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Fuel Economy the Role of Friction Modifiers and VI Improvers

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Fuel Economy the Role of Friction Modifiers and VI Improvers TECH beaT Dr. Neil Canter / Contributing Editor Special additive RepoRt Fuel economy The role of friction modifiers and VI improvers These two additives are helping lubricant suppliers improve fuel economy and comply with new engine oil specifications. The lubricanT indusTry is Facing enormous challenges to develop products that Key ConCepts function optimally under severe conditions for long operating periods. One other factor emerging from the automotive standpoint is ways to improve the vehicular • Fuel economy improvement fuel economy. Part of the reason is driven by the challenge faced by the U.S. auto- has become a key objective motive industry to boost Corporate Average Fuel Economy (CAFE) by 20 percent in the development of PCMOs by 2016. In addition, the U.S. government has established a goal of raising CAFE and HDDEOs. to 54.5 miles per gallon by 2025, a doubling of the existing CAFE. The desire to improve fuel economy has also moved to the heavy-duty diesel • Two additives that will play vehicles, as the U.S. government established requirements for reducing carbon di- an important role in improv- oxide emissions in August 2011 by 10 to 20 percent for 2018 model year vehicles. ing fuel economy are friction The objective is to not only reduce emissions but also improve fuel economy. The modifiers and VI improvers. U.S. EPA predicts a savings of 530 million barrels of oil over the lifetime of vehicles built between the 2014 and 2018 model years. • Further reduction of engine One of the main ways to address fuel economy has been through the reduction oil viscosity can lead to of engine oil viscosity. This is ongoing for passenger car motor oils (PCMOs) but is in its initial phase for heavy-duty diesel engine oils (HDDEOs). increasing fuel economy, but Both the new PCMO specification, GF-6, and the new HDDEO specification, there may be limitations PC-11, are under development, and each will be split into two categories to take from the engine design and into account the use of lower-viscosity oils. One of the categories will be backward lubricant standpoints. integrated to cover lubricants used in current and older engines. The second cate- gory is for lower-viscosity engine oils. 14 Nikola Tesla’s father, Milutin Tesla, was a Serbian Orthodox Priest. His mother, To seek a broad range of opinions, TLT interviewed the following repre- Organic Friction Modifiers (OFM’s) sentatives from nine additive suppliers: Van der Waals • Dr. Jai Bansal, global technical forces advisor, Infineum USA LP O FM examples • Ian Bell, technical director-new NH2 Long, non -polar chains Oleylamide product development, Afton Van der Waals OH forces Chemical Corp. OH O O • Dr. Frank DeBlase, Chemtura Glycerol mono-oleate dipole-dipole Fellow-petroleum additives and interactions fluids, Chemtura Corp. Polar heads OOOO adhesive • Chris Donaghy, sales director- hydrogen bonding polymer additives and lubri- cants, Croda Inc. Oxidised and/or hydroxylated metal surface • Dr. Carl Esche, Global P.C.M.O. technical manager-petroleum Figure 1 | Friction modifiers such as the two organic types shown arrange themselves to department, Vanderbilt Chemi- metal surfaces in a stacked vertical manner similar to carpet fibers. (Courtesy of Croda Inc.) cals, LLC • David Gray, technical service FuncTIons oF a “Each friction-modifier molecule is manager, Evonik Oil Additives FrIcTIon modIFIer stacked vertically besides another.” USA Inc. STLE-member Chris Donaghy, sales Two examples seen in Figure 1 are director-polymer additives and lubri- glycerol monooleate and oleylamide. • Mark Rees, global business cants for Croda Inc. in New Castle, Dr. Jai Bansal, global technical ad- manager-passenger car engine Del., says, “There are two types of fric- visor for Infineum USA LP in Linden, oil additives, The Lubrizol tion modifiers: organic friction modi- N.J., says, “Friction modifiers provide Corp. fiers (carbon, hydrogen and oxygen a highly labile and lower friction film • Dr. Kaustav Sinha, associate sci- only) and metal-containing friction separating the contacting metal sur- entist, & John Cuthbert, princi- modifiers (MFMs) such as molybde- faces.” pal research scientist, The Dow num dithiocarbamate (MoDTC). Or- Dr. Frank DeBlase, Chemtura Fel- Chemical Co. ganic friction modifiers consist of two low, petroleum additives and fluids for key segments—a polar group that can Chemtura Corp. in Naugatuck, Conn., • Dr. Mark Sztenderowicz, man- attach to metal surfaces and a lipophil- discusses the mechanisms for how ager-automotive engine oil de- ic group that provides not only oil friction modifiers adsorb onto metal velopment, & Alex Boffa, global solubility, but also a cushioning or surfaces. “In the boundary lubrication viscosity index improver-tech- spring-like effect to prevent surfaces region, surface metal-metal asperities nical team leader, Chevron from coming into contact.” contact occurs and the bulk hydrody- Oronite Co. LLC “Friction modifiers minimize light namic forces separating these contacts surface contacts (sliding and rolling) are insufficient or not available,” De- TLT asked these reps to provide that may occur in a given machine de- Blase says. “Friction modifiers reduce further insight into how specific addi- sign,” Donaghy says. “As long as the the coefficient of friction by forming tives may be used to boost fuel econo- frictional contact is light, these mole- ordered structures on metal surfaces my. The discussions involve the use of cules provide a cushioning effect when through chemisorptions, physisorp- friction modifiers, which have been one of the coated surfaces connects tions or more complex physisorption- well-known for improving fuel econo- with another coated surface. If the chemisorption transitions. The latter my and viscosity index (VI) improvers contact is heavy, then the molecules transitions can occur, particularly at that are being closely examined for are brushed off, eliminating any po- higher temperatures and pressures their ability to improve the perfor- tential additive benefit.” (e.g., >130 C, and 100 Newton applied mance of lower-viscosity engine oils Donaghy indicates that friction force).” (For more information on VI improvers, modifiers orient themselves to metal DeBlase summarizes, “There is a see the September 2011 TLT issue, avail- surfaces in a similar fashion to carpet range of intermolecular attractive forc- able digitally at www.stle.org).1 fibers, as shown in Figure 1. He adds, es acting in concert: dipole-dipole, Djuka Mandic, was an inventor in her own right of household appliances. 15 ionic, coordinate covalent bond inter- actions to the metal surfaces and additional weaker van der Waals inter- actions between the nonpolar hydro- carbon chains. The combination of all of these molecular designed forces is responsible for the development of the friction-modifier ‘assembled’ struc- tures at these boundaries.” STLE-member Dr. Carl Esche, Global P.C.M.O. technical manager, petroleum department for Vanderbilt Chemicals, LLC, in Norwalk, Conn., says, “The MFM forms a molybde- num-sulfur bond to the metal surface to reduce friction. Molybdenum is the Figure 2 | The impact friction modifiers have in improving fuel economy is dependent upon traditional metal used but recently the specific type used and the other components present in the engine oil formulation, as other metals have been investigated shown in this Sequence VID engine test data. (Courtesy of Chevron Oronite Co. LLC) for their friction-reducing properties, with one example being tungsten.” relative speeds between parts such as vide a benefit ranging from a few the interface between cams and fol- tenths of a percent to one percent in lowers and cylinder liners and piston standardized engine and vehicle test- ‘current work is showing that a total fuel rings where the piston is near top or ing compared with similar oils con- economy improvement (Fei) value for bottom center.” taining no friction modifier. Under XW-20 oils of 3.6 can be realized for gF-6 some conditions, friction modifiers as compared to 2.6 for gF-5.’ use In Pcmos can provide even higher impacts.” — dr. Frank deblase, chemtura corp. Most respondents indicated that fric- The impact of different friction tion modifier use started in the 1970s modifiers in a prototype ILSAC GF-6 when fuel economy standards were es- passenger car engine oil formulation is Besides the primary type, Ian Bell, tablished. DeBlase mentioned that us- shown in Figure 2. Sztenderowicz technical director-new product devel- age of friction modifiers started in auto- says, “Each of the friction modifiers opment for Afton Chemical Corp. in matic transmission fluids in the 1950s. provides a fuel economy improvement Richmond, Va., defines a second fric- Esche feels that organic friction benefit relative to a reference engine tion modifier type. “This second type modifiers were first developed in the oil (with no friction modifier), but the can be described as chemicals that de- early 1960s as partial esters of fatty ac- impact of each one is different and de- compose under the high temperatures ids.2 Shortly thereafter, MFMs were in- pends on the other components in the and pressures within an engine and vented, as noted in a U.S. Patent issued engine oil formulation.” their decomposition products form in 1967.3 Esche says, “MFMs hit their While friction modifiers are effec- graphitic layered structures on the en- stride in the 1970s with the advent of tive (otherwise they would not be see- gine surface,” Bell says. “These impart two oil embargos. They are now used ing continued use in automotive lubri- very low friction characteristics due to not only for friction modification but cants), their absolute value is the crystalline layer structure of the also for their antiwear and antioxidant impossible to quantify, according to decomposition species.” properties.” Previously, fatty acid esters Bell. “The lubricants industry would STLE-member Dr. Mark Sztendero- and molybdenum-containing com- not be able to achieve the challenging wicz, manager-automotive engine oil pounds were used in various types of fuel economy targets seen in the in- development for Chevron Oronite Co.
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