interesting abstract on ZDDP deterioration vs wear

[friendly_jacek]

from http://www.chemeng.titech.ac.jp/~mmasuko/english/research_e/zndtp/zndtp1e.html

Nothing earthshattering but confirms the facts on ZDDP.

"Fundamental Study of Changes in Friction and Wear Characteristics due to ZnDTP Deterioration in Simulating Engine Oil Degradation during Use."

Masabumi MASUKO, Takeshi Ohkido, Akihito Suzuki and Takafumi Ueno.

Transient Process in Tribology

(Proceedings of the 30th Leeds-Lyon Symposium on Tribology, Lyon, Sept. 2003),

(2004) 359-366..

ABSTRACT

Zinc dialkyldithiophosphate (ZnDTP) is a well-known multi-functional additive for lubricating oils that has superior oxidation inhibition and antiwear performance. All the engine oils for four-stroke automotive engines contain ZnDTP because no additive has been found to have better performance. However, since it was pointed out that ZnDTP poisons the exhaust catalyst, reducing ZnDTP concentrations in engine oil without losing the superior antiwear performance has become an important priority. The friction and wear characteristics of intentionally deteriorated ZnDTP, which can simulate used engine-oil, were studied using a four-ball tribometer. Both sec-C6 and prim-C8 ZnDTP were degraded by reacting with cumenehydroperoxide (CHP), which modeled the hydroperoxide present in combustion gas. Several simulated used oils with different degrees of degradation were prepared by changing the molar ratio of [CHP]/[ZnDTP]. Hydro-refined mineral oil was used as a base oil without other additives. Changing the degree of degradation simulated the gradual change in deterioration during actual use. Fresh ZnDTP-containing oil showed lower wear and higher friction than the base oil. However, the anti-wear performance gradually decreased with increasing ZnDTP degradation, and an appreciable wear increase was observed after dissipation of ZnDTP. Beyond this point, further degraded oils showed larger wear and lower friction than those with the additive-free base oil. In other words, simulated used-oils were found to accelerate wear but to decrease friction. ZnDTP produced various kinds of phosphorous-containing compounds after reacting with CHP. Some degradation products from ZnDTP accelerated what appeared to be corrosive wear that might have been due to the excess reaction of surfaces with sulfur in the degraded compounds.

 

[1sttruck]

Similar to some articles suggesting that used oil increases wear, not similar to others suggesting that used oil decreases wear :^)

 

[toocrazy2yoo]

Ok, but how does one decrease friction, but increase wear? Solely due to the corrosion?

 

[1sttruck]

Lowering ZDDP levels seems to reduce friction. Wear doesn't have to be over large areas and continuous.

 

[ebaker]

Perhaps adding cumenehydroperoxide to oil has little similarity to real world conditions.

 

[Rickey]

In discussing reduced ZDDP it seems that a lot of attention is given to flat tappet cams and extreme contact pressures. I am also wondering about the effects of reduced ZDDP in the ring/land/piston and cylinder areas. I am thinking that at WOT some EP wear mechanisms may creep in here also. Rickey.

 

[1sttruck]

Check the site below for other related articles. He notes a rule of thumb of friction being related to viscosity, there is an obvious interest in reducing viscosity in order improve fuel economy, but the tradeoff is increased everything else being equal.

http://iantaylor.org.uk/papers/future_challenges.pdf

Reductions in ZDDP levels (required due to chemical constraints) will generally help fuel economy but impact on durability and oxidation control need careful attention

Impact on lubricants
– Treat rate of ZDDP reduced
– Supplementary antioxidants needed (since ZDDP is also an antioxidant)
– Supplementary antiwear additives (which do no contain sulphur, phosphorus or sulphated ash) are needed
– TBN level of lubricant will generally be reduced with these chemical limits (may be an issue for heavy duty applications)
– At present levels, chemical limits are such that backward compatibility (with earlier API and industry specifications) is possible. Any future tightening of chemical limits carries the risk that backward compatibility may not be possible

 

[Nebraskan]

Please pass the SLOB!

 

[Leo]

I wonder what the upper limit of ZDDP concentration they found where the antiwear performance 'leveled off'. But interesting they say that ZDDP is still the best antiwear additive. Btw do motor oils use ZDDP or ZDTP? Ie Di vs Tri.

 

[Doc8404]

would you bother using it with an SM rated blend (aka: MC 5W-20) in a 5.4L (Ford) engine???

worried about cat damage.