What is pinking?

[No 1]

From what I understand, the higher the octane of the fuel, the more advanced you can have your timing. So if your running on super all the time, the timing can be more advance than premium unleaded. Surely, if if the fuel is of a higher octane, it means it's more explosive (or am I already wrong?), if that's the case, if you advance the spark to x degrees BTDC, you're going to have an even bigger explosion taking place while the piston is still on the way up, that can't be right can it?

If you then put premium in, you get pinking under load, what is this? And what damage is it going to cause?

[BogBeast]

At risk of sounding a complete idiot, from what I understand....

Pinking is known (amongst other things) as pre-ignition. I.e the fuel/air mixture igniting before it is supposed to. A number of conditions can cause this but the principle one is the compression ratio. As the piston compresses the mixture it heats it up. If it heats up enough it can self ignite (like diesel). Octane is a measure of a fuels ability to resist this. Higher octane fuels can take higher compression ratios. Higher compression ratios = more power..

Changing the timing can work around this by firing the mixture earlier than it self ignites, but change it too much an you start firing whilst the piston is still compressing, killing the efficiency of the engine.

There. I believe that’s basically right..

[Pigeon]

Higher octane fuels are *less* "explosive" (to use the term loosely). Octane number is simply a measure of (lack of) tendency to detonate.

There are two phenomena commonly called "pinking":

1) Pre-ignition: hot spots in the pot, eg. glowing coke deposits or hot-running sharp edges, ignite the fuel/air mixture before its due time; the charge burns more or less normally but efficiency drops.

2) Detonation - either the entire charge "diesels", or the pressure/temperature rise from the spreading flame front causes the unburnt portion of the charge to "diesel". The portion of the charge which "diesels" burns explosively, all at once, hence "detonation".

[Mr2Mike]

Just to add to Pidgeons wise words, higher octane fuels generaly burn more slowly. All else being equall, and engine will typicaly require slightly more advance to produce the same power running on a higher octane fuel.

[No 1]

Well that explains a lot, but if higher octane fuel burns more slowly, what's the advantage, a longer more controlled explosion?

[Boosted LS1]

I'd suggest that the higher octane fuel takes more time to burn, hence the timing advance but being higher octane it produces more power and there will be your advantage . You could use some toulene with every tank fill up

[Mr2Mike]

No 1 said:

Well that explains a lot, but if higher octane fuel burns more slowly, what's the advantage, a longer more controlled explosion?

The advantage is that you can run with a higher compression ratio without detonation with higher octane fuel. Thermal efficiency (and hence power/economy) is directly related to compression ratio. With a turbo/supercharged engine, the higher octane allows more boost for an arbitrary compression ratio.

A slow burning mixture is not desirable, the increased time that the cylinder head and piston is exposed to increases heat losses and reduces thermal efficiency* The slower speed of burning of high octane fuel is simply a side effect, not a desireable property. However, this means that putting high octane fuel in an engine not designed to take advantage of it could theoreticaly lose power rather than gain it.

* this is the reason that retarded igntion timing can cause overheating.

[350zwelgje]

Pinking occurs also because petrol consists of a high number of different ingredients. So it is not a pure liquid as diesel, so it can use heat generated by compression only to ignite and no spark plugs are required. Due to different ingredients in the petrol one will start to burn first. Higher octane uses less easily ignitable ingredients, and the benefit is a higher compression ratio can be used (= more efficient engine). But the engine has to be designed for it. If it is not, high octane adds nothing. A spark will set off a set of different ingredients, capable of igniting the rest. Petrol is a complex mix to be able to cope with all sorts of situations. That is why for example the mix in petrol is different in summer and winter, to assure an easy cold start. And part of the reason that long stored cars have difficulties to start, because the necessary ingredients for a cold start have evaporated over time.

Back to the topic of pinking, I would like to add the following information. Two types of pinking exist.
-Low speed pinking. Which is the type you can hear.
-High speed pinking. You can't hear, and it will take all your bearings out (without you knowing)! But this type is rare.

Rob

[Al.]

Slightly off topic, but I'm interested in getting a programable ECU for my car (1990 200SX) as a way of getting into callibration. I don't have a lot of experience with engines, I'm a chassis engineer, but I'd like to get into it.

Anyway, the point of this is to ask if anyone knows any good books I can read on the 'art' of engine callibration. Something that doesn't assume too much prior knowledge would be good, but not Janet and John, I know the basics of how an engine works.

[annodomini2]

Basically, with an engine with predfined maps, plug in the new remappable ecu, to the car and load in the standard maps. Put car on a dyno, the maps will have ranges based upon certain information such as engine speed, tweak each of these values to determine what effect this has on the operation of your engine and attempt to find the most optimal set of values for what you require. I believe there are some equations (they will be related to the engine in question) to determine optimal ranges i.e. less values to try but trial and error as far as i am aware is still the most effective method. I would recommend though trying to obtain or determining the calculations as it stands less chance of damaging the engine on the dyno.