Lubricant Reactivity wrt Engine Knock

[Shannow]

Interesting preso on lubricant reactivities with regard to low speed engine knock.

http://energy.gov/sites/prod/files/2014/03/f8/deer11_alger.pdf

Basically oil in the cylinder is found to be twice as reactive (prone to self combustion) as diesel fuel.

Interesting testing with oil mixed with solvents and the effect on cetane value that arises...possible (IMO) analogue for why detonation is becoming a problem with GDI...there's no fuel in the end gasses to get mixed with the lubricant/vapours.

 

[d00df00d]

Interesting! Thanks for posting!

Thinking this is highly relevant for rotary engines. What do you think?

 

[SteveSRT8]

I agree.

But it's nothing new, other than a more precise quantification of effects we already are aware of. We drag racers have been battling this since the beginning of time (and PCV)...

 

[Shannow]

Originally Posted By: SteveSRT8
But it's nothing new, other than a more precise quantification of effects we already are aware of. We drag racers have been battling this since the beginning of time (and PCV)...


But you drag racers have never been running GDI with nothing but oil vapours in the ring crevice area like a modern GDI does.

The oil's effect, PCV, ring belt, of mixed with the fuel is reduced markedly as the fuel that it is in contact/mixed with kills the cetane effect just by sheer quantity.

 

[jrustles]

Originally Posted By: d00df00d
Interesting! Thanks for posting!

Thinking this is highly relevant for rotary engines. What do you think?


You might be onto something. Considering the CN of PAOs is high, maybe this is one reason for the "no synthetics" push from the 80s. Then again, ester oils have the lowest CN of the synthetics, according to the paper. But then again OTOH, the presence of fuel should offset some of the cetane-rising effect despite still being present.

Originally Posted By: Shannow

But you drag racers have never been running GDI with nothing but oil vapours in the ring crevice area like a modern GDI does.


Ahh, well logically a high-cetane vapour would detonate much more rapidly than liquid phase lubricant, thus a resistance to vapourisation in this area, one would think, would reduce the preignition?

 

[BearZDefect]

To me this also suggest that as GDI engines wear, especially the oil control ring, this is another reason why they will become more prone to knock than PFI engines.
(The other being more potential carbon build-up that some GDI engines are infamous for.)

 

[Olas]

For a forum full of engineers, enthusiasts and other mechanically minded folk, I'm stunned at how few of you with DI just vta and be done with it.
Or maybe you like having ongoing problems to deal with??

 

[SteveSRT8]

Olas, despite all the hoo hah here over DI the facts are that an awful lot of them are out there and doing ok for the majority of folks.

It would seem that a few mfgrs have mastered their difficulties, and others are still learning.

But the typical DI owner is not on BITOG...

 

[Olas]

Originally Posted By: SteveSRT8
Olas, despite all the hoo hah here over DI the facts are that an awful lot of them are out there and doing ok for the majority of folks.

It would seem that a few mfgrs have mastered their difficulties, and others are still learning.

But the typical DI owner is not on BITOG...


I agree that the typical DI owner has never even heard of Bitog, but the whole 'doing okay' part really gets me. As an anal autist with OCD there is no 'okay', there is functioning as designed(aka correct) and there is junk. Bad design, idiosyncratic, whatever - all different ways of saying 'junk'
The latest and greatest technology sets us back 50 years, to a time when a decoke was thought to be normal and acceptable, granted the decoke is now due to a different reason, but, design is a collection of compromises and it makes me question the motives, knowledge, passion and desire for shareholder satisfaction of the people who make the decisions.

Show me a car designed and built by a mechanic and it will function exactly as it should, with no job taking more than a couple of hours.
Let the accountants and marketing guys have a say, then asking the shareholders permission before making the tech change his design is a sure way for problems like these to come about.

 

[Shannow]

After reading, I put a quart of lightly used 15W40 shell helix in the last tankful of fuel on my Nissan (3.0L direct injection turbodiesel).

It has made more difference than any cetane improving additive that I have ever (expensively) purchased...amazing.

Probably not the best idea long term, but for a tank, the reduction in knock, and easier starting is notable.