yr right
Your changing cylinders is undeniable. Your correlation and causation are where the issues are.
I notice you avoided all the simplest of questions I asked. Please have a go at them. I am not here to to embarrass an anonymous person, but if I can help educate all the better.
As Leadsled has pointed out, the cylinder does not know how it is arranged, whats more the fuel does not know either, nor who made the cylinder. And why does brand C have several orders of magnitude more trouble than brand L, or P&W or......?
You are correct in saying the heat is transferred through the seat (65-75%) and through the stem (25-35%), and it is the incomplete contact through the face/seat that starts the burning of valves, not the exhaust gas going past. In fact you could be surprised at a little data here dating back to before WWII.
Gases going out the exhaust not fully combusting can be made happen at VERY lean mixtures, so lean the engine is hardly producing power. People with good balanced air/fuel ratio's some times see this as a "second peak" of EGT. This happens when they are well past peak, off the curves above and then EGT rises slightly (just off the graph) and the drops as no more combustion occurs. More commonly known as ICO.
Which temperature is hottest? 50dF ROP or 50dF LOP ? And which has the highest valve temperatures? You might find this helpful from NACA
http://ntrs.nasa.gov/archive/nasa/ca...9930091891.pdf
Whyalla, I have the coronial reports where all the real data came to the surface. Two of my colleagues were at the centre of this very material and I can assure you this helps a lot because reading a coronial is a cure for insomnia. But let me summarise it for you.
1. The left engine failed with a crankshaft failure, a manufactured in defect, which may have gone many more hours was exposed due to very high loads imposed on it during the period from installation and up until a few weeks prior to failure. This was a result of magneto timing being advanced several degrees. This failure was likely to happen some time, however the excessive loads brought the failure on sooner and unfortunately the swiss cheese started to have holes lining up.
2. The right engine failed by way of a preignition event. Preignition events are catastophicly destructive if let go for more than a minute. These engines were routinely run in the climb with the mixture leaned to a setting that was
not rich enough but they were still RICH mixtures. This engine had the power increased considerably to deal with the loss of the right engine and the failure sequence of preignition followed once the circumstances were created.
Please note that the detonation in the engines cruise climb life could vary from light to medium and the engine could survive this and they often do their whole lives, particularly light detonation (as scientifically defined). However periods of heavy detonation will start to damage things and the most likely victim is in fact the spark plug ceramic. Once this fails, you now have a source of ignition long before the magneto fired spark event should happen. And I mean long before. On a Chieftan with statically correct timing, the actual spark event goes of in a range of 13-16 degrees before TDC, and yes that is not where you set the magneto for static timing purposes.
Once the preignition is started, it will continue unless it is deliberately stopped or until the cylinder pressures eventually beat the piston into submission and it fails.We have lots of data files to show you this and the post failure evidence to go with it.
I will answer one of my questions above for you, as this is crucial to your understanding how these events happen.
Detonation happens at?
A:Full Rich-150dF ROP ?
B:40dF LOP - Peak EGT ?
C: 35-50dF ROP?
The answer is C
I have a dyno-detonation test run with several fuels being tested on my laptop right now. The engine is 300HP standard compression (not low) and the detonation starts around 23GPH and is extinguished around 17-18 GPH. This detonation was all on the RICH side of peak EGT and thus by definition can only be a rich mixture. We can never get a typical LOP mixture to detonate when LOP.
You would be surprised at what we have to do to get even a min spec avgas to detonate. In includes, running CHT's up above 430dF (not as high as red line) run the oil temp up at 220df, get the IAT up to 150dF and use about 34-35"MP. This then gets you into the kind of territory the engine on MZK was in. I would dearly love to post the screen shots but it is highly confidential test data. Happy to let you see it on my laptop screen though.
Light detonation is not particularly harmful, medium can be stressful and reduces longevity, heavy is damaging to plug ceramics and other area's such as pistons.
Fuel cooling. Another of the worlds best OWT's. Fuel only ever adds heat. ONLY. One post on pprune is not able to pass on the full education of how extra fuel on the rich side of peak reduces CHT. It works EXACTLY the same way that having a LOP mixture does it by reducing fuel. You will have to believe me on face value here, but the rate of transfer of BTU's to the head are affected by ICP and that alone. ICP is a function of spark timing and thetaPP which affects the volume when the peak is reached. I could write for days and not convey this properly.
Remember rich mixture fast burn , lean mixture slow burn.
This is only half the story. Rich mixtures (by true definition) can burn faster or slower depending on where on the mixture scale they are. You are assuming that fast burns are a good thing and slow are bad. But you seem happy with the same slow burn with a richer mixture, which coincidently would have more fuel available to burn in the exhaust.
Take Aussie Bob's lead and book in for Perth. If you are not satisfied at the end that you did not learn a heap....money back
PS: Leadsled....thanks for the recognition.