December 6, 2017
Volume 17 Issue 49
High-Performance Organic Friction Modifier Retains Performance
Studies from the United States Environmental Protection Agency indicated that 60 percent of greenhouse gas emissions emanate from light-duty vehicles (passenger cars and light-duty trucks). This discovery led to the 2012 Clean Air Act that mandated increased fuel efficiency standards. Specifically, U.S. standard EPA-420-F-12-051 established a required fuel efficiency for light-duty vehicles of 54.5 miles per gallon by 2025.
Subsequently, the International Lubricants Standardization and Approval Committee (ILSAC) set forth developing next generation specifications – GF-6 for passenger car motor oils and API CK-4 and FA-4 for heavy-duty diesel engine oils. To reach 2025 corporate average fuel economy standards, GF-6 requires significant improvements in both fuel economy and fuel economy retention. These targets will likely be reached by new, durable engine designs in partnership with better lubricants and additive technologies for greater friction and wear protection.
A New Friction Modifier
The development of better friction modifiers and in particular nonmetal-containing, ashless organic friction modifiers such as LANXESS’s Experimental Exp-OFM provides measurable fuel economy improvements, effective over a range of oil viscosities, including SAE 0W-20 or 0W-16. The robust performance of this additive is shown in Figure 1, which indicates the percent reduction in coefficient of friction for motor oils containing 1% wt Exp-OFM compared to a molybdenum dithiocarbamate (MoDTC) friction modifier (4.0% Mo).
In addition to fuel economy and friction reduction, Exp-OFM shows measurable antiwear performance and full compatibility with a variety of base oils not competing with other lubricant additives typically used to formulate motor oils. These include antiwear zinc dialkyldithio phosphate, MoDTC, calcium- and magnesium-based detergents, dispersants, viscosity improvers, pour-point depressants, and antioxidants.
This Exp-OFM also passed a large battery of no-harm tests to ensure compatibility with materials found in modern engines, and provides the additional formulating benefit of being ashless (protecting catalytic converters and particulate filters) with no sulfated ash, phosphorus or sulfur (SAPS). It is also metal-free, noncorrosive, storage stable and passes multiple no-harm tests, indicating that oxidation stability and materials compatibility are maintained.
LANXESS evaluated the friction reduction performance of Exp-OFM and MoDTC in tribological tests and the Sequence VIE fuel economy test. The results shown in Figure 1 indicate that both friction modifiers provide good response over a range of passenger car motor oil viscosities, with MoDTC needing heat to be activated. In heavy-duty engine oils (15W-40), MoDTC performs very well by comparison at 160°C, when enough heat and time allow it to activate and form an effective tribofilm. However, durability studies indicate its performance can decrease with time.
Tribo tests were run in the Cameron Plint TE-77, which records the coefficient of friction (CoF) vs. until the temperature reaches 165°C. As shown in Figure 2, Exp-OFM reduced CoF at both 0.5% and 1.0% treat rates in SAE 0W-20 engine oil, an improvement over commercially available organic friction modifiers. MoDTC also reduced friction significantly at a 1.0% treat rate.
MoDTC shows good performance when heat activated at more than 85°C; however, subsequent isothermal studies show that this performance cannot be maintained with continued testing at elevated temperatures. Exp-OFM, on the other hand, maintains level performance longer.
Isothermal testing was performed under conditions similar to those of the standard TE-77 test, with an added isothermal hold period of 50 hours at 160°C. The results, shown in Figure 3, reveal that both MoDTC and Exp-OFM are very effective at reducing friction.
The data indicates that MoDTC is more effective than Exp-OFM for up to 18 hours, at which point CoF rises for up to 36 hours. Here, MoDTC lost a significant amount of performance but still reduced CoF compared to oil with no friction modifier.
Exp-OFM, on the other hand, maintains friction reduction longer, and MoDTC and Exp-OFM are equivalent at 26 hours. Exp-OFM holds the same low level of friction for another 20 hours, then rises to the same level as MoDTC after 46 to 50 hours.
Composite Stribeck curves in Figure 4 show the elastohydrodynamic lubrication (EHL) through boundary lubrication (BL) impact on CoF for Exp-OFM and MoDTC in the same SAE 0W-20 test oil. At speeds approaching 5 mm/s, the BL impact is measured. Mixed EHL and BL are measured at intermediate speeds. The results indicate that the addition of 1% Exp-OFM reduces friction considerably. Even 0.5% addition provides reasonable friction reduction, similar to 1% MoDTC held for the same amount of time at 150°C. (With longer running time increasing tribofilm at 150°C, MoDTC is expected to show further friction reduction.)
Sequence VIE Testing
In the Sequence VIE test, an initial fuel consumption is measured over six engine conditions in an SAE 20W-30 baseline oil. The engine is drained and flushed, and the test oil is added and aged for 16 hours in a running engine at 120°C, followed by fuel consumption measurements over six test stages. Then, the engine is flushed and the reference oil tested again following 109 hours of aging. Fuel economy improvement is then calculated to determine the initial fuel economy for the fresh oil (FEI-1), as well as the fuel economy over an extended oil drain (FEI-2).
ILSAC GF-6 prescribes a potential specification of 1.7% increase of FEI-2 final fuel economy and 3.6% improvement in the sum of initial FEI-1 plus FEI-2 over a 20W-30 reference oil. Testing shows a fuel economy sum of 5.09% for oil containing 1% Exp-OFM, 5.16% for oil with 0.5% Exp-OFM and 5.18% for oil with 1% MoDTC. Extended drain fuel economy (FEI-2) was 2.39% for 1% Exp-OFM, 2.35% for 0.5% Exp-OFM and 2.46% for 1% MoDTC. All three results are well above the proposed specified target of 3.6% for fuel economy-sum and 1.7% for extended drain fuel economy. The small drop between the two fuel economy measurements indicates good performance durability.
LANXESS has developed a light colored fully organic, ashless, phosphorus and sulfur free organic friction modifier providing effective lubrication that delivers significantly enhanced friction reduction, performance retention and antiwear protection. It provides formulators options to increase fuel economy while reducing the levels of metallic friction modifiers, without compromising fuel efficiency performance. Importantly, beside strong friction modifier performance Lanxess Exp-OFM is storage stable (-20°C to 62°C), noncorrosive and compatible with a range of engine oil types while maintaining good oxidation stability.
Frank J. DeBlase, Ph.D., LANXESS Solutions US Inc. in Naugatuck, Connecticut, U.S.