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Info Centre >> Fuel and Lube Oil Technical Manual >> Appendix 3: List of Terms
Antioxidant
A substance that retards the process of oxidation.
API Gravity
An arbitrary scale adopted by the American Petroleum Institute (API) for expressing the relative density of oils. Its relation to relative density is:
141.5
API gravity (degrees) = —————————————— - 131.5
Specific gravity at 60 / 60°F
(The term Relative Density can be substituted for Specific Gravity)
Small quantity of residue, free from carbonaceous matter, remaining after burning in air, of oil fuel at a prescribed temperature.
Asphaltenes
Those components of asphalt that are insoluble in petroleum naphtha but are soluble in carbon disulphide. (Other solvents may be stipulated). Hard and brittle compounds, made up largely of high molecular weight polynuclear hydrocarbon derivatives containing carbon, hydrogen, sulphur, nitrogen, oxygen and usually the three heavy metals - nickel, iron and vanadium.
Ash
Non-combustible fuel residues usually containing a mixture of aluminium, calcium, iron, nickel, silicon, sodium and vanadium. Contamination may be derived from the crude oil stock or from catalyst fines, downstream storage and airborne dirt.
Barrel
Unit of volume measurement used for petroleum and petroleum products.
1 barrel = 42 US gallons, = 35 Imperial gallons, = 159 Litres
Blending
The intimate mixing of various components in the preparation of a product of specified properties.
Blow-by
Passage of combustion gases past the piston rings of an engine.
BN
See TBN.
Boundary Lubrication
Lubrication between 2 rubbing surfaces without development of a full lubricating film. It occurs under high loads and low speeds.
Bulk Modulus
The reciprocal of compressibility of oil. The higher the BM, the less the fluid can be compressed.
Cams
Eccentric lobes typically used to open valves.
Calorific Value
See Specific Energy.
Carbon Residue
Residue left when an oil is heated under prescribed conditions. Hence carbon residue is an indicator of the coke-forming tendencies of an oil.
Catalyst
A substance which accelerates or changes the course of a reaction without itself undergoing any chemical change.
Catalyst Fines
Small (typically less than 50 micron) particles in the form of complex alumino- silicates which may be present in residues from a catalytic cracking plant.
Catalytic Cracking
Process whereby cracking is accomplished by the use of heat and catalysts. Used primarily to convert high-boiling distillate to gasoline, gas oil, butanes and lighter gases.
centiPoise (cP)
See Viscosity.
centiStoke (cSt)
See Viscosity.
Cetane Index
A measure of the ignition quality of a distillate fuel, indicating the relative ease with which the fuel will ignite when injected into the combustion chamber of a compression-ignition engine. Higher cetane indices and numbers indicate shorter ignition lags and are associated with better all-round performances in most types of compression-ignition engines. Cetane Index is calculated from the API gravity and the boiling point characteristics of the fuel.
Cetane Number
Cetane Number is measured from a prescribed engine test.
Cloud Point
The temperature at which a cloud or haze begins to appear when an oil, which has been previously dried, is cooled under the prescribed conditions. Such cloud or haze is due to the separation of paraffin wax. Since a fuel must be “clear and bright” for the clouding to be observed, this parameter is only applicable to some distillate fuels. Clouding may be regarded as an advance warning of the onset of “pour” problems due to either low temperature or high wax content of a fuel.
Compatibility
When blending two or more fuels of different crude oil origins and/or different refinery processes, the resultant blend should be an homogeneous mixture in which asphaltenes remain in stable equilibrium. Conversely, when blending two or more fuels of different crude oil origins and/or different refinery processes, should the resultant blend precipitate asphaltenes, then the two or more fuels are incompatible.
Corrosion Inhibitor
A substance added to lubricating oil to protect active metal surfaces from corrosion.
Cross Head Engine
Slow-speed diesel engine where the piston rod is confined to move vertically and the piston pin is replaced by a cross head to transfer thrust to the connecting rod.
Crown
The top of the piston of a diesel engine exposed to the cylinder.
Cylinder Oil
Lube oil used in the cylinders of cross head diesel engines. Usually high viscosity and TBN greater than 70.
Density
Mass per unit volume.
Detergent
The ability of a lubricant to keep oil-wetted parts clean. Commonly metallic soaps with an alkaline reserve.
Dispersant
The ability of an oil to hold debris in suspension and thus prevent deposition on oil-wetted surfaces.
Diesel Oil
Oil used as fuel in diesel and other compression-ignition engines.
Diluent
In fuel oil blending, low viscosity materials having suitably high flash points are used to reduce the viscosity of residues.
Distillate
Any product obtained by condensing the vapours distilled from petroleum or its products.
Distillation Range
The range of temperature, usually determined at atmospheric (Boiling Range) pressure by means of standard apparatus, over which boiling or distillation of a liquid proceeds. Only a pure substance has one definite boiling or distillation temperature at a given pressure. Mixtures of substances such as petroleum distillates have a distillation temperature range.
Emulsion
An intimate mixture of fine particles of one liquid in another. An emulsion is said to “break” when the particles join and the liquids become separate.
End Point
The highest temperature is indicated on the distillation (Final Boiling Point) thermometer when a light distillate is subjected to one of the standard laboratory methods of distillation.
Ester
Compounds of alcohol and fatty acid which form the major constituent of many synthetic oils.
EP additives
Additives provided to limit micro-seizure of contacting surfaces under Extreme Pressure lubricating conditions.
Flash Point, Closed
The lowest temperature at which application of a small flame causes the vapour above a petroleum product to ignite when the product is heated under prescribed conditions in a ‘closed’ container.
Flash Point, Open
The lowest temperature at which an application of a small flame causes the vapour above a petroleum product to ignite when the product is heated under prescribed conditions in an ‘open’ container.
Fuels - Residual
The residue remaining after removal of the lighter products.
Fuel Oil
The result of selective blending of various residues and distillate cutter stocks.
Fuels - Marine
A distillate or blended product containing some residue. Diesel Oil.
Fuels - Gas OilA distillate fuel.
Grease
A lubricant composed of oil, thickened with a metallic soap or other compound to produce a semi solid lubricant.
HydrocarbonsCompounds composed entirely of carbon and hydrogen. They form the basic building blocks of most fuel and lubricating oils.
Inhibitor
A compound added to lubricant to prevent or retard undesirable changes.
Insolubles Contaminants that remain after extraction of the sample with a solvent.
KV
Kinematic Viscosity, measure of resistance to flow under gravity and at a specific temperature.
Lands
The vertical surfaces of a piston between the piston rings and or crown.
Mineral Oil
Lubricant derived from crude oil.
Multigrade
A term used to describe a lubricant where the viscosity temperature relationship has been altered by the addition of polymers that control viscosity limits at different temperatures.
Nitration
The process whereby nitrous oxides attack petroleum fluids at high temperatures. Common in gas fuelled engines and often associated with viscosity increase, deposits formation and oxidation.
Oxidation
A process whereby oxygen attacks the lubricant. Oxidation is continuous in the presence of air but greatly speeded at high temperatures.
inhibitor pH
A measure of acidity or alkalinity expressed as the log of the hydrogen ion concentration. 0-acid, 7-neutral, 14-alkali.
Petroleum
Crude Oil, i.e. oil in its natural state before it has been refined. Mineral Oil, normally a liquid mixture consisting essentially of many different hydrocarbons, occurring naturally and having a wide range of colours from yellow to black and characteristic odours. It is the raw material from which gasoline, kerosene, lubricating oil, fuel oil, paraffin wax, bitumen, petro-chemical feedstocks, etc. are obtained.
Pour Point
The lowest temperature at which a petroleum oil is found to pour or flow when it has been chilled under prescribed conditions.
Relative Density
The ratio of mass of a given volume of a substance to that of the same volume of pure water at constant temperature. Relative density decreases with increase of temperature and increases with decrease of temperature. It can only be compared at constant temperature. The standard temperature for quoting the relative density for most petroleum products is 15°C. Density is also referred to in absolute terms in units of kg/m3 at a particular reference temperature - usually 15°C.
Residue
The material remaining, as an un-evaporated liquid or solid, from a process involving distillation or cracking.
Scuffing
The abnormal wear that occurs due to seizure, micro-welding and subsequent tearing of the sliding surfaces.
Specific Energy
The amount of heat liberated by the combustion of a unit quantity under specified conditions. The gross specific energy is the sum of the heat produced by the total combustion of the fuel and the heat released by the condensation of the water formed by such combustion. This is applicable to a boiler. The net specific energy is the gross value minus the heat released by condensation of the water vapour formed by the combustion. The net value is applicable to a diesel engine.
Straight Run
Produced by distillation without cracking or alteration to the structure of the constituent hydrocarbons.
Thermal Cracking
A cracking process in which the reaction is prompted purely by the action of heat and pressure.
Viscosity
The measure of a fluid’s resistance to flow. With increasing temperature the viscosity decreases. There are two types of viscosity: kinematic and dynamic or absolute. The more common is kinematic viscosity, which is measured by the time taken for a fixed volume of oil to flow through a capillary tube.
The usual unit is the centiStoke (cSt); one cSt = mm2/s
Dynamic (absolute) viscosity is usually measured by a rotating viscometer and is commonly expressed in centiPoise (cP). 1 cP = 1 mPa.s
Viscosity Index (VI)
An arbitrary scale used to measure a fluid’s change in viscosity with temperature.
VI Improver
A compound used to raise the VI of a mineral oil or other product (see also multigrade).