High temperature oxidation stability of automotive crankcase oils and their base oils

A modified open test tube type of apparatus has been used to assess the high-temperature oxidation stabilities of two grades of automotive crankcase oils and their base oils under conditions that simulate those encountered in the internal combustion engines. The method involved keeping the oil temperature at 180°C with an air flow of 1.0 L/min for 65 hours and evaluating the soluble oil acidity, pentane insolubles, volatile acidity and total oxidation products formed. The procedure detected that the oil acidity increased exponentially and sludge formation started after a threshold level of oxidation products had been formed. Volatility losses were found to be appreciable, and the antioxidant additives were quickly used up under the simulated conditions. Therefore only a mineral oil of high natural antioxidant capability could provide improved performance at high temperatures. The total oxidation product proved to be a valuable source of information on the extent of oil oxidation and oxidation stability study.     

Composition and oxidative stability of hydro‐cracked base oils and comparison with a PAO

The oxidative stability of nine hydrocracked base oils from seven producers and a PAO was compared using the standard IP 48 test. After a comprehensive characterisation of the oils, an evaluation of oxidative stability was carried out by measuring some common oil parameters, such as viscosity characteristics, carbon residue, pentane insolubles, and acid number. Additionally, the compound‐class composition of the fresh and oxidised oils was determined, and an FTIR spectroscopic analysis was carried out. The oxidative stability of the hydrocracked oils was largely affected by the sulphur and aromatic hydrocarbon concentration in the oils. Oils with an increased sulphur content (above 80 ppm) had better oxidative stability than oils with a low sulphur content (20 ppm and lower), and there was a relatively large variability in the stability of the oils depending on the sulphur concentration. The oxidative stability of most of the hydrocracked oils with a low sulphur content was similar, and matched somewhat the stability of the polyalphaolefin.     

Thermo‐oxidative stability of high‐temperature stability polyol ester jet engine oils — a comparison of test methods

Thermo‐oxidative stability in aerospace turbine oils is an important criterion. A new category (HTS) of turbine oil has been introduced, and the present work compares data on the oxidation stability of HTS oils obtained using the FTM 791, method 5308 test, at various temperatures, and PDSC experimental data, to standard class oils (STD). PDSC has become established in recent years as an effective means with which to establish the thermo‐oxidative stability of oils. The purpose of the present work was to find out whether PDSC could identify HTS oils correctly, and also to increase our understanding of some of the chemical processes behind the test results. Analogies in the degradation of the oligomer antioxidants have been confirmed by MALDITOF mass spectra.     

Piston crevice hydrocarbon oxidation during expansion process in an SI engine

Combustion chamber crevices in SI engines are identified as the largest contributors to the engine-out hydrocarbon emissions. The largest crevice is the piston ring-pack crevice. A numerical simulation method was developed, which would allow to predict and understand the oxidation process of piston crevice hydrocarbons. A computational mesh with a moving grid to represent the piston motion was built and a 4-step oxidation model involving seven species was used. The sixteen coefficients in the rate expressions of 4-step oxidation model are optimized based on the results from a study on the detailed chemical kinetic mechanism of oxidation in the engine combustion chamber. Propane was used as the fuel in order to eliminate oil layer absorption and the liquid fuel effect. Initial conditions of the burned gas temperature and in-cylinder pressure were obtained from the 2-zone cycle simulation model. And the simulation was carried out from the end of combustion to the exhaust valve opening for various engine speeds, loads, equivalence ratios and crevice volumes. The total hydrocarbon (THC) oxidation in the crevice during the expansion stroke was 54.9% at 1500 rpm and 0.4 bar (warmed-up condition). The oxidation rate increased at high loads, high swirl ratios, and near stoichiometric conditions. As the crevice volume increased, the amount of unburned HC left at EVO (Exhaust Valve Opening) increased slightly.     

Oxidation stability of gasoline engine lubricants: Effect of base-oil chemistry in laboratory and engine tests

This paper presents a laboratory test called the Iron Catalysed Oxidation Test (ICOT), where air is bubbled through an oil sample at 165 °C. This test, shorter than the CEC L-48 test, provides an easy method of gasoline engine lubricant screening. A basic study has shown that this kind of test is suitable for the discrimination of base-oil properties and that the oil viscosity increase at the end of the test is highly indicative of the oxidation processes at work. In this study, the base-oil assessment is carried out with an API SG SAE 15W-40 oil, and the results depend directly on the aromaticity of the base oil. Several engine test sequences, including CEC L-55-T-95: TU3M HT, were also applied to these formulations, which differ only in their base oils. The results of those sequences where oil consumption was low roughly correlated with the laboratory test results. However, when there was a high loss of volatile matter in the engine tests, the oil viscosity increase was greatly modified, and this parameter can override the effect of oxidation.     

Thermal stability of synthetic oils in aviation applications

The thermal decomposition of selected synthetic base fluids has been investigated. The effects of temperature and time on the rate and extent of thermal degradation were studied in a modified steel bomb test device. The effects of chain length and branching are important factors in the thermal stability of hydrocarbons and similar fluids. In order to overcome the 350°C limit of thermal stability, other classes of chemical have to be used.     

Sulphur-phosphous components in gear oils: part 1, oxidation stability studies by P-NMR spectroscopic techniques

In the present investigations, the mechanism of oxidation stability of sulphur and phosphorus-based additives such as S-alkyl O,O-dialkyl phosphorodithioate, alkyl amine salt of dialkyl dithiophosphoric acid, dialkyl hydrogen phosphite and zinc dialkyl dithiophosphate used in lubricants has been studied by liquid and solid state ³¹P/^lH-NMR spectroscopic techniques. These techniques have enabled to monitor the complex changes that occur during oxidation at different intervals during long duration oxidation tests and provide qualitative and quantitative information of products formed during degradation of S–P based additives. The nature of both soluble and insoluble products of decomposition has been /determined. The studies have revealed few important aspects regarding thermal stability of these additives. The ashless S-alkyl O,O-dialkyl phosphorodithioate have better thermal oxidative stability and retain their identity for longer period compared to other similar ashless additives and zinc dialkyl dithiophosphates. The loss of additives during oxidation is 12% in case of S-alkyl O,O-dialkyl phosphorodithioate compared to other mentioned additives (40–100%) during 64 h of heating at 165 °C in the presence of air and catalyst. The decomposed products are also solublised in case of S-alkyl O,O - dialkyl phosphorodithioate and dialkyl hydrogen phosphite, and small amount of solids are formed compared to other additives. During oxidation the main components are being converted into more complex insoluble polyphosphates. The nature of soluble and insoluble products of decomposition as a result of thermal degradation are similar irrespective of the types of additive used. The mechanism of degradation and subsequent composition and structure of products formed has been discussed in detail. These studies will facilitate correlation of the structure and performance of these additives in lubricants.     

Evaluating thermal and thermooxidation stability for lubricating oils via microscale methods

Differential thermal analysis (DTA) and thermogravimetry (TG) methods have been developed to evaluate the thermal and thermooxidation stability of different lubricating oils. Measurements are carried out either by heating the oil sample at a constant rate (direct programme) or by keeping it at a fixed high temperature (isothermal programme). Oxygen at a constant flow rate is used for thermooxidation measurements. Tested samples included different viscosity grades: neutral base oils, unadditivated lubricating oil blends, and industrial oils. The mechanism of thermal decomposition for ZDDP and the estimation of its optimum concentration was also considered.     

两种合成航空润滑基础油高温氧化衰变机理研究

为研究航空润滑油的热氧化安定性,模拟聚α-烯烃(PAO)和酯类油(DE)两种合成航空润滑基础油在发动机内的高温工况,借助傅里叶红外光谱(FTIR)、气相色谱/质谱(GC/MS)联用等仪器对反应油样的黏度和结构组成进行测试与分析.结果表明,PAO具有较差的热氧化安定性能,在200℃时就发生分解,而DE的分解温度可达到300℃.在两种航空润滑基础油的高温衰变中,均有不同的产物生成.PAO衰变产物主要包括烷烃和烯烃,而DE的衰变产物主要是含氧化合物.最后,根据实验结果分析了航空润滑基础油的高温衰变机理.     

Improvement of thermooxidative stability of non‐edible vegetable oils of Indian origin for biodegradable lubricant application

For environmental reasons, as well as the dwindling source of petroleum, a new class of environmentally acceptable and renewable lubricants based on vegetable oils is available. Even though vegetable oils possess excellent lubricant‐related properties, there are some concerns about using it as lubricant base oil. Still, unmodified and modified varieties of soybean, rapeseed, sunflower and canola oils have been in use in the USA and Europe. In India, with the shortage of edible oil, alternate sources of vegetable oils stocks are being explored. With this aim, a comprehensive study has been conducted earlier in the authors' laboratory. In this study, numerous options of non‐edible vegetable oil sources were explored, and a few potential vegetable oils were studied in the laboratory. It was found that even though the oils performed much better in comparison with other vegetable oils, it still required improvement in thermooxidative stability. Therefore, in the later part of the study, different options were explored to improve thermooxidative stability. With a background on the initial studies of the authors as described above, the present paper deals with the studies on improvement of these non‐edible candidate vegetable oils of Indian origin for lubricant by treating with selected antioxidants for applying them in lubricants. Copyright © 2010 John Wiley & Sons, Ltd.     

A study of the purification of used engine oils with a montmorillonitic clay

The present paper looks at percolation, a recycling technique for engine oils that is non‐polluting and dispenses with the use of acid. The technique employs Algerian bentonite as a complementary purifier of used SAE 20W–50 engine oils which have first been dehydrated and had the light hydrocarbons (gasoline) removed. In order to understand the nature of the used oil, the characteristics of an oil in service were closely monitored over 7000 km. Various tests were performed on the bentonite to find the most satisfactory form of clay filtration bed. The species retained by the beds were analysed.     

Study of the lubrication mechanism of two-stroke engine oils using a disc machine

A technique has been developed to evaluate scuffing characteristics of two-stroke engine oils on a high speed disc machine. This paper deals with the lubrication mechanisms involved in the test adopted. The influence of h/σ, surface conformity and boundary characteristics of lubricants were examined. It was observed that the lubrication mode changed from hydrodynamic to mixed to boundary conditions leading to eventual failure. This situation is similar to that observed in two-stroke piston tightening tests where the lubrication mode changes from hydrodynamic to mixed lubrication as the temperature increases.     

Maximising the fuel efficiency of engine oils: The role of tribology

Improvement of engine fuel efficiency is one of the most important goals of current automotive development. Maximising the contribution of engine oils to fuel efficiency is a very important part of this process. Engine friction modelling, based on fundamental tribological considerations, has shown that further engine friction improvements are possible through engine oil reformulation. This reformulation should minimise friction under hydrodynamic conditions through modification of the rheological properties of oils, and also minimise friction under mixed and boundary lubrication conditions through changes in the chemical composition of the oils. These improvements can be achieved by appropriate selection of a base oil as well as by the use of effective friction‐reducing additive systems. A very important consideration in formulating these highly fuel‐efficient oils is their ability to retain their fuel efficiency during the entire oil service interval. This paper describes the role of tribological research in the development and introduction of advanced fuel‐efficient engine oils.     

Vegetable oil-based lubricants—A review of oxidation

Vegetable oils are being investigated as a potential source of environmentally favourable lubricants, due to a combination of biodegradability, renewability and excellent lubrication performance. Low oxidation and thermal stability, poor low-temperature properties and narrow range of available viscosities, however, limit their potential application as industrial lubricants. This review addresses oxidation as a limitation of vegetable oil-based lubricants. The basic mechanism of vegetable oil autoxidation is presented, along with methods used to monitor and analyse the products of oxidation. The potential impact of such oxidation products on lubrication performance is discussed. A brief discussion of methods used to assess and improve oxidation stability completes the review.     

The effect of water on the acid-base properties of new and used IC engine lubricating oils

The absolute values of total base number (TBN) were determined for several sets of both fresh and used engine oil samples. Basic and acidic compounds from these oils have been extracted into water, 7% sea water and ethanol-water (1:1, v/v) mixtures. The extracts have been determined by potentiometric titration as pH extracts, TBN (water extract) and alkalinity. The oil formulations are not resistant to the presence of water but basic additives in fresh oil are more resistant than those for used oils. The percentage of TBN extractable into water significantly increases with service life. The presence of significant amounts of water in lubricating oil is serious and should form part of any lubricant condition monitoring system. The case is argued for both the use of dehydration canisters in oil systems and for the development of a new method of water content determination for used formulated lubricating oils which is quick, accurate and suitable for automated condition monitoring systems. The pH of aqueous extracts for condition monitoring of lubricating oils is shown to be only meaningful for TBN values of 2 or less.     

Phosphorus volatility of engine oils: Use of the phosphorus emission index

The concept and principles of the phosphorus emission index (PEI) were introduced during 2002. This paper reviews the background of the benefits and concerns regarding phosphorus additives. In particular, the paper focuses on the two factors until recently assumed important in phosphorus volatility and catalyst contamination: oil volatility and initial phosphorus concentration. Studies of Selby—Noack data on 1300 oils collected in 1999 and 2000 by the Institute of Materials showed the invalidity of the two assumptions and this led to the concept of the PEl. Further studies in conjunction with a field taxi study by the Ford Motor Company to determine the correlation of the PEl with catalyst contamination not only showed correlation, but also proved that phosphorus volatility was independent of either oil volatility or fresh oil phosphorus levels. Rather, phosphorus volatility was, as earlier predicted, found to be highly dependent on its chemistry and the chemistry of other additives. Engine oil formulation using the PEl technique should markedly reduce phosphorus volatility and resultant catalyst contamination.     

Effect of chemical structure on the hydrolytic stability of lubricating base oils

Base oils differing in chemical structure, representatives of hydrocarbon fluids, ester fluids, and water-insoluble polyalkylene glycols (PAGs), were tested (ASTM D2619) for comparison of their hydrolytic stability, which was found to depend on both their chemical structure and purity. The variations observed after hydrolytic degradation in oil acid numbers, water layer acidity, and copper (Cu) strip weight are indicative of excellent hydrolytic stability of hydrocarbon oils, very good hydrolytic stability of PAG oils, and good hydrolytic stability of polyolester oils (characterized by high purity and an acid number lower than 0.1 mg KOH/g). The positive effect of steric hindrance around the ester bonds on the hydrolytic stability of polyolesters was substantiated by the results obtained for the oils of a pentaerythrite tetracaproate and pentaerythrite tetra(sec-caproate) structure.     

Test procedure for rapid assessment of frictional properties of engine oils at elevated temperatures

A fifteen-minute test sequence has been developed for screening and ranking base oils and friction modifiers. The tests are run on a high-frequency friction machine developed at the authors' company and based on the Mills-Cameron design. The procedure can distinguish clearly and repeatably between the behaviour of different friction modifiers and with a degree of discrimination which is better than has been achieved in engine mechanical loss tests     

Performance testing of lubricants based on high oleic vegetable oils

Owing to growing environmental concerns, vegetable oils are finding their way into lubricants for industrial and transportation applications. Vegetable oils can of Ser significant environmental advantages with respect to resource renewability and biodegradability, as well as offering satisfactory performance in a variety of applications. Synthetic ester-based fluids may also offer these advantages, however their cost can be prohibitively high. Formulating with vegetable oil does, however, present unique challenges. These are, most notably, the oxidative and hydrolytic instability and low temperature problems associated with the triglyceride. However, through advanced plant breeding techniques, vegetable oils are becoming available which exhibit excellent thermal and oxidative stability and other improved performance properties. The cost of these oils is much lower than synthetic esters, thereby making them attractive ‘environmental’ base fluids.     

Torque loss of type C40 FZG gears lubricated with wind turbine gear oils

Five fully formulated wind turbine gear oils were characterised. The gear oils have 320 ISO VG grade and different formulations: ester, mineral, PAO, PAG and mineral+PAMA.A back-to-back FZG test machine, with re-circulating power, was used and a torque-cell was included on the test rig in order to measure the torque loss. Eight thermocouples were included to monitor the temperatures in different locations of the test rig.Tests at 1.13, 2.26 and 6.79 m/s were performed for different FZG load stages: K1, K5, K7 and K9. Both gearboxes were jet-lubricated with an oil flow of 3 l/min. The input flow temperature was kept almost constant (80 ±1 °C).Friction generated between the meshing teeth, shaft seals and rolling bearing losses was predicted.