GM ESC modules and matched knock sensors.

[Tom H]

Pre-ignition (ignition before spark) and "Knock" Detonation (after ignition) are two different events.

I understand a little more now... with knock the plug ignites the mixture and a flame front starts from it's tip. Normal ignition the front continues, pressure builds and all is good. With Knock what happens next. Could someone point to a good link that describes all this??

-Tom

[LeMarky Dissod]

Pre-ignition is when the electrical spark is not the start of the flame front. It often but not quite always leads to knock. Even if it somehow is not knock is still bad because pressure builds before the piston is ready to convert the pressure to useful work.

Knock is a sudden explosion - detonation - rather than a smooth controlled burn. Instead of building, pressure spikes so fast it's like a hammer striking the piston or the cylinder or the valves.

Depending on the amount of air & fuel involved in the knock event as well as when it occurs, has an effect on its acoustics, but it always sounds like some kind of metal on metal.

[Tom H]

Knock is a sudden explosion - detonation - rather than a smooth controlled burn. Instead of building, pressure spikes so fast it's like a hammer striking the piston or the cylinder or the valves.

Using this definition, knock isn't a result of the spark timing. How does retarding spark eliminate the knock?

I am interested in this because of some other info I came across. Some early aviation engines with turbos and so on had problems with knock. In some cases, this was cured by injecting a water/alcohol mix. In my PCM code I can see where spark retard is applied... wondering if one of the un-used outputs can be used to signal an external pump to inject water. I think this sort of setup would be quite easy in terms of setting up the pump and so on. Software would also be quite easy. Question comes as to how much to inject. This is where things get complicated.. Probably a constant pressure with some sort of jet to control the flow. Just thinking out loud.
-Tom

[LeMarky Dissod]

Using this definition, knock isn't a result of the spark timing. How does retarding spark eliminate the knock?

I am interested in this because of some other info I came across. Some early aviation engines with turbos and so on had problems with knock. In some cases, this was cured by injecting a water/alcohol mix. In my PCM code I can see where spark retard is applied … wondering if one of the un-used outputs can be used to signal an external pump to inject water. I think this sort of setup would be quite easy in terms of setting up the pump and so on. Software would also be quite easy. Question comes as to how much to inject. This is where things get complicated. Probably a constant pressure with some sort of jet to control the flow. Just thinking out loud.

Using this definition, knock isn't NECESSARILY a result of spark timing.

Less-than-ideal timing - like, say, the factory spark timing maps we tend to improve on - does not cause knock in and of itself.
Some engines, regardless of timing, are very resistant to knock, whereas others are much less so.

Anyway, did you mean something like the BMW M4 GTS' water injection system?
https://www.bmw-m.com/en/topics/maga...00-horses.html

It's blatantly obvious how old this idea is.

[Tom H]

Anyway, did you mean something like the BMW M4 GTS' water injection system?
https://www.bmw-m.com/en/topics/maga...00-horses.html

It's blatantly obvious how old this idea is.

Thank you for the info & link.

-Tom