Summary

James has asked, if you advance the timing too much, is that where pinking happens? Or he's put in brackets here, pre detonation? OK so in essence it can be but there's a few terms you've used there that I just want to clear up, so first of all this term pre detonation. I hear this a lot, so you're definitely not alone in getting this a little bit mixed up there James but pre detonation is not actually a term.

00:00 - James has asked, if you advance the timing too much, is that where pinking happens? Or he's put in brackets here, pre detonation? OK so in essence it can be but there's a few terms you've used there that I just want to clear up, so first of all this term pre detonation.
00:15 I hear this a lot, so you're definitely not alone in getting this a little bit mixed up there James but pre detonation is not actually a term.
00:23 We have two types of abnormal combustion that often are confused so we have detonation or knock which are the same thing.
00:32 We also have pre ignition which I think is the confusion you've got in there.
00:36 And again don't worry James, you're definitely not alone in that mistake there but pre ignition and detonation/knock are very different things.
00:44 Pre ignition, as its name implies, is a type of abnormal combustion that starts before the ignition event occurs so generally what this is a result of is something in the combustion chamber, maybe glowing red hot that's enough to actually ignite the fuel air charge before the spark plug does.
01:05 That's actually a really dangerous type of abnormal combustion, it does a lot of damage very very quickly.
01:10 Detonation is more common and that happens after the spark event and in essence what happens here is we have the spark event, it begins the combustion process and when that happens, the pressure and heat in the combustion chamber start to rise very quickly and in some instances, particularly if we're running on a low octane pump fuel, we can get a situation where the heat becomes so great in the combustion chamber, that pockets of unburned fuel and air spontaneously combust so that's detonation or knock.
01:37 So to get back to your other question, if we advance the timing too much, is this where detonation can happen? And the answer is that yes it can but not in all circumstances.
01:45 You would have noted during our MBT timing demonstration there, we went all the way to 50° of timing, I had no detonation occurring, I could have gone to 60 or 70°, it would still not have caused knock and that's simply because of the operating point that I was using for the demonstration.
02:03 We're under relatively light load, relatively low throttle position so no amount of timing was going to cause detonation to occur under that circumstance.
02:11 However if I'd done this at wide open throttle, things would have been very different.
02:14 So it's important just to understand that engines are not always going to be knock limited but generally the higher the load, the more throttle opening, the more boost, that's when they become more and more prone to detonation and yes too much timing will result in detonation.
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