So here is graphic example of what happens when too much heat builds up in a combustion chamber as a result of spark knock, the resulting timing retard, and the engine trying to run phi=1 with enrichment only to cool exhaust temps which was not working quite as well as it should have. Modern 2.0L GDI engine on the dyno at 6000 rpm, 22 bar BMEP working on a development cal. This happened so fast by the time the load was removed, it was already too late.
The melting and pitting of the surface is incredible. There is aluminum vapor deposition all over the piston, inside the head all the way out the exhaust port into the turbo.
Even the bearing was hammered to hell from the knocking.
Here's a shot of the bore.
Just thought you guys might like to see why avoiding detonation is rather important.
Strange to see damage on the lower bearing shell. It only sees load as the piston approaches TDC and reverses direction. The upper bearing shell supports combustion pressure and would suffer the shock from detonation.
Pretty sweet how it blowtorched down the side of the piston. I bet it took the path of the upper ring end gap.
turbodan wrote:Strange to see damage on the lower bearing shell. It only sees load as the piston approaches TDC and reverses direction. The upper bearing shell supports combustion pressure and would suffer the shock from detonation.
Pretty sweet how it blowtorched down the side of the piston. I bet it took the path of the upper ring end gap.
The upper shell is even worse. I thought I took a pic of it but I couldn't find it. It is odd that the lower shell looks that bad. The plug electrode was gone and the damage was directly across from the DI injection stream. It literally created a torch and made a cool desk ornament.
Coldswede wrote:Looks like thing go to "Hell in hand basket" pretty quick at 22psi!
Do I understand the mixture alone was intended to stop the detonation, timing was not planned to be adjusted?
Maybe the cooling effect of enrichment is too slow at those pressures? (Can you tell I'm guessing here? )
The strategy of this ECM is to try to run stoich when it can, as long as the turbine inlet temperatures do not exceed a certain value. This is also a good indicator of in cylinder temps. This temp value is modeled based on fuel rate, AFR and other parameters. It will enrich only enough to reduce this temperature, then try to return to stoich. The problem arose when the knock sensor kept pulling timing which would spike the exhaust temps and enrichment couldn't save it at that point.
Jeremy wrote:
Coldswede wrote:Looks like thing go to "Hell in hand basket" pretty quick at 22psi!
22 bar. 319 psi.
Not boost pressure, but "brake mean effective pressure", BMEP. It's the pressure in the cylinder, calculated based on power output.
BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)
(319 x 122)/ 150.8 = 258 lb-ft
HP = (2 x Pi x Tq x RPM)/33,000 = 295 hp
295/258 aren't bad numbers for a 2 liter.
I hope you're keeping that for garage wall-candy, Brad. It's impressive!
Thanks for the explanation of BMEP Jeremy. Boost pressure was about 190kPa. And yes, the piston is sitting on my desk as I type.
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