Diesel engine oil formulators are by now well accustomed to revising their recipes. They do so on a regular basis, not only as a matter of product improvement, but more often to comply with requirements of the auto industry and regulators.
According to one lubricant additive company, however, formulators in the next few years will have to make wholesale changes unlike any the market has seen for decades. Chevron Oronites William Kleiser told the Society of Tribologists and Lubrication Engineers last month that looming upgrades in the United States and Europe will curtail, if not prohibit, use of some of the industrys most trusted weapons in the fight to protect engines.
Finding adequate replacements, he said, will require an unprecedented amount of research, and could spell an end to backward compatibility of diesel oils.
As we go into this decade, Kleiser said during a May 22 presentation at STLEs annual meeting in Houston, diesel engine lubricants are facing the biggest change they ever faced.
Changing recipes is nothing new for engine oil formulators. According to Kleiser, though, much greater changes will be required to comply with emissions limits mandated by U.S. Environmental Protection Agency for 2007 and the Euro 4 and Euro 5 standards scheduled to take effect in Western Europe in 2004 and 2008.
In both regions, Kleiser said, the new rules will force engine manufacturers to install new exhaust treatment technologies – diesel oxidation catalysts, diesel particulate filters, selective catalytic reduction, nitrous oxide absorbers, de-NOx catalysts. Manufacturers are still working to develop solutions but Kleiser said that some of these devices will certainly be used.
Its likely that engines will have more than one of these technologies, he said. Manufacturers are talking of using several devices in sequence.
In order to protect these devices, Kleiser said, automakers will apparently demand sharp reductions in limits of phosphorus, sulfated ash and sulfur – byproducts of longtimeoil additives.
Phosphorus is introduced by ZDDP (zinc dialkyl dithiophosphate),widely recognized as the most effective and most economical anti-wear agent available. Automakers, however, have implicated phosphorus for damaging emissions control catalysts. Kleiser said future phosphorus levels for diesel oilscould be significantly resticted, perhaps as low as0.05 percent of total weight, a level that would sharply curtail use ofZDDP.
Also on the not-wanted list is sulfated ash, which comes mostly from any of a variety of metallic detergents and to a lesser degree from ZDDP. The problem with sulfated ash, in the eyes of automakers, is that it may form deposits on diesel particulate filters. Kleiser said engine oil formulators may have to reduce sulfated ash levels.
Formulatorsmay have to reduce levels of sulfur bothbecause of potential effects on treatment systems andbecause of its engine oil contributions to particulate emissions. These limits come at a critical time because sulfur is a common ingredient in the most likely alternatives to ZDDP and other phosphorus-containing additives.
There are alternatives but they come with their own problems and generally are untested – or at least less tested than existing technologies. ZDDP substitutes, for example, often contain otherelements of concern – such as sulfur or chlorine – or lack proven field performance. Additive companies have identified a variety of ashless dispersants that can be used instead of metallic detergents, but at high levels they cause seals to deteriorate.
Kleiser says he is confident that additive companies will meet the challenge of finding new formulas to protect tomorrows diesel engines. But he warned that it will take a lot of work – and money.
For the past 70 years, weve been going through a progression of developing our understanding of the materials we use today and refining how we use them, Kleiser said. What were looking at now is a step-change, where were forced to substitute materials for which we simply dont have that base of knowledge.
The next five years are going to require a tremendous amount of learning and millions of dollars in research.
The end product, he said, may be so different from todays diesel engine oils that it they may not meet the auto industrys demands for compatibility in engines that pre-date the new emissions rules.
Backward compatibility may not be practical or even desirable, Kleiser said. Even if it were possible to achieve, backward compatibility implies forward compatibility. It could give people a false sense that old engine oils can be used in new vehicles and that could lead to immediate and severe damage to expensive after-treatment systems.
My own opinion is that we should not pursue backward compatibility. Of course, that would require a large-scale campaign to educate users of these lubes about the need to use a specific lubricant. But I think that can be done.