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 category 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 interactions to the metal surfaces and additional weaker van der Waals interactions between the nonpolar hydrocarbon chains. The combination of all of these molecular designed forces is responsible for the development of the friction-modifier ‘assembled’ structures 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 molybdenum-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. lubricants for purposes not related to dustry now if it were not for the use of LLC in Richmond, Calif., points out friction reduction. friction modifiers,” Bell says. “The ab- the engine areas where friction modi- solute impact of friction modifiers on fiers are most effective. “Friction mod- Effectiveness of fuel economy is highly dependent ifiers provide a reduction in friction Friction modifiers upon the vehicle/engine and the oper- under boundary or mixed lubrication Sztenderowicz states that friction- ating conditions.” conditions where there is some sur- modifier effectiveness is variable and Donaghy agrees that the benefit of face-to-surface contact,” Sztenderow- depends on the lubricant formulation, friction modifiers is based on the fac- icz says. “In engines, these are the ar- engine design and operating condi- tors described previously. He says, “In eas with higher loads and lower tions. He says, “Friction modifiers pro- commonly used bench engine tests,

16 • SEPTEMBER 2013 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG friction modifiers are capable of in- effectiveness has been going down creasing fuel efficiency by up to 2-3 ‘Formulating engine oils is a balance over time because of engine improve- percent. In formulating engine oils, between engine durability, which is para- ments made by OEMs. He says, other components also can be surface mount, emission system durability and “Strides made in the last two decades fuel efficiency.’ active and interfere with the surface by OEMs to minimize friction losses in activity of the friction modifier. Spe- — Mark Rees, The Lubrizol Corp. the engine has made it more difficult cifically, polar compounds used in en- for friction modifiers to do their job. gine oil formulations can also act as As a result, modern engines tend to solubilizing agents and prevent the knowledge in the industry that the operate more in the hydrodynamic friction modifier from reaching the more friction modifier added to the and mixed lubrication regimes and metal surface.” formulation, the better the fuel econo- less in the boundary regime where Such problems may necessitate in- my. Consequently, today’s formulators friction modifiers are most effective.” creasing the concentration of or even are adding more friction modifiers to changing the friction modifier type used. the engine oil. Screening Tests Esche contends that engine oil lu- DeBlase believes that common fric- Most of the respondents cite the chal- bricants have only about a 10 percent tion modifiers can be effective in reach- lenge of correlating bench screening or less influence on the total friction/ ing an additional 1.5-2.5 percent fuel tests to real-world engine tests such as energy loss in an engine. Axel and economy improvement for organic automobile fleet trials. “Screening tests transmission lubricants can affect an- types and just over 3 percent for very are notoriously unrepresentative of re- other 5 percent or less of the friction/ effective organic and metal-containing al-world operations. However, it is chal- energy losses. types above the gain realized from de- lenging to conduct powerful research The benefits of both organic fric- creasing oil viscosity. “For HDDEOs and formulation evaluations in non- tion modifiers and MFMs are shown in (for example, 15W-40 reduced to 5W- standard conditions. We have a dilem- the Sequence VID consortium data in 40), an additional 1 percent fuel econo- ma,” Bell says. “There exist many fric- Figure 3. Esche adds, “This data shows my improvement is possible, but this tional and surface chemistry tests that that friction modifiers have a positive may be tempered if boundary friction can be used to evaluate lubricant chem- effect on engine oils across several dif- increases at the same time,” DeBlase istry. Common instruments used in ferent viscosity grades. It also shows says. “This necessitates the need for these screening tests include the Mini- the performance advantage a molybde- greater use of friction modifiers to meet Traction-Machine (MTM) and High- num-based friction modifier has over the demands generated by high loads Frequency Reciprocating Rig (HFRR). an organic friction modifier.” and low viscosity.” These are quick, cheap and repeatable. Generally speaking, it is common Bansal feels that friction-modifier However, they are nothing more than indicative of how a system responds under a unique set of operating conditions, and we know that vehicles in the Consortium Seq. VID Data field see many sets of conditions.” Bell continues, “Electrically mo- Formulation effects (with ASTM engine hour correction) tored engines are the next level of test-

2.00 ing options, but while they are clearly more relevant to operating conditions 1.80 • Viscosity effects (Oils A & E) and are relatively reliable, they lack 1.60 1.51 - 5W-20 v. 10W-30 = +0.37% FEI 1.42 the full operational influence of a fired 1.40 Oil Oil •Organic FM effects (Oils A & B) B I engine, and as such they can only as- 1.20 1.13 - Oil B v. Oil A = +0.38%Oil A FEI (5W-20) 1.04 Oil Oil B (5W-20, OFM) sess the instantaneous frictional per- FEI 1.00 A % 0.76 •Mo ly bdenum0.77 FM e ffect Oils (Oil E (10W s G -30) & I) formance of a lubricant.” 0.80 0.72 0.73 Oil G (5W-30) Oil 0.59- Oil I v. Oil G = +0.70% FEI Bell finishes by stating that fired- 0.60 E Oil Oil I (5W-30, Moly) G engine tests also have their limitations. 0. 40 RUN V V V IV IV Oils A & B 0.21are 5W-20 (HTHS=2.52 cP), Technology 1 Although they are a lot more closely

0.20 Oil E is 10W-30 (HTHS=NOT 3.10 cP), Technology 1 n=7 n=6 n=5 n=2 n=3 linked to vehicle operation, they are 0.00 Oils G & I are 5W-30 (HTHS=3.05 cP), Technology 2 FEI1 FEI2 limited to one type of hardware and limited operational conditions. He Figure 3 | Consortium Sequence VI data shows the fuel economy improvements obtained says, “The ultimate screening and through changes in engine oil viscosity and the use of organic friction modifiers and metal- evaluation tool is a fully operational containing friction modifiers (MFMs) in several PCMO viscosity grades. (Courtesy of Vanderbilt vehicle, operating under a repeatable Chemicals LLC) and appropriate driving cycle and prac-

Call for papers: STLE is now accepting abstracts for its 2014 annual meeting in Lake Buena, Vista, Florida. Deadline: Oct. 1. Details: www.stle.org. 17 tically on a dynamometer. These can be on Plint TE-77 operates in the friction be determined in pure sliding, pure run very quickly and accurately, afford- mode (dowel-pin-on-plate) to provide rolling and a mixture of sliding and ing very precise data and evaluations.” a coefficient of friction (COF) versus rolling conditions. The SRV, HFRR and Bansal agrees, “Many bench screen- temperature profile in the range be- the Cameron Plint are limited in that ing tools are used in the lubricant in- tween 60 C-165 C. This test allows a they measure friction only in sliding dustry to measure the performance of complete characterization from milder contacts,” Donaghy says. “The SRV friction modifiers. However, little or conditions at low temperatures to high- test is perhaps the most versatile of the no effort has been reported in the lit- er temperatures where physisorption to three sliding contact tests in that it is erature to determine the relevance of chemisorptions transitions can occur.” feasible to determine friction between these tools to the real world. Realisti- “The MTM provides a range of materials actually used in an engine cally, it is nearly impossible to repli- friction conditions from hydrodynam- (for example, by taking a slice of the cate the exact engine environment in a ic, mixed to boundary lubrication cylinder liner and the piston rings).” bench scale test. Therefore, we believe when operated in the Stribeck config- Esche indicates that the efficacy of that a suitably field-correlated engine uration, providing COF versus en- a friction modifier ultimately comes test is the only reliable method to eval- trainment speed at isothermal temper- down to its performance in an engine uate the fuel efficiency performance of atures (e.g., 50 C, 80 C, as well as test. He says, “Due to cost constraints, a friction modifier.” higher, 120 C-150 C). HFRR measure- bench testing is the preferred route to ments can provide simultaneous mea- screen a large number of candidate en- surements of both a wear-scar and the gine oils. Once the top several candi- ‘Due to cost constraints, bench testing boundary coefficient of friction and date oils have been selected, they are is the preferred route to screen a large offer a high-speed, reciprocating mea- then run in an engine test. The engine number of candidate engine oils.’ surement of friction on smaller vol- test may be a stand-alone engine in a — Dr. Carl Esche, ume samples,” DeBlase continues. test stand or a vehicle that has been Vanderbilt Chemicals, LLC “These measurements can be done iso- placed on a chassis dyno. In either thermally or at a temperature ramp, case, the fuel economy of the engine similar to the Cameron Plint. Another oil is determined by the amount of fuel Sztenderowicz also agrees with the option is the SRV tribology testing in- consumed during the test.” approach of using field testing but strument that can provide boundary cautions that there is a trade-off with layer coefficient of friction data with a Sequence VIE Fuel the cost involved. He says, “Field test- flexible array of specimen geometries Economy Engine Test ing, engine test stand or chassis dyna- such as ball-on-disk, pin-on-disk, cyl- In GF-6 the key engine test to evaluate mometer testing is most relevant, es- inder-on-disk and disk-on-disk.” fuel economy has been designated as pecially when realistic driving cycles DeBlase finishes up by cautioning the Sequence VIE test. A new lower- are used. However, such testing is ex- that no-harm testing needs to be done viscosity grade known as SAE 16 has pensive and is subject to two impor- to make sure that specific friction been approved and may provide addi- tant limitations. First, variability for modifiers do not function adversely tional fuel economy benefits, but those such tests can be high, making it hard under operating oxidation conditions will need to be established. Oils used in to discern differences between two en- that could result in metal corrosion or SAE 16 will have a viscosity of 0W-16. gine oil formulations. Second, the re- elastomeric degradation. “Friction- The new viscosity grade will require sults are specific to engines or vehicles modifier additives must also be evalu- that GF-6 be split into two categories used, as well as the operating condi- ated in the presence of variations in known as GF-6A and GF-6B. All oils tions and, therefore, may not relate di- base oil types (both mineral oil and that are backward compatible with old- rectly to others.” synthetic) and in the presence of other er engines will be in GF-6A. The new Sztenderowicz continues, “For this additives such as antioxidants, anti- SAE 16 will be assigned to GF-6B and reason, a variety of laboratory bench wear, dispersants, detergents and VI not be backward compatible. friction tests can be used as screeners improvers,” DeBlase says. “The Falex The industry representatives con- to evaluate friction modifiers. These four-ball wear (ASTM D4172) and tacted were asked for comments on are usually very repeatable, easily ad- Cameron Plint wear tests are useful to the Sequence VIE and whether testing justed to cover a wide range of condi- insure compatibility between extreme will differ for the new SAE 16 viscosity tions and are relatively inexpensive.” pressure, antiwear additives and fric- grade. For the most part, most respon- DeBlase believes that the Cameron tion modifiers.” dents indicated that it is too early to Plint TE-77, MTM and HFRR tribolo- Donaghy agrees about the types of tell how the new engine test will work gy tests are useful in assessing the per- bench screening tests that are used to with specific friction modifiers. formance of friction modifiers in lab screen friction modifiers. “The MTM DeBlase says, “Current work is screening tests. He says, “The Camer- has the advantage in that friction can showing that a total fuel economy im-

18 • SEPTEMBER 2013 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG provement (FEI) value for XW-20 oils of 3.6 can be realized for GF-6 as compared to 2.6 for GF-5. A similar improvement from 1.9 to 2.9 can be achieved for XW-30 oils.” The FEI is determined from mea- suring the fuel economy of virgin engine oil (FEI1) and engine oil aged for 100 hours (FEI2). DeBlase states that this increase is for GF-6A oils, while work is in progress to determine the FEI for new lower viscosity GF-6B oils. DeBlase adds, “If oil oxidation occurring from the FEI2 impacts the friction-modifier additive needed, then friction-modifier additive dura-

bility will also be very important to help reach the FEI level targets. In ad- Figure 4 | Fuel economy improvements are seen by reducing viscosity and using friction dition for longer drain intervals, fric- modifiers in the Volvo D12D diesel engine. A better benefit is seen by reducing viscosity as compared to using friction modifiers. (Courtesy of Chevron Oronite Co. LLC) tion modifier durability will no doubt be important.” Donaghy says, “The Sequence VI Fuel Economy and FE durability Improvement From engine test uses a different engine than was used in the Sequence VID (current ILSAC GF Series 5W‐30 Engine Oil 1995 to 2016 GF-5 test), but it is expected that friction modifiers will provide a similar GF-5 effect in the new engine. The SAE 16 specification will give rise to a decrease in viscosity at higher operating temperatures in the engine, which will lead to thinner films and potentially higher wear. This need not be a high concern for new engines designed to operate under thin film/boundary lubrication, but the use of friction modifiers to increase film thickness and still maintain low friction will still be highly desirable.” Figure 5 | In moving from GF-2 in 1995 to the development of GF-6A (due to be available in Bansal says, “On fundamental prin- 2016), the contribution of the engine oil to fuel economy has shown a progressive improve1 - ciples, the SAE 16 grade should pro- ment. (Courtesy of The Lubrizol Corp.) vide better fuel economy performance than other grades, primarily due to sented within the industry has demon- to improve the fuel economy of auto- lower energy losses in the hydrody- strated that these fluids can perform mobiles. But how do they compare and namic mode. However, it remains to significantly better than the current potentially complement each other? be seen whether the Sequence VIE test GF-5 specification limits for SW-20 Sztenderowicz says, “Usually, re- is configured for the appropriate bal- oils when tested in the Sequence VID ducing viscosity has a larger benefit ance of the various lubrication regimes test. Whether or not this improvement than friction modifiers when moving to be able to accurately measure the will be observed in the new hardware from ‘traditional’ viscosity grades to hydrodynamic response of this very and test will be determined through the latest OEM-recommended low- light grade.” industry matrix testing.” viscosity grades. This is shown in Fig- Bell says, “The current intent for ure 4 in which the effects of both re- 0W-16 low viscosity engine oils is that Friction Modifiers vs. duced viscosity (from 15W-40 to they will exhibit improved fuel econo- Reducing Viscosity 5W-30) and the addition of three fric- my over XW-20 (0W-20 or 5W-20) Both friction modifiers and reducing the tion modifiers is shown for a heavy- oils in the Sequence VIE test. Data pre- viscosity of engine oils have been shown duty diesel engine.”

20 During his trip to the U.S. in 1884, Nikola Tesla’s ticket, money and luggage were stolen and he was nearly thrown overboard “One possible option for friction reduction would be through the introduction of polyalkylene glycols (PAGs) as an additive/co-basestock in a fully- formulated fluid,” Sinha says. “Due to their oxygen polarity, PAGs have sol- vent properties different from those of hydrocarbons. The polarity of PAGs, including oil-soluble versions, further enhances their affinity for metal surfaces, forming a durable, low-friction lubricating film.” Figure 6 shows the friction reduction benefit of two prototype, PAG- based PCMO formulations in MTM studies. David Gray, technical service manager for Evonik Oil Additives USA, Inc. in Horsham, Pa., observes, “The

Figure 6 | MTM (T= 100 C; FN= 50 N, SRR= 150 percent, 12th repeat) traction curves for PAG- question can be very difficult to an- based prototype passenger car engine oils are benchmarked against a typical 5W-20 GF-5 swer for a variety of reasons. First, the formulation. (Courtesy of The Dow Chemical Co.) majority of published data available uses fully formulated lubricants, But Sztenderowicz cautions that ment in fuel economy from GF-2 to which are highly likely to contain fric- continuing to reduce engine oil viscos- GF-6A, as shown in Figure 5. “Formu- tion modifiers so the impact of lower- ity will not lead to further fuel econo- lating engine oils is a balance between ing viscosity along is difficult to deter- my benefits without friction modifiers. engine durability, which is paramount, mine. Second, different engine or He says, “For prototype oils of viscos- emission system durability and fuel ef- bench tests used to generate the data ity below 0W-20, Sequence VID en- ficiency. Optimizing fuel efficiency is may respond more strongly to either gine test results flatten out. Due to much more than just adding friction reducing viscosity or changes in fric- this, friction modifiers become in- modifier and switching to a lighter vis- tion modification than can be seen in creasingly important for low-viscosity cosity grade,” Rees says. “The core for- the field. As such, it would be fair to oils, and, in fact, enable further fuel mulation must be built from the say both are critical, but the art is de- economy improvements when con- ground up in order to properly balance termining the balance.” tinuing to reduce viscosity.” the many components, including the Bell agrees that engine oil viscosity friction modifier that act together to will, in general, more effectively im- maintain durability while also reduc- ‘An engine is a very complex system that prove fuel economy. He says, “The im- ing overall friction.” at any one time can have multiple frictional regimes occurring simultaneously.’ pact of a viscosity grade change is typ- STLE-member Dr. Kaustav Sinha, ically four to five times larger than the associate scientist for The Dow Chem- — David Gray, maximum one might expect from a ical Co. in Midland, Mich., expressed Evonik Oil Additives USA Inc. friction modifier in a typical test. How- concern that reducing the engine oil ever, friction modifiers still play a part viscosity to reduce friction in the hy- in lubricants. First, there is a limit (or drodynamic region may lead to a pre- Gray continues, “An engine is a indeed several limits) to how low one mature transition to the boundary/ very complex system that at any one might drive viscosity. Second, the fric- mixed regime that could lead to fric- time can have multiple frictional re- tion modifiers allow the formulator to tional losses and wear, if the right gimes occurring simultaneously. Ad- tune performance (boost) within the combination of friction modifier/ex- dressing one frictional regime alone range of the viscosity grade.” treme pressure/antiwear components while ignoring others will not maxi- Mark Rees, global business manag- are not used. He believes there are op- mize all potential gains that are possi- er-passenger car engine oil additives portunities to improve fuel economy, ble. As such one should look at specific for The Lubrizol Corp. in Wickliffe, particularly for heavy-duty diesel en- viscosity measurements such as High Ohio, indicates that engine oil formu- gine oils that use the 15W-40 viscosity Temperature High Shear (HTHS) vis- lations have evolved over the past 20 grade and mostly operate in the hydro- cosity, which can be directly correlated years, showing a progressive improve- dynamic region. to improvements in fuel economy.”

during a ship-wide mutiny. He arrived in NYC with four cents in his pocket, a letter of recommendation and a few belongings. 21 DeBlase also believes that friction modifiers will be needed with the low- viscosity GF-6B engine oils. He says, “The higher FEI expected for GF-6B PCMO: 35-45% frictional losses in I Additives that can help: Friction Modifiers will no doubt also require sufficient, durable friction-modifier additives in Friction Coefficient PCMO: 55-65% frictional losses in II & III their formulation to overcome in- Additives that can help: Viscosity Modifiers, creased boundary layer asperity friction Friction Modifiers from the SAE-16 lower viscosity oils.” HDD: 95% frictional losses in III Introduction of thinner fluids is a big opportunity For heavy-duty diesel oils, viscosi- Additives that can help: Viscosity Modifiers ty reduction will be very important, according to DeBlase. He says, “Re- ducing oil viscosity reduces mixed and Boundary Mixed (M) Hydrodynamic (H) hydrodynamic losses, which, if signifi- Lubrication Lubrication Lubrication cant, can improve fuel economy.” Log (Oil Viscosity x Velocity/ Load) How low can the viscosity be reduced? Figure 7 | VI improvers and friction modifiers can be used in a complementary fashion in Most respondents consider the answer properly formulated engine oils to reduce friction because they operate in different lubrica- to this question to be more a matter of tion regimes, as noted in the Stribeck Curve. (Courtesy of Infineum USA LP) how effective OEMs are in developing new engine technology that will be of the engine metallurgy and surfaces improve fuel economy, some OEMs be- compatible with the new SAE 16 grade through coatings such as diamond- lieve the fuel economy benefit seen and even lower viscosity oils. Bell says, like carbon or other alloys, working in with lower-viscosity oils will be more “This is a critical question that essen- concert with friction modifiers, may than offset by the cost needed to ensure tially cannot be answered in isolation. be needed.” durability. He says, “How low the vis- It is possible to develop an effective Bansal speculates about how far the cosity can be reduced depends to a large lubricant at viscosities well below viscosity can be reduced without ma- extent on engine design, and bigger those used today and well below 0W- jor adverse consequences. “It is gener- bearings may be more tolerant of lower 16. However, it necessitates the co-de- ally believed that at a sufficiently low viscosity. However, at least one OEM velopment of hardware to accommo- viscosity, the boundary losses will be- has stated that the added cost to ensure date that fluid. This is the direction gin to wipe out any benefits gained durability may more than offset the fuel that we believe the industry will need from the reduced hydrodynamic loss- economy benefit that can be realized.” to move toward in the future to truly es,” Bansal says. “However, we feel Gary adds, “Newer engine designs access extreme fuel economy benefits.” that other factors such as oil volatility have been developed using lower vis- Bell continues, “We are beginning will be potential barriers to going too cosity fluids and have greater flexibility to see these hardware limitations below in viscosity, well before the point in the range of viscosities that can be come evident. The fact that not all of diminishing returns on energy effi- safely used without impacting durabil- OEMs will use 0W-16 oils and not all ciency is reached. Input will be needed ity, but we must be mindful of protect- will use 5W-20 oils means there are from the basestock manufacturers on ing the engines currently in use.” limitations in the current hardware this issue.” Sztenderowicz says, “Various and engine configurations preventing STLE-member John Cuthbert, OEMs have different opinions on how the use of lower viscosity fluids.” principal research scientist for The low engine oil viscosity can drop. In- DeBlase stresses that friction modi- Dow Chemical Co., says, “At low vis- creased wear, especially in highly- fiers will be instrumental as engine oil cosities (such as 0W-20), there are sig- stressed contacts like the valve train, viscosity continues to be reduced. “Be- nificant formulation challenges with have been noted for oils below 0W-20 sides viscosity, other key parameters to limited basestock options (with con- using industry standard tests such as consider when reducing friction are trolled Noack volatility) and little or the Sequence IVA. But there are now the load and the speed of moving parts no room for VI improvers. In order to OEMs that use oils below 0W-20 as in contact. Lowering engine oil viscos- push the envelope, the lubricant in- their factory fill in some vehicles. The ity without reducing boundary friction dustry has to look into novel antiwear bottom line is that both engines and provides little improvement (especial- chemistries, friction modifiers and al- oils continue to improve and, when ly at high loads),” DeBlase says. “To ternative co-basestocks.” designed together as a system, using achieve lower boundary friction, ei- Gray states that while the current oils of SAE 0W-16 and lower without ther friction modifiers or modification trend is to reduce viscosity in order to negative impacts is possible.”

22 • SEPTEMBER 2013 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Donaghy says, “Reducing the FUEL ECONOMY DATA – NEDC CYCLE HTHS viscosity too far can have a negFuel- EconomyFUEL ECONOMYData – NEDC DATA – NEDC CYCLE ative effect on fuel economy. Too low a Fuel Economy Data – NEDC HTHS viscosity results in not having a sufficient film to support the increases in load and friction. Some polymeric friction modifiers that form thick, low traction films show potential to reduce HTHS beyond the current limits.” Esche cautions that thin oils are not a problem when used in the correct engine. He says, “The problem arises when thin oils are used in older technology engines that were not designed to use a thin oil. If this were to happen, then it would not be unrea- sonable to expect friction and wear to increase, as the engine would tend to spend more time operating in the boundary lubrication regime.”

Effectiveness of VI Improvers In looking at the Stribeck Curve (see Figure 7 on page 22), VI improvers can reduce frictional losses in the mixed and hydrodynamic lubrication re- Figure 8 | Evaluation of three VI improvers by the new European driving cycle (NEDC) test showed that a comb type poly alkyl methacrylate polymer and a dispersant poly alkyl meth- gimes. This is in contrast to friction acrylate polymer display fuel economy improvements as compared to a baseline low ethylene modifiers, which provide benefits in olefin copolymer. (Courtesy of Evonik Oil Additives USA, Inc.) the boundary lubrication and mixed regimes. If properly formulated, VI improvers and friction modifiers can says. “Furthermore, VI improvers with acrylate (dPAMA) polymer as com- work in a complementary fashion. specific chemistry and unique archi- pared to the baseline. Rees believes that VI improvers are tecture can be utilized to optimize vis- Gray summarized by saying, “Com- an important element in improving cosity across a much wider range of bining friction modifiers with the cor- fuel economy. He says, “VI improver temperature and shear regimes. This rect VI improver has been proven to use can result in a lower bulk oil vis- would allow a marketer to further low- make engine oils a very effective tool in cosity under the actual operating con- er the kinematic viscosity at critical improving overall vehicle efficiency.” ditions of the vehicle, and thereby temperatures, while ensuring engine Bell notes that VI improvers have lower viscous pumping losses for any durability by maintaining the critical an important role to play in improving given viscosity grade. Testing through minimum level of HTHS viscosity.” fuel economy, mainly through the use a variety of protocols, including dyna- In a study using the new European of new polymers that can enable for- mometer testing under various drive driving cycle test, engine oils were formulators to access specific viscometric cycles, and in the Japanese FTT Fuel mulated with 4 cSt group III base oil properties not allowed with current Economy Test has demonstrated the using the same DI package.4 Three dif- ones. He adds, “As engines get smaller fuel economy improvements of VI im- ferent types of VI improvers were used and more powerful, there will be in- prover-containing formulations.” at a HTHS 150 C level of 3.5 mPas. creased thermal stress on the lubricant, Gray feels that significant fuel The results in Figure 8 (over three runs so the industry will need effective VI economy improvements are possible that are averaged) show that a comb improvers that minimize polymer with the use of VI improvers by raising type poly alkyl methacrylate (comb) loading. Specific dispersant-VI improv- the viscosity index of an oil. “Selection polymer displayed superior fuel econo- ers could be very helpful in reducing of the correct VI improvers for the ap- my improvement over the baseline low soot agglomeration in the emerging plication will allow an oil marketer to ethylene olefin copolymer (LE-OCP). gasoline direct-injection engines and meet the minimum HTHS viscosity Fuel economy improvements were also their inherent wear benefits should be while lower kinematic viscosity,” Gray seen with a dispersant poly alkyl meth- useful in lower viscosity engine oils.

24 STLE is offering CLS, OMA (I&II) and CMFS certification exams Sept. 27, Oct. 17, One potentially important area will be sponse for both fuel economy and en- Engine Wear HDDEOs as the industry moves to low- gine durability benefits. Properly de- With the growing use of lower-viscosity er viscosity lubricants for PC-11.” signed VI improvers support higher oils, engine wear may become more of a Viscosity modifiers contribute to lubricant viscosities in the hotter en- problem. The contributors were asked lubricant fuel efficiency primarily gine operating environments for robust to comment on whether VI improvers through shear thinning and viscosity- wear protection, while maintaining and other additives may be used to temperature properties. Since viscosity lower viscosities in moderate engine minimize this potential concern. modifier technologies differ signifi- temperature environments, which pro- Boffa indicates that rheological re- cantly in terms of these properties, vides fuel economy benefits.” sponse has a significant impact in con- they differ significantly in their rela- He continues, “Depending on the trolling engine wear. He says, “Proper tive contributions to lubricant fuel ef- engine design and operating condi- understanding of the full rheological ficiency, according to Bansal. “All vis- tions, hydro- and elasto-hydrodynam- response curve can mitigate the effects cosity modifiers exhibit some amount ic lubrication are predominant within of seeing higher wear in lower viscos- of shear thinning, i.e., temporary loss the engine and, consequently, viscosity ity oils. For instance, higher HTHS vis- of viscosity with the shear field applied measurements such as HTHS show cosity measured at 150 C (which is by the engine operation. This tempo- strong correlations with fuel economy. commonly reported given its inclusion rary reduction in viscosity can trans- This is particularly important for state- in SAE J300), provides better wear late into fuel economy benefits, espe- of-the-art engines designed to mini- protection and strong correlation with cially in hydrodynamic and mixed fuel economy at temperatures ranging lubrication operations,” Bansal says. from 40 C to 100 C.” “The extent of shear thinning depends ‘However, we feel that other factors such Boffa continues, “Certain OCP VI on the degree to which the viscosity- as oil volatility will be potential barriers improvers provide a good balance of modifier polymer coiling in the oil can to going too low in viscosity, well before robust HTHS 150, which is important align itself with the shear field. By suit- the point of diminishing returns on for low wear while having reduced vis- energy efficiency is reached.’ ably manipulating the chemical struc- cosity contributions at lower temperature of the polymer backbone, the — Dr. Jai Bansal, Infineum USA LP tures important for fuel economy. Fur- shear thinning response of a viscosity ther, certain functionalized VI modifier can be enhanced.” improvers can also help to reduce wear Bansal also points out that driving by forming a protective film on metal conditions impact the temperatures mize boundary and mixed friction surfaces or finely dispersing soot to seen by the oil, which, in turn, makes with specialty features. As a result, VI help minimize wear.” the viscosity-temperature behavior of improvers have a far greater role in to- Gray agrees that HTHS viscosity is the oil an important property for the day’s engine oils beyond their tradi- critical for engine durability when us- lubricant fuel efficiency. He says, “A tional thickening capabilities.” ing low and ultra-low viscosity oils. VI lubricant in a vehicle driven mainly in DeBlase says, “VI improvers offer a improver choice will be very important short-haul drive (e.g., urban commut- compromise allowing effective viscosi- in minimizing wear and maximizing er traffic) would rarely operate at the ties to be low on cold start-up at low fuel economy. He says, “While some VI kind of sump temperatures seen in speeds but allow the viscosity to in- improvers can maintain or boost HTHS long-haul highway driving. Therefore, crease at warm temperatures so that viscosity, many do it at the expense of a lubricant that exhibits lower viscosity boundary lubrication friction is not as low temperature viscosity potentially at the moderate temperatures prevalent severe a problem.” negating fuel economy gains. Addition- in short-haul drive cycles would offer The use of other synthetic base- ally, some VI improvers have been fuel economy benefits over a higher vis- stocks that have high viscosity indexes shown to form very effective films at cosity lubricant under similar condi- may play a role in improving the ef- the surface, reducing friction and wear tions. Recent advances in viscosity- fectiveness of VI improvers. Donaghy and improving efficiency.” modifier technology has made it says, “The use of unconventional base Rees feels that VI improvers will possible to maximize the lubricant fuel oils such as esters may help to produce have a strong role in minimizing wear efficiency in low temperature opera- less viscosity drag at lower tempera- in low viscosity engine oils. “VI im- tions by minimizing the lubricant vis- tures, while also reducing traction in provers have the capability to provide cosity under such driving cycles.” the hydrodynamic regime.” thicker lubricating films under certain Alex Boffa, global viscosity index Cuthbert says, “The very broad operating conditions. A thicker lubri- improver-technical team leader for product design space possible with cant film can protect metal surfaces, Chevron Oronite Co. LLC, says, “VI polyalkylene glycols enables them to thereby minimizing wear,” Rees says. improvers can be tailored to provide be potentially useful as a co-basestock “As the use of lower viscosity engine optimum temperature and shear re- for VI improvement.” oils increases, the role of VI improvers

Oct. 19, Oct. 25. Contact Alicia Shearer at [email protected] for more information. 25 to provide wear protection increases. one cannot rule out the use of supple- improves fuel economy by several The combination of a robust engine oil mental antiwear additives.” tenths of one percent (see Figure 4 on additive package, VI improver and page 20). Additionally, other compo- base oil can optimize engine oil perfor- Heavy-Duty nents such as detergents and disper- mance to ensure durability, emission Diesel Engine Oils sants can impact friction in an engine, system compatibility and optimize The movement to improve fuel econo- while base oils and viscosity modifiers fuel efficiency.” my in heavy-duty diesel vehicles raises can be chosen to optimize viscometric Besides seeing a need for viscomet- the questions about what additive properties.” ric balance, Bell believes that maximiz- technologies, in general, and whether Bell considers friction modifiers to ing soot control and antiwear perfor- friction modifiers and VI improvers, in probably not be a factor for HDDEOs. mance are important for low viscosity particular, will have a role in formulat- He says, “It seems unlikely that fric- engine oils. He says, “Wear protection ing future engine oils in the two PC-11 tion modifiers will see mainstream use will need to be supported via soot con- categories under development. Feed- in HDDEOs. The technology is lagging trol and inherent antiwear properties.” back from most contributors indicates behind PCMOs and as such there are that VI improvers will play a signifi- far bigger gains to be had through the cant role. But there is uncertainty continued drive down in viscosity ‘Wear protection will need to be support- about how much influence friction grade. As such, VI improvers will like- ed via soot control and inherent antiwear modifiers will have at this point. ly have a bigger part to play. Further, properties.’ Bansal says, “Our research in there are no current fuel economy tests heavy-duty diesel fuel economy over for HDDEOs that would likely show an — Ian Bell, Afton Chemical Corp. the last six years indicates that lubri- impact from friction modifiers.” cant viscosity is a much bigger factor Sinha says, “We expect the data on than friction modifiers. These observa- fuel economy testing obtained from DeBlase sees the use of VI improvers tions are further supported by our PCMOs will slowly trickle down to being very important in HDDEOs and work on engine friction mapping, HDDEOs. An added stress will be the agrees that minimizing soot formation which shows that hydrodynamic and need to minimize soot induced wear, will be very important in low tempera- mixed lubrication regimes, and not the which is a major component of the ture oils. “Since frictional losses in die- boundary regime, are the dominant HDDEO specification testing. Control- sel engines are more heavily weighted modes of operation in modern heavy- ling soot induced wear will be a key toward hydrodynamic lubrication, it is duty diesel engines.” factor, while lowering the viscosity in expected that VI improvers can be use- Rees agrees that VI improvers will HDDEOs to achieve improved fuel ful in controlling the losses at low tem- continue to have an important role in economy.” peratures,” DeBlase says. “The impact meeting the requirements of future Esche says, “One thing is for cer- of soot formation from burning diesel fuel economy in HDDEOs. “For PC- tain given the lubricant industry’s will be decreased by effective disper- 11, the industry is considering the bal- push for improving diesel engine oil sants capable of reducing the viscosity ance point between fuel efficiency and fuel economy is that you can be cer- impact from soot accumulation.” engine wear associated with the HTHS tain that formulators will select the Bansal says, “Viscosity modifiers viscosity of the lubricant,” Rees says. best VI improvers, friction modifiers, can contribute to wear protection by “Daimler is sponsoring a scuffing wear antioxidants and any other additives providing thicker oil films under the test to assure that HDDEOs protect the they think are necessary to maximize shear conditions prevalent in the en- engine from scuffing (adhesive) wear the fuel economy performance of their gine. However, the proper choice of in traditional SAE 15W-40 viscosity engine oils.” the antiwear additive system is the grades, as well as at reduced oil vis- DeBlase cautions that the friction most important factor in wear protec- cosities such as SAE 10W-30 and 5W- modifiers used in HDDEOs will need tion in low viscosity regimes. Indeed, 30.5 VI improvers are the fundamental to be compatible with dispersants. He some recent advances in antiwear design component used in meeting the says, “The use of friction modifiers technology have the potential to sig- several viscometric requirements of should help the effort to reduce the nificantly reduce the viscosity sensitiv- modern HDDEOs.” viscosity to a greater extent by protect- ity of engine wear.” Sztenderowicz feels that friction ing boundary lubricant friction in- To date, no conclusive evidence has modifiers will have a role in future creases. In addition, the impact of the been presented to the industry show- HDDEOs. He explains, “We published accumulation of soot and dispersant ing this should be a problem, accord- data showing that friction modifiers use to counteract this potential prob- ing to Esche. He says, “The current also can provide a benefit in on-high- lem will require friction modifiers that GF-5 antiwear technology will be suf- way commercial diesel engines. Effec- will avoid negative interactions with ficient to protect engines. However, tive application of friction modifiers dispersants.”

26 During his second year of college, Nikola Tesla developed a gambling addiction and lost his Gray says, “At this time, the Engine “This will require extensive additional ‘VI improvers can be tailored to provide Manufacturers Association has deter- work to develop oils that provide the optimum temperature and shear mined that no specific fuel economy needed performance and durability at response for both fuel economy and test is recommended for PC-11. In- lower viscosities. Since there is no pro- engine durability benefits.’ stead, a viscosity specification specifi- posed industry fuel economy test for — Alex Boffa, Chevron Oronite Co. LLC cally reducing the HTHS viscosity of PC-11, field testing will be highly de- the fluid will be used to impact and sired to demonstrate both the fuel con- improve fuel economy.” sumption benefits as well as real-world Donaghy says, “Friction modifiers “In a similar fashion to gasoline en- durability.” will come into their own as (and gine OEMs, the primary concern of Now that fuel economy has become when) oil viscosity is reduced to im- diesel engine OEMs when reducing a focal point for the lubricant industry, prove fuel efficiency. Much will de- HTHS viscosity is durability,” Gray undoubtedly, a good deal of attention pend on whether heavy-duty diesel continues. “Accordingly, the OEMs will be paid to what additives will be engines run in the mixed or hydrody- have adopted a fairly modest reduc- needed for both PCMO and HDDEOs. namic lubrication regime. If principal- tion in the minimum requirements for The end result at this point is uncer- ly hydrodynamic, then viscosity, base PC-11, which they believe will still af- tain, but it appears that both VI im- fluid and VI improver technologies ford measurable and significant fuel provers and friction modifiers will be will have the greatest impact.” economy improvements.” involved in the development of engine Gray says, “Fuel economy will be They are, however, working on a oil lubricants with even better fuel extremely important in heavy-duty split specification with a second, high- economy characteristics. diesel vehicles. How it will be defined er and more traditional HTHS limit in and how much can be achieved by order to protect heritage equipment friction modifiers and how much can still in use in the field, which is less ReferenceS be achieved by reduced viscosity will tolerant of lower viscosity fluids. 1. Canter, N. (2011), “Viscosity likely be quite different than in a gaso- Bansal draws a parallel between the Index Improvers,” TLT, 67 (9), line engine.” current PC-11 category and the work pp. 10-22. done to improve the fuel economy of PC-11 2. Calhoun, G. (1963), “Liquid PCMOs. “Fuel economy is one of the Hydrocarbon Composition,” U.S. Most respondents feel that fuel econo- major reasons for the introduction of Patent 3,11,271. my benefits in HDDEOs will be real- the PC-11 category,” Bansal says. “We 3. Farmer, H. and Rowan, E. (1967), ized by using lower viscosity oils. believe this is the beginning of a long “Molybdenum Oxysulfide DeBlase notes that the higher vis- march to low-viscosity lubricants for Dithiocarbamates and Processes cosity oils needed for the backward the heavy-duty diesel segment, much for Their Preparation,” U.S. compatible PC-11 subcategory will as the introduction of the SAE 5W-30 Patent 3,356,702. mean that higher treat rates of friction grade was for light-duty vehicles in the 4. Lauterwasser, F., Hutchinson, P, modifiers may be needed to begin to early 1980s.” Wincierz, C., Ulzheimer, S. and make an impact on the fuel economy “It will take some time for the mar- Gray, D. (2012), “The Role of VI improvement. He says, “The improve- ket to warm up to low viscosity grades, Improvers in the Formulation of ments in HDDEOs by PC-11 will be but the benefits of such lighter grades Fuel Efficient Engine Oils with more likely targeted for newly de- over the current SAE 15W-40 lubri- Long Oil Drain Intervals,” signed heavy-duty diesel engines de- cants is not in question,” Bansal contin- Presented at STLE’s 67th Annual signed for lower viscosity lubricants. ues. “OEMs and end-users will need to Meeting, St. Louis, Mo., May In effect, the PC-11 category may have be convinced that these lighter viscosi- 6-10. to compromise on fuel economy im- ty grades will not compromise engine 5. Belay, M. “PC-11 Scuffing Test,” provement in order to keep the other durability before large scale migration Daimler presentation, Dec. 6, 2011. required performance characteristics.” to these viscosity grades takes place.” http://www.hddeo.com/Daimler%20 Bell says, “The fuel economy focus Sztenderowicz sees the need for Scuffing%20Presentation.pdf for PC-11 will manifest itself in areas field testing to demonstrate both bet- other than fuel economy. The fuel econ- ter fuel economy and durability with omy benefit will be realized through a PC-11 engine oils. “For PC-11, there Neil Canter heads his own shift in viscosity grade, so the technical will be much greater emphasis on de- consulting company, Chemical challenge will manifest in durability veloping fuel-efficient, low-viscosity Solutions, in Willow Grove, Pa. (wear). Also, the use of lower viscosity oils such as 5W-30 and 10W-30 com- Ideas for Tech Beat can be basestocks may have a secondary im- pared with any previous API heavy- submitted to him at pact on oxidation and cleanliness.” duty category,” Sztenderowicz says. [email protected].

tuition and expense money. He recouped his losses in his third year and promptly quit gambling. 27