Chemical Limits Loom for Diesel Oils


The next heavy-duty diesel engine oil standard is not due to hit the market for another month, but the following upgrade is already beginning to take shape. The ASTM panel drafting the PC-10 specification recently approved the first-ever chemical limits for diesel oils.

Observers say those limits will sharply curtail the use of popular additives when PC-10 makes its market debut in two years. The standard could also further reduce applications for Group I base oils.

To date, diesel engine oils have not had chemical limits, but they are needed to meet strict new U.S. emissions rules that go into effect for model year 2007 on-road trucks. ASTMs Committee D-2’s Heavy Duty Engine Oil Classification Panel voted at its June 22 meeting to cap levels of sulfur, phosphorus and sulfated ash at 0.4 percent, 0.12 percent and 1.00 percent, respectively.

Those familiar with the process said those levels were compromises.

The people who work with [exhaust] aftertreatment [equipment] wanted to be lower on phosphorus, lower on ash, lower on sulfur, said VolvoMacks Greg Shank, co-chairman of the American Petroleum Institute/Engine Manufacturers Association Diesel Engine Oil Advisory Panel. But you also had the concern that lower limits would result in oils that werent compatible with existing engines. The EMAs position is that this was a good compromise between aftertreatment compatibility and backward compatibility.

Even so, observers say the new chemical limits could require a significant rejiggering of diesel oil formulas. Infineums Pat Fetterman, a member of the ASTM classification panel, said the limits will force formulators to reduce, if not eliminate, the use of zinc dialkyldithiophosphates (ZDDP), popular antioxidants that also help protect against wear. Detergents used today would also need rethinking.

All of these limits have significant implications, Fetterman said. The sulfur limit especially is a three-way whammy because there is sulfur that is coming [into the formula] from ZDDP, the detergents and from any use of Group I base stocks. I think its going to be a pretty tough upgrade.

Base oil marketers agree that there will probably be restrictions on types of base oil that can be used in PC-10 oils – not just because of chemical limits, but also because of tougher requirements for soot-handling ability, which will be measured by engine tests. Several sources said the new standard could, as a practical matter, restrict the ability of formulators to use all but the highest quality Group I oils.

A blender might be able to correct for the sulfur content of Group I by blending with a Group II, said one base oil marketer, who spoke on condition on anonymity. Of course, they would have to have the tankage needed to store both [types of base oil]. And they might even be able to find a way to get some Group I in there if they are just trying to hit the sulfur limits. But the question is, what do they have to do to meet the requirements for soot-handling and oxidative stability?

When you put it all together, it seems to me that PC-10 is going to mean that most Group I producers lose a significant market.

ASTM Committee D-2 on Petroleum Products and Lubricants is still developing engine tests for PC-10. The group plans to select tests in December of this year, conduct matrix testing during the first half of 2005, and set test limits in December of that year. Marketers seeking to license their oils to the standard would have them tested during the first half of 2006, with API starting to license themthat June.

The current diesel oil specification is CI-4, but API is scheduled in September to begin commercial licensing of a mini-upgrade, CI-4 Plus.

– LubesnGreases Automotive Editor David McFall contributed to this article and covers the topic further in the August issue of LubesnGreases magazine.

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