In the past couple of decades, diesel engine emissions regulations necessitated changes to heavy-duty diesel engine oils. “Each time there has been a change, with the exception of 2010, there has also been a change in the type of lubricant necessary to lubricate those engines,” says Dan Arcy, Global OEM Technical Manager for Shell and a member of the API committee to develop the PC-11 oil category.
Last year, the National Transportation Highway Safety Administration (NHTSA) issued a regulation that limits greenhouse gases (GHG) and mandates fuel economy improvements for the first time in medium- and heavy-duty trucks. These rules phase in from 2014 to 2018.
Truck manufacturers have different technologies that can be added or operating systems that can be changed in order to meet these requirements. One technology is the use of low viscosity, fuel efficient engine oils. While thinner oils reduce parasitic losses and increase fuel economy, concerns can arise in regards to the ability of the oil film to adequately protect critical surfaces. These low viscosity engine oils must provide the same durability as current engine oils, which make development of a new oil classification necessary.
Engine changes since 2007 are also driving the demand for a new oil category. Since the introduction of CJ-4 oils in 2007, engine designs have evolved. “The pressures in the cylinders have gone up. The metallurgy inside the engines changed, and the coatings on parts within the engine are different,” says Arcy.
In addition, the CJ-4 oil specification has been the prevailing standard longer than any modern diesel engine lubricant category. “API came out with CJ-4 in October of 2006,” recalls Arcy.” The testing procedures used to qualify CJ-4 type oils may not be the most representative of the current engines and hardware that we are seeing in the field.”
Engine test obsolescence is also becoming an issue. “There will be no parts available to run some tests [needed to qualify for CJ-4] around the 2015 timeframe,” says Arcy. “We could develop new tests to replace the ones that are [available], but when you [look into] the cost of developing a new test, you want to make it with current hardware and you want to make sure it is viable for the new engines coming out.”
In June of 2011, engine manufacturers requested the American Petroleum Institute (API) develop a new oil category to meet the demands of engines in development. The engine manufacturers wanted oils that could help reduce CO2 and improve fuel economy. They requested improvements in oxidation stability, resistance to aeration, biodiesel compatibility, a scuffing and adhesive wear test, and increased shear stability.
Upon receiving the request, API established a new category evaluation team. This team works with the engine manufacturers, additive industry and oil marketers to determine if the request is warranted. “After extensive review, it was determined there is a need for a new category that meets the requirements,” says Arcy. That was the beginning of PC-11. PC stands for Proposed Category. The actual naming convention is determined prior to the actual release. For instance, the current CJ-4 oil actually began as PC-10.
Nothing is set in stone at this point, except the release date. “PC-11 is in its infancy right now because it was just February 1 that the new category development team had its first meeting,” says Arcy. “The typical category takes around four years to develop. PC-11 is being asked to be in the marketplace and available by January 1, 2016.”
PC-11 may actually be split into two distinct subcategories. One part of the category would be fuel economy oils. The other part of the category would be oil that maintains the performance of CJ-4 oils in higher viscosity grades, like 15W-40s. These oils would also have the benefit of the additional oxidation stability, resistance to aeration, biodiesel compatibility, resistance to scuffing, and adhesive wear and increased shear stability.
A shift to lighter viscosities
North America currently lags Europe in the acceptance of lighter oil viscosity grades, and around 80% of the U.S. market uses 15W-40 oil. Expect this to change over time. “Lighter viscosity grades are becoming more acceptable and those are the grades that are going to be necessary to provide the fuel economy benefit,” says Arcy. “Gaining the fuel economy out of lubricants comes down to lower viscosity, lower friction lubricants.”
Some of this shift is already taking place, with an increase in the usage of 10W-30 oils. “A number of engine manufacturers support the use of lighter viscosity oils, like 10W-30,” says Arcy. “Two years ago Volvo started factory filling with 10W-30. Cummins allows 10W-30 to well over 100 F now. We are seeing a slow change.” Arcy claims a 1.6% fuel economy benefit can be achieved by switching from a 10W-40 to a 10W-30 oil.
With PC-11, there will be an emphasis placed on fuel economy oils. Fuel economy oils could be more in the 10W-30 or 5W-30 range. They could even be a 5W-20 or a 0W-20. “It is the high temperature viscosity that we really look at for fuel economy,” says Arcy.
The final specification on the actual weight of the fuel economy oils has yet to be determined. “We evaluate these lubricants to see how far we can push them to get the best fuel economy without compromising the durability,” says Arcy. “If you compromise durability, it is not going to be acceptable to our customers or the industry.”
The days of producing engines and oils separately are quickly drawing to a close. Going forward there needs to be a shift to co-engineering the engine and the lubricant to provide the best fuel economy or the best use of energy that is put into the vehicle. “That is what we are going to need to do in order to meet requirements of the future,” says Arcy.
Compatibility a question
Until this point, the industry has been very fortunate that every time a new oil category was introduced, it has been backwards compatible to all previous or historic engines. With PC-11, this might not be the case. The PC-11 product that covers the 15W-40 and traditional viscosities should be backwards compatible, but the product intended for fuel economy may not. There is talk of tightening the limits where you may have light 30 weights and heavy 30 weights. “It is those light 30 weights that might not be backwards compatible,” says Arcy.
Due to concern over the compatibility of previous engine designs with these new light oil classifications, the backwards compatibility may become a question for each engine manufacturer to determine. “The engine manufacturer may say it is backwards compatible to 2007, but not anything before 2007,” says Arcy. “Those are the kinds of details that have to come out yet.”
Regulations have reached a point where compromises to make an oil backwards compatible may not be acceptable. Higher performance oils that can yield a 1.5% fuel economy benefit justify the decision to market more than one type of oil for heavy-duty diesel engines. Things may get a little more complicated for large fleets, but there is a measurable payback.
“We are going to have to start looking at things differently in order to meet the energy challenges of the future,” says Arcy. “We have always been lucky that the engine oils we design have always been useful in the previous engines. That may not be the case anymore. We may have to actually draw a line in the sand and say anything from this year on uses these engine oils and anything from this model year takes these. If we can achieve an extra 1.5% or 2% in fuel economy, long term it is going to pay off.”