Talk:Engine knocking

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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 Aug 2003 (UTC)

I clarified the difference between knocking and pre-ignition, and added some external links. In the USA at least, engine knocking is also called "pinging" (or just "knock"), but I've never heard it called "pinking". -- Arteitle 05:03, 17 Sep 2003 (UTC)

It's "pinking" in the UK. As my car used to suffer from it I'd describe the sound as a sort of tinkling sound.

Exile 16:08, 20 Jan 2005 (UTC)

[edit] what it is

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 Jun 2005 (UTC)

Pre-ignition is the igniting of the fuel by a source other than the actual spark. It does not follow necessarily that detonation will occur because of it. Detonation refers to the creation of a high pressure wave that traverses the combustion chamber potentially causing damage. This pressure wave is akin to the wave of a sonic boom.--=Motorhead 04:42, 12 Jun 2005 (UTC)

It's not really detonation unless that pressure wave travels faster than the speed of sound in that compressed fuel-air mixture. Given the high compression and the density of fuel, I would expect the speed of sound to be relatively high. I'd really like to see some proof that detonation occurs, because it's a fairly wild claim and because people so often casually call things "detonation". AlbertCahalan 02:20, 14 Jun 2005 (UTC)

The term detonation, as applied to internal combustion engines, is not new. (Not something made up by a couple of mechanics over a case of beer hehe!) Since the first works of Sir Harry Ricardo (Knighted for his work in this very area) in 1922 to the present there have been numerous research papers written on it. Probably the most studied area of engine performance since detonation limits maximum performance. The term “detonation is used to describe the very high pressure shock waves traveling at supersonic (compared to immediately local conditions) velocities (which is the only way you can create a shock wave). These waves cause real life broken parts and are observable on pressure traces taken from real engines. Your own ears will tell you something nasty is going on in the engine. For further proof read:

“The internal combustion engine in theory and practice” Vol 2 ch.2 “Detonation”[1] by C.F. Taylor (The M.I.T. press) for an authoritative, detailed report from a founding researcher on the topic.

There are numerous other sources if you are interested.

Asside from the symantics of it all, the term "Detonation" is the defacto standard term used to decribe this phenomenon in the field of internal combustion engine engineering.

--=Motorhead 04:26, 15 Jun 2005 (UTC)

The statement that "detonation" is a standard term is highly debatable. Detonation has a very specific meaning in reacting flow, and engine knock does not fit under this description. I suggest that the application of the term "detonation" to engine knock is obsolete and should be removed to avoid confusion between knock auto-ignition processes and true detonation phonomena.

Also, the book by Taylor that is cited is quite dated, I think that this 1985 edition is a just a reprint of the 1961 edition. The current "Bible" of engine engineering is:

J.B. Heywood, Internal Combustion Engine Fundamentals, New York: McGraw Hill, 1988.

Another popular book is:

R. Stone, Introduction to Internal Combustion Engines, 3rd Ed., Warrendale, Pa: Society of Automotive Engineers, 1999.

--128.115.101.190 17:35, 10 August 2005 (UTC)

There is no "bible" in existence when it comes to engines. Saying Taylor is dated is a little like saying Newton is dated. Not to mention that Heywood refers extensively to Taylor in his book. The current Taylor edition is updated not just reprinted. The term detonation is used extensively in the body of literature on engines. Should Wikipedia take it upon itself to try to change the terminology? Not in my opinion.--=Motorhead 20:32, 11 August 2005 (UTC)

Just be aware that the term detonation is inaccurate when applied to knock. Detonation involves a shockwave propagation sustained by chemical heat release, which is not generally descriptive of engine knock processes. I will say that the term detonation is no longer used commonly in the technical literature (like SAE), but the term is still used more outside of the literature as a legacy. Should Wikipedia use incorrect terminology because of historical use? If you like.

Tongue-in-cheek,I will say that very few engineers pull Newton's Principia off the shelf to calculate a F=ma (I do of course, and only the original Latin for me!). Taylor is an excellent text, I have it on my shelf, along with Heywood, Stone, Furgueson, and Obert - another excellent text written at the same time as Taylor's first edition. Still, great advances in the scientific understanding of combustion and knock have come in the last 30 years, and these are more reflected in other texts.

--63.203.74.117 02:17, 12 August 2005 (UTC)

I believe the general description of "knock" refers to the sound: engines subject to "knock" make a lot of noise. Traditionally defined, "knock" is brought about by ignition of the fuel/air charge prior to TDC of the piston, however that happens. Whenever it happens, rapidly expanding, burning charge encounters a piston that is still moving toward TDC as a function of the momentum imparted by the crank and flywheel. This causes a confrontation between the rising piston/crank/flywheel assembly and the expanding charge wishing to drive the piston down; hence lots of things are driven into each other when they don't want to be, and noise and wear and damage result. Knocking, or pinging/pinking, can commonly happen in a spark-ignited crank piston engine when the timing is too far advanced, even though detonation does not occur.

"Detonation" essentially refers to things burning really fast, such that there is no flame front, or essentially no flame front. It happens in HCCI, and in "engine run-on" when ignition in a very hot crank-piston engine is turned off, especially when running on low-octane fuel. HCCI engines are often referred to as "knock engines" although they are actually not so, according to the definition above. That is, HCCI engines really do detonate, in that pretty much all of the micro-droplets of fuel in a homogeneous mixture combust nearly simultaneously, which is more than can be said for either SI or CIDI engines. But they do not "knock" unless this detonation happens prior to TDC. Actually, though, recall that knock as defined above really just means making a lot of noise. According to this definition, crank-piston HCCI engines also "knock," because, even when spontaneous ignition happens exactly at TDC (which it hardly ever does, by the way), the high peak pressures and energy release rates of HCCI tend to hammer the piston against connecting rod and crank, even when they are already moving downwards. They are simply not moving downward "fast enough," such that the piston is driven downward faster than it would "like" to be, thus again creating lots of wear and making lots of noise.

So get rid of the connecting rod and crank. Now, if the thing still detonates, which it will, on an HCCI model, as long as the charge is homogeneous and the compression pressure is sufficient to initiate spontaneous combustion, you have an engine running on detonation alone, without the phenomenon of "knock." I.e., run a double-acting free-piston HCCI engine and there is no such thing as knock, but lots of such thing as detonation. Run it as rich as you want-- as rich as stoich will let you. It doesn't make lots of noise, because there are no connecting rods and no crank to oppose the piston motion. It wants to move extremely rapidly in a direction opposite to that which caused the compression; OK, go for it. There's nothing stopping you. No noise, no knock. Total detonation. It has been built in the past, and it worked exactly as described. It is presently being built again, and it will once again work exactly as described. It's exactly the same thing as a pulse-detonation jet engine, only smarter and incomparably cheaper and more reliable. So there. No references; don't need 'em. References are for people who don't have confidence in what they are talking about. I am not one of those people. 04:30, 24 December 2005 66.80.111.18

Your (66.80.111.18) statement...

"Traditionally defined, "knock" is brought about by ignition of the fuel/air charge prior to TDC of the piston, however that happens"

Not so , in all practical spark ignition engine applications, ignition is ALWAYS before TDC. This is required to allow sufficient time for combustion and as a rule of thumb half the combustion will be before TDC and half after for a system with optimal timing.

Thus there is no “confrontation” between the gas and piston.

On your statement…

“No references; don't need 'em. References are for people who don't have confidence in what they are talking about. I am not one of those people”

The point of references is to allow others to follow the reasoning without having to draw pictures and to add credibility by showing that research done supports the fact in question. You may have all the confidence in the world but without facts its just annother baseless opinion. You learned whatever you know ( or think you know) somewhere. Where? Share it with us.--=Motorhead 16:26, 30 December 2005 (UTC)

[edit] Merge proposals

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

Actually, the proposal is for the Detonation internal combustion engine article to be eliminated and moved in this article on Engine knocking. I don't know enough about the other article to comment. Samw 22:09, 5 February 2006 (UTC)

Whichever way they are merged they should be because they deal with exactly the same topic under different names. Kind of inconvenient for readers to have 2 different articles on the same subject.--=Motorhead 02:02, 6 February 2006 (UTC)

[edit] Flame front

What is it? This needs to be explained or linked to in the article. 67.185.236.40 22:58, 25 March 2007 (UTC)