Results are presented from tests on a formulated 15W-40 mil-spec engine/transmission fluid to examine the impact of additives on improving its reliability and durability under extreme tribological conditions. A block-on-ring (BOR) configuration was used to measure the effect of five additives (an emulsion-based boric acid, tricresyl phosphate, particulate-based boron nitride, particulate-based MoS2, and particulate-based graphite) on the critical scuffing load as a function of additive concentration and time to scuff during oil-off tests (starved lubrication). A four-ball configuration was used to evaluate the impact of simulated engine grit/sand on the abrasive wear of steel as a function of grit size and loading. The results demonstrated that the additives increased the load for scuffing by 50 to 100% for the formulated oil and by 50 to 150% for the unformulated base fluid used in the formulated oil. Two of the additives (emulsion-based boric acid and tricresyl phosphate) doubled the time to scuffing for the formulated fluid. The use of boric acid and tricresyl phosphate in the base fluid increased the time to scuff significantly more. In both fluids, a low-friction regime was frequently observed during the tests and, when present, resulted in greatly increased survival times. Oil-off tests were performed to simulate a loss-of-lubricant condition. The results revealed a novel trend – the formation of a low-friction regime under the starved (drained-oil) lubrication condition. When a low-friction regime occurred (after the oil was drained from the test cup), the time to scuffing increased dramatically.

The Department of Defense is a major consumer of petroleum products – over 700 million gallons per day. While the majority of fuel consumed is for aircraft, in terms of logistics and exposure of personnel to hazardous conditions, the amount of fuel consumed in ground vehicles is considerable, with the cost (in-theatre, delivered) ranging from $100 to $600/gallon. This paper addresses the impact that parasitic friction mechanisms (boundary lubrication and lubricant viscosity) have on engine friction and overall vehicle efficiency. A series of mechanistic models of friction losses in key engine components was applied to investigate the impact of low-friction technologies on the fuel consumption of heavy-duty, on-road vehicles. The results indicate that fuel savings in the range of 3 to 5% are feasible by reducing boundary friction and utilizing low-viscosity engine lubricants. The paper will discuss the implications of the studies (as performed for commercial heavy-duty trucks) for military ground vehicles, which have significantly different driving modes. The paper will also discuss the potential of different strategies to implement low-friction/low-viscosity solutions and the impact of these strategies on reliability and durability.

The ceramic-based heat exchanger is one of the leading contenders for high-efficiency concentrating solar power plants using a molten salt heat transfer fluid and a supercritical carbon dioxide Brayton power cycle operating at temperatures above 700 °C due to the excellent resistance of ceramics to corrosion, oxidation, erosion, creep, and fouling. In the present study, the thermal performance of a ceramic silicon carbide prototype heat exchanger, with semi-elliptical heat transfer channels, integrated header channels, and a counterflow configuration fabricated by using binder jetting additive manufacturing, was experimentally investigated. Experimental heat transfer tests of the prototype were conducted at high temperatures and under various test fluid flow rates and inlet temperatures. The experimental heat transfer rates compared favorably with simulation predictions.

White etching cracks (WECs) have been associated with premature failure of wind turbine roller bearings. Various drivers for the generation of WECs have been identified such as loading conditions, slip, steel quality, lubrication, hydrogen embrittlement, corrosion fatigue cracking, and stray electrical currents passing through the surface. In this work, a benchtop test rig utilizing a three-ring-on-roller test configuration was used to investigate the effect of electrical current and operation in different lubricating regimes, defined by lambda (λ), on high-quality bearing steel samples tested in a commercially available power transmission EP gear lubricant. It was observed that there is an inverse correlation between the magnitude of electric current applied to the ring/roller system and time-to-failure. Higher current magnitudes lead to shorter time-to-failure than lower current magnitudes, with macropitting as the main failure mode. Sub-surface investigation revealed the presence of WECs in all cases. For the same current magnitude, tests conducted in boundary and mixed lubrication regimes showed that time-to-failure increased as λ increased, and the tests resulted in WEC related macropits, whereas tests conducted in near-hydrodynamic regime resulted in surface damage with no macropit. It was also noted that a shift toward near-hydrodynamic lubrication resulted in a distinct surface distress on the roller surface. Furthermore, there seems to be a transition in the mixed regime during which the surface distress occurred. The damage on the surface of the test samples resembled non-spatially, periodic, groove-like corrugations and, in some cases, crater-like depressions. Sub-surface imaging, performed by sequential sectioning, revealed the presence of WECs in all cases, and broad, branching cracks that were more prevalent under the more severe boundary conditions.

Pitch bearings, main bearings, and gearboxes in conventional wind turbine drivetrains often do not meet their 20-year minimum specified lifetime, resulting in turbine downtime as well as expensive, time-consuming repairs or replacements. The dominant failure modes of the drivetrain components and the conditions that lead to their failure are not fully accounted for during product design or routinely modeled for life management. Drivetrain reliability improvements and O&M cost reductions remain top priorities for both land-based and offshore wind turbines, especially as wind turbines continue to be deployed in increasingly remote and offshore locations, continue to increase in size, and are becoming expected to be in service beyond their original design life, all of which correspond to an increase in the impact of any reliability issues on O&M costs. This presentation summarizes the most recent activities by NREL and ANL on drivetrain reliability.

This study investigates the elemental composition and surface morphology of solid tribochemical films formed on steel surfaces. The reversible addition-fragmentation chain transfer (RAFT) method was used to synthesize nine different metal-free polymers, which were blended into commercial base oils. The polymers were either homopolymers of dodecyl methacrylate and ethylhexyl methacrylate or were co-polymers of these monomers with six polar monomers. After tribological testing at 100 °C using the ball-on-flat geometry, the resulting tribochemical films were imaged using scanning electron microscopy (SEM) and optical microscopy. The resulting tribochemical films have thicknesses around 50–100 nm. Two of the films corresponding to small (P1—imidazole-containing copolymer) and large (P3—less polar homopolymer) wear were cross-sectioned using focused ion beam (FIB) and analyzed for elemental composition using energy-dispersive X-Ray (EDX) mapping. Oxygen and nitrogen enrichment was observed, consistent with the relative chemical composition of the precursor polymers. Transmission electron microscopy (TEM) evidence suggests that at the worn surface, some organic elements penetrate or are mixed into the steel substrate giving an interlocking appearance. The two samples examined with TEM showed that P1 tribofilm is diffused or mixed with the steel substrate more so than P3, suggesting a stronger affinity and contact during tribofilm formation.

Premature failures associated with microstructural degradation, i.e. white etching cracks (WECS), are becoming commonplace as applications are requiring tribological components to operate under extreme conditions. Although the specific drivers of WECs are still debated, the failures are often found in applications where cyclic loading is combined with added energy from stressors such as slip, impacts, or stray current. The aim of the current work is to elucidate effect that variable current has on premature failure. Numerous commercially available lubricants were tested, and both lubricant base oil type and additive package were found to have an effect on WEC failure time.

This paper describes the design, synthesis, and characterization of linear, polar, and nonpolar polymethacrylates designed for use as lubricant viscosity index (VI) improvers with enhanced shear and antiwear resistance. The polymers were prepared via reversible addition-fragmentation chain transfer to obtain relatively low and narrow molecular weights, with random polar moieties. The resulting polymers were evaluated as oil solutions to determine their VI, shear stability performance, and antiwear characteristics. The polymers had molecular weights (M-w) ranging from 120 to 170 kDa, and the resulting VIs, in general, tracked the M-w. Although the VIs were modest (140-189), all polymers displayed higher values than a commercial product designed for similar applications, both at 2% (w/w) and when kinematic viscosities (KVs) were normalized to the lowest KV100 of similar to 6 cSt. One of the imidazole-containing polymers displayed an anomalously high VI for a low apparent M-w. As hypothesized, many of the polar polymers demonstrated substantial wear reduction compared to the nonpolar homopolymers or a commercial benchmark. The low-molecular weight imidazole-containing polymer produced less than 4% of the wear displayed by the commercial standard. The higher molecular weight polymers containing imidazole, hydroxy group, and amino group also produced as little as 10% of the wear shown by the benchmark. The strategy demonstrated the benefit of low and narrow molecular weight polymers to achieve good shear stability in viscosity modifiers while minimizing wear, rendering them suitable for fluid power applications.

On behalf of the Vehicle Technologies Office of the U.S. Department of Energy, we are pleased to introduce the Fiscal Year (FY) 2019 Annual Progress Report for the Advanced Engine and Fuel Technologies Program. In support of the Vehicle Technology Office’s goal for future U.S. economic growth, the Program focuses on early-stage research and development to improve understanding of combustion processes, fuel properties, and emissions control technologies, generating knowledge and insight necessary for industry to cost-effectively develop the next generation of engines and fuels. One of the most promising and cost-effective approaches to improving the fuel economy of the U.S. vehicle fleet is to introduce the next generation of higher-efficiency, very-low-emission combustion engines that meet future federal emissions regulations into the passenger and commercial vehicle markets. Advanced fuel formulations that can incorporate non-petroleum-based blending agents could further enhance engine efficiency, reduce greenhouse gas emissions, and provide fuel diversification. Also, innovations in combustion, fuels, emissions control, air control, turbomachinery, and energy recovery could potentially increase fuel economy considerably compared to today’s vehicles. The expected national economic, environmental, and energy security benefits from these next-generation engines and fuels would be significant inasmuch as the majority of vehicles sold over the next several decades will still include an engine. The Program has set the following goals for passenger and commercial vehicle fuel economy improvements. By 2030, increase light-duty engine efficiency to demonstrate 35% improvement in passenger vehicle fuel economy (25% improvement from engine efficiency and 10% from fuel co-optimization) relative to a 2015 baseline vehicle, while meeting the U.S. Environmental Protection Agency Tier 3 Emission and Fuel Standards. By 2030, improve heavy-duty engine efficiency by 35% relative to a 2009 baseline vehicle and identify cost-effective high-performance fuels that can further increase efficiency up to an additional 4%, while meeting prevailing U.S. Environmental Protection Agency emissions standards. The Program utilized advanced combustion processes to increase engine efficiency, resulting in a modeled passenger vehicle fuel economy improvement of 19.4% (over a Model Year 2015 baseline) in FY 2019. This report highlights progress achieved by the Advanced Engine and Fuel Technologies Program during FY 2019. The nature, current focus, and recent progress of the Program are described together with summaries of National Laboratory, industry, and university projects that provide an overview of the exciting work being conducted to address critical technical barriers and challenges to commercializing the next generation of higher-efficiency engine, emissions control, and fuel technologies for passenger and commercial vehicles.

In this work, methacrylate-type ionic liquid (IL) monomers containing a quaternary ammonium cation and two different counter-anions were synthesized and used as co-monomers to obtain functional poly(alkyl methacrylates) (PAMAs). They were then evaluated as friction and wear reducing additives for lubricants. The effect of molecular weight, polymer topology (random or diblock), and IL counter anion on friction and wear behavior of polymer PAO (poly-alpha olefin) solutions have been investigated. The results were compared to those of PAO solutions additized with a small molecule, non-polymeric ionic liquid, or non-ionic copolymers containing 2-(dimethylamino)ethyl methacrylate (DMAEMA) as the polar comonomer. No clear correlation between polymer molecular weight and friction or wear behavior was observed. Random ionic liquid copolymers led to lower wear volumes than their block counterparts. Polymers containing dicyanamide (DCA) counter anion showed lower wear volume compared to those containing bis((trifluoromethyl)sulfonyl)imide (TFSI) anion. Surprisingly, none of the IL copolymers studied outperformed the DMAEMA containing block copolymer in terms of wear volume reduction, suggesting the IL moiety had no beneficial effect on wear.

In 2016, the Vehicle Technologies Office (VTO) of the Department of Energy (DOE) issued a solicitation for the AOP Lab Call research in FY2017 on a number of topics related to vehicles. Topic 6A of the Lab Call focused on research related to advanced lubricants: "…(in) support of the lubricants program goal to, by 2020, demonstrate novel formulations for powertrain and driveline lubricants, compatible with new and legacy vehicles, to achieve at least a 4 percent real-world fuel economy improvement." Argonne National Laboratory (ANL) in collaboration with Oak Ridge National Laboratory (ORNL) and Pacific Northwest National Laboratory (PNNL) was awarded a 3-year multilab project on "Lubricant Technology - Innovation, Discovery, Design, and Engineering." Research on the project began in FY2017 at the three laboratories with industry participation; however, in FY2018, the project was terminated due to budgetary constraints. The following is the final report for the project and highlights progress made during the first year of research. The report is divided into sections that highlight the following: Goals, objectives, milestones and deliverables, project highlights, outreach – publications, conferences, and reports, milestones accomplished, and research progress.

The presence of reduced zirconium in fluorozirconate (FZ) glasses is highly unfavorable due to its detrimental effect on glass quality. Previous researchers have relied upon the use of a fluorine-containing processing gas to prevent the reduction of zirconium in FZ glasses deposited as thin films by pulsed laser deposition (PLD). However, the use of a fluorine-containing processing gas as an oxidizing agent is disadvantageous, due to its toxicity. Eliminating the need for the processing gas would lead to a significantly safer and simpler process. Our approach is to incorporate indium, which is multivalent, into the PLD ablation target in order to stabilize the zirconium and remove the need for a processing gas. A ZLANI glass, based on the composition 60.24ZrF(4)-4.13LaF(3)-3.54AlF(3)-31.49NaF-0.59InF(3) (values are in mol%), was synthesized for use as an ablation target. Using the ZLANI target, FZ glass films were successfully deposited on fused silica substrates by HD, without the need for any processing gas. Multiple depositions were performed to observe the effects of deposition duration on growth rate and on film roughness. The deposited films are transparent with a brownish coloration. The source of this coloration is postulated to be color centers that are created during synthesis. Thermal annealing increases light transmission through the films up to 400%, depending upon wavelength, in the UV and visible spectrum (350-600 nm), after a series of heat treatments culminating at 300 T. The fact that the transparency of the films can be correlated to annealing temperature suggests that the films may be of use as passive temperature sensors.

Despite the growing research field of polymeric ionic liquids used as materials for electrolytes and energy materials, catalysts, separation aides, and carbon materials, reports of lipophilic polymeric ionic liquids for lubricants are essentially nonexistent. Oil-miscible single molecule ionic liquids (Its) are reported to perform well as neat lubricants and as additives in lubricating base oils. In this work, methacrylate type ionic liquid monomers containing ammonium or imidazolium cations and two different counter-anions were synthesized and used as co-monomers to obtain functional poly(alkyl methacrylates) (PAMAs) as viscosity index improvers (VII) additives for lubricants. The structure of the IL, including the cation, the anion, and the spacer's length separating the IL from the methacrylate group, plays an important role in the resulting polymer solubility in PAO (poly-alpha olefin), solution rheology, friction, and wear behavior. Depending on the IL structure, VIIs containing up to 20% mol IL are soluble in PAO (grade 4), and demonstrate friction and wear reduction, compared to a conventional oil-soluble PAMA. Notably, wear volume reduction of up to 80% compared to the oil-soluble control poly(dodecyl methacrylate) is observed.

Nitrogen- and oxygen-containing compounds were designed empirically and subsequently synthesized, and their rheology, friction, and wear performance as multifunctional base oils (MFBOs) were evaluated. Two of the compounds displayed good viscosity/rheology profiles without the addition of polymeric viscosity modifiers, displaying high viscosity indexes (VIs) above 200. Furthermore, all three MFBOs had lower coefficients of friction compared to well-established and accepted benchmarks. The most significant advancement is their impressive wear improvement by a factor of 5.5 to 70 compared to either of the benchmarks, which is attributed to the polar nature of the base oil which promotes boundary lubrication with metal surfaces. Moreover, these compounds were easily synthesized in one step from commercial starting materials. This work demonstrates that a careful design could provide the features/performance/functions of base oil, rheology modifiers (or VI improvers), and antiwear and friction-reducing additives, all-in one molecule.

The effect of two nanoparticle oxides on friction and wear was studied under laboratory test conditions using a reciprocating test machine and two test configurations. The addition of these nanoparticles in base stock oil under certain conditions reduced the coefficient of friction and improved wear, but that depended on the test configuration. Examination of the rubbed surfaces showed the pronounced formation of a tribofilm in some cases, while polishing on the surface was also observed in other cases. Contact configuration is important when oxide nanoparticles are being evaluated and the conclusions about their efficacy can be vastly different.

ABSTRACT Star‐shaped poly(alkyl methacrylate)s (PAMAs) were prepared and blended into an additive‐free engine oil to assess the structure–property relationship between macromolecular structure and lubricant performance. These additives were designed with a comparable number of repeating units per arm and the number of arms was varied between 3 and 6. Well‐defined star‐shaped PAMAs were synthesized by atom transfer radical polymerization (ATRP) via a core‐first strategy from multi‐functional head‐groups. Observations of the polymer‐oil blends suggest that stars with less than four arms are favorable as a viscosity index improver (VII), and molecular weight dominates viscosity‐related effects over other structural features. Star‐shaped PAMAs, as oil additives, effectively reduce the friction coefficient in both mixed and boundary lubrication regime. Several analogs outperformed commercial VIIs in both viscosity and friction performance. Increased wear rates were observed for these star‐shaped PAMAs in the boundary lubrication regime suggesting pressure‐sensitive conformations may exist. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 43611.

We report novel polymeric materials that may be used as viscosity index improvers (VII) for lubricant applications. Our efforts included probing the comb-burst hyper-branched aryl polyester architecture for beneficial viscosity and friction behavior when utilized as an additive in a group I oil. The monomer was designed as to undergo polymerization via polycondensation within the architectural construct (AB2), typical of hyperbranched polymers. The monomer design was comprised of aliphatic arms (12 or 16 methylenes) to provide the necessary lipophilicity to achieve solubility in a non-polar medium. Once polymerized, via catalyst and heat, the surface alcohols were functionalized with fatty acids (lauric and palmitic). Controlling the aliphatic nature of the internal arms and peripheral end-groups provided four unique flexible polymer designs. Changing the reaction time and concentration provided opportunities to investigate the influence of molecular weight and branching density on oil-solubility, viscosity and friction. Oil-solubility was found to decrease with fewer internal carbons, but the number of internal carbons appears to have little influence on the bulk solution viscosity. At concentrations of 2 wt % in a group I base oil, these polymer additives demonstrated an improved viscosity index and reduced friction coefficient, validating the basic approach.