Recent Innovations In Marine Lubricant Technology that aid in Environmental Compliance

Introduction

The need for adequate lubrication is essential for any industry dependent on moving machinery. From water, vegetable fat, and animal fat in antiquity, to modern-day petroleum-based and synthetic lubricants, industrial lubricants continue to advance alongside the industries that depend on them [1]. As industrial maritime sectors such as shipping and power generation grow, reliance on marine lubricants subsequently increases. Conservative estimates place the global market for marine lubricants at 6.5 billion USD in 2024, with projected growth through 2030 valued at 7.5 billion USD [2]. Alongside providing necessary lubrication, marine lubricants face another challenge stemming from environmental considerations. Due to the sensitive nature of marine ecosystems, governments and regulatory bodies such as the International Maritime Organization (IMO) are now driving the marine industries as well as the environmentally compliant lubricants. In 2020, the IMO reduced sulfur limits in fuel oil from 3.5% to 0.5%, thereby reducing sulfur oxide emissions from shipping vessels [3]. The U.S EPA’s Vessel General Permit (VGP) in 2013 and the Vessel Incidental Discharge Act (VIDA) in 2018 both regulate discharge, such as ballast water, greywater, and deck runoff from ship operations to mitigate harm to marine ecosystems [4]. Such regulations necessitate the need for continual improvement in lubricant technology. 

Steady, incremental advancements are frequently made in pursuit of the ideal lubricant. This paper examines three of these recent advancements on marine lubricant technology, specifically lubricant additive technology in the form of nanoparticles and ionic liquids, alongside lubricant delivery technology with common rail oil injection systems. These developments are but a few of the many advancements permitting the smooth operation of maritime technology, currently and in the future. Advancements such as these usher marine lubricants towards greater environmental safety while simultaneously enhancing their tribological functions.  

U.S. Dept. of Energy and ORNL’s New Ionic Liquid Oil Additive

Marine ecosystems are an important asset to the global economy and biosphere. Governments, businesses, and individuals all derive food, income, transportation, and recreation from these diverse aquatic ecosystems. The Earth’s interwoven biosphere relies heavily on a healthy marine ecosystem to function properly [5]. Therefore, it is paramount that the damage incurred to these ecosystems is minimized. To better ensure the continued health of our marine ecosystems, Qu et al. at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) alongside Solvay, Dow Chemical, Biosynthetic Technologies, and Driven Racing Oil, recently developed a new class of oil additives that claim superior lubricity coupled with reduced environmental impact to supplement conventional oil blends [6], [7]. Oil additives play an essential role in the formulation of lubrication oils. These additives, such as anti-wear agents, detergents, antioxidants, viscosity modifiers, and pressure-specific additives, improve the functional qualities of the lubricant, including but not limited to operating range, lubricity, and deposit removal [8]. While effective for improving lubricity, these additives pose an environmental challenge stemming from their toxicity to aquatic ecosystems when used in a marine setting [9].

The new additive proposed by ORNL’s collaboration is an ionic liquid (IL). ILs are molten at room temperatures, and their great surface adsorption, low flammability, high viscosity index, and self-healing lubrication film makes them an excellent candidate for lubricant additives [10]. ORNL’s formulation consists of “quaternary ammonium or phosphonium cations bonded to phosphorus-containing or carboxylate anions” [11]. Qu et al. incorporated shorter hydrocarbon chains to aid in non-toxicity, noting that four carbon chains work best for non-toxicity and base oil solubility [12]. This formulation is easily soluble in an environmentally acceptable lubricant (EAL) base oil while remaining compatible with existing manufacturing frameworks [12]. Figure 1 highlights numerous tests conducted by ORNL demonstrating the differences in wear rate and biological impact from formulations of polyalkylene glycol (PAG) oil against PAG oil with the IL additive. The tests in the figure      include wear rate testing (gray), reproductive rate testing (green), and survival rate testing (blue). Wear rate examination was conducted using frictional testing of metal pieces under conditions simulating wind turbine gear motion, examining the samples     using electron microscopy [12].     Biological testing was conducted using ‘tiny planktonic crustaceans,” also known as “water fleas” in the genus Cerodaphnia. Their sensitivity to toxins in the environment, coupled with their fast reproductive cycles, made Cerodaphnia an ideal candidate for biological testing in this 
study [12].  

EALs are lubricants optimized for improved biodegradability, reduced toxicity, and reduced bioaccumulation potential to mitigate adverse impact on aquatic life [13]. Used as base oils in lubricants, EALs by themselves have a very low anti-wear capability, requiring mitigation with oil additives. This deficiency is demonstrated in Figure 1, with the EAL sample displaying the highest wear rate of all three samples (~2.21x10-9 mm3/N-m). The addition of IL additives to the base oil reduced this wear by ~94% (~1.2x10-10 mm3/N-m). Following its reduced toxicity, the EAL sample demonstrated the greatest affinity with Cerodaphnia reproduction and survival rates, with 100 percent of the population surviving. 

PAG oil with Zinc Dialkyl Dithiophosphate (ZDDP) demonstrated moderate frictional wear compared to the other samples — approximately 1.42x10-9 mm3/N-m [7]. ZDDP is a zinc-based oil additive commonly used in anti-wear, antioxidant, and anti-corrosion applications [14]. Although not harmful to humans in relatively small doses, ZDDP is very toxic to aquatic life with low biodegradability [14]. This toxic effect on aquatic life is demonstrated in Figure 1, as PAG oil with ZDDP scored a 0% on Cerodaphnia survival rate and reproduction rate, therefore ZDDP’s competitive wear protection comes with the caveat of ecotoxicity. 

The PAG oil with the IL additive achieved the lowest wear at approximately 1.2x10-10 mm3/N-m while matching the biocompatibility of EAL. ORNL designed this blend of proprietary ionic liquid with EAL base oil for offshore tidal turbines used in power generation [6]. Since the operating environment differs from that of terrestrial wind turbines, marine wind turbines must also consider unique issues like water pollution. This new blend harmonizes the need for a high-performance turbine lubricant with the biocompatibility necessary for aquatic ecosystems. Implementation of this new additive for wider adoption  is not without challenge. ZDDP’s eighty years of research, development and usage since the 1940s, established it as a reliable lubricant additive [14]. The competitive anti-wear properties and long-established practices of using additives such ZDDP, create a logistical challenge for implementing newer, less-toxic alternatives. The purported ease with which this new additive can be integrated into existing manufacturing processes lowers this barrier for entry, and bolsters its potential as an economically viable oil additive for marine applications.

Nanoparticle Size Study 

Oil additive advancements are not exclusive to improving biocompatibility. A class of additives garnering interest in the petrochemical industry is nanoparticles. Nanoparticles (NPs) are a class of particles between 1 to 100 nanometers (nm) in size [15]. For comparison, the diameter of human hair ranges from 17,000 to 180,000 nm, and the wavelength of visible light ranges from 380 to 700 nm [16], [17]. This small size allows NPs to directly interact with microscopic asperities on contact surfaces, aiding in surface protection and repair. NPs, when emulsified in a lubricant, improve lubricity in multiple ways. For example, NPs can reduce friction and improve lubricity by acting as ball bearings between contact surfaces, filling and polishing surface imperfections, and by producing lubricating films [18]. These characteristics make NPs an attractive material for lubrication engineering. 

To better understand the effect of NPs on tribology, Kulkami et al. at the Maharashtra Institute of Technology in India conducted a study in 2024 to determine the influence of hardness and concentration of NPs on metal wear [19]. The researchers chose calcium carbonate (CaCO3), titanium dioxide (TiO2), and aluminum oxide (Al2O3) as test samples for their differing Mohs hardness levels, film-producing qualities, durability, high plasticity, possible recrystallization tendencies, and higher operational range [19]. Table 1 lists the physical characteristics of the NPs for each material [19].

Jojoba oil was used as the carrier oil for the NPs due to its chemical stability and inertness; the wear properties were tested using a four-ball tribo-tester under ASTM D4172, and the concentration of NPs was adjusted for each test [19]. The researchers used wear scar analysis on the three steel testing balls to determine the tribology of the nanoparticles [19]. The results from the experiment are shown in Figure 2, with the blue, orange, and gray bars represent 0.1%, 0.25%, and 0.4% by weight, respectively, for each NP sample.

Figure 2 demonstrates the relative wear scar diameters (μm) of each additive as a function of additive concentration and hardness. CaCO3,, with a hardness of 3, experienced decreasing wear as the concentration increased. TiO2,, with a hardness of 6, experienced decreasing wear up to 0.25% wt concentration, which then increased after the concentration was raised to 0.40% wt. This increase in wear can be attributed to the polishing effect of TiO2 particles on the test surface, which is further magnified at higher concentrations [19]. Al2O3,, with a hardness of 9, exhibited an increase in wear scar diameter as concentration increased [19]. The lowest wear rate occurred with a medium concentration of moderately hard TiO2 at 329 μm. Figure 2 demonstrates an optimal point of concentration and hardness, with anything beyond compromising between wear, concentration, and hardness. These differing trends offer clear insight into the relationship between wear and NP properties. As Kulkami et al. noted, increased wear occurs with low concentrations of soft materials and high concentrations of hard materials. In other words, wear is inversely proportional to concentration on soft materials and directly proportional on hard materials. 

CaCO3, TiO2, and Al2O3 are not the only materials applicable to NPs, as there are a variety of materials available for use as NPs. A few examples include oxides such as zirconium oxide, zinc oxide, copper oxide; sulfides such as tungsten sulfide, copper sulfide; carbon allotropes, and clays [18]. To address environmental concerns, green nanoparticles are also currently being researched. For example, cellulose nanocrystals are NPs derived from plant matter [20]. Due to being plant-based, these NPs are bio-degradable, renewable, and non-toxic; and in a lubricating context, they can act as a “sacrificial” layer protecting wear surfaces [20]. Although better for the environment than standard nanoparticles, cellulose nanocrystals exhibit poor dispersibility in base oils, making them difficult to implement in lubricating oils without further research [21]. The challenge going forward with lubricant NPs will be balancing the cost of material with required lubrication qualities, as well as potential environmental impact. Being able to quantify the relationship between wear and NP properties allows lubrication engineers to better optimize lubricants for value and performance.

Common Rail Oil Injection Systems

Lubricant impact on marine ecosystems does not end at the manufacturing stage. The use cases and environmental conditions also affect lubricant consumption rate, emissions rate, and replenishment costs. A heavily relied on asset in the marine shipping industry is the two-stroke diesel engine. Being able to utilize low-cost heavy fuel oil (HFO) coupled with a simple design and high torque output makes the two-stroke diesel engine an essential asset to the marine shipping industry [22]. For these engines, lubricant consumption and cost remain a pressing issue for ship owners and engine designers. Minimizing lubricant consumption ultimately lowers operating costs and emissions, with one such method achieving this goal by optimizing lubricant delivery. A novel pathway involves re-purposing the common rail fuel delivery system used for diesel fuel injection to deliver engine oil. Utilizing a common rail to deliver oil to high-pressure atomizing injectors instead of circumferential quills found on pulse jet lubrication systems was shown to reduce oil consumption [23], [24]. During laboratory tests on engines at 100 percent load, common rail oil injection was shown to reduce oil consumption by 56 percent compared to pulse jet lubrication systems [24]. 

To further improve upon common rail oil injection, a study was conducted in 2023 by Dueholm et al. at Aalborg University in Denmark to better understand dosage and flow characteristics for two-stroke cylinder oil at operating temperature. This study was established according to the Bosch rate of injection (ROI) method. The Bosch ROI method, as shown in Figure 3, involves an oil injector connected to a coiled measurement pipe (4 mm I.D. x 8 m Length) with a partially open ball valve at the end acting as a throttle. A pressure relief valve at the end provides back pressure (8 bar). A pressure sensor mounted 11 mm from the injector nozzle was used to measure pressure changes. The study was performed using a fluid that closely mirrors the viscosity of typical engine cylinder oil at operating temperatures (Hydraway HVXA15) [23]. 

Dueholm et al. used the Bosch ROI method paired with physical measurements to determine the relationship between injector ramp time to the mass of oil injected. Injector ramp time is the duration during which the current in the injector coil increases, or “ramps up,” before the injector nozzle fully opens [25]. Controlling ramp time in 0.1 millisecond intervals, the injected oil weight was found for each ramp time between 6.6 milliseconds to 7.3 milliseconds. The results for injected oil mass as a function of injector ramp time are shown in Figure 4.

Figure 4 shows a linear relationship between injector ramp time and injected oil mass. As the injector ramp time increases, the injected oil mass increases. This trend highlights the importance of precise injector timing. Accurately controlling lubrication quantity based on engine load and temperature can vastly reduce oil consumption as oil is injected on a load-specific basis. Injector delivery also allows for better atomization of lubricant oil due to higher delivery pressures, thereby reducing lubricant waste [23]. As well as mapping potential injection strategies, the researchers used this trial to experimentally validate the Bosch ROI method for marine engine oil delivery applications [23]. The calculations based on the ROI method deviate within 5 percent from the physical measurements, falling within industry standards for accuracy [23]. Experimentally validating the ROI method within a 5 percent error margin improves the modeling of injection strategies for highly viscous marine engine oil applications [26]. This as-needed lubrication approach can be used to better optimize the lubricating film on the cylinder liner and piston rings, reducing mechanical wear and oil consumption. Reduced expenses from maintenance, repair, and oil consumption, as well as environmental benefits from reduced particulate matter and sulfur emissions, can be achieved via improved lubricant delivery.  

Conclusion

Lubricants ensure the smooth and continued operation of machinery responsible for driving the global economy forward. Every industry, from production to transportation and consumption, relies on effective lubrication to keep machines operational, with maritime industries following suit. The continued push spurred by environmental concern, lubricant performance, and operating cost drives innovation in the petrochemical, marine lubricant, and engine design industries. The push for an environmentally friendly lubricant for offshore turbine applications spurred the development of biocompatible ionic liquid additives. Meanwhile, intensive NP tribology research on metal oxides allows engineers to better formulate application-dependent additive packages while minimizing cost. Finally, advancements in lubrication delivery methods like common rail injection allows engineers to optimize lubricant usage for improved emissions and lubricant consumption. Engineers are subsequently required to address potential issues when implementing novel technologies. Such issues include the sourcing and scalability of NPs, the complexities involved in common rail usage for thicker oils, and implementation strategies to replace traditional, toxic oil additives with ILs. Taking inspiration from renewable sources and ideas from other industries expands the breadth of resources lubricant engineers can use to improve their products and address new challenges.  Advancements drawn from novel and existing technologies ensure that marine lubricants will continue to comply with ever-changing industry and regulatory demands.

About the Authors 

Dr. Raj Shah, Director at Koehler Instrument Company, is a chemical engineer specializing in tribology, petroleum and fuels. Dr. Shah was also named an eminent engineer by Tau Beta Pi, the oldest engineering honor society in the U.S., a distinction reserved for individuals with remarkable technical achievements and exemplary character as well as being a member of IchemE, joining a global network of over 35,000 members. Further, he was elevated as a Fellow by the Chartered Management Institute (CMI), the world’s largest institution for management, and by the Institute of Measurement and Control (InstMC), the UK’s leading body for professionals in automation and control. He was recently inducted as a Fellow of the Royal Society of Chemistry (RSC), whose historic membership includes figures such as Newton and Einstein. In a rare achievement, Dr. Shah was named a Chartered Petroleum Engineer by the Energy Institute, a distinction afforded to only seven Americans. He has been recognized by ASTM International with multiple awards, including three Awards of Excellence, the Eagle Award, and the PM Ku and John A. Bellanti Sr. Memorial medals. Dr. Shah also serves as a volunteer adjunct professor at SUNY Stony Brook and has held advisory roles at several academic institutions. At Koehler Instrument Company, he oversees a thriving internship program containing over . He is currently an elected Fellow of ASTM, STLE, NLGI, AIC, IOP, RSC, InstMC, IChemE, CMI, and EI. Most notably, he is the only person in the global chemical industry to hold all six elite professional certifications: Certified Professional Chemist, Certified Chemical Engineer, Chartered Engineer, Chartered Chemist, Chartered Scientist, and Chartered Petroleum Engineer.

Mathew Roshan is a Chemical and Molecular Engineering Undergraduate Student at Stony Brook University where he is a research assistant at the Advanced Energy Research and Technology Center performing research on carbon capture and hydrogen storage . He also works as an intern under Dr. Raj Shah studying tribology, alternative energy, and fuels at Koehler Instrument Company and is a member of the SBU chapter of the American Institute of Chemical Engineers (AIChE) .

Michael Lotwin is a Chemical and Molecular Engineering undergraduate student at Stony Brook University, where he conducts research in the on vascular grafts for aneurysm treatment by evaluating the mechanical properties of polymer blends. He is also a petroleum research intern at Koehler Instrument Company under Dr. Raj Shah. Previously, Michael interned at the Engineered Microstructures and Radiation Effects Laboratory, studying ultra-high temperature ceramics for nuclear applications, and at the Garcia Center for Polymers at Engineered Interfaces, where he explored the angiogenic effects of titanium dioxide nanoparticles.

Yedu Unnithan is a petroleum research intern at Koehler Instrument Company, AND A STUDENT AT Farmingdale Univeristy 
 

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