Browse Topic: Lubricant additives
Lubricant additives have a strong influence on the tribological performance of internal combustion engine components, and it is currently one of the leading research driving forces within lubricant companies. However, the anti-friction and anti-wear additives work forming surface tribofilms may have their performance affected by ethanol or water contamination. As both ethanol and water are polar, they may compete on the surface with the additives, avoiding or delaying the additive tribofilm formation. In this work, the effect of ethanol and water on the performance of 4 different fully formulated SAE 0W-20 engine oils, differing only on the friction modifier (FM) additive technology employed, was investigated. In order to emulate fuel dilutions, three tests conditions were carried out for each engine oil: (i) fresh, (ii) in the presence of ethanol, and (iii) in the presence of ethanol and water. Friction and wear of actual piston ring and liner were evaluated in a reciprocating test designed to emulate actual thermomechanical conditions of both urban and highway car use. Amine and ester FM containing engine oils did not show a significant difference in friction in the fresh condition of the hot-running phase. However, with ethanol and water, amine and ester FM oils provided 30% and 20% friction reduction on the contact, respectively. In its fresh condition, molybdenum type FM-containing oil reduced the CoF (71%) drastically, and even worsening its performance with the ethanol and water dilutions, molybdenum-containing oil still kept a high level of CoF reduction when compared with the baseline oil and the other friction modifiers. The wear of the cylinder liner and piston ring was low, not being affected by the oil dilutions. Those results evidence that somehow the friction modifier performance, nowadays of utmost importance to achieve targets of fuel economy, is affected by the presence of ethanol and water in the lubricant, and the level of influence depends upon temperature and the formulation technology applied.
The acidification of lubricating oils during engine operation, and the subsequent additive neutralization, is an important challenge for Original Equipment Manufacturers and end-users. Often the decline in Total Base Number (TBN) and increase in Total Acid Number (TAN) is measured during engine operation as an indication of the oil’s condition and lifetime. This is clearly an oversimplification given that no consideration is given to the type of acid, how corrosive it is, or the type of base and how effective it is at neutralizing. Acids can be broadly categorized into mineral acids such as sulfuric/nitric and organic acids such as acetic. Traditionally, research has focused on understanding the effects of mineral acids such as sulfuric, which can be formed during the combustion of sulfur-containing fuel. However, emissions legislation has driven a reduction in sulfur levels, and there has been an increase in the use of biofuels, such as methanol and ethanol, which typically oxidase to form corrosive short-chain organic acids. Understanding the effects of organic acids and how these can be controlled by lubricant additives is of growing importance. This work explores how the presence of such acids can be controlled by lubricant additives through appropriate control of neutralization rates. To achieve this, stopped-flow Fourier-transform infrared (FT-IR) Spectroscopy and Small-Angle Neutron Scattering (SANS) have been used to understand the reaction between an overbased detergent and organic acids. Overbased detergent particle surface area-to-volume ratio is shown to be more important than TBN for acid neutralization ability, and evidence that surfactant shell-type affects neutralization rate is communicated (phenate > salicylate > sulfonate). Calcium is more effective than magnesium at oil phase acid neutralization (due to basicity), and reactions are shown to occur on the metal particle surface, rather than the core.
Pre-ignition remains a significant bottleneck to further downsizing and downspeeding technologies employed for reducing CO2 emissions in modern turbocharged spark-ignited engines. Pre-ignition, which occurs rarely, may lead to high peak pressures that auto-ignite the entire charge before TDC. The resulting high-pressure oscillations are known as super-knock, leading to sudden and permanent hardware damage to the engine. Over the years, numerous researchers have investigated the stochastic phenomenon’s source and concluded that there is a role of lubricant additives, deposits, gasoline properties, and hot surfaces in triggering pre-ignition. No single source has been identified; the research continues. Here, we take a different approach; rather than continue the search for the source(s) of super-knock, we explore mitigating super-knock by detecting pre-ignition early enough to take immediate evasive action. Such evasive action is expected to suppress knock intensity, thereby saving the engine from any permanent damage. In this regard, the current work offers ways to detect pre-ignition (using ion sensors) and then mitigate engine damage by using immediate fuel enrichment. We present three related explorations. In exploration #1, we explore if the occurrence of ions products from the exhaust can warn that the next cycle has a high probability of pre-ignition. For this next cycle, the intake fuel injection can be suspended or increased to operate engine fuel-rich. We find strong ion activity on every cycle. However, there is a weak correlation between the ion signal and pre-ignition occurrence. In exploration #2, an in-cylinder ion-current sensor is used to discover pre-ignition event unfolding during the compression stroke. When such a rare event is detected, more fuel is immediately injected, making the end gas far less reactive and avoiding autoignition and knock. These explorations #1 and #2 were conducted with a DC-based ion sensor. These explorations showed exciting and promising findings. However, our DC-based ion sensors are prone to low signal-to-noise ratio SNR, leading to false positives (unacceptably high number of false positives.) In Exploration #3, the signal-to-noise ratio improvement is explored by replacing the DC-based system with a novel AC-based system. We find the bandpass filtering of the ion signal is key to improved SNR.
The purpose of this article is to study the antifriction and anti-wear effect of GCr15 bearing steel under paraffin base oil and the base oil with two additives of T405 sulfurized olefin and nano-MoS2 and compare the synergistic lubrication effect of two different additives (MoS2 and T405) in paraffin base oil. The tribological properties of GCr15 bearing steel under different lubrication conditions were tested on a ball-on-disk tribometer. The three-dimensional profile of disk’s worn surfaces and the scanning electron microscope (SEM) micrographs of corresponding steel balls were analyzed at the same time. The wettability of lubricating oils on the surface of friction pairs and the dispersibility of MoS2 in base oil were characterized. Furthermore, the Energy Dispersive X-ray Analysis (EDAX) of the disk’s worn surfaces under the nano-MoS2 base oil were measured by the Field Emission Environmental Scanning Electron Microscope to observe the variation of chemical elements on the worn surface of the disk after tests. The results show that these additives have a good synergistic lubrication effect with the base oil in terms of friction coefficient, wear volume, and surface wettability, and nano-MoS2 is better than T405 as the additive in the base oil. Moreover, active elements such as Mo and S were observed on the worn surface of the friction pair, indicating that the MoS2 additive can form a deposited film on the contact region to achieve antifriction and wear resistance effect.
Particles generated from lubricant in a gasoline direct injection (*GDI) engine were investigated in detail with the aim to understand the influence of components in lubricant on the amount of particles generated as well as their size. Analytical approach employed in this study was real-time engine tests combined with X-ray spectroscopic and electron-microscopic analyses. Real-time engine tests where particle number (PN) and particle size distribution were consecutively measured with oil consumption for lubricants with different formulas enabled us to extract information regarding lubricant-derived particles. This can be achieved only when sulfur species in lubricant are used as a “tracer” and thus, sulfur-free fuel possessing low PM Index (i.e., isooctane) needs to be used for the measurements. It was revealed that the size of particles increased with an increase in oil consumption in the vicinity of 10 nm, and such particles were assumed to be mainly generated as a result of combustion of metal-based additives used in lubricant. Moreover, STEM-EDX images strongly indicated that the particles with a ~10 nm diameter are composed of metal oxides, sulfates and/or phosphates with Ca, Mo and/or Zn as a cation. This study clearly suggested that novel molecular design of metal-free lubricant additives for wear-protection, detergent, and dispersant will be a key area to dramatically decrease nanoparticles smaller than ~50 nm which particularly threaten human health.
The aim of this study is to investigate how lubricants used for transaxles in hybrid electric vehicles (HEVs) and electric vehicles (EVs) give an impact on the cooling performance for electric motors. As a result, reducing lubricant viscosity improve heat transfer in both natural and forced convection conditions. Quantitative analysis could reveal that kinetic viscosity and heat conductivity of fluids are highly influential on the cooling performance. In addition, we investigated the effect of lubricant additive on fatigue life in bearing components by using a thrust needle roller bearing tester. Extreme pressure agent could control a morphology of the bearing raceway surface, playing a role in extending a fatigue life of the bearing.
Characterization of soot nanoparticle morphology can be used to develop understanding of nanoparticle interaction with engine lubricant oil and its additives. It can be used to help direct modelling of soot-induced thickening, and in a more general sense for combatting reductions in engine efficiency that occur with soot-laden oils. Traditional 2D transmission electron microscopy (TEM) characterization possesses several important shortcomings related to accuracy that have prompted development of an alternative 3D characterization technique utilizing electron tomography, known as 3D-TEM. This work details progress made towards facilitating semi-automated image acquisition and processing for location of structures of interest on the TEM grid. Samples were taken from a four cylinder 1.4 L gasoline turbocharged direct injection (GTDI) engine operated in typically extra-urban driving conditions for 20,284 km, with automatic cylinder deactivation enabled. Soot nanoparticles were extracted from the used oil drawn from the sump, and prepared on TEM support grids. From a feedstock of chosen grid locations, 30 soot nanoparticles were reconstructed and characterized in 3D and morphological characterization results compared to those derived using 2D-TEM. Results showed significant deviations between the two methods for important morphological parameters such as volume, surface area, and circularity. While volume and circularity were on average underestimated by 23% and 19% respectively, surface area was overestimated by 36%. However, a pixel-based 2D-method for radius of gyration measurements was highly accurate (< 2% deviation on average). Qualitative assessment of complex morphological features, unrecognisable with standard 2D-TEM, was carried out via 3D rendering of soot volumes, highlighting unique outputs of this technique. Presence of morphological features such as bridge-structures and enclosed cavities were observed in numerous particles, and confirmed through observation of tilt-series data.
Many studies on low speed pre-ignition have been published to investigate the impact of fuel properties and of lubricant properties. Fuels with high aromatic content or higher distillation temperatures have been shown to increase LSPI activity. The results have also shown that oil additives such as calcium sulfonate tend to increase the occurrence of LSPI while others such as magnesium sulfonate tend to decrease the occurrence. Very few studies have varied the fuel and oil properties at the same time. This approach is useful in isolating only the impact of the oil or the fuel, but both fluids impact the LSPI behavior of the engine simultaneously. To understand how the lubricant and fuel impacts on LSPI interact, a series of LSPI tests were performed with a matrix which combined fuels and lubricants with a range of LSPI activity. This study was intended to determine if a low activity lubricant could suppress the increased LSPI from a high activity fuel, and vice versa. The results showed that a low activity fuel was insensitive to the lubricant used in the test, while a high activity fuel could be moderated by a low activity lubricant. The combination of a high activity fuel and high activity lubricant, as expected, yielded a large number of LSPI events. These results help to understand how formulation changes to the lubricant or to the fuel may impact the other fluid, particularly with respect to regional variations in fuel specification and in lubricant additive standards.
Numerous studies have attributed pre-ignition events in turbocharged spark ignited engines to the auto-ignition of lubricant oil-fuel mixture droplets. These droplets result from the interaction of the directly injected fuel spray on the lubricant oil film on the cylinder walls, causing fuel splashing to pull oil off the walls, forming droplets. The dilution of the oil by the fuel also changes lubricant oil droplet properties. Therefore, it is important to understand lubricating oils, with and without fuel dilution, as a possible ignition source in pre-ignition and super knock events. In this work, a constant volume (4 L) combustion chamber (CVCC) that allows the introduction of a single droplet of lubricating oil has been built. It is capable of operation at elevated pressures and temperatures. To simulate the droplet-induced pre-ignition event, a droplet injection system was incorporated into the vessel. The oil droplet was suspended on the junction of a thermocouple where the instantaneous internal droplet temperature was measured throughout the oil droplet lifetime. The experiments were carried out in an air atmosphere heated to 300 °C. The ambient pressure was varied from 2-15 bar. In the present work, the effect of pressure on droplet ignition of conventional engine oil (SAE 15 W-40), its surrogate hexadecane (C16H34), and hexadecane mixed with lubricant oil additives has been investigated to understand the fundamental physics of droplet-induced ignition. The objective of this study is to determine the probability that an oil droplet will ignite at temperatures and pressures relevant to modern turbocharged GDI engines.
Diesel particulate filter (DPF) is necessary for diesel engines to meet the increasingly stringent emission regulations. Many studies have demonstrated that the lubricant derived ash has a significant effect on DPF pressure drop and engine fuel economy, and this effect becomes more and more severe with the increasing of operating hours of the DPF because the ash accumulated in the DPF cannot be removed by regeneration. It is reported that most of the DPFs operated with more ash than soot in the filter for more than three quarters of the time during its lifetime [1]. In order to mitigate this problem, the original engine manufacturers (OEM) tend to use an oversized DPF for the engine. However, it will increase the costs of the DPF and reduce the compactness of the engine aftertreatment system. With the development of the lubricant additives technology, some OEMs and lubricant oil manufacturers are concerning that if there is any possibility to reduce DPF size using low ash lubricant oil. In this work, a numerical DPF model was built to estimate the DPF pressure drop at different soot loading and ash loading levels. With the model, the lifetime averaged fuel penalty of the DPFs with different sizes and operating with different ash content lubricant oils were calculated. Based on the calculation results, the potential of reducing DPF size using low ash lubricant oil was analyzed under the same design criteria of engine fuel consumption penalty. The analysis results show that the DPF size can be reduced by about 6% by lowering the lubricant oil ash content from 1.0% to 0.75%, and 14% by lowering from 1.0% to 0.5%. The DPF size can be maximally reduced by lowering the lubricant oil ash content from 1.0% to 0.25%, which can reduce about 22% of the DPF size. While the DPF size can be only reduced by 7% by using no ash lubricant oil because of no “membrane effect” of the ash on the soot depth filtration in the DPF. The role of engine-out particulate matters (PM) emission and DPF regeneration control strategy on this potential was also studied, and the potential is slightly increased when the engine has a higher engine-out PM emission or a DPF regeneration control strategy with ash effects corrections is applied.
SAE International has retracted this article.
A Joint Aircraft Survivability Program (JASP) project was awarded in 2014 in order to accelerate the research and development on military helicopter transmission loss of lubrication survivability. This JASP project, "Helicopter Transmission Loss-of-Lubrication" was a collaboration between the US Army, US Navy, and NASA and completed in 2018. The approach for the effort was to first screen emerging technologies using coupon-level methods, then test those showing the most promise at the component level, and finally to downselect and evaluate these technologies at the system level. Several concepts to reduce heat generation, increase heat rejection, increase material tolerance to higher temperatures, and increase material resistance to damage were evaluated for this effort. Included in this evaluation were: a ceramic material for bearings, four different gear steels, various levels of gear surface roughness, six gear coatings, five lubricant and lubricant additive variations, and gearbox noble gas injection. After gear testing at the component level, isotropic superfinishing and ionic liquid lubricant additive were down selected as the two most suitable technologies for the system level testing. These technologies underwent loss of lubrication testing to failure in an intermediate gearbox from a standard configuration medium lift helicopter. A baseline loss of lubrication test, without these technologies, was also performed for comparison.
Traditional methods for monitoring corrosion processes and mechanisms in real time can be both time consuming and challenging to interpret, especially when evaluations at multiple temperatures are required. Reported at SAE world congress 2017 by this author, a new method for measuring the change in resistance of a thin copper wire was applied to provide a way to monitor the corrosion of copper in situ. In this work, a copper alloy in thin wire form has been used to compare the corrosion rates to pure copper. New insights on the kinetics and mechanisms of corrosion in the presence of lubricant additives over a range of operating temperatures using the wire resistance test will be discussed. The corrosion processes observed here are highly dependent upon temperature. Making assessments of corrosion performance through elevated temperature differentiation testing can provide less optimal corrosion protection at the actual operating temperature condition. This work highlights how long-duration elevated temperature testing does not provide the reassurances required for in service corrosion protection.
The global trend to reduce CO2 emissions, combined with the popularity of Sport Utility Vehicles (SUV’s), has prompted automakers to design and manufacture lighter vehicles with suspension architectures that may require halfshafts (HS’s) to operate at higher continuous angles than in the past. Noise, Vibration and Harshness (NVH) characteristics of a halfshaft, as well as its durability, are functions of the operating angle and the lubricating grease in the joints. Newer vehicles require driveline solutions that can provide consistent dynamic performance over a wide range of operating angles. Tripot-type Constant Velocity Joints (CVJ’s) are commonly used as inboard joints in a halfshaft. Through proper grease selection, premium tripots may be lubricated with greases containing solid additives, which provide consistent dynamic performance and durability.
Items per page:
50
1 – 50 of 184