Philosophy of Modern Oil Formulation: The Environmental and Economic Importance of Mixed and Boundary Friction

[naav]

What's even more interesting about ZDDP is actually how pointless it is to look at concentrations of it to make decisions based on VOA.

Researchers have optimized the molecular structure of ZDDP by adjusting the length of alkyl chains and incorporating various substituents. These modifications improve the thermal stability and efficiency of ZDDP, ensuring better formation of protective films on metal surfaces even at lower viscosities.

Studies have shown that combining ZDDP with other advanced additives such as molybdenum dithiocarbamates (MoDTC), functionalized fluoropolymers like PTFE (in grease) , and nanoparticles can significantly enhance its performance. For example, the addition of Ni nanoparticles or functionalized PTFE to ZDDP formulations results in a more robust and reactive anti-wear film, providing superior protection under high-pressure and high-shear conditions.

Enhanced ZDDP formulations are designed to decompose at lower temperatures in the presence of certain fluorinated compounds, leading to the formation of more effective protective films. This advancement ensures that the protective phosphate glass layer forms more readily and remains durable under extreme operating conditions

The incorporation of nanoparticles, such as fluorinated ZnO, enhances the formation of the ZDDP tribofilm. These nanoparticles work synergistically with ZDDP to create a more uniform and resilient protective layer, which significantly reduces wear and maintains MOFT even at low viscosities

These advancements have been validated through extensive empirical testing, including tribological studies, high-frequency reciprocating rig (HFRR) tests, and detailed chemical analyses of the resulting tribofilms. These studies confirm that modern ZDDP formulations can effectively maintain MOFT and provide robust wear protection, even in ultra-low viscosity oils like 0W-16 and 0W-8, and there is still a lot room for improvement. Many of these ZDDP doping strategies are not even implemented commercially yet.

Synergistic and Competitive Effects between Zinc Dialkyldithiophosphates and Modern Generation of Additives in Engine Oil

The increasing demand for low-viscosity engine oil has underscored the role of zinc dialkyldithiophosphates (ZDDP) as a conventional anti-wear and antioxidant additive. It is essential to investigate the influence of modern additives such as cyclopropanecarboxylic acid (CPCa) and Ni...

www.mdpi.com

Mechanism of Friction and Wear in MoS2 and ZDDP/F-PTFE Greases under Spectrum Loading Conditions

Two different greases formulated using MoS2 and a combination of ZDDP and functionalized PTFE (F-PTFE) were examined under spectrum loading conditions where loads, frequency, and duration of the steps were treated as variables. Combination of ZDDP and F-PTFE were synergistic resulting in a...

www.mdpi.com

 

[ZeeOSix]

Speaking of ZDDP.

"More Zinc = More Wear?" with Lake Speed Jr

Lake Speed Jr goes into detail here about ZDDP and how you can have too much of it. He also touches on balancing oil formulas and using the proper oil for your application. He also discusses being weary of deceptive marketing tactics.

bobistheoilguy.com

 

[DirectRejection]

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I think I found my favorite thread.

In the case of my Insight UOA (spec 0W20), basic hypermiling techniques were employed, RPMs were most often in the 1500 range. Hondas hybrid system uses the ICE to recharge the workhorse electric motor.

With my Corolla Cross (spec 0W16-now spec 0W8) UOA, it must be noted that Toyota designed temperature mitigating factors into this engine, deviating from the older engines used in the studies mentioned.

As can be seen, this oil formula uses minimal boron, and lots of moly and zinc, along with highest quality, novel base stocks.

I will remain cognizant of natural concerns about wear at the bearings, valve seats and hydraulic valve lifters, as well as cleanliness at the piston rings.

I will steadfastly report on and use HPL PP 0W8 with 30k mi OCIs, and will be at 200k miles in about 14 months, as per Signature.

 

[naav]

No matter how hard I look I simply don't see too many mitigating factors in engine designs that allow them to use 0w8 engine oils except one: oil pump design. Engine main and journal bearing clearances for many Toyota and BMW simply haven't budged much since the 1990s. The 0w8 and 0w16 oils are simply that much stronger than previous designs as the totality of their design features comes together to make an extremely strong oil under pressure. I strongly suspect if your engine's oil pump can generate the appropriate pressure and flow rate you could back spec 0w8 to all cars produced in the last 20 years at a minimum. I feel much more confident running 0w16 now. 0w20 is the new 20w50.

 

[twX]

I will steadfastly report on and use HPL PP 0W8 with 30k mi OCIs, and will be at 200k miles in about 14 months, as per Signature.

I'd be interested to know what the difference in engine friction is between relatively fresh oil and the HPL that's been aged for 30k miles. The increased viscosity from oxidation will have some small effect. Moly friction modifier and ZDDP will also have degraded, potentially to the point that friction greatly increases, especially at low rpm. The UOA can't show how degraded these additives are. Wear seems to have remained low, but that may not be the case for friction.

If you wanted to measure engine friction, the easiest way to do this accurately is to log the MAF sensor reading with an ODB2 scanner in controlled conditions, which should be an accurate measure of fuel consumption. This reading should be very consistent at warm idle as long as the engine temperature and ambient temperature are similar, the battery is charged, and accessory load is kept to a minimum. It could be trickier with a hybrid.

I did a test like this and posted about it here. Given how effective FM is at low rpm, you should see a very obvious increase in fuel consumption at warm idle if the additives are spent. If the increase is <10%, it's probably just the increase in viscosity that's causing the increased friction.

There's a good study by Toyota from 2000 (2000-01-2053) that tests the effects of ZDDP and MoDTC degradation. The additives were pretty much used up after 5,000 to 12,000 km. However, since this study came out, fuel economy test standards have required the oil to be aged a lot more, and so additive package durability has probably improved a lot in recent years.

 

[twX]

No matter how hard I look I simply don't see too many mitigating factors in engine designs that allow them to use 0w8 engine oils except one: oil pump design. Engine main and journal bearing clearances for many Toyota and BMW simply haven't budged much since the 1990s. The 0w8 and 0w16 oils are simply that much stronger than previous designs. I strongly suspect if your engine's oil pump can generate the appropriate pressure and flow rate you could back spec 0w8 to all cars produced in the last 20 years at a minimum.

Increased oil flow rates would definitely help with bearing durability with thinner oils. It would certainly help keep pressure at the bearings high enough to prevent cavitation. This is the single biggest concern with thin oil, as it can quickly cause catastrophic bearing damage. What I'm not sure of is whether a higher oil flow rate increases bearing MOFT in normal running conditions. If it does, then a larger oil pump may be all that's needed for the bearings. Otherwise, as ZeeOSix mentioned, larger bearings are a solution.

Oil cooling would have a large effect as well. If worst-case oil temperatures are kept lower, an engine might be able to safely use an oil that is multiple grades thinner. The piston rings could still an issue even with colder oil though, because the temperature of oil film at the rings tends to approach the piston and liner temperature. Keeping the oil in the sump cooler will only have a muted effect on MOFT at the rings, though with piston squirters it could make a big enough difference. In the Toyota study I mentioned before, it was the piston rings that first experienced increased wear with the thinner grades of oil.

 

[ZeeOSix]

No matter how hard I look I simply don't see too many mitigating factors in engine designs that allow them to use 0w8 engine oils except one: oil pump design. Engine main and journal bearing clearances for many Toyota and BMW simply haven't budged much since the 1990s. The 0w8 and 0w16 oils are simply that much stronger than previous designs as the totality of their design features comes together to make an extremely strong oil under pressure. I strongly suspect if your engine's oil pump can generate the appropriate pressure and flow rate you could back spec 0w8 to all cars produced in the last 20 years at a minimum. I feel much more confident running 0w16 now. 0w20 is the new 20w50.

The sole purpose of the oil pump is to simply get adequate oil flow volume to the parts that require lubrication. Over flooding components with oil volume doesn't change the way the oil viscosity and formulation behaves between moving parts. The only wrinkle are the journal bearings where excess flow over their natural side leakage flow can help keep the oil film temperature inside the bearing down, and therefore help keep the MOFT up. But over flooding say the valve train isn't going to make the lucubration any better as long as the minimum adequate volume is supplied. And the oil pressure from the pump does not really enhance the function of the oil as a lubricant. The relatively small amount of added oil pressure due to the pump supplying oil to a journal bearing really doesn't enhance the oil pressure created in the hydrodynamic oil wedge inside the bearing due to natural bearing operation. The oil pressure is just the vehicle used to make oil volume flow to the required parts in the engine oiling system.

There is a reason the oil makers do not recommend using a 0W-8 or 0W-16 in a vehicle not specifically designed to use that thin of oil. You could certainly can do it, but over the long run you'd probably cause more engine wear ... can't totally get around the physics of viscostiy with respect to Tribology.

 

[Jetronic]

I agree, and this is addressed in other studies, like the Honda study I mentioned. You can also check out these studies:

Toyota R&D - Low Friction Gasoline Engine Oil - Effects of Lower Viscosity and Friction Modifiers
SAE 892154

These studies show that oil viscosity needs to get very low before wear starts to increase.


That quote is in relation to the only test in the study that showed increased fuel consumption with thinner oil; 0W-8 oil without friction modifier in a turbodiesel engine. The same test with MoDTC added to the oil showed a reduction in fuel consumption.

This is an engine that specs a Euro 5W-30 with an HTHS of >3.5 cP, so a 0W-8 with an HTHS of 1.7 cP is a huge reduction in viscosity, yet friction and fuel economy were still improved so long as the oil was fully formulated. Of course, wear would probably increase, which is why Toyota doesn't recommend 0W-8 in these engines.

I do cars tore down a GM 1.6 silent diesel engine. I don't jnow what oil was used in that engine but believe the latest spec is 0W-20. The engine is derived from a Fiat design, who spec a higher viscosity oil (5W-30 ACEA C2, older versions C3 or A3/B4). Have a look at the conrod bearings. I'd say wear is not probable to increase, it's sure in a turbo engine

 

[ZeeOSix]

Increased oil flow rates would definitely help with bearing durability with thinner oils. It would certainly help keep pressure at the bearings high enough to prevent cavitation. This is the single biggest concern with thin oil, as it can quickly cause catastrophic bearing damage. What I'm not sure of is whether a higher oil flow rate increases bearing MOFT in normal running conditions. If it does, then a larger oil pump may be all that's needed for the bearings.

From what I've read about cavitation in journal bearings, the thicker the oil, the more prone cavitation can be. Same goes with things like oil pumps, etc that can experience cavitation. I have a study someplace on my computer specifically looking at journal bearing cavitation. If I find the link, I'll post it up later.

As I mentioned above, supplying more flow to the journal bearings than what their side leakage is can help keep the oil film temperature down inside the bearing, and that should help keep the MOFT up because the oil viscosity in the film would be slightly higher if the temperature is lower.

 

[twX]

And the oil pressure from the pump does not really enhance the function of the oil as a lubricant. The relatively small amount of added oil pressure due to the pump supplying oil to a journal bearing really doesn't enhance the oil pressure created in the hydrodynamic oil wedge inside the bearing due to natural bearing operation. The oil pressure is just the vehicle used to make oil volume flow to the required parts in the engine oiling system.

It's still important that a certain minimum pressure is maintained at the bearing. Below a minimum pressure, the air contained in the oil will hit its saturation limit and start to dissolve out of the oil and cause cavitation. Thinner oil will reduce the oil pressure closer to this limit. I believe that thinner grades of oil can be more susceptible to aeration as well, and more highly aerated oil requires higher minimum oil pressure.

SAE 940792 goes into this in some detail. SAE 932785 is good too, and includes some real-time measurements of bearing MOFT vs oil pressure and aeration rates.

 

[ZeeOSix]

It's still important that a certain minimum pressure is maintained at the bearing. Below a minimum pressure, the air contained in the oil will hit its saturation limit and start to dissolve out of the oil and cause cavitation. Thinner oil will reduce the oil pressure closer to this limit. I believe that thinner grades of oil can be more susceptible to aeration as well, and more highly aerated oil requires higher minimum oil pressure.

SAE 940792 goes into this in some detail. SAE 932785 is good too, and includes some real-time measurements of bearing MOFT vs oil pressure and aeration rates.

Yes, with all other factors held constant, a higher oil supply pressure at the inlet to the journal bearing can help mitigate cavitation, but there are other factors besides the supply pressure involved, so having a relatively low supply pressure won't automatically mean the bearings will cavitate.

Based on the fact that there are not millions of engines needing new journal bearings every year, I'd surmise that bearing cavitation is not a common thing going on in automobile engines. And I'm sure it's a factor the bearing design engineers take into account. As you mentioned, lots of cavitation will destroy relatively soft bearing surfaces pretty fast from cavitation erosion. The mass majority of automotive journal bearings show signs of wear from MOFT going to zero (like shown below), not so much if any from cavitation erosion. There may be some low level of cavitation going on that really doesn't do much if any damage to the bearing. If major cavitation damage is occurring, it's pretty easy to see by inspecting the bearing surfaces.

And of course, if there's a lack of lubrication or the bearing is running too tight, they smoke themselves pretty quickly, even seize and snap a rod and maybe window the block.

 

[ZeeOSix]

Here's a link to the study I was talking about. I don't see a PDF download anymore, think they want people to pay for it from what I'm seeing. Maybe do some more searching for a free PDF download. Here's a shot of the conclusions.

https://www.sciencedirect.com/science/article/abs/pii/S1001605815604942

Conclusions. They say thinner oil has less cavitation than thicker oil (all other factors being constant), which makes sense to me.

Here's another study (PDF link) on the effect of cavitation on journal bearings.

https://typeset.io/pdf/effect-of-cavitation-on-the-performance-of-journal-bearings-49taeomehi.pdf

 

[BMWTurboDzl]

What I don't understand is if modern cars operate in mixed/boundary lubrication at lower RPM (due to aggressive gearing) why should it matter much for fuel efficiency to use a low viscosity oil since we aren't reaching into the higher rpm regions (where the engine operates mostly in the hydrodynamic regime)?

It takes more hp to move a thicker oil through an engine. Oil coolers keep thinner oils in their goldilocks zone. This is why for example BMW and other have been using a variable displacement oil pump with mapping and oil coolers.