Engine oil

[Gay-neth]

Can anyone explains few questions of mine? Were currently doing a research on these.

1.) How does synthetic oil actually works?
- Example: a chemical that will be activated once it reaches the temperature of 50C and by that time it increase viscosity of the oil or bla bla bla

2.) What is the pros & Cons of this particles/foreign items that contains in the engine/engine oil?
- Metals
- Graphite
- Teflon
- Wax
- Detergent additives

3.) How do graphite formed in the engine oil? Can it be removed when graphite formed in engine?

[Raptor22]

Can anyone explains few questions of mine? Were currently doing a research on these.

1.) How does synthetic oil actually works?
- Example: a chemical that will be activated once it reaches the temperature of 50C and by that time it increase viscosity of the oil or bla bla bla

synthetic base oils like Poly alphaOlefins (PAO) are highly stable to oxidation so they do not "craack" i.e. shorten their hydrocarbon chains under high stress like temperature and pressure. They are poor carrier fluids of additives so a bit of mineral oil is added to PAO or special additive need to be used. The oxidation stability and the molecular stability allows for the hydrocarbon chains to not alter their behaviour significantly over a wider stress range than mineral oils can achieve.
VI (viscosity improvers) are added to further enhance theirtemperature performance under extreme conditions. These viscosity improvers are temperture and pressure activated. A different molecule is required for temperature activation than is required for pressure activation. Not to be confused with Extreme Pressure additives or anti wear additives.

2.) What is the pros & Cons of this particles/foreign items that contains in the engine/engine oil?
- Metals
- Graphite
- Teflon
- Wax
- Detergent additives

metals are not really desired in an engine oil, however they are used in various additives. ZInc Phosporus and Sulfates are most commonly used. These are usually in Anti wear additives and extreme pressure addtives. Detergents are also often metllic based.
Graphite and teflon are not desirable in an engine oil so they are not used. Hard particals like graphite wll score bearing surfaces and damage piston rings. Teflon does not decompose very nicely under pressure and heat and can cause ring sticking.
Wax is also not a desirable contaminant in an engine oil since it is solid at room temperature. Paraffinic wax made through Fischer-Tropsch process could be beneficial to provide high temperature viscosity in a F1 engine oil but it would need to be added in significant quantity to makeit beneficial and requires a preheating of the oil.

3.) How do graphite formed in the engine oil? Can it be removed when graphite formed in engine?

graphite does not form in an engine oil. Carbon residue is indicative or poor base oil quality or too high viscosity and poor detergency and solvency of the oil. This is not desirable.

[aussiegman]

Very nice write up Raptor22.

The "additives" I have seen used in engine oils are:

1) Molybdenum Disulfide (MoS2)
2) Tungsten Disulfide (WS2)
3) Hex-Boron Nitride (hBN)

Personally, WS2 is my choice and has always worked extremely well despite is high molecular weight as there are various sources of nano-sized powers (90nm particle size).

WS2 has extremely high load bearing as well as high lubricity and thermal stability high as well with a melting point at 1250C and decomposition at 1260C.

While older larger particles would fall out of suspension in engine oils, newer smaller particles sizes allow extended suspension and that which does fall is easily re-activated through oil circulation.

[Raptor22]

Yes those can be used, but are more desirable where piston velocity is low and hydrodynamic lubrication is hard to achieve i.e. LArge ships engines.
F1 engines is a different matter as well. Oil filtration is pretty fine with high pore density and small micron apertures. Along with the metallics one needs to use metal deactivators to ensure no catalytic reactions between the oil and the engne components under the high temperature environment.
The tungsten disulphide you are refering to I assume for use as a friction reducer?

Molybdenum disulphide is more typically used in greases but I guess if the partical size is in the nanometer range and concentration is high in the percentile range then for a slow revving engine theres benefit.

hex boron nitride is fairly common in engine oils as anti wear component.

A note on Waxe, specifically Fischer Tropsh wax is that is excellent feedstock for making highly shear and oxidation stable XHVI or group III base oils.

[Gay-neth]

Thanks Guys. Very detailed explanation.

[olefud]

They are poor carrier fluids of additives so a bit of mineral oil is added to PAO or special additive need to be used. The oxidation stability and the molecular stability allows for the hydrocarbon chains to not alter their behaviour significantly over a wider stress range than mineral oils can achieve.

Excellent write up! When synthetics were new the rap was that, while petroleum oils increased viscosity under pressure, synthetics didn’t. This supposedly caused excess wear at the cam/tappet interface. Your explanation that synthetics don’t carry EP additives well makes more sense than there being some pressure/viscosity mechanism inherent in petroleum oils.

[Raptor22]

Yeah there is no pressure viscosity mechanism in group I or Group II base oils. They rely solely on blends of different viscosity range base oils to make a High Viscosity Index (HVI) base oil. Additives then are used to tweak the VI performance with temperature and pressure.
The Group I and group II base oils tend to boil off with an increase in pressure and temp, combine this with the viscosity dropping off and wear becomes a real problem for these oils under high load. VI improvers are typically polymers of Butene that extend as the temperature or pressure rises so they are able to attract more hydrocarbon molecules to their extended arms. Shell illustrated this quite nicely in an add campaign over a decade ago where they used roller blade's skating in circles and extending when extra energy was available.

Synthetics, thanks to their high VI, are not as volatile and therefore the temperature and pressure range they can operate under without boiling off is much higher, often up to over a 100degrees Celcius higher. The standard tactic of blending a few base oils together is still employed to improve the overall performance and often mineral oil is still added any way as a carrier for detergent, EP and Anti wear additives.
There are newer packages that don't need mineral oil but these are generally very expensive and will only be used in motorsport applications. A litre of Helix Ultra Racing used the Ferrari 058 costs between GBP150-00 to GBP200-00. The Poly Urea grease used in the CV joints is around GBP1-00 per gram.
this is mostly because the lubricants used in the F1 car is essentially lab blended product and not production lots from a blending plant.

[riff_raff]

Excellent write up! When synthetics were new the rap was that, while petroleum oils increased viscosity under pressure, synthetics didn’t. This supposedly caused excess wear at the cam/tappet interface. Your explanation that synthetics don’t carry EP additives well makes more sense than there being some pressure/viscosity mechanism inherent in petroleum oils.

In general, any type of lube oil will experience an increase in viscosity as the fluid film pressure increases. On the other hand, most lube oils will also experience a decrease in viscosity within a hydrodynamic fluid film contact due to flash temperature effects. The primary difference between petroleum oils and synthetics is that synthetics tend to have more stable viscosity characteristics with regards to temperature changes.

[Raptor22]

also with pressure changes synthetics have superior characteristics but the difference is not as big. The performance stability with delta T is the most desirable feature as you rightly point out.
We just must not forget about pressure changes because throughout the oil flow path inside an engine the pressure on the lubricating fluid changes dramatically and if total system pressure drops, synthetics gives us a bigger safety margin than does a mineral or conventional hydrocarbon (Group I or Group II)

[Alan97]

raptor- interesting comments. May I ask your background please? Are you involved in the lubricants industry at a technical level?

[flynfrog]

Its really not polite to ask Alan.

[Raptor22]

raptor- interesting comments. May I ask your background please? Are you involved in the lubricants industry at a technical level?

Mechanical engineer by education, tribologist by profession

[Alan97]

Its really not polite to ask Alan.

Disagree, no point wasting time learning from people who aren't qualified to teach

It's not like I am asking who this person works for.

[riff_raff]

also with pressure changes synthetics have superior characteristics but the difference is not as big. The performance stability with delta T is the most desirable feature as you rightly point out.
We just must not forget about pressure changes because throughout the oil flow path inside an engine the pressure on the lubricating fluid changes dramatically and if total system pressure drops, synthetics gives us a bigger safety margin than does a mineral or conventional hydrocarbon (Group I or Group II)

Raptor22- the point I was trying to make has to do with the significant flash temperature rise and viscosity change that can occur within a hydrodynamic fluid film contact. The situation is a very complex relationship between the oil film fluid mechanics and heat transfer to the bearing and journal surfaces.

With lube oils that operate close to boundary conditions, it is beneficial to have EP additives to prevent scoring failures.

[Raptor22]

also with pressure changes synthetics have superior characteristics but the difference is not as big. The performance stability with delta T is the most desirable feature as you rightly point out.
We just must not forget about pressure changes because throughout the oil flow path inside an engine the pressure on the lubricating fluid changes dramatically and if total system pressure drops, synthetics gives us a bigger safety margin than does a mineral or conventional hydrocarbon (Group I or Group II)

Raptor22- the point I was trying to make has to do with the significant flash temperature rise and viscosity change that can occur within a hydrodynamic fluid film contact. The situation is a very complex relationship between the oil film fluid mechanics and heat transfer to the bearing and journal surfaces.

With lube oils that operate close to boundary conditions, it is beneficial to have EP additives to prevent scoring failures.

+1