDC.
Although the two are both ignition problems whereas the air fuel mixture is ignited either too soon or too late, or burns too long. But the difference being that the 'Knock' is usually much more audible than the 'Ping' since the piston is already on its way down. You can actually have ping without the knock, or knock without the ping. You could even have a ping and not know it, but chances are you'd hear a knock!
The two terms when used properly actually do better define which part of the cycle is malfunctioning. -- DP67 ( talk/ contribs) 23:28, 4 December 2007 (UTC)
Until someone actually quantifies the impulse associated with the shock waves associated with the collision of flame fronts, I will continue to regard all such talk as a load of nonsense. The energy associated with those shock waves cannot possibly be anywhere near as great as the total amount of energy released by the combustion of the fuel. In fact, if you stop and think about it for a few minutes, you will likely find yourself doubting that the energy associated with these shock waves could be more than a few percent of the total energy released by the combustion. Besides that, what exactly does it mean to say that two flame fronts collide with each other? It would seem that they burn each other out. When two pressure waves collide, they each bounce off the other, but you don't end up with something that is greater than the sum of the parts. All in all, there is ample reason to regard all this talk about flame fronts colliding and shock waves, etc., as all just a load of nonsense. What makes a whole lot more sense, and what also happens to be inordinately simpler, is that if the temperature at any location within the combustion chamber reaches the necessary threshold, ignition will occur spontaneously at that point and will spread from there, with the net effect being that the combustible mixture throughout the combustion chamber burns in the manner of spontaneous combustion, in which case all of the energy is released in a very short period of time, i.e., the impulse is orders of magnitude greater than it is with normal combustion, where combustion proceeds in an orderly way from the spark plug and no part of the mixture ignites until that "flame front" reaches that point. It is thus MANIFEST that all this talk about colliding flame fronts and shock waves is not the least bit necessary to explin the phenomenon, in addition to it being nonsensical from the standpoint of a simple energy perspective as I already explained. All in all, I for one find all this talk about colliding flame fronts, shock waves, and the speed of sound to amount to a whole lot of specious garbage. As for pre-detonation vs. pre-ignition or whatever, that also has been turned into something far more complex than it actually is. If the metal reaches a temperature high enough to ignite the combustible mixture before the spark plug fires, it will ignite the combustible mixture before the spark plug fires, duh. If that happens, the absolute pressure and temperature early in the power stroke will be much greater than is intended, which will greatly increase the chance of spontaneous combustion. —Preceding unsigned comment added by Princesscheetah ( talk • contribs) 21:45, 26 April 2008 (UTC)
What is it? This needs to be explained or linked to in the article. 67.185.236.40 22:58, 25 March 2007 (UTC)
[1], be sure to read the discussion (ion sensor).
I think it is better than this English article. It seems that I have to look in all languages again (sometimes French or Spain link to very good images). They mention tail gas.
[2] is as bad as the English article.
Maybe we should merge Automatic Performance Control into the present article and make it a section called knock sensor.
Nice images on [3].
Can we link to glow plug engine. I read it is a small catalytic converter. I still do not understand why a glow plug doesn't ignite the charge at the intake stroke. An why does Klopfen_(Verbrennungsmotor) mention soot as source for knock? It sounds similar to this controlled self ignition stuff based on exhaust recirculation.
Has anybody a reference which proves that this is detonation? Everything I read said that the combustion of the tail gas is somewhat faster than the original flame front, but they could not prove that it is faster than the speed of sound in that hot turbulent charge.
Nice images about the pressure fluctuations due to knock and many references on: [4]. Be sure to inherit in this article that the mean pressure is only marginally higher, but that knock is fast enough to be in resonance with cavity modes.
And what about self ignition after the flame front? We should mention that this is believed to be a measurement artifact of the very old (1940) measurements or so. Arnero ( talk) 14:19, 5 April 2009 (UTC)
you need to do it encyclopædically rather than damaging the structu I only see a structured layout. But I am glad to read your reversion reasons in the history. As no one seems to be going to copy edit this article, I will just add my plans into this talk subsection and when I am retired in 100 years or so take a day to rewrite the article.
The ignition of the tail gas is due to temperature and pressure. Not sure why pressure is so important, but measurements hint at that direction. The turbulence in the chamber leads to pressure fluctuations. Sorta like in a freak wave somewhere in the volume of the rest charge a critical mass may get at high temperature and pressure and ignite the charge. Combustion is at least fast enough that the air cannot leave this area of the cylinder due to inertia. Therefor the combustion is faster there. Literature talks about negative temperature gradients, as to why the fast combustion is mostly triggered by self ignition and not by the flame front reaching the area. It seems that at high temperature the combustion somehow fizzles out. As said above: Pressure is important. This is the only knock prevention technique which directly prevents ignition: Low compression ratio (or throttle).
And about this Dieseling. This stems from one of the layman's references I think. As seen with the glow plug engine, Dieseling is not generally a bad thing. In real Diesel the ignition occurs shortly after mixing. As the ignition does not occur at the intake stroke, Dieseling is a very bad name.
Knock sensor and glow plug can only work because weak knock is no detonation. Arnero ( talk) 12:28, 7 April 2009 (UTC)
I just grabbed my edits out of the history to keep them in context:
Preflame chemical reactions are important for engine knock, sources:
When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat (about 400 °C) and pressure (above 50 bar) for a certain duration (1 ms) it is converted into a chemical cocktail which detonates already at 1000 °C, while the original mixture needs more than 2000 °C. Therefor a cold air intake is used. The mixture is cooled by the cylinder walls and the piston, which have a temperature of 100 °C (far below 400 °C). Liquid fuel droplets are sprayed into the cylinder for evaporation cooling since gasoline boils below 100 °C. Small intake valves are used to create turbulence to equalize the temperature and prevent hot spots or pockets. The turbulence also later speeds up the flame front to burn all mixture before the above mentioned certain duration passes. A central spark plug and a small bore radius reduce the distance the front has to travel. Any pockets in the piston for the valves or for two-stroke scavenging or for stratified combustion are omitted. The exhaust valves benefit from sodium cooling and still are so hot that they need to be placed close to the spark plug. Never is unburnt air fuel mixture allowed to leave through the exhaust valve and burn on its outer size and aggravate the cooling problem. It may be noted that a central glow plug creates ideal conditions for knock in the center of the combustion chamber without experiencing any damage, but unfortunately also heats the rest of the cylinder.
Alternative explanation: flame front acceleration
When the flame grows it heats (by radiation) and pressurizes the surrounding unburned fuel/air mixture. If the compensation by cylinder expansion and wall cooling is too low, the flame front will get faster and faster as it travels through the ever hotter mixture and may reach the speed of sound. Then the pressure rise cannot be distributed equally through the cylinder, but is concentrated into the flame front, leading to locally high combustion temperatures and a slightly supersonic speed of the flame front. If this front hits any wall, it separates the insulating boundary layer (of cold gas) and applies temperatures far beyond the melting point of the wall material. The sudden heating leads to expansion of the surface material and thus to cracks into the bulk.
Octane rating covers the same topic in a much better way.
skimming over the revision history I am a bit hopeless about this article. On the other hand there IS hope: "removed idiotic colliding flame reference" Arnero ( talk) 18:10, 7 April 2009 (UTC)
try to give information about subjects in simple languages for genaral people —Preceding unsigned comment added by Vuradi praveen ( talk • contribs) 03:15, 16 March 2010 (UTC)
I think someone should add an audio file with the characteristic sound of engine knock. Also a video demonstration would be nice (perhaps a mod of this >)-- MarsInSVG ( talk) 19:18, 10 August 2010 (UTC)
According to "Internal combustion engine fundamentals", by John B. Heywood (1988) it is more correct to divide knock into the types spark knock and knock caused by surface ignition. Where spark knock is a knock that is caused by end gases in front of the propagating flame igniting because of the increased pressure, temperatue and density. The resulting self ignition will result in a energy release that is far faster than in the propagating flame resulting in vibrations which is heard as the knock. This type of knock is generally fixable by delaying the ignition.
Surface ignition on the other hand is presented as a combustion happening outside of the propagating flame caused by a hot spot, which might be a hot particle, overheated plugs or valves or similar. A surface ignition might result in a knock or it might not... a surface ignition happening before the ignition is what is called pre-ignition here. But the exact same thing might also happen in other parts of the cylinder after the ignition have started, without being a regular spark knock, and therefore not being fixable by delay of the ignition. — Preceding unsigned comment added by 122.150.97.195 ( talk) 10:55, 19 June 2012 (UTC)
I searched Wikipedia for "misfire" and all I found (car related) was "An engine misfire, see engine knocking." Of course this article doesn't say anything about misfires. I'm thinking a new page should be made for that, or adding a section in this one, but I am not an expert on the topic. What I understand as a "misfire" just means no combustion. Maybe that can lead to knocking or other problems, but not always.
Anyway, just wondered if anyone agrees with that, or knows of another article that talks about misfires. Autumn Wind ( talk) 21:09, 6 October 2015 (UTC)
Pre-ignition is the normal meaning of this, isn't it? Note that true detonation is a supersonic process. Many times people say that something detonates, but it doesn't really. Note that "supersonic" would refer to the compressed fuel-air mixture, so you can't call the result supersonic just for exceeding the speed of sound in sea-level air. AlbertCahalan 06:23, 7 January 2005 (UTC)
Echoing what a couple of posters have observed, it is indeed called "pinking" in the UK. Captain deathbeard ( talk) 08:23, 20 May 2010 (UTC)
In the chapter Pre-ignition there is a sentence claiming that methanol is prone to pre-ignition. However this seems nonsense, as methanol is a high octane fuel. Also the offered reference does not say anything about methanol (on page 165). — Nikolas Ojala ( talk) 12:15, 17 October 2016 (UTC)
This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
I deleted this para: "Knock is detonation within the cylinder. Uncontrolled combustion. It is not the same as pinging/pinking which is pre-ignition.". As far as I'm aware (25 years of experience with engines aware, that is), this is wrong - preignition and pinking ARE the same thing. It's also pinKing, not pinGing, though perhaps in some parts of the world it's called that? - I suppose the sound is a sort of ping GRAHAMUK 06:35, 3 August 2003 (UTC)
I saw the suggestion on merging this article with Engine Knocking. If to merge means also move, ie the original article willo ceases to exist then I am against this. Detonation is not unique to engine knocking at all. The Detonation process is also core to the Pulse Detonation Engine [no cylinders] among many other things which is why I found it. Had it been merged with Engine Knocking I doubtfully would have come across it. I would suggest keeping the original article and continue to add to it from the detonation science theoretical point of view but additionally incorporate whatever is needed in the Engine Knocking Article.
Just my 2 cents ? Any thoughts ? Steve Mew Sunday, 5 February 2006, 07:07:19 GMT
detonation occurs when the flame fronts pressure wave ignites the air fuel mixture instead of the heat of the front itself causing the burn to advance at the local speed of sound rather than the relatively benign rate of 50-100 feet per second these multiple pockets and colliding flame fronts you speak of are fictional —Preceding unsigned comment added by 99.164.52.146 ( talk) 04:26, 16 October 2007 (UTC)
As I have been taught, knock and ping are actually two different things. Although they are somewhat related in this topic they do occur at different stages of the cycle.
Knocking can occur under pre-ignition due to poor quality fuel, carbon deposits, etc. or due to improper timing (advanced), many reasons have been mentioned earlier in this discussion. The 'knock' comes from the piston being forced down on its up-stroke by the pre-ignition or the spark firing too soon, banging the piston down while it's trying to move up and against the cylinder wall, rattling the works all the way to the crank. This opposition of forces is what makes it louder and more pronounced.
Pinging occurs from post ignition, after the piston reaches TDC and begins its down-stroke. Caused by poorly ignited fuel resulting in an extended or delayed ignition, too much fuel resulting in an extended combustion cycle or improper timing (retarded), Etc.. Basically anything that could cause an undesirable ignition after TDC.
Although the two are both ignition problems whereas the air fuel mixture is ignited either too soon or too late, or burns too long. But the difference being that the 'Knock' is usually much more audible than the 'Ping' since the piston is already on its way down. You can actually have ping without the knock, or knock without the ping. You could even have a ping and not know it, but chances are you'd hear a knock!
The two terms when used properly actually do better define which part of the cycle is malfunctioning. -- DP67 ( talk/ contribs) 23:28, 4 December 2007 (UTC)
Until someone actually quantifies the impulse associated with the shock waves associated with the collision of flame fronts, I will continue to regard all such talk as a load of nonsense. The energy associated with those shock waves cannot possibly be anywhere near as great as the total amount of energy released by the combustion of the fuel. In fact, if you stop and think about it for a few minutes, you will likely find yourself doubting that the energy associated with these shock waves could be more than a few percent of the total energy released by the combustion. Besides that, what exactly does it mean to say that two flame fronts collide with each other? It would seem that they burn each other out. When two pressure waves collide, they each bounce off the other, but you don't end up with something that is greater than the sum of the parts. All in all, there is ample reason to regard all this talk about flame fronts colliding and shock waves, etc., as all just a load of nonsense. What makes a whole lot more sense, and what also happens to be inordinately simpler, is that if the temperature at any location within the combustion chamber reaches the necessary threshold, ignition will occur spontaneously at that point and will spread from there, with the net effect being that the combustible mixture throughout the combustion chamber burns in the manner of spontaneous combustion, in which case all of the energy is released in a very short period of time, i.e., the impulse is orders of magnitude greater than it is with normal combustion, where combustion proceeds in an orderly way from the spark plug and no part of the mixture ignites until that "flame front" reaches that point. It is thus MANIFEST that all this talk about colliding flame fronts and shock waves is not the least bit necessary to explin the phenomenon, in addition to it being nonsensical from the standpoint of a simple energy perspective as I already explained. All in all, I for one find all this talk about colliding flame fronts, shock waves, and the speed of sound to amount to a whole lot of specious garbage. As for pre-detonation vs. pre-ignition or whatever, that also has been turned into something far more complex than it actually is. If the metal reaches a temperature high enough to ignite the combustible mixture before the spark plug fires, it will ignite the combustible mixture before the spark plug fires, duh. If that happens, the absolute pressure and temperature early in the power stroke will be much greater than is intended, which will greatly increase the chance of spontaneous combustion. —Preceding unsigned comment added by Princesscheetah ( talk • contribs) 21:45, 26 April 2008 (UTC)
What is it? This needs to be explained or linked to in the article. 67.185.236.40 22:58, 25 March 2007 (UTC)
[1], be sure to read the discussion (ion sensor).
I think it is better than this English article. It seems that I have to look in all languages again (sometimes French or Spain link to very good images). They mention tail gas.
[2] is as bad as the English article.
Maybe we should merge Automatic Performance Control into the present article and make it a section called knock sensor.
Nice images on [3].
Can we link to glow plug engine. I read it is a small catalytic converter. I still do not understand why a glow plug doesn't ignite the charge at the intake stroke. An why does Klopfen_(Verbrennungsmotor) mention soot as source for knock? It sounds similar to this controlled self ignition stuff based on exhaust recirculation.
Has anybody a reference which proves that this is detonation? Everything I read said that the combustion of the tail gas is somewhat faster than the original flame front, but they could not prove that it is faster than the speed of sound in that hot turbulent charge.
Nice images about the pressure fluctuations due to knock and many references on: [4]. Be sure to inherit in this article that the mean pressure is only marginally higher, but that knock is fast enough to be in resonance with cavity modes.
And what about self ignition after the flame front? We should mention that this is believed to be a measurement artifact of the very old (1940) measurements or so. Arnero ( talk) 14:19, 5 April 2009 (UTC)
you need to do it encyclopædically rather than damaging the structu I only see a structured layout. But I am glad to read your reversion reasons in the history. As no one seems to be going to copy edit this article, I will just add my plans into this talk subsection and when I am retired in 100 years or so take a day to rewrite the article.
The ignition of the tail gas is due to temperature and pressure. Not sure why pressure is so important, but measurements hint at that direction. The turbulence in the chamber leads to pressure fluctuations. Sorta like in a freak wave somewhere in the volume of the rest charge a critical mass may get at high temperature and pressure and ignite the charge. Combustion is at least fast enough that the air cannot leave this area of the cylinder due to inertia. Therefor the combustion is faster there. Literature talks about negative temperature gradients, as to why the fast combustion is mostly triggered by self ignition and not by the flame front reaching the area. It seems that at high temperature the combustion somehow fizzles out. As said above: Pressure is important. This is the only knock prevention technique which directly prevents ignition: Low compression ratio (or throttle).
And about this Dieseling. This stems from one of the layman's references I think. As seen with the glow plug engine, Dieseling is not generally a bad thing. In real Diesel the ignition occurs shortly after mixing. As the ignition does not occur at the intake stroke, Dieseling is a very bad name.
Knock sensor and glow plug can only work because weak knock is no detonation. Arnero ( talk) 12:28, 7 April 2009 (UTC)
I just grabbed my edits out of the history to keep them in context:
Preflame chemical reactions are important for engine knock, sources:
When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat (about 400 °C) and pressure (above 50 bar) for a certain duration (1 ms) it is converted into a chemical cocktail which detonates already at 1000 °C, while the original mixture needs more than 2000 °C. Therefor a cold air intake is used. The mixture is cooled by the cylinder walls and the piston, which have a temperature of 100 °C (far below 400 °C). Liquid fuel droplets are sprayed into the cylinder for evaporation cooling since gasoline boils below 100 °C. Small intake valves are used to create turbulence to equalize the temperature and prevent hot spots or pockets. The turbulence also later speeds up the flame front to burn all mixture before the above mentioned certain duration passes. A central spark plug and a small bore radius reduce the distance the front has to travel. Any pockets in the piston for the valves or for two-stroke scavenging or for stratified combustion are omitted. The exhaust valves benefit from sodium cooling and still are so hot that they need to be placed close to the spark plug. Never is unburnt air fuel mixture allowed to leave through the exhaust valve and burn on its outer size and aggravate the cooling problem. It may be noted that a central glow plug creates ideal conditions for knock in the center of the combustion chamber without experiencing any damage, but unfortunately also heats the rest of the cylinder.
Alternative explanation: flame front acceleration
When the flame grows it heats (by radiation) and pressurizes the surrounding unburned fuel/air mixture. If the compensation by cylinder expansion and wall cooling is too low, the flame front will get faster and faster as it travels through the ever hotter mixture and may reach the speed of sound. Then the pressure rise cannot be distributed equally through the cylinder, but is concentrated into the flame front, leading to locally high combustion temperatures and a slightly supersonic speed of the flame front. If this front hits any wall, it separates the insulating boundary layer (of cold gas) and applies temperatures far beyond the melting point of the wall material. The sudden heating leads to expansion of the surface material and thus to cracks into the bulk.
Octane rating covers the same topic in a much better way.
skimming over the revision history I am a bit hopeless about this article. On the other hand there IS hope: "removed idiotic colliding flame reference" Arnero ( talk) 18:10, 7 April 2009 (UTC)
try to give information about subjects in simple languages for genaral people —Preceding unsigned comment added by Vuradi praveen ( talk • contribs) 03:15, 16 March 2010 (UTC)
I think someone should add an audio file with the characteristic sound of engine knock. Also a video demonstration would be nice (perhaps a mod of this >)-- MarsInSVG ( talk) 19:18, 10 August 2010 (UTC)
According to "Internal combustion engine fundamentals", by John B. Heywood (1988) it is more correct to divide knock into the types spark knock and knock caused by surface ignition. Where spark knock is a knock that is caused by end gases in front of the propagating flame igniting because of the increased pressure, temperatue and density. The resulting self ignition will result in a energy release that is far faster than in the propagating flame resulting in vibrations which is heard as the knock. This type of knock is generally fixable by delaying the ignition.
Surface ignition on the other hand is presented as a combustion happening outside of the propagating flame caused by a hot spot, which might be a hot particle, overheated plugs or valves or similar. A surface ignition might result in a knock or it might not... a surface ignition happening before the ignition is what is called pre-ignition here. But the exact same thing might also happen in other parts of the cylinder after the ignition have started, without being a regular spark knock, and therefore not being fixable by delay of the ignition. — Preceding unsigned comment added by 122.150.97.195 ( talk) 10:55, 19 June 2012 (UTC)
I searched Wikipedia for "misfire" and all I found (car related) was "An engine misfire, see engine knocking." Of course this article doesn't say anything about misfires. I'm thinking a new page should be made for that, or adding a section in this one, but I am not an expert on the topic. What I understand as a "misfire" just means no combustion. Maybe that can lead to knocking or other problems, but not always.
Anyway, just wondered if anyone agrees with that, or knows of another article that talks about misfires. Autumn Wind ( talk) 21:09, 6 October 2015 (UTC)
Pre-ignition is the normal meaning of this, isn't it? Note that true detonation is a supersonic process. Many times people say that something detonates, but it doesn't really. Note that "supersonic" would refer to the compressed fuel-air mixture, so you can't call the result supersonic just for exceeding the speed of sound in sea-level air. AlbertCahalan 06:23, 7 January 2005 (UTC)
Echoing what a couple of posters have observed, it is indeed called "pinking" in the UK. Captain deathbeard ( talk) 08:23, 20 May 2010 (UTC)
In the chapter Pre-ignition there is a sentence claiming that methanol is prone to pre-ignition. However this seems nonsense, as methanol is a high octane fuel. Also the offered reference does not say anything about methanol (on page 165). — Nikolas Ojala ( talk) 12:15, 17 October 2016 (UTC)