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CARBON RESIDUE TESTING - using ASTM D 198 Conradson Carbon or D 524 Ramsbottom Carbon, the carbonaceous material left after destructive distillation.

CARBONACEOUS DEPOSIT (CARBON) - a firm deposit composed primarily of organic residue most readily definable by thickness or volume and texture. Such deposits will be found primarily on surfaces operating above engine bulk temperature but below the ashing point.

CARBURETOR - device in an internal combustion engine that atomizes and mixes fuel with air in the proper proportion for efficient combustion at all engine speeds, and controls the engine’s power output by throttling, or metering the air-fuel mixture admitted to the cylinders. The automobile carburetor is a complex mechanism designed to compensate for many variables over a wide range of speeds and loads. Intake air is drawn through the venturi, a constricted throat in the air passage that causes a pressure reduction in the air stream, which draws fuel from the carburetor bowl through either the main jet or the idle jet. The fuel is atomized by the high velocity air, and the resulting air-fuel mixture is piped through the intake manifold to the individual cylinders, where it is burned. A throttle plate between the venturi and the cylinders control power and speed by controlling the volume of air-fuel mixture reaching the cylinders. In most carburetors, closing of this (venturi) throttle valve shuts down the main jet and activates the idle jet, which provides the fuel-rich mixture that idling requires. An accelerator pump in the carburetor provides momentary fuel enrichment when the accelerator pedal is depressed rapidly, to compensate for the sudden influx of air. During cold starting, a choke (or butterfly valve) restricts airflow to the carburetor, thus enriching the mixture for faster starting. The choke on most automotive engine carburetors is operated automatically by a thermostatic spring, which opens the choke as the engine warms up. See fuel injection, supercharger.

CATALYTIC CONVERTER - an emissions control device, incorporated into an automobile’s exhaust system, containing catalysts - such as platinum, palladium, or rhodium - that reduce the levels of hydrocarbons (HC), carbon monoxide (CO), and - in more recent designs - nitrogen oxides (NOx) emitted to the air. In the catalytic converter, HC and CO are oxidized to form carbon dioxide (CO2) and NOx are reduced to nitrogen and oxygen. Three-way catalytic converters that control all three substances require associated electronic controls for precise regulation of oxygen levels in the exhaust gas. Catalytic converters are also effective in removing PNA (polynuclear aromatic) hydrocarbons. Cars equipped with catalytic converters require unleaded gasoline, since the lead in tetraethyl lead, an anti-knock compound, is a catalyst “poison”. See emissions (automotive), hydrocarbon emissions, lead alkyl.

CATALYTIC CRACKING - in refining, the breaking down at elevated temperatures of large, high-boiling hydrocarbon molecules into smaller molecules in the presence of a catalyst. The principal application of catalytic cracking is the production of high-octane gasoline, to supplement the gasoline produced by distillation and other processes. Catalytic cracking also produces heating oil components and hydrocarbon feedstocks, such as propylene and butylene, for polymerization, alkylation, and petrochemical operations.

CAVITATION - formation of an air or vapor pocket (or bubble) due to lowering pressure in a liquid, often as a result of the collapse of a vapor bubble. Cavitation can occur in a hydraulic system as a result of low fluid levels that draw air into the system, producing tiny bubbles that expand explosively at the pump outlet, causing metal erosion and eventual pump destruction. Cavitation can also result when reduced pressure in lubricating dispensing systems forms a void, or cavity, which impedes suction and prevents the flow of greases.

CETANE - colorless liquid hydrocarbon, C15H34, used as a standard in determining diesel fuel ignition performance. See cetane number.

CETANE IMPROVER - additive for raising the cetane number of a diesel fuel.

CETANE INDEX - an approximation of cetane number based on API gravity (see specific gravity) and mid-boiling point (see distillation test) of a diesel fuel.

CETANE NUMBER TESTING - using ASTM D 613, a measured value indicating the ignition quality of diesel fuel.

CLAY FILTRATION - refining process using fuller’s earth (activated clay) or bauxite to absorb minute solids from lubricating oil, as well as remove traces of water, acids, and polar compounds.

CLEVELAND OPEN CUP (COC) - test (ASTM D 92) for determining the flash point and fire point of all petroleum products except fuel oil and products with flash points below 79°C (175°F). The oil sample is heated in a precisely specified brass cup containing a thermometer. At specified intervals a small flame is passed across the cup. The lowest temperature at which the vapors above the cup briefly ignite is the flash point; the temperature at which the vapors sustain combustion for at least five seconds is the fire point. See Tag open cup.

CLOGGING - restriction of a flow path by the accumulation of debris along the flow path boundaries.

CLOSED CUP - method for determining the flash point of fuels, solvents, and cutback asphalts, utilizing a covered container in which the test sample is heated and periodically exposed to a small flame introduced through a shuttered opening. The lowest temperature at which the vapors above the sample briefly ignite is the flash point. See Pensky-Martens closed tester, Tag closed tester.

CLOUD POINT TESTING - using ASTM D 2500, the temperature at which haze appears in an oil sample.

COASTAL OIL - common term for any predominately naphthenic crude derived from the fields in the Texas Gulf Coast area.

COLD CRANKING SIMULATOR - an intermediate shear rate viscometer that predicts the ability of an oil to produce satisfactory cranking speed in a cold engine.

COLD-FLOW IMPROVER - additive to improve flow of diesel fuel in cold weather. In some instances, a cold-flow improver may improve operability by modifying the size and structure of the wax crystals that precipitate out of the fuels at low temperatures, permitting their passage through the fuel filter. In most cases, the additive depresses the pour point, which delays agglomeration of the wax crystals, but usually has no significant effect on diesel engine performance. Another means of improving cold flow is to blend kerosene with diesel fuel, which lowers the wax appearance point by about 1°C (2°F) for each 10% increment of kerosene added.

COMBUSTION - rapid oxidation of a fuel (burning). The products of an ideal combustion process are water (H2O) and carbon dioxide (CO2); if combustion is incomplete, some carbon is not fully oxidized, yielding carbon monoxide (CO). A stoichiometric combustible mixture contains the exact quantities of air (oxygen) and fuel required for complete combustion. For gasoline, this air-fuel ratio is about 15:1 by weight. If the fuel concentration is too rich or too lean relative to the oxygen in the mixture, combustion cannot take place.

COMPOUNDED OIL - mixture of a petroleum oil with animal or vegetable fat or oil. Compounded oils have a strong affinity for metal surfaces; they are particularly suitable for wet-steam conditions and for applications where lubricity and extra load-carrying ability are needed. They are not generally recommended where long-term oxidation stability is required.

COMPRESSION-IGNITION ENGINE - diesel engine. See internal combustion engine.

COMPRESSION RATIO - in an internal combustion engine, the ratio of the volume of the combustion space in the cylinder at the bottom of the piston stroke to the volume at the top of the stroke.   High-compression ratio gasoline engines require high octane fuels. Not to be confused with the pressure ratio of a compressor.

CONDENSATE - in refining, the liquid produced when hydrocarbon vapors are cooled. In oil and gas production, the term applies to hydrocarbons that exist in gaseous form under reservoir conditions, but condense to a liquid when brought to the surface.

COPOLYMER - See polymer.

COPPER STRIP CORROSION - the tendency of a petroleum product to corrode cuprous metals, as determined by test method ASTM D 130; the corrosion stains in a test copper strip are matched against standardized corroded strips.

CORROSION - any observed chemical attack on metal parts. Rust is a special case of the corrosion of iron.

CORROSION INHIBITOR - additive for protecting lubricated metal surfaces against chemical attack by water or other contaminants. There are several types of corrosion inhibitors. Polar compounds wet the metal surface preferentially, protecting it with a film of oil. Other compounds may absorb water by incorporating it in a water-in-oil emulsion so that only the oil touches the metal surface. Another type of corrosion inhibitor combines chemically with the metal to present a non-reactive surface. See rust inhibitor.

CORROSIVE WEAR - progressive removal of material from rubbing surface caused by a combination of chemical attack and mechanical action.

CRACKING - petroleum refining in which large-molecule liquid hydrocarbons are converted to small-molecule, lower-boiling liquids or gases; the liquids leave the reaction vessel as unfinished gasoline, kerosene, and gas oils. At the same time, certain unstable, more reactive molecules combine into larger molecules to form tar or coke bottoms. The cracking reaction may be carried out under heat and pressure alone (thermal cracking), or in the presence of a catalyst. (catalytic cracking).

CROWN - that part of the piston which is exposed to the combustion chamber and therefore to high temperature and pressure.

CRUDE TYPES - based on the predominate type of hydrocarbon present, crudes are classified as Paraffinic, Naphthenic, Asphalitic (Naphthenic/Aromatic) and Mixed Base (Paraffinic/Naphthenic/Aromatic).

CUT - segregated part, or fraction, separated from crude in the distillation process. See distillation.