Pre-Ignition vs. Detonation 1

[JOJOMO]

The octane thread got me thinking about pre-ignition vs. detonation. My truck, a 93 toyota with the 22-re engine with 192k miles on it, 'pings' under what I would consider a higher load condition (in 5th gear climbing grades while trying to accellerate under mid to full throttle situations). I run mid-grade fuel and this seems to reduce the problem.

The question is how can I tell if it is pre-ignition problem, which I understand to be hot spots of carbon igniting the fuel prematurely, or, detonation, which I understand to be heat/pressure from the advancing flame front igniting the remaining af mix before the flame front reaches it causing high pressure peaks and unsmooth combustion?

Once I find this out, what are the best ways to alleviate this? Patprimmer suggested a water spray treatment into the throttle under a power run. Is that a WOT condition, or what? How much water? Is there a better way to clean the combustion chamber?

 

[dicer]

Simply put:

Preignition is considered hot spot ignition.

Detonation is caused by self ignition from pressure rise after normal ignition.

And for your rpm deal, try it yourself using low octane fuel. Just advance the timing. You can detonate just starting it up or at 10k plus rpms. CR and VE and spark advance all play into it as well as combustion chamber design and size.

 

[patprimmer]

It might also heat up due to being compressed.

Draw ambient air into a cylinder, it cools of due to decompression, then heats up during compression. The more air in their, the greater the final pressure and temperature.

Poor exhaust flow leaving residual hot exhaust will also add to the problem, but that is not all other factors being equal if the original exhaust is reasonably efficient.

every car I have driven that is prone to knock has been most prone at full throttle around maximum torque rpm.



Regards

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[r2800]

I had thought that this one was already done to death,detonation is a condition due to the end gas within the combustion chamber being spontaneously ignited by the heat generated by the advancing flame front,normal combustion ceases and an explosion occurs.Detonation is also referred to as knock or pinking and a host of other terms.It is due to the chamber design,compression ratio,fuel suitability,intake temperature and pressure,ignition advance,throttle angle and a whole host of other intangibles.I can only recommend that my fellow colleagues refer to their Ricardo and Taylor books so that we can now at least agree on this point.

 

[evelrod]

r2800
When I refer to pre ign, I mean 'knocking', pinging, pinking, whatever. A problem with temp, load, hot spots, timing, jetting, etc. I have never heard destructive detonation, not even on the dyno. In all cases, it was discovered through instrumentation or post inspection.

Rod

 

[r2800]

During my career I have seen many examples of holed pistons due to insipient detonation as opposed to the short lived temporary transient form brought about by being in the wrong gear,poor batch of fuel from the supermarket etc.The range of effects from good old fashioned detonation/knocking can be limited to metallic deposits from the pistons on spark plugs to collapsed pistons.As piston design improved over the years they became more resilient to this percussive force, a good example is the style as fitted to the Heron type of combustion chamber.Due in the main to its 3 dimensional form.Knocking today is used as the upper limit of the advance/load curve as seen by the knock sensor and relayed to the ECU,the ECU will be constantly making adjustments.