Fuel economy - The role of friction modifiers and VI improvers

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,
Fuel economy - The role of friction modifiers and VI improvers
To seek a broad range of opinions,
     TLT interviewed the following repre-
     sentatives from nine additive suppliers:
                                                          Organic Friction Modifiers (OFM’s)
                                                                                     (OFM s)
                                                                                           Van der Waals
         • Dr. Jai Bansal, global technical                                                   forces

           advisor, Infineum USA LP
                                                                                                                                 FM examples
         • Ian Bell, technical director-new
                                                           Long non-polar
                                                           Long, non polar chains
                                                                                                                     NH 2

           product development, Afton                                                      Van der Waals                          Oleylamide
           Chemical Corp.                                                                                                   OH


         • Dr. Frank DeBlase, Chemtura                                                                                  Glycerol mono-oleate
           Fellow-petroleum additives and                                                   interactions
                                                                     Polar heads     O                       O
           fluids, Chemtura Corp.
         • 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.            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                        T R I B O LO GY & LU B R I CAT I O N T EC H N O LO GY                              W W W. ST L E .O RG
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
active and interfere with the surface                       fuel efficiency.’                                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 un-
                                                                                                             der a unique set of operating condi-
                                                                                                             tions, and we know that vehicles in the
                      Consortium Seq.
                                   q 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
       1.80                                      • Viscosity effects (Oils A & E)                            more relevant to operating conditions
       1.60          1.51
                                                   - 5W-20 v. 10W-30 = +0.37% FEI                            and are relatively reliable, they lack
                                                                                                             the full operational influence of a fired
       1.40          Oil
                                          Oil    •Organic FM effects (Oils A & B)
                                           I                                                                 engine, and as such they can only as-
       1.20   1.13                                 - Oil B v. Oil A = +0.38%
                                                                          Oil AFEI
                                                                    1.04          Oil B (5W-20, OFM)         sess the instantaneous frictional per-

       1.00    Oil
                            0.76                 •Molybdenum
                                                  M l bd 0.77 FM effects
                                                                       ff tOil (Oils
                                                                                        & I)
                                                                               E (10W-30)                    formance of a lubricant.”
       0.80                        0.72                0.73
                            Oil                    - Oil I v. Oil G = +0.70% FEI
                                                                           Oil G (5W-30)
                                                                                                                 Bell finishes by stating that fired-
       0.60                         Oil                                           Oil I (5W-30, Moly)
                                                                 NOT RUN

                                    G                                                                        engine tests also have their limitations.
       0 40
               V   V         V   IV  IV          Oils A & B 0.21
                                                            are 5W-20 (HTHS=2.52 cP), Technology 1           Although they are a lot more closely
       0.20   n=7 n=6       n=5 n=2 n=3          Oil E is 10W-30 (HTHS=3.10 cP), Technology 1
                                                 Oils G & I are 5W-30 (HTHS=3.05 cP), Technology 2
                                                                                                             linked to vehicle operation, they are
                           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                        T R I B O LO GY & LU B R I CAT I O N T EC H N O LO GY                              W W W. ST L E .O RG
provement (FEI) value for XW-20 oils
of 3.6 can be realized for GF-6 as com-
pared to 2.6 for GF-5. A similar im-
provement 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 en-
gine 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 oc-
curring 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
tion modifier durability will no doubt         compared to using friction modifiers. (Courtesy of Chevron Oronite Co. LLC)
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 fric-
tion 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 tem-
peratures 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 lu-
brication, but the use of friction modi-
fiers to increase film thickness and still
maintain low friction will still be high-
ly 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 improve-

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 intro-
                                                                                                        duction 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 sur-
                                                                                                        faces, forming a durable, low-friction
                                                                                                        lubricating film.”
                                                                                                           Figure 6 shows the friction reduc-
                                                                                                        tion benefit of two prototype, PAG-
                                                                                                        based PCMO formulations in MTM
                                                                                                           David Gray, technical service man-
                                                                                                        ager 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 fric-
     pact of a viscosity grade change is typ-             STLE-member Dr. Kaustav Sinha,                tional regimes occurring simultaneously.’
     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,
                                                                            Friction Modifiers
creased boundary layer asperity friction
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                                   Gray 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 be-       low 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                      T R I B O LO GY & LU B R I CAT I O N T EC H N O LO GY                                               W W W. ST L E .O RG
Donaghy says, “Reducing the           FUEL ECONOMY DATA – NEDC CYCLE
HTHS viscosity too far can have a neg-Fuel Economy  Data – NEDC
                                               FUEL ECONOMY 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 cor-
rect engine. He says, “The problem
arises when thin oils are used in older
technology engines that were not de-
signed 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 im-
provers 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 for-       mulators 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-
     ably manipulating the chemical struc-             energy efficiency is reached.’                 cosity contributions at lower tempera-
     ture of the polymer backbone, the                                                                tures important for fuel economy. Fur-
                                                               — dr. Jai bansal, infineum usa lP
     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 ashearer@stle.org 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                  2. Calhoun, G. (1963), “Liquid
     Pc-11                                              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.                                  neilcanter@comcast.net.

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

   Reprinted with permission from the September 2013 issue of TLT, the official monthly magazine of the Society of Tribologists and
   Lubrication Engineers, a not-for-profit professional society headquartered in Park Ridge, Ill., www.stle.org.
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