What is this talk about mixed boundary running...

[KrisZ]

...conditions being the norm for future engines? In a recent thread about high VI oils and VIIs few members mentioned that in the near future we will see more and more engines running in a mix of hydrodynamic and boundary conditions. I understand that even today's engine do run in boundary conditions, but I think it's very rare or when the engine is pushed too hard during warm up time and that it is not desirable, so why make this condition a common occurrence? What are the advantages of such a move? Are we going to save on fuel because oils will be really thin? How is it going to play out with engine longevity? Experts please chime in.

 

[JHZR2]

That doesn't make much sense as the coefficient of friction for boundary lubrication is much higher than hydrodynamics. You want to get closer to the edge, because closer to it should mean lower pumping and parasitic losses. That makes sense. But I personal can't imagine staying in a boundary regime is good. Now, I've long mentioned that surface finish, not "clearance" can drive thinner lubes, as the requisite film thickness can drop. Smoother finish prevents as many situations where boundary lubed ovation regimes occur due to surface irregularities. As finishes are better, perhaps the effects of boundary lubrication are less (eg less friction factor when in the regime, etc), but I still can't see why one would want to spend more time in that regime... The losses would still be higher than hydrodynamic with high pumping losses.

 

[Solarent]

Depending on conditions, most of today's engines will be operating at all four lubrication regimes (elastohydrodynamic, hydrodynamic, mixed, and boundary conditions) simultaneously in different parts of the engine. For example, where you may have hydrodynamic in the journals, on the cam and lifters you may have instances of mixed and boundary conditions. As engine designs change to allow the use of thinner oils - for example the use of roller rocker arm type valve train systems, thinner oils reduce viscometric resistance under hydrodynamic lubrication condition at low temperature, maintaining sufficient viscosity at high temperature condition. (This has been discussed at length in the current VI thread.) It has been long held in the engine oil business that viscosity alone is no longer adequate to ensure wear protection and engine longevity. This is why along with improved viscosity performance, oils are being designed with stronger and more tenacious fm/aw/ep technology to ensure proper protection in the increased instances of mixed and boundary conditions. These additives combined with reduced viscosity resistance is what will give you the fuel economy improvements.

 

[Shannow]

^ What Solarent said... There's an extension to the Stribeck curve showing the results of FM additives http://www.threebond.co.jp/en/technical/technicalnews/pdf/tech09.pdf Provided by JAG in http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1164745 The shows with friction modifiers there is lower overall friction in the mixed area than with oil alone... Sequence VI economy testing http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf They purposely chose the test engine to be a modern one in which it spent more time in mixed/boundary than the older design engine, and established the test regime to represent that operation. The load/speed profile isn't that off "normal" operation, and certainly not where you'd intuitively think an engine was running it. (Has some interesting conclusions, however the benefits of FM are clear...and it indicates no FM carryover from change to change). There's one or another of the 0W-16 papers on the site somewhere that demonstrates that the newer engines are spending more time in mixed lube regimes....just can't place finger on it.

 

[Clevy]

Originally Posted By: Shannow

^ What Solarent said... There's an extension to the Stribeck curve showing the results of FM additives http://www.threebond.co.jp/en/technical/technicalnews/pdf/tech09.pdf Provided by JAG in http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1164745 The shows with friction modifiers there is lower overall friction in the mixed area than with oil alone... Sequence VI economy testing http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf They purposely chose the test engine to be a modern one in which it spent more time in mixed/boundary than the older design engine, and established the test regime to represent that operation. The load/speed profile isn't that off "normal" operation, and certainly not where you'd intuitively think an engine was running it. (Has some interesting conclusions, however the benefits of FM are clear...and it indicates no FM carryover from change to change). There's one or another of the 0W-16 papers on the site somewhere that demonstrates that the newer engines are spending more time in mixed lube regimes....just can't place finger on it.

Thanks for the links. Just when I thought I was getting it I find that I'm barely scratching the surface and due to an engine oil having multiple functions,and having to multi task a person really has to consider the entire package and the balance between its multiple functions. It's becoming much more clear to me that focusing on a single ,or even a couple attributes of any particular oil doesn't really show the entire picture and where an oil is excellent in a particular aspect it may lack in another and it's truly a balancing act to formulate an oil that does everything excellent. Thanks for the links.