ABSTRACT
The largest players in the lubricant market in Nigeria are the low-price commercial bulk engine oil manufacturers. Five different oils from different outlets were analyzed for physicochemical properties in order to determine their conformity to standards. The results obtained for pH was 7.67, 7.41, 4.82, 4.49, 4.74; viscocity index was 164.64, 142.00, 95, 96, and 90 for mobile, oando, E1, E2, and E3 respectively. Viscosity at 100 oC ranges from 14. 40 to 20.00, this determines the suitability for use under severe conditions. The result showed that mbil oil is best for long journey followed by Oando. Generally, all the oils have their parameters within the SAE standard; hence they are safe for use in our engines.
CHAPTER ONE
INTRODUCTION
1.0 Background to the study
From time immemorial, liquids, including water, have been used as lubricants to reduce friction and wear and remove heat between two surfaces in contact. At present, lubricating oil also called lube oil is the most commonly used lubricant because it has found a wide range of applications in the field of engineering. A lubricant, sometimes called lube, is a substance (often a liquid) which is introduced between two surfaces in contact moving relative to each order to keep them separate under all loads, temperatures and speed thus minimizing friction and wear. The substance may act as cooling fluid removing heat from the system and also protect surfaces from the attack of aggressive products formed during the operation. Lubricants may also perform the function of dissolving and transporting foreign particles [1].
Majorly, there are solid and liquid lubricants. Air and other gas based lubricants are there, but for the purpose of this research work, consideration is limited to liquid lubricants. Examples of liquid lubricants are: mineral oils, vegetable oils and synthetic oils. The most common liquid lubricants are the mineral oils. This is because of the supply of crude oil. The term mineral oil is used here to mean lubricating base oil derived from crude oil that is refined from naturally occurring petroleum. Since they are commonly used, important information about their properties is now available. As products, derived from crude oil, they can be produced in a wide range of viscosities for the various applications. There are low-viscosity oil (for easy starting at low temperatures) having hydrogen-carbon chain of about 200 atomic mass unit (amu) and there are also high viscosity oils (for better engine protection at the normal running temperatures) with high molecular weight of about 1000 amu. All other mineral based oils have viscosities that fall within this range (API 1509 2002) [2].
1.1 Classification
The American petroleum institute (API) has a designation for several types of lubricant base oils as follows [3]:
- Group I-saturates < 90%. This is known to have the Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120
- Group II- Saturates over 90% and SAE VI of 80 to 120
- Group III- Saturates > 90% and SAE VI over 120
- Group IV-Polyalphaolefin
- Group V All others not included above.
Groups III, IV and V are synthetic oil with group III usually described as synthesized hydrocarbons, SHCs. The lubricant used in the internal combustion engine could solely consist one of the groups mentioned above, yet additives are added to improve the performance properties of the oil.
The effectiveness of lubricating oil was known to contribute to the life span of an engine. Different lubricating oils are used in various engines because the fuels used differ chemically from one another and hence resulting products of combustion differ [10,11]. When physicochemical properties of fresh and used engine oils were carried out, it was found that the degrading trend in the properties depend on the operating temperature of the engine, the distance covered and the age of the engine [4,12] Another test on lubricating oils was the comparable investigation of wear metals in virgin and used lubricating oil [26]. Choosing the best motor oil was observed to come up frequently in discussion between motor heads either on motorcycle or cars. There are various brands and types of automobile oils in the markets, the choice of which is left to the users’ discretion [13].
However, the Nigeria lubricant market is littered with varieties of products, ranging from net, untreated base oils to low quality formulated oils, and to premium quality products. The dominant is the low quality formulated oils, due to the high demand for such category of oils by the consumers, predicated on the low-price range. Using a low quality lubricating oil can lead to excessive energy loss through friction, which is estimated at 20–25% of the energy produced through the burning of fuel by the engine, and early engine ‘spent’ before the expected duration of its salvage value. It also poses high risk or denies the consumer the benefits of extended oil drain interval, and rather subjects them to frequent and early change of oil which has been estimated to be up to 40 times the lubricant price [6].
The motivation for research into the integrity of this class of engine oils arose from the fact that it is about the cheapest available in Nigeria at any time. The low-price class is also the highest selling product type even though it is the lowest quality of engine oils available and allowed by statutory regulations. They are used as lubricating oils in passenger cars, buses, heavy trucks, light engines, and power generator sets. While these classes of engine oils are contributing to the sustaining of our economy in terms of market indices, the worry is whether they are capable of equally sustaining our machineries. The general norm is that cheap things are inferior in quality. The preliminary and basic probe tool into the capabilities of these products to sustain the Nigerian vehicles and equipment is therefore important. The outcome will wisely advise the users of lubricants on their choices, enlightens the ignorant users of the products, and also addresses or confirms the fears of the oil and equipment users who are skeptical about the satisfactory performance of this class of products.
1.2 Review of Past Work
Engine oils being the most effective lubricant in automobiles have attracted researchers’ interest. Extensive research has been carried out on lubricants and their performance properties by international research institutes and students in the field of engineering and sciences. In 2012, Shi Yanping and Zang Yong in the Department of Mechanical Engineering, Huaihai Institute of Technology, Lianyungang, Jiangsu 222005 China, published an article titled “A Novel Lubrication Oil Pressure Measuring Method Based on Magneto-elastic Effect for Auto Engines”. A measuring method that uses Fe-based amorphous alloy was studied to achieve accurate measurement of the lubrication oil pressure of auto engines. In 2008, Gray Belvins and Dan Burger published an article titled “Mapping Oil Pressure to Measure Bearing Wear”. One of the buzzwords used in regard to condition monitoring is “Oil Pressure Mapping”. This article explains oil pressure mapping, why this diagnostic technique was developed and how it is used to measure engine bearing wear. Dauda and Obi [15] (2000) determined some properties of engine oils. It was recommended that other methods should be used to determine the performance properties of lubricating oils. Obi [21] (2010) presented an article titled “Conformity to standards of Engine oils manufactured in Nigeria” at the Nigeria Institute of Mechanical Engineers Conference organized by Port Harcourt. Shafiqur [22] investigated the hydrodynamic lubricating properties of some common oils. This investigation was necessary as oils can best be selected for a given application when its properties are known to be suitable for that application. Nunaya [23] did measurements of physical and chemical properties of some selected Nigerian lubricants and Mathias [24] determined the service specifications of Nigeria produced engine oils using their hydrodynamic, thermal and chemical properties. It was then recommended that there is need for regular investigation of these properties for the purpose of monitoring the oils in our local markets. Osebi [25] investigated the hydrodynamic lubricating properties of some Nigerian made oils. He then concluded that multi-grade oils performed better and recommended that similar work be carried out to verify the chemical properties of these oils. Aremu [26] did the evaluation of some Nigerian engine lubricating oils, he concluded that the result he obtained could help users to make good choices and that the inability to challenge the oils in a way similar to the normal working condition of lubricants is a major limitation. Otu [27] did the evaluation and performance characteristics of some Nigerian made engine oil. He then recommended that similar work be done in our local market.
1.3 Functions/Applications of lubricants
One of the largest applications of lubricants is protecting the internal combustion engine in motor vehicles and powered equipment. To do this lubricants perform the following key functions.
1.3.1 Lubricants keep moving parts apart
The major function of lubricants is to separate two surfaces moving relative to each other in a system thereby reducing friction, surface fatigue, heat generation, noise of operation and vibrations. This function is made possible by the formation of physical barrier i.e a thin layer of lubricant in between the two surfaces. This phenomenon is known as hydrodynamic lubrication. In a situation where the pressure and temperature on the surfaces are high, the oil layer gets thinner and part of the forces are transmitted between the surfaces through the thin films of lubricant. This is referred to as elasto-hydrodynamic lubrication [27].
1.3.2 Lubricants reduce friction
Ordinarily, a system without lubrication posses much higher friction as compared to one with lubrication. Thus the fact that the use of lubricant in a system reduces the overall friction of the system should be agreed with. The reduced friction is to an advantage as the heat generated between the surfaces is reduced as well as wear particles and as such there is an improvement in the efficiency of the entire system. Friction modifiers which may be contained in lubricants as additives, chemically bind to metal surfaces reducing the frictions on the surface even when the lubricant present in the system is not enough for hydrodynamic lubrication, for example, in protecting a car engine at start up [28].
1.3.3 Lubricants carry away contaminants and debris
In internal combustion engines, there are usually filters fixed along the circulation path of the lubricants. The internally generated debris and external contaminants that may enter the system are carried in the oil where they are removed by filtration. Additives such as detergents and dispersants are always added to motor oil for use in internal combustion engine. These additives help for transporting debris and contaminants that may have entered the system, the filter gets clogged up and would require to be replaced. At this time it may be recommended to change the filter and the oil in the system. In gear bones however, the system is closed. Instead of filter, magnet may be used to attract microscopic metal chips that may be in the system as a result of wear [29].
1.3.4 Lubricants transfer heat
Liquid lubricants for their high specific heat capacity are very effective in the transfer of heat in internal combustion engines. Generally lubricants in a system could be used to cool or warm the system when it’s required to regulate temperature. The rate of flow of lubricant in the system determines the amount of heat that is transferred or carried away at any given time. High flow rate would carry away larger amount of heat per unit time and an additional benefit is the reduction of thermal stress that is built up within the lubricant in the system. The disadvantage of the high flow rate is that it requires a large sump and big cooling unit which eventually will amount to additional cost of operation and maintenance. Also a high flow that depends on flow rate to protect the lubricant from thermal stresses can be faced with catastrophic failure during sudden system shut down. A good example of this is an automotive oil cooled turbochargers. Turbochargers get red hot during operation and the cooling oil only survives as the total time in the turbocharging system is very short. If the system is suddenly shut down, the oil in the turbocharger gets oxidized blocking oil ways with deposits of the products of oxidation. This blockage reduces cooling and eventually the turbocharger totally fails [29].
1.3.5 Lubricants protect against wear and corrosion
A good quality lubricant is formulated with additive that can chemically bind to metal surfaces to prevent corrosion. Lubricants also contain anti wear or high pressure additives for better performance against wear and fatigue [24].
1.4 Quality of lubricants
Lubricant marketers may claim superior quality of their lubricants but sometimes with no factual evidence. The quality of a lubricant is proven by reference to famous brands, sporting figures or some professional endorsement. All motor oil labels have mark of outstanding quality or quality additives. In most applications, lubricants are required to be non-resinous palecoloured, odorless, and oxidation resistant. Several tests to reveal the typical technical properties of the lubricants are used to grade and classify lubricating oils. According to the American society for testing and materials ASTM, the typical technical properties of lubricants are measured by the followings tests [28].
1.4.1 Kinematic viscosity
The proper operation of equipment depends on the proper kinematic viscosity at operating temperature of the oil used for its lubrication. This means that kinematic viscosity is a measure of a liquid’s flow under the influence of gravity. Kinematic viscosities are midrange, close to neither the high nor low limits. That helps components work their best and helps the lubricants stay in grade [26].
1.4.2 Viscosity Index
Viscosity index indicates how much a lubricant‟s viscosity will change according to changes in temperature between 40°C (104°F) and 100°C (212°F), which roughly define the normal temperature range of most operations. This means that the smaller a lubricant‟s viscosity change as a result of temperature change, the higher that lubricant‟s viscosity index. High viscosity index lubricants protect better in operations with temperature variations. The viscosity of oil generally decrease with increase in temperature but the rate or extent of decrease in viscosity varies among the oils. Some oil’s viscosity change rapidly with change in temperature and are said to have low viscosity index. Oils with high viscosity index have minimum change in viscosity with change in temperature.
1.4.3 Cold Crank Simulator Apparent Viscosity
Apparent viscosity has been established as a valid predictor of engine cranking viscosities at specified low temperatures. Apparent viscosity depends on temperature and shear rate. This means that cold cranking viscosity affects the start-ability of engines and other equipment in cold temperatures. Low cold cranking viscosities make for easier cold cranking and more dependable cold temperature starting.
1.4.4 Borderline Pumping Temperature
Borderline pumping temperature is a measure of the lowest temperature at which engine oil can be continuously and adequately supplied to the components of an automotive engine. This means that the lower the borderline pumping temperature, the lower the temperature in which the engine is protected by circulating oil. Synthetic motor oil’s extremely low borderline pumping temperatures assure excellent low temperature protection.
1.4.5 Pour Point
The test determines the lowest temperature at which an oil flows as the jar is tilted for a prescribed period. The pour point of oil indicates the lowest temperature at which an oil may be used in some applications. This means that the lower the pour point, the more useful the lubricant is in cold temperatures.
1.4.6 Flash and Fire points
Flash point is the lowest temperature at which application of a flame causes specimen vapors to ignite. Flash point is used to assess the overall hazard of a material and is used in shipping and safety regulations to define “flammable” and “combustible” materials. Fire point is the lowest temperature at which a specimen sustains burning for five seconds. This means that lubricants with high flash and fire points, such as synthetic lubricants, are safer to use and transport than lubricants with lower ones and have a greater high temperature operating ranges.
1.4.7 Noack Volatility
Test determines the evaporation loss of lubricating oils at high temperature. Evaporation loss is particularly important to motor and cylinder lubrication, due to the high temperature of these operations and the tendency of evaporative loss to increase in high temperatures. Significant evaporative loss of oil leads to excessive oil consumption and destructive changes in oil properties. This means that lubricants with low Noack scores, lose less to volatility than lubricants with high scores. Low-loss oils keep their original protective and performance qualities longer than high-loss oils do, which keeps oil consumption low and fuel economy and equipment protection high
1.4.8 High Temperature/High Shear Viscosity
Viscosity at the shear rate and temperature of this test is considered representative of the condition encountered in the bearings of automotive engines in severe service. Lubricant viscosity in the bearings of automotive engines in severe service is a critical factor in bearing wear. This means that lubricants with high scores, maintain their viscosity in high temperatures after exposure to high shear. That means they continue to protect engine bearing even after exposure to severe service conditions.
1.5 Sources of Lubricating Oil
Lube oils are one of many fractions, or components that can be obtained from crude oil or raw petroleum which is actually an oily well of yellow-to-black, flammable liquid mixture of several hydrocarbons i.e. organic compounds containing carbon and hydrogen atoms only. Petroleum deposit is formed by the decomposition of organic matter (Plants and animals) that lived several years ago. As a result of difference in climatic and geographical changes occurring in the earth‟s crust, the decomposition rate of the organic matter differ from region to region. Consequently, the nature and percentage of the hydrocarbons formed differ from region to regions; the physical and chemical properties of the crude oil obtained from different sites also differ widely. For instance, the California crude oil has specific gravity of 0.92 gram/milliliters; the pennsylvania crude has 0.81 gram/milliliters. Specific gravity is an important property speaking, the specific gravity of crude oils range from 0.8 to 0.97 gram/milliliter. Other oils like the vegetable oils which are triglyceride esters are obtained or extracted from plants and animals and are capable of lubrication. Lubricating oils such as polyalphaolefin (PAO), polyalkylene-glycol (PAG), Alkylated Naphthalene etc are synthetic oils synthesized through laboratory reactions [32].
1.6 The Motor Oil
The motor oil is oil used in the lubrication of internal combustion engines. It functions mainly in the lubrication of moving parts; it can also clean, prevent corrosion, and cool the engine by carrying heat between the moving parts. Motor oil also improves sealing. Motor oils are derived from petroleum based chemical compound i.e. mineral base oil and from non-petroleum-synthesized chemical compound i.e. synthetic oil. The minerals, polyalphaolefins (PAO), polyinternalolefins (PIO) are motor oil base oils derived from hydrocarbons, thus they are organic compounds which consist of carbon and hydrogen only [33].
1.6.1 Uses of Motor Oils (engine oils)
This is a lubricant used in internal combustion engines. The internal combustion engine include motor or road vehicles such as cars and motorcycles, there are also heavier vehicles such as buses, lorries trucks and other commercial vehicles, non-road vehicles such as boats, large agricultural equipment locomotives and static engines such as electrical generators. In engines, the parts which move against each other cause friction which waste energy that would have being useful in the system by converting it to heat energy. When the moving parts make contact, wear occurs and this in turn reduces the efficiency of the engine. This could lead to increase in fuel consumption and a decrease in power output of the engine and could even lead to engine failure if not checked [32]. The lubricating oil forms a separating film between surfaces moving relative to each other to minimize or avoid direct contact between them thus reducing wear and decreasing heat produced by friction thereby protecting the engine. When the motor oil is in use in the engine, by means of air flow ever the surface of the oil pan, an oil cooler and through the buildup of oil gases evacuated by the positive crankcase ventilation system, heat is transferred through convection. In spark ignition engines, towards the top of the cylinder, the top piston ring can expose the oil to a temperature of about 3200 F (1600C) while in compression ignition engines i.e diesel engines oils can be exposed to a temperature of 6000 F (3150C). The oil with higher viscosity index thins less at these elevated temperatures and provides or maintains better lubrication properties. When metal parts are coated with oil, the parts are said to be isolated from the environment. Thus they are no longer exposed to oxygen and so oxidation is inhibited at elevated operating temperatures preventing rust or corrosion. Additives for corrosion inhibition can sometimes be added to enhance the property of the oil as desired. In other to keep the engine clean and minimize oil sludge build-up, dispersants and detergents are added to some oils [32].When the metallic parts of an engine rub against each other, microscopic metallic particles are produced from the wearing of the surfaces. The particles so produced could circulate as carried in the oil and grind against moving parts thereby causing wear. In the internal combustion engine, there is an oil filter in the oil lubricating system which removes or filters off harmful particles from the oil as it circulates the system. Oil pumps are used to pump the oil from the oil pan usually at the base of the engine throughout the engine and the oil filter. Motor oil lubricates rotating and sliding parts between the crankshaft journal bearing and connecting rods connecting the piston to the crank shaft within the crankcase of a vehicle engine. In horse power rated small engines like lawn mowers, dippers are found at the bottom of the connecting rods which dip into the bottom plate and splash the oil in it around the crankcase to lubricate the internal parts as desired. In car engines, the oil pump pumps oil from the oil pan/bottom plate through the filter to the oil galleries. The oil from here lubricates the main bearings which hold the crankshaft in place at the journals and the bearings of the camshaft which operates the valves. In modern vehicle engines, the oil from the oil galleries which move under the influence of the pumping pressures to the main bearings enters holes in the main journals of the crankshaft from where it moves through passage ways inside the crankshaft to the holes in the rod journals to lubricate the rod bearings and connecting rods. Simpler designs depend on the rapidly moving parts to splash and lubricate the surfaces between the piston rings and the interior surfaces of the cylinders. Modern design is such that there are passage ways through the rod to carry oil from the rod bearings to the rod piston connections to lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. The oil film here seals up the gap between the piston rings and cylinder walls separating the combustion chamber on the cylinder head from the crankcase [33].
1.6.2 Properties of Motor Oil
Most of the engine oils are made from petroleum hydrocarbon base stock obtained from crude oil containing additives to improve performance properties. Any engine oil consists of hydrocarbon with 18 to 34 carbon atoms per molecule. For an oil to maintain lubricity between moving parts one of the most important properties is its viscosity. The viscosity of oil or a fluid is that property of the fluid that makes it to resist flow; it can be thought of as a measure of the thickness of the fluid. The viscosity of lubricating oil must be high enough to maintain a lubricating film and also low enough such that the oil can always flow around the internal parts of the engine even at low temperatures (start up). Viscosity index is a measure of the extent to which the viscosity of oil changes with change in temperature. Oil is said to have a high viscosity index if its viscosity changes less with temperature. Generally the smaller a lubricant’s viscosity changes as a result of change in temperature, the higher that lubricant’s viscosity index. High viscosity index lubricants protect better in operations with temperature variation. Oil must be able to flow adequately at the lowest possible temperature in its service environment in order to maintain lubricity between moving parts at start up of the engine. This property of the motor oil is described by its pour point. The Pour Point of oils is the indication of the lowest temperature at which the oil may be used in an application, that is to say “an index of the lowest temperature of its utility” for a given application (ASTM D97). Flash point is another very important property of engine oil. The flash point is the minimum temperature at which vapors from a lubricant mixed up with air ignites on the application of flame. As is it dangerous for oil in an engine to ignite and burn, a high flash point is desirable. Total Base Number (TBN) is another important property of engine oils. This is a measure of the reserve of alkalinity in the oil i.e the oils ability to neutralize acids. Total acid number (TAN) is analogous to TBN. It is the measures of the acidity of the oil. The properties mentioned here are those of the physical and chemical properties of oil which are usually reported after analysis in oil test labs. However some other important properties known to be imparted to the oil by additives but which are not routinely reported can be revealed by “performance” test. These “performance” tests are not carried out during routine oil samples analysis because they are expensive, involve prolonged test periods and may require large sample volumes. However it is important that those in charge of machine reliability and the user community get to know what they get from the oil they buy and use in their equipments [33].
1.6.3 Motor Oil Performance Tests
The performance tests that are used to portray the quality and the performance capability of any oil are unlike the ordinary used oil analysis that reveals the physical and chemical properties of the oil mentioned above. The performance tests really challenge the lubricants in some ways similar to the real working environment where that oil is expected to serve. The result of such tests gives the extent to which the oil will respond in service. The following are typical examples of performance tests
1.6.3.1 Film Strength
This is the ability of lubricant to reduce friction and control wear under wide-ranging rolling and sliding conditions. The ASTM has several methods that attempt to measure this property of engine oil. Adhesive wear, contact fatigue and two-body abrasion are examples of wears that can be affected by lubricants film strength. For this purpose, anti-wear and extreme pressure additives are added to the lubricants. With time and as the lubricant ages and gets contaminated these additives are subject to depletion and impaired performance. The common oil analysis tests do not measure film strength.
1.6.3.2 Air-handling Ability
This is the ability of a lubricant to release entrapped air rapidly and to suppress the formation of foam. Use of certain additives and the quality of a lubricant’s base stock can define the air-handling ability of the lubricant [34].
1.6.3.3 Water-Handling Ability
This is the ability of the oil to efficiently shed water during static condition. Loss of water handling ability reveals risks from oil-water emulsions and poor performance of other properties. The common used oil analysis may not reveal the water-handling ability of a lubricant [34].
1.6.3.4 Corrosion Control
A fundamental objective of the formulation of any lubricant is corrosion control. The ability of a lubricant to neutralize acidic or corrosive agents or form a protective covering on surfaces of machine parts reveals the extent to which the lubricant controls corrosions. Many additives known as sacrificial additives are used for this purpose. These additives can loss their effectiveness with time. The total base number (TBN) test is capable of reporting the effectiveness of the corrosion protecting quality of oil in use [34].
1.6.3.5 Oxidation Stability
Most lubricants are formulated with oxidation inhibitors to reduce the rate of oxidation. Almost all lubricants in our market today emphasize on this important property of lubricants. It is therefore evident that oils with low oxidation stability are not desirable especially in high temperature service environment like in internal combustion engines [35].
1.6.4 Grades of Motor Oil
Motor oils are graded according to their viscosity characteristics. The society of automotive engineers (SAE) has a numerical code system under which motor oils are graded. The SAE viscosity grading include: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. The numbers 0, 5, 10, 15 and 25 are suffixed with the letter W, the W here means winter or cold start viscosity i.e at low temperatures the number 20 sometimes comes with W in which case it is used to denote cold viscosity grade and some time without W in which case it denotes hot viscosity grade. The grading of kinematic viscosity is done by measuring the time it takes for a calculated amount of standard oil to pass/flow through a standard orifice at standard temperature and pressure. The more time it takes for given oil to flow through the orifice, the higher the viscosity of that oil and as such higher SAE number. However, it should be noted that gear, axle and manual transmission oils have a separate SAE grading system which should not be confused with engine oil viscosity (SAE J 306). For instance 75W-140 is gear oil with high number. The higher numbers than that of engine oil does not mean that it has higher viscosity than engine oil. The motor oil can be divided into single grades motor oil and multigrade motor oil [35].
1.6.4.1 Single Grade Motor Oil.
The oils which contain no viscosity modifier additives, whose viscosities are appreciably affected by changes in temperature, are the monograde oils. Viscosities generally reduce with increase in temperature but the extent to which viscosity changes with respect to temperature can be reduced or controlled with the presence of polymeric viscosity index improvers. Since the single grade motor oil does not contain this, it is not suitable in applications involving a wide range of temperature. There are eleven (11) viscosity grades available for the monograde oils; they are 0w, 5w, 10w, 15W 20W, 25W, 20, 30, 40, 50 and 60. Six out of the eleven are known to be winter grades and so have the W designations (SAE J 300) the viscosities are measured at different cold temperatures in MPa or centipoises (cP) using the Cold Cranking Simulator (ASTM D5293) and the mini-rotary viscometer (ASTM D4684). Based on the coldest possible temperature at which the oils flow, they are graded as SAE viscosity grade OW, 5W, 10W, 15W, 20W or 25W. The lower the viscosity grades of the oil, the lower the pour point of the oil i.e the lowest temperature at which the oil can flow or below which the oil solidifies. For instance if an oil passes at 5W and 10W specifications but failed to pass at OW specification, it cannot be labeled OW because it is not suitable for applications that require that specifications as it does not flow at that very low temperature. It cannot as well be labeled 10W as it could be suitable for applications below temperature specifications of 10W. The viscosities of the single non-winter grades are measured at 1000C (2120 F) in mm2 /S or centistokes (cSt) depending on the viscosity range an oil fall at the measuring temperature, the monograde non-winter oils are graded as SAE 20,30,40,50 or 60. The higher the viscosity of oil measured at this temperature, the higher the SAE viscosity grade. In applications where the temperature range in use is not too wide like in classic cars, lawn mowers etc the single grade motor oil is recommendable.
1.6.4.2 Multi-grade Motor Oil
In most applications the motor oil is exposed to a wide range of temperature from low start up temperatures in winter to high operating temperatures in summer. Some will have high viscosities when cold and low viscosities at high operating temperatures of the engine in which they serve. For the single-grade oils discussed above and as mentioned earlier, the difference in viscosities between to low temperature and the high temperature is too large. In the multi-grade oils, the polymer additives called viscosity index improvers are added to bring the difference in viscosities closer so that the oil can serve in applications where there is a wide range of temperatures. The additives make a monograde oil a multigrade one because of the properties they will impart to it. However a multi-grade oil can be made without additive, the idea is to make an oil have a viscosity of the base grade when cold and the viscosity of the second grade when hot so as to be suitable for a wide range of temperatures i.e an oil can be used in winter when cold and also in summer when it’s hot. The viscosity of multigrade oil also varies with temperature but to a very much less extent as compared to that of mono-grade oil. The variation of viscosity with temperatures depends on the amount and kind of additives added to the base oil. The multi-grade oil has SAE designation of two viscosity grades, for example, 20W-40 is one of the common multi-grade oil. The two numbers have their individual definition in mono-grade oils and as such an oil labeled as 20W-40 must have the SAE viscosity requirements of both 20W and 40 and their limitations i.e. an oil labeled 20W-40 will and must not have the viscosity requirement for 10W. If an oil has no additives but has the viscosity requirement of a multi-grade oil can be labeled either multi-grade or mono-grade. For example 20W-20 is simple multi-grade oil that can be made from the base stock without additives. This oil can be labeled 20W-20, 20W, or 20. If however viscosity index improvers are used, the oil cannot be labeled mono-grade.
1.7 Oil Additives
As the demand for lubricants for use in internal combustion engines and other applications increases by the day, research efforts have being devoted to developing improved lubricants. Additives are chemical compounds added to base oils to improve their lubricating and aging properties. Depending on the desired properties and service environment, oils today contain additives to make them do their best in service. The additives are grouped according to functions they perform in the oil [36].
1.7.1 Oxidation Inhibitors
These additives slow down the rate of oxidation in the internal combustion engine. As the lubricants are exposed to high temperature during operation, the tendency for the oil to get oxidized is high but at this stage, the chemical compound containing nitrogen, phosphorus and alkyl-phenol now react with the hydrogen peroxide formed initially by the oxidation of the lubricant. This single action now stops the chain reaction which could have led to the formation of sludge and vanish in the engine. The prevention of the formation of these aggressive compounds minimizes the corrosion of zinc and copper bearing alloys. Zinc, barium and calcium thiophosphates are used in internal combustion engines.
1.7.2 Anti Wear Additives
These additives prevent the wearing away of surfaces by minimizing friction. The friction is minimized when the anti-wear agent produces protective film/coating on the surface by chemical or physical absorption mechanism under the conditions of boundary lubrications. Anti wear agents are compounds of oxygen, sulfur, chlorinated wax, phosphorus and organic lead. In hydraulic pumps, gear and the likes, zinc dialkyldithiophosphates are widely used. In extreme pressure applications where asperities may penetrate oil film and make contact with asperities of mating surfaces i.e. severe metal-to-metal contact, active sulfur, chlorine and lead compounds have to be used. These additives undergo chemical reaction forming sulfides and chlorides in form of a film on the surface. This low shear strength film allows for relative movement of the surfaces and avoids direct contact of asperities thereby enhancing the lubricating property of the lubricant
1.7.3 Viscosity Index Improvers
These additives function to improve the viscosity index of engine oils. In internet composition engine, the operating temperature is usually high and so an oil with low viscosity index will not find use. With these additives the change in viscosity with respect to change in temperature is kept within a small range so that the oil becomes useful in applications where temperature variation is high as in internal combustion engine. It is also needed that these additives have an advantageous effect on the pour point of the oil in which it is in use. The common types of viscosity improvers are the polymethacrylates, polyisobutylsuccinic acid. The primary function of the viscosity improver is to thicken light oil to a higher viscosity while maintaining the original viscosity temperature coefficient.
1.7.4 Detergents
Detergents as additives help to clean the internal part of the engine by preventing and/or removing deposits of oil sludge, varnish and lead. B.arium and calcium sultanates and phenates are used in automotive and diesel engines. Ash less detergents has now been developed to minimize low temperature sludge formation. Detergents are multifunctional as they can in addition to detergent properties prevent rusting and improve the viscosity index and pour point of the oil.
1.8 Statement of the Problem
Over time, it has been noticed that there is an increasing demand for engine oil as it remains the most effective lubricant in automobiles. As a result of this, existing lubricant producing companies now increase their volume of production to meet with the increasing demand and make more profit. The US lubricant market now exceeds 2.5 billion gallons per year. For the 1970 to 1980 period it was estimated that the petroleum lubricant market would grow 25% from the 2.1 billion gallons per year to 2.6 billion gallons per year. Synthetic lubricants were projected to grow about 40% over the decades to a volume of some 60 million gallons per year by 1980. The overall growth rate for all lubricants has been averaging less than 2% per year, the ever increasing demands being placed on lubricants for improved performance in automotive engines, transmissions, hydraulic fluids, e.t.c. have resulted in very significant growth for the oil additive segment of the market [36]. This is not different from the present situation in Nigeria. There is expansion in the automobile market as cars and other vehicles are continuously being imported into the country. The consequence of the increased demand for engine oil which may have resulted from the use of more cars and power generating sets (diesel/petrol) in our society is the tendency to find substandard engine oils in our local markets. Therefore, there is the need for the evaluation of the general physicochemical properties of selected locally produced engine oil and sealed oils.
1.9 Aim and objectives of the research
The aim of this work is to perform a comparative physico-chemical analysis of locally produced and sealed lubricant oils obtained from Portharcourt Area, Rivers state.
The specific objectives are:
- To investigate the performance properties of the lubricants in our local market through laboratory tests considering specific gravity, kinematic viscosity, viscosity index, pour point, and flash point, and then total base number
- To compare the results obtained from the laboratory experiments with standards.
- To provide useful and essential information to users of these oils by discussing the results obtained from the Laboratory Experiment.
1.10 Scope of the research
Three samples of low price product obtained from road sides were tested of basic physical parameters including colour, odour, pH, specific gravity, kinematic viscosity, viscosity index, pour point, flash point, moisture content and then total base number, acid value as two important chemical property capable of estimating the oxidation stability and corrosion/rust protection stamina of the oil which will be compared with sealed oils.
1.11 Justification
To say that the use or demand for lubricants (Engine Oil) in Nigeria is on the increase cannot be over emphasized. This is true as vehicles and equipment that use internal combustion engine which require engine oil for lubrication are continuously been imported into the country. This in turn will lead to the expansion of the lubricant market in Nigeria as there will be a continuous increase in the demand for lubricant. The expansion of lubricant market in Nigeria means that the existing manufacturers may increase their volume of production, other entrepreneurs may venture into the business and importers may import more to meet demand and achieve their aim. To ensure quality products in our market, it is important to continuously monitor the products through quality assurance tests of lubricants (Engine Oil) in our market. For this reason, analysis of physicochemical Properties of Selected Locally Produced Lubricants (Engine Oil) is inevitable.
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