Motor oil


Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. Motor oils typically consist of base oils enhanced with various additives, particularly antiwear additives, detergents, dispersants, and, for multi-grade oils, viscosity index improvers. The main function of motor oil is to reduce friction and wear on moving parts and to clean the engine from sludge and varnish. It also neutralizes acids that originate from fuel and from oxidation of the lubricant, improves the sealing of piston rings, and cools the engine by carrying heat away from moving parts.
In addition to the aforementioned basic constituents, almost all lubricating oils contain corrosion and oxidation inhibitors. Motor oil may be composed of only a lubricant base stock in the case of non-detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts.
Motor oils are blended using base oils composed of petroleum-based hydrocarbons, polyalphaolefins, or their mixtures in various proportions, sometimes with up to 20% by weight of esters for better dissolution of additives.

History

On 6 September 1866, American John Ellis founded the Continuous Oil Refining Company. While studying the possible healing powers of crude oil, Dr. Ellis was disappointed to find no real medicinal value, but was intrigued by its potential lubricating properties. He eventually abandoned the medical practice to devote his time to the development of an all-petroleum, high-viscosity lubricant for steam engines – which at the time were using inefficient combinations of petroleum and animal and vegetable fats. He made his breakthrough when he developed an oil that worked effectively at high temperatures. This meant fewer stuck valves and corroded cylinders.

Use

Motor oil is a lubricant used in internal combustion engines, which power cars, motorcycles, lawnmowers, engine-generators, and many other machines. In engines, there are parts which move against each other, and the friction between the parts wastes otherwise useful power by converting kinetic energy into heat. It also wears away those parts, which could lead to lower efficiency and degradation of the engine. Proper lubrication decreases fuel consumption, decreases wasted power, and increases engine longevity.
Lubricating oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing frictional heat and reducing wear, thus protecting the engine. In use, motor oil transfers heat through conduction as it flows through the engine. In an engine with a recirculating oil pump, this heat is transferred by means of airflow over the exterior surface of the oil pan, airflow through an oil cooler, and through oil gases evacuated by the positive crankcase ventilation system. While modern recirculating pumps are typically provided in passenger cars and other engines of similar or larger in size, total-loss oiling is a design option that remains popular in small and miniature engines.
In petrol engines, the top piston ring can expose the motor oil to temperatures of. In diesel engines, the top ring can expose the oil to temperatures over. Motor oils with higher viscosity indices thin less at these higher temperatures. Diesel engines operate under high pressure and extreme heat, making them particularly reliant on proper lubrication.
Coating metal parts with oil also keeps them from being exposed to oxygen, inhibiting oxidation at elevated operating temperatures preventing rust or corrosion. Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergents and dispersants added to help keep the engine clean and minimize oil sludge build-up. The oil is able to trap soot from combustion in itself, rather than leaving it deposited on the internal surfaces. It is a combination of this and some singeing that turns used oil black after some running.
Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against moving parts, causing wear. Because particles accumulate in the oil, it is typically circulated through an oil filter to remove harmful particles. An oil pump, a vane or gear pump powered by the engine, pumps the oil throughout the engine, including the oil filter. Oil filters can be a full flow or bypass type.
In the crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journal bearings and rods connecting the pistons to the crankshaft. The oil collects in an oil pan, or sump, at the bottom of the crankcase. In some small engines such as lawn mower engines, dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries, from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves. In typical modern vehicles, oil pressure-fed from the oil galleries to the main bearings enters holes in the main journals of the crankshaft.
From these holes in the main journals, the oil moves through passageways inside the crankshaft to exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. However, in modern designs, there are also passageways through the rods which carry oil from the rod bearings to the rod-piston connections and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. This oil film also serves as a seal between the piston rings and cylinder walls to separate the combustion chamber in the cylinder head from the crankcase. The oil then drips back down into the oil pan.
Motor oil may also serve as a cooling agent. In some engines oil is sprayed through a nozzle inside the crankcase onto the piston to provide cooling of specific parts that undergo high-temperature strain. On the other hand, the thermal capacity of the oil pool has to be filled, i.e. the oil has to reach its designed temperature range before it can protect the engine under high load. This typically takes longer than heating the main cooling agentwater or mixtures thereofup to its operating temperature. In order to inform the driver about the oil temperature, some older and most high-performance or racing engines feature an oil thermometer.
Continued operation of an internal combustion engine without adequate engine oil can cause damage to the engine, first by wear and tear, and in extreme cases by "engine seizure" where the lack of lubrication and cooling causes the engine to cease operation suddenly. Engine seizure can cause extensive damage to the engine mechanisms.

Non-vehicle motor oils

The traditional two-stroke engine design is used in most small gasoline-powered consumer equipment, such as snow blowers, leaf blowers, chainsaws, model airplanes, hedge trimmers, soil cultivators, and so on. It is also used in some trolling motors for personal watercraft. In this design, motor oil is blended into the fuel to lubricate the cylinder and reciprocating assembly, in ratios such as 25:1, 40:1, or 50:1 fuel-to-oil. This two-stroke oil is burned during combustion and contributes to emissions and inefficiency. Non-smoking two-stroke oils, often composed of esters or polyglycols, are designed to reduce visible emissions and environmental impact. Environmental legislation, particularly in Europe, has driven the adoption of ester-based two-stroke oils, especially for leisure marine applications. Often, these motors are not exposed to as wide of service temperature ranges as in vehicles, so these oils may be single viscosity oils. Newer two-stroke engines used in outboard motors and some personal watercraft use direct-injection systems which eliminate the need for oil to be blended into the fuel, offering cleaner and more efficient operation at the expense of separate oil maintenance procedures. Portable electricity generators and "walk behind" lawn mowers use four-stroke engines similar to those in automotive vehicles and use standard motor oils.

Properties

Most motor oils are made from a heavier, thicker petroleum hydrocarbon base stock derived from crude oil, with additives to improve certain properties. The bulk of a typical motor oil consists of hydrocarbons with between 18 and 34 carbon atoms per molecule. One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity. The viscosity of a liquid can be thought of as its "thickness" or a measure of its resistance to flow. The viscosity must be high enough to maintain a lubricating film, but low enough that the oil can flow around the engine parts under all conditions. The viscosity index is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index.
Motor oil must be able to flow adequately at the lowest temperature it is expected to experience in order to minimize metal to metal contact between moving parts upon starting up the engine. The pour point defined first this property of motor oil, as defined by ASTM D97 as "...an index of the lowest temperature of its utility..." for a given application, but the cold-cranking simulator and mini-rotary viscometer are today the properties required in motor oil specs and define the Society of Automotive Engineers classifications.
Oil is largely composed of hydrocarbons which can burn if ignited. Still another important property of motor oil is its flash point, the lowest temperature at which the oil gives off vapors which can ignite. It is dangerous for the oil in a motor to ignite and burn, so a high flash point is desirable. At a petroleum refinery, fractional distillation separates a motor oil fraction from other crude oil fractions, removing the more volatile components, and therefore increasing the oil's flash point.
Another manipulated property of motor oil is its total base number, which is a measurement of the reserve alkalinity of an oil, meaning its ability to neutralize acids. The resulting quantity is determined as mg KOH/. Analogously, total acid number is the measure of a lubricant's acidity. Other tests include zinc, phosphorus, or sulfur content, and testing for excessive foaming.
The Noack volatility test determines the physical evaporation loss of lubricants in high temperature service. A maximum of 14% evaporation loss is allowable to meet API SL and ILSAC GF-3 specifications. Some automotive OEM oil specifications require lower than 10%.
Table of thermal and physical properties of typical unused engine oil:
Temperature Density Specific heat Kinematic viscosity Conductivity Thermal diffusivity Prandtl NumberBulk modulus
0899.121.7964.28E-030.1479.11E-08471007.00E-04
20888.231.889.00E-040.1458.72E-08104007.00E-04
40876.051.9642.40E-040.1448.34E-0828707.00E-04
60864.042.0478.39E-050.148.00E-0810507.00E-04
80852.022.1313.75E-050.1387.69E-084907.00E-04
100840.012.2192.03E-050.1377.38E-082767.00E-04
120828.962.3071.24E-050.1357.10E-081757.00E-04
140816.942.3958.00E-060.1336.86E-081167.00E-04
160805.892.4835.60E-060.1326.63E-08847.00E-04