Ash content corrolations to Pre-Ignition

[joff]

Originally Posted by vex

8 cycles on a single rotor test bed. Just because you have a pre-ignition event does not mean you'd have a catastrophic pre-ignition event.

Yeah, I missed the part where 1 cycle = 2.5 hours and thought it was meant 8 rotations of the rotor which sounded absurd.

Originally Posted by vex

As for speculation on why the ash causes pre-ignition events it's nothing more than a few ideas being passed around. As it stands right now the Pre-ignition is a direct result of ash because of carbon build up on the combustion surfaces. The carbon build up carries over heat causing the pre-ignition event where the gas reaches its flash point with contact to the surface. But that's just a theory.

This theory could be tested by replacing oil with ashless oil and seeing if a high preignition rate continued. I presume carbon build-up accumulated would not instantly vanish?

[vex]

Originally Posted by joff

Yeah, I missed the part where 1 cycle = 2.5 hours and thought it was meant 8 rotations of the rotor which sounded absurd.



This theory could be tested by replacing oil with ashless oil and seeing if a high preignition rate continued. I presume carbon build-up accumulated would not instantly vanish?

That presumption would be correct (however the carbon instantly vanishing is not necessarily true. It will still need to be burned off, or dieseled to remove the built up carbon, which in and of itself may cause issues with the cars setup). NSU papers did multiple tests. The problem comes with the oil not containing ash, but impurities that produce ash when burned. Hence the high PPM of Calcium causing more sulphated ash, and the respected correlations. VOA and UOA are helpful in narrowing it down to oils that would work stellar in our engines. The problem comes in that a majority of "high end" oils contain low calcium numbers, but those numbers are still too high for our engines (remember the lower the sulphated ash the better; <500ppm of Calcium). Running a pure base, or synthetic that has <<<500ppm of Calcium is the better.

On that note; I did not find VR1 oils at Pepboys in Alexandria, VA. Next time I go to an autoparts store I'll check for it.