Role of thermal,mechanical and oxidising treatment on structure and chemistry of carbon black and its impact on wear and friction: Part 2 – Boundary lubrication condition

Mineral oil formulations with zinc dialkyl dithiophosphate (ZDDP) and dispersant (poly isobutylene succinimide ashless dispersant or ‘PIBSA’) and fully formulated oils with and without carbon black were subjected to thermal and mechanical treatment and tribologically tested on TE 77 (high frequency reciprocating rig or ‘HFRR’) machine to examine the frictional performance during the test. These results were compared to oils without carbon black and oils with diesel soot. Results indicate that oils with just ZDDP and dispersant had the highest friction that remains constant for the duration of the test while oils with carbon black in the milled and oxidised condition had the lowest coefficient of friction and the smallest surface roughness in the tribofilm. The mechanism of wear with treated carbon black and diesel soot was found to be polishing wear as evidenced by the scanning probe microscopy images of the tribofilms. Tribofilms were analysed with X-ray absorption near edge structure (XANES) and it was seen that oils without carbon black or even with untreated carbon black had sulphates at the surface, while the oils with carbon black that were treated had a higher proportion of sulphides. A combination of both FeS and ZnS was found in the tribofilms along with short chain phosphates of Zn.     

Antagonistic Interaction of Antiwear Additives and Carbon Black

It is well known that the presence of soot in engine oils can lead to an increase in wear of engine parts. This is a growing problem as soot levels in diesel engine oils are rising due to a combination of extended drain intervals and the various methods employed to reduce NO _x formation such as retarded ignition and exhaust gas recirculation. Several different mechanisms have been proposed by which soot might lead to an increase in wear in mixed lubrication conditions, of which the most widely favoured is abrasion by soot, either of the rubbing metallic parts in engines or of the antiwear additive films formed on rubbing metal surfaces. In this study it is shown that the combination of mixed alkyl ZDDP and carbon black (used as soot surrogate) is strongly antagonistic in terms of wear. In a lubricant containing carbon black, the presence of ZDDP leads to considerably more wear than if ZDDP is left out. A similar, though less severe antagonism is also seen with primary ZDDP and other antiwear and EP additives. By varying the lubricant film thickness it is shown that the effect of carbon black in ZDDP-containing oils is to promote wear up to quite thick hydrodynamic film conditions, approaching the secondary carbon black particle size. It is proposed that the antagonistic wear effect results from a corrosion-abrasive mechanism in which the reaction film formed by antiwear additive and rubbing metal surface is very rapidly and continually abraded by carbon black. At most carbon black concentrations, wear rate then becomes controlled by the rate of initial antiwear additive film formation, which for secondary ZDDP is very rapid, rather than by the kinetics of the abrasive process. From this understanding, strategies for reducing the impact of engine soot on wear can be deduced.     

Thermogravimetric analysis of carbon black and engine soot—Towards a more robust oil analysis method

This work examined the thermal behaviour of diesel engine produced soot and commercial carbon black using thermogravimetric analysis (TGA). It was found that during TGA analysis of the carbon matrices (at a temperature range commonly used for soot-in-oil content determination), a gradual mass loss occurred. This was attributed to pyrolysis effects and combustion processes occurring due to poor hydrodynamic design of some commercial thermobalances. This process resulted in a significant mass loss of the carbon during TGA. This finding may strongly effect soot-in-oil analysis conducted using current methods. Experiments were conducted using a range of soot-in-oil mixtures according to the widely used thermogravimetric standard method ASTM 5967-08 which showed a significant underestimation of the soot content in the oil as a result of carbon mass loss due to combustion and/or pyrolysis effects. An improved oil analysis method is proposed which provides a significantly increased accuracy of soot determination in lubricant oils.     

Thermogravimetric analysis of carbon black and engine soot—Towards a more robust oil analysis method

This work examined the thermal behaviour of diesel engine produced soot and commercial carbon black using thermogravimetric analysis (TGA). It was found that during TGA analysis of the carbon matrices (at a temperature range commonly used for soot-in-oil content determination), a gradual mass loss occurred. This was attributed to pyrolysis effects and combustion processes occurring due to poor hydrodynamic design of some commercial thermobalances. This process resulted in a significant mass loss of the carbon during TGA. This finding may strongly effect soot-in-oil analysis conducted using current methods. Experiments were conducted using a range of soot-in-oil mixtures according to the widely used thermogravimetric standard method ASTM 5967-08 which showed a significant underestimation of the soot content in the oil as a result of carbon mass loss due to combustion and/or pyrolysis effects. An improved oil analysis method is proposed which provides a significantly increased accuracy of soot determination in lubricant oils.     

Morphology,structure and chemistry of extracted diesel soot: Part II: X-ray absorption near edge structure (XANES) spectroscopy and high resolution transmission electron microscopy

Chemical composition of diesel soot extracted from used diesel engine has been investigated using X-ray Absorption Near Edge Structure (XANES) spectroscopy and high-resolution transmission electron microscopy (HRTEM). The XANES spectra indicate the presence of phosphates of zinc and calcium and sulfates of zinc and calcium as well as the presence of sulfides of zinc. HRTEM coupled with EDS and lattice imaging indicates the presence of nanoparticles of Ca₃(PO₄)₂ and Fe₂O₃ embedded in the turbostratic soot structure. Both Ca₃(PO₄)₂ and Fe₂O₃ are hard particles and appear to have been incorporated within the turbostratic soot structure during third body wear.     

Morphology,structure and chemistry of extracted diesel soot—Part I: Transmission electron microscopy,Raman spectroscopy,X-ray photoelectron spectroscopy and synchrotron X-ray diffraction study

Inclusion of soot in lubricating oil can result in increased wear and decreased lubricity. In this study we have attempted to gain fundamental insight into the morphology, structure and chemistry of diesel soot. Energy dispersive spectroscopy using TEM suggests interaction between lubrication additives and crankcase soot resulting in the presence of C, Ca, S, P, O and Zn. Synchrotron X-ray diffraction indicates the presence of different sulfates of calcium as well as the presence of amorphous zinc based compounds. Raman spectroscopy and selected area diffraction using TEM indicates that the turbostratic structures of the carbon in both are very similar.     

Characteristics of diesel engine soot that lead to excessive oil thickening

This is a study of soot from a heavy duty diesel (HDD) engine test designed to evaluate the soot handling ability of a lubricant. This study aims to understand what properties of diesel soot produced under certain conditions contribute to loss of viscosity control through examination of the morphology, nanostructure and oxygen functionalization of particulates obtained from two heavy duty diesel engine tests with different levels of EGR. Particulate samples obtained from the used engine oil that lost viscosity control at relatively low soot levels showed that the soot in this case was more graphitic and had lower oxygen functionalization.     

Soot–additive interactions in engine oils

Soot is known to cause engine wear. In this work, we focus on how engine oil formulation affects soot‐related wear, and how the lubricant‐derived anti‐wear film changes when soot is present. Friction and wear experiments of fully and partially formulated diesel engine oils (containing basestock, dispersants and viscosity modifiers) are conducted with a ball‐on‐disk rig in the presence of carbon black (CB) as a soot surrogate. The friction coefficient was largely unaffected by CB dispersed in the oils, but electrically insulating film formation, an indication of the formation of anti‐wear films, was decreased. Wear on the disk was found to either remain the same or decrease when CB was present, depending on the oil formulation. An examination of the lubricant‐derived films using Raman and Auger electron spectroscopies found that the presence of more abundant amorphous carbon and lesser amounts of anti‐wear film components on the surface was associated with higher wear. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of nanoparticle tracking analysis platform for the measurement of soot-in-oil agglomerates from automotive engines

Nanoparticle Tracking Analysis (NTA) has been applied to characterising soot agglomerates of particles and compared with Transmission Electron Microscoscopy (TEM). Soot nanoparticles were extracted from used oil drawn from the sump of a light duty automotive diesel engine. The samples were prepared for analysis by diluting with heptane. Individual tracking of soot agglomerates allows for size distribution analysis. The size of soot was compared with length measurements of projected two-dimensional TEM images of agglomerates. Both the techniques show that soot-in-oil exists as agglomerates with average size of 120 nm. NTA is able to measure particles in polydisperse solutions and reports the size and volume distribution of soot-in-oil aggregates; it has the advantages of being fast and relatively low cost if compared with TEM.     

X-ray Absorption Spectroscopy and Atomic Force Microscopy of Films Generated from Organosulfur Extreme-Pressure (EP) Oil Additives

This study examines the interaction of sulfur-based oil additives on steel. Sulfurized isobutylene, dialkyldithiocarbamate and sulfurized esters were the additives investigated in this report. For the first time, X-ray absorption near edge structure (XANES) spectroscopy has provided detailed insight into the chemistry of both the thermo-oxidative and tribochemical films generated from these additives. It was found that the chemical nature of these films was strongly dependent on the operating environment for the additives. The XANES revealed that thermally, all three S additives reacted very similarly with steel to form a film mainly comprised of iron sulfate at temperatures as low as 100 °C. The ample supply of diffused oxygen from the base oil along with oxide naturally present on the substrate allowed for the complete oxidation of the S from the decomposed additive to iron sulfate. Tribochemical films were comprised of different forms of sulfur than observed for the thermo-oxidative films. The moderate AW conditions yielded a mixture of both oxidized and reduced forms of sulfur, with pyrite, FeS₂, being the major constituent. Rubbing between the steel pin and the substrate partially depleted the oxide layer present, allowing the additive to interact intimately with the fresh substrate, yielding FeS₂. Under extreme-pressure conditions, complete removal of the oxide layer occurred with a drastic increase in the interfacial temperatures between the pin and v-block, allowing for the complete thermal decomposition of FeS₂ to FeS to occur. AFM imaging of the AW films revealed the presence of tiny smooth domains randomly oriented, which were completely different from the pad-like structures observed for AW films generated from a typical ashless thiophosphate additive. The inability of the sulfur-based additives to form large pad-like structures, which can ultimately support the load, resulted in poor AW protection to the metal.     

Laser particle sizing of diesel soots in two formulated oils after different engine tests

Soots of four types were extracted from two different formulated diesel oils, namely oil ‘A’, a 15W40, and oil ‘B’, a 20W40, after engine (50 h) and tribological (20 h + 20 h) tests. The soots were dispersed into four different model solvents and base oils, and analysed by Photon Correlation Technique. In a first study, soot particle size measurements were conducted after dilution in n-heptane, Kerdane solvent, 60N and 130N base oils. The influences of engine running-time and solvent nature have been particularly considered. The second study has been devoted to the aggregation kinetic of soots in these solvents. These data are important for a better understanding of soot dispersion stability and the rheology of used oils in diesel engines.     

柴油醇的燃料性质和排放特性

为解决柴油醇在应用中存在的相分离、十六烷值低下等问题,提出一种由中碳醇 低分子醚 高分子聚合物 有机硝酸酯构成的复合添加剂.结果表明:添加1%～2%容积百分比的复合添加剂后,柴油醇的溶解度明显提高;并且发动机的冷启动试验也表明加入复合添加剂后,柴油醇的着火性能己同于柴油的水平.由发动机台架试验还研究了柴油和不同乙醇掺合率的柴油醇给与发动机的燃料经济性、排气烟度和THC、CO、NOx气体排放的影响.结果表明:柴油醇以重量计的比油耗较柴油的相应地增加,但以能量计的有效热效率却较柴油的略有提高;各种乙醇掺合率下的排气烟度都大幅地降低;NOx排放浓度则随负荷增加而逐渐增大,但在高负荷工况时,随乙醇掺合率的增加,NOx排放浓度呈下降趋势.     

Effect of coconut oil‐blended fuels on diesel engine wear and lubrication

This paper presents the results of an experimental investigation into the wear and lubrication characteristics of a diesel engine using ordinary coconut oil (COIL)‐blended fuels. The blended fuels consisted of 10, 20, 30, 40, and 50% COIL with diesel fuel (DF2). Pure DF2 was used for comparison purposes. The engine was operated with 50% throttle setting at a constant speed of 2000 rpm for a period of 100 h with each fuel. The same lubricating oil, equivalent to SAE 40, was used for all fuel systems. A multi‐element oil analyser was used to measure wear metals (Fe, Cr, Cu, Al, and Pb), contaminant elements (Si, B, and V), and additive elements (Zn, Ca, P, and Mg) in the used lubricating oil. Fourier transform infrared analysis was performed to measure the degradation products (soot, oxidation, nitration, and sulphation products) in the used lubricant. Karl Fischer (ASTM D 1744) and potentiometric titrations (ASTM D 2896) were used to measure water concentration and total base number (TBN), respectively. An automatic viscometer (ASTM D 445) was used to measure lubricant viscosity. The results show that wear metals and contaminant elements increase with an increasing amount of COIL in DF2. An increasing amount of COIL in the blends reduces additive elements, with the reduction for blends of up to 30% COIL being quite similar to that for DF2. Soot and sulphation decrease with increasing COIL in the blended fuels due to reduced aromatics and sulphur in comparison to DF2. The water concentration increases for blended fuels with more than 30% COIL. The TBN and viscosity changes are found to be almost normal. The engine did not appear to have any starting and combustion problems when operating with the COIL‐blended fuels. The lubricating oil analysis data from this study will help in the selection of tribological components and compatible lubricating oils for coconut oil‐ or biofuel‐operated diesel engines.     

悬浮碳烟微粒对在用柴油机油粘度影响的研究

现代柴油机技术清洁了排放，却使进入机油中的碳烟微粒大量增加，本文研究报道了悬浮碳烟微粒对在用柴油机油粘度的影响；粘度随碳烟浓度提高而增大；二者符合Eilers和reiger-Dougherty粘度方程，分散剂能阻止碳烟微粒发生聚结，进而降低相对粘度，其中碱性分散剂作用性能远优于中性分散剂。     

Influence of Dispersant and ZDDP on Soot Wear

Diesel engines and gasoline direct injection (GDI) engines both produce soot due to incomplete combustion of the fuel and some enters the lubricant where it accumulates between drain intervals, promoting wear of rubbing engine components. Currently the most favoured mechanism for this wear is that the anti-wear additives present in engine oils, primarily zinc dialkyldithiophosphates (ZDDPs), react very rapidly with rubbing surfaces to form relatively soft reaction products. These are easily abraded by soot, resulting in a corrosive-abrasive wear mechanism. This study has explored the impact of engine oil dispersant additives on this type of wear using combinations of dispersant, ZDDP and carbon black, a soot surrogate. It has been found that both the concentration and type of dispersant are critical in influencing wear. With most dispersants studied, wear becomes very high over an intermediate dispersant concentration range of ca 0.1–0.4 wt% N, with both lower and higher dispersant levels showing much less wear. However a few dispersants appear able to suppress high wear by ZDDP and carbon black over the whole concentration range. A series of experiments have been carried out to determine the origin of this behaviour and it is believed that high levels of dispersant, and, for a few dispersants, all concentration levels, protect the iron sulphide tribofilm initially formed by ZDDP from abrasion by carbon black.     

悬浮碳烟微粒对柴油发动机磨损的影响

进入机油的碳烟微粒增多是现代低排放车用柴油发动机突出问题。探讨了碳烟微粒对发动机各摩擦副磨损的影响，分析了碳烟微粒的磨损机制，并指出提高分散剂性能与用量是减少碳烟微粒磨损的重要方法。     

The influence of soot and dispersant on ZDDP film thickness and friction

The effect of dispersed soot in engine oils is an increasingly important issue in terms of both engine durability and fuel efficiency. Using carbon black as a soot analogue, a study has been carried out to investigate the main factors that determine the impact of soot on friction and ZDDP film formation in formulated oils. It has been found that dispersed carbon black can rapidly remove ZDDP reaction films by abrasion. However, this removal can be prevented or limited by the choice of an optimal dispersant additive.     

甲醇裂解气-柴油混合燃料对柴油机排放的影响

为研究甲醇裂解气-柴油混合燃料对柴油机排放的影响,设计了一种集成式尾气裂解甲醇反应器和进气共轨系统,将YC6A220型柴油机改装成燃烧由甲醇裂解而成的氢富气与柴油混合燃料的柴油机。实验研究表明,改装后的柴油机在中、高负荷运行时可以使NOx、HC和碳烟大幅度降低,且随着甲醇裂解气掺烧量的增加,各排放物质的减少量增加。     

Effects of refined palm oil (RPO) fuel on wear of diesel engine components

In this particular research work, the effects of refined palm oil (RPO), as alternative fuel, on wear of diesel engine components are assessed. Fleet testing is carried for the qualifying candidates diesel fuel replacement, i.e. 100% RPO fuel or 50% RPO and 50% conventional diesel fuel mixture. The base line of the fleet testing is using pure conventional petroleum diesel fuel as an energy source in one of the tested vehicles in the fleet. Analysis of used engine lubrication oil, taken when the oil was changed on the vehicles, was compared to the analysis of used oil samples pulled from 100% diesel fuel engines. The finding suggested that the pure RPO and RPO blended fueled engines were wearing at a normal rate.     

基于柴油发动机国六排放应用的氮氧化物传感器碳颗粒堵塞问题研究

针对目前国六柴油发动机应用的氮氧化物传感器被碳颗粒堵塞的问题进行了分析与讨论.为验证影响传感器积碳堵塞的内部和外部条件,采用了发动机台架和整车路试试验方法.通过总时长100 h以上的巴黎循环试验,测试分析了市面上两家主流供应商提供的氮氧化物传感器对于积碳堵塞的鲁棒性差异.试验结果表明:供应商1和供应商2氮氧化物传感器的...