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Phosphorus: GF-5s Hot Spot


Tradeoffs are a sad part of life. No one gets everything he wants, and thats as true in engine oil development as in everything else. Formulators have long struggled to balance the ideals of wear protection, cleanliness, fuel economy, lower emissions and cost – and ILSAC GF-5, the engine oil specification moving towards industry approval in 2009 and commercial introduction in 2010, offers no respite from that challenge.

GF-5 may not require many brand new chemistries across the board, but it will mean more additives, because of the proposed increase in protection against deposits, sludge and coking deposits, pointed out Alex Boffa, global PCMO coordinator at Chevron Oronite in Richmond, Calif. Maybe it will mean an overall increase in the overall additive package, and particularly in the dispersant/detergent additives. We may see increased levels of friction modifiers, too.

Steve Haffner, North American market manager, crankcase, at Infineum USA L.P. in Linden, N.J., echoed that thought. A balanced formulation must take into account the debits in fuel economy associated with components such as detergents, dispersants and antioxidant/antiwear agents (such as ZDDP) while maintaining piston cleanliness and wear protection. Alternative additives such as ashless antiwear and ashless detergent would be quite costly versus the chemistries that exist today and are field-proven.

Performance packages are always balanced, commented Jim Puckace, global marketing manager for engine oil additives at Wickliffe, Ohio-based Lubrizol Corp. Using existing components may be possible, but there are real trade-offs between cost and overall performance. Performance requirements will increase in GF-5, and Lubrizol has invested in developing new components to meet and exceed the category need.

A major driver for the GF-5 specification, he added, is improved emissions system durability. The phosphorus in the engine oil package must have less impact on the three-way catalyst. Using lower-volatility ZDPs to retain engine sump phosphorus provides this performance dimension, but it must be done without sacrificing engine wear protection.

Phosphorus in engine oils comes from the antiwear agent zinc dialkyl dithiophosphate (ZDDP, or ZDP). While it contributes to wear and oxidation control, it has a ruinous effect on catalytic converters. To counter this, phosphorus levels have been whittled down to a present-day 0.08 percent maximum (with a minimum of 0.06 percent to allay concerns about wear). Now, GF-5 will target phosphorus volatility – the elements ability to migrate past the cylinders and gum up the cars three-way catalyst.

Auto companies are asking that phosphorus volatility be measured on end-of-test oil samples from the Sequence IIIG engine wear test. They want GF-5 engine oils to show they still retain 85 percent of their original phosphorus content, after 100 hours in the IIIG.

In late October, though, the engine oil industry presented data showing that this requirement was unrealistic and would screen out many good performing oils that are known to have excellent phosphorus retention. It countered with a proposal that the phosphorus retention limit be set at 78 percent, which would still eliminate oils with less-stable ZDDPs. Automakers agreed to consider this.

While that limit is still awaiting industry consensus, Puckace confirmed that reducing phosphorus volatility will help preserve the efficiency of the three-way catalyst in the emission system. Lubrizol cooperatively investigated not only the impact of phosphorus volatility on emission system durability but also quantified the impact of phosphorus on three-way catalysts, he said. On, we have posted all of our published technical papers, presentations, OEM interviews, and field-test work that discuss the relationship between volatility and emission system durability.

This research led Lubrizol to develop what it calls high phosphorus retention ZDDP. This new class of antiwear ZDP couples excellent phosphorus retention with strong wear protection, Puckace said. Other component innovations are on the horizon. Their use in general market GF-5 products is dependent upon the outcome of the final tests and limits. These innovations can enable our customers to differentiate their oils within the GF-5 product category.

Competitors also are busy creating additive packages with less-volatile ZDDPs. Currently the most significant change is that all additive systems will need to use LV – low volatility – ZDDP to minimize the volatilization of the phosphorus in the ZDDP and help reduce vehicle emissions, commented Infineums Haffner, adding, Meeting the new phosphorus retention requirements will require the use of ZDDPs manufactured from less-volatile alcohols. This is an evolutionary change, but like all changes, bringing even a modified new molecule into the supply chain, and eventually the market place, can add cost.

While none of the additive companies would disclose their investment in producing low-volatility ZDDP, those interviewed for this article expect no delays in supplying it for GF-5.

Nor do they think that the low-volatility ZDDP will underperform in current vehicles. By definition, Haffner said, GF-5 oils must be vigorously tested to show they are backward compatible. Only Infineum products which have been significantly engine and field test-proven are commercialized. Thus, if we reduce an ingredient, customers can be certain that product will still provide appropriate performance.

Phosphorus volatility is not the only issue on the anvil in GF-5. The new oils are also expected to deliver 0.5 percent greater fuel economy and better coking deposit protection for turbochargers (see last months issue, page 42). Additionally, they must address:

Seal Compatibility. Individual OEMs have their own requirements for seal compatibility, pointed out Glenn Mazzamaro, OEM liaison manager at R.T. Vanderbilt Co. in Norwalk, Conn., and oil and additive companies typically work with the major elastomer types to assure their formulations create no conflicts. But GF-5 will be the first engine oil category to include this requirement, he observed. Five types of elastomers will be tested in the oil, including rubbers based on polyacrylate, hydrogenated nitrile, silicone, fluorocarbon and ethylene acrylic.

In many cases, this is formalizing work thats being done already, said Boffa. And elastomer compatibility is part of the heavy-duty and European specifications already too, so the additive companies have experience in dealing with this. However, that doesnt mean its easy, he added. Some nitrogen compounds can negatively affect some elastomers, Boffa noted, including some nitrogen compounds popularly used in detergent packages. So this requirement could drive the selection of dispersant additives.

Flex-fuel Vehicles and E85 Blends. Pressure is growing to reduce U.S. dependence on petroleum-based transportation fuels, and General Motors expects 50 percent of its production will be flex-fuel vehicles by 2012, able to run on blends of gasoline and up to 85 percent ethanol. These vehicles will need engine oils that deliver greater rust protection – ethanol is very harsh. And the oils will have to pass a test for emulsion retention, to assure that corrosive water and acids are retained in the oil, and do not separate out. This will require more robust formulations that include emulsion retention protection, pointed out Lubrizols Puckace.

Oil Aeration. At the recent Independent Lubricant Manufacturers meeting in Scottsdale, Ariz., Staff Scientist Jim Linden of General Motors Research & Development explained that nearly all his companys engines now use variable valve timing, which relies on camshaft phasing to shut down unneeded cylinders and save fuel. The benefit can be 1 to 3 percent fuel economy improvement, but theres a downside for the oil, he said. Cam phasing uses the engine oil as a hydraulic fluid to lift the cams, and as the engine oil is used for hydraulic lifters, it has less time in the sump to release air.

To ensure rapid air release, automakers want GF-5 to include a used oil aeration test (ASTM D6894) that runs on a diesel engine, plus much stricter limits on foaming characteristics.

The automakers say oil aeration in GF-5 will be based on the HEUI [diesel] engine test, and we have some experience with this already on the heavy-duty side. Its already a requirement there, said Oronites Boffa. At limits being discussed, foam inhibitor that is already in the formulation will likely be sufficient. That wont drive a significant change or cost of formulation.

On technical grounds, however, the engine oil industry has questioned the use of a diesel engine test in this specification, as well as the need for stricter limits on foam. Said Haffner of Infineum, With regard to the aeration test, we are not convinced that the HEUI test, or tighter limits on the current foam tests, will bring any additional protection over GF-4 oils to the hydraulic valve actuation systems. We believe aeration issues are mostly resolved by engine hardware.

Looking at this list of wants and needs, Boffa reflected that each again poses the question of balance. Our biggest formulating issue is to balance fuel economy and increase deposit performance. Were always dealing with formulating challenges, whether to reduce additives or add something new. GF-5 is a step increase in performance, and the additive treat will increase accordingly.

Inherently, theres only so much engine oil can deliver in the way of fuel economy, and GF-4 limits are set so that we already get a lot of fuel economy effect based on viscosity improvements, he mused. However, other components, such as detergents and dispersants, can hurt fuel economy due to viscometric effects. It will be quite a challenge to balance these needs – fuel economy and cleanliness. The current additives can meet the demand for cleanliness, deposit protection and sludge control, and its fairly well known how to do this. To ensure this while not negatively affecting fuel economy – thats more difficult.

The challenge is getting an appropriate return on investment as we reformulate to deliver robust and cost-effective products to the marketplace that the consumer will value, commented Haffner. Budgets are under pressure, and we face major reformulation costs for new ACEA specifications in Europe, not to mention the many OEM specifications such as the new GEOS A and B specifications by General Motors. The industry does not have endless budgets and resources, so like any business you want to invest in the projects with the highest returns.

We hope that the final specification is right sized, stated Puckace, balancing the OEM and oil market needs. Further, the supporting tests and variables can be critical uncertainties that drive elongation of the roll-out timeline and escalate R&D costs. Their quick and fair definition allows Lubrizol to deliver GF-5 technology to the OEMs and oil marketers without delay.

In the end, getting the a right sized GF-5 specification with room for customer differentiation is key. Our customers need to be able to provide end users with a compelling offer that allows for commercial success. In that way, all parties win.

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