Low Sulphur 2

[Knap]

In the UK we have Ultra Low Sulphur Fuel

http://www.greenergy.com/products/petrols.html

http://www.wipo.int/pctdb/en/wo.jsp?KEY=02/18521.020510

The feature of the invention is that the use of a low sulphur fuel enables the amount of anti-wear agents containing phosphorus such as eg ZDDP to be halved without any adverse effect on the antiwear performance of the lubricating oil.

Is the fuel quality a major player in the general ZDDP reduction for anti wear?

 

[drwebb]

Not in the conventional wisdom, but in scanning the description that appears what is claimed as novel. The claims seem based on the observation that using low P oils along with low S fuel reduced dissolved Fe by half in the Sequence IIIF test.

S contributes lubricity to gasoline and diesel so it's reduction would be expected to increase wear severity in engines. However, it also places stress on the oil when combusted, so that could help oil performance. The patent appears to report that the reduction in lubricant stress outweighs the loss of fuel lubricity, at least in the engine stand test.

As fuel quality is changing significantly in many markets and engine oils are becoming more highly tuned to applications the oil companies are aggressively researching fuel/lubricant interactions, and in some cases with surprising results.

As the patent alludes, there are non-P-containing antiwear agents so ZDDP is not irreplaceable technology. It is however highly effective and very cheap, so choosing suitable substitutes can offer significant competitive advantage.

 

[romke]

i am afraid some things get mixed up here. the use of lowsulphur fuels can lead to cleaner combustion products and what still is dirty in the exhaust gas can then be converted by a suitable catalyst. however, the surface of those catalysts can be covered with deposits originating from either the sulphur in the fuel or from the metallic additives used in the engine oil and then inhibit the working of the catalyst. therefore low sulphur fuel is needed and when emission regulation is tightened up also a socalled lowSAPS oil - an oil with a lower amount of S, ashgiving additives like Ca, Mg, Zn, and P(hosphorous). that means that the original antiwear protection has to be provided by an ashless type of additive, because antiwear protection still is a requirement - and to fullfil that need additves are required - but of another nature and possibly less efficient. from the oilformulators point of view a certain amount of sulphur would be advantagous, because it acts as a natural anti-oxidant and anti-wear agent. when you take it nearly all out you have to substitute that with an ashless component that gives you the protection you need.

both the latest US and EU specifications now call for socalled lowSAPS oils - oils that make it possible to treat the exhaust gases further then hitherto possible with conventional oils.

 

[Knap]

Two points I found intriguing

The lubricating oil compositions used in conjunction with the ultra-low sulphur fuels in the present invention are suitably Group II, Group III or Group IV basestock as defined by the API and are preferably Group II basestock.

Why would Group II be preferred?

The stepwise reduction in Fe levels from test 1 to test 2 to test 3 may give the impression of a gradual decrease in severity over time., However, current knowledge of engine testing would not support this. Furthermore, the test engine was not new at the start of this study and thus had been fully run-in in earlier test work.

Engine testing results may differ - do UOAs provide a complete picture despite being repeatable and are the factory fill oils specifically designed to provide lasting protection for the engine life?

 

[25362]

Knap, the following link may help to answer your question:

http://www.chevron.com/products/prodserv/BaseOils/docs/nlgi_10-99.pdf

 

[romke]

there might be several reasons to prefer Group II oils. Group II oils are clearly better then Group I oils because of the hydrotreating they have been put through. This makes them more stable and less prone to oxidation. You would expect Group III and Group IV oils to be better still but due to the more uniform structure of these oils they have lost some of their natural resistance to oxidation (by getting the S out) and Group IV oils also need additional esters added to accept the usual additive packages. They are ofcourse also much more expensive then Group I and II baseoils, which makes then only suitable for premium grade products where the higher cost of the baseoil can be recovered. So for most applications Group II oils would be the best bet - but unfortunately they are still in limited supply.