|LACQUER - a thin, varnish-like deposit composed primarily of organic residue most readily definable by color. It is resistant to saturated solvents such as petroleum naphtha, but is soluble in other solvents such as benzene, chloroform, ketones and similar compounds classed as “lacquer solvents.” Most often association with diesel engines.
LEAD ALKYL - any of several lead compounds used to improve octane number in a gasoline. The best known is tetraethyl lead (TEL), Pb (C2H5)4. Another is tetramethyl lead (TML), Pb (CH3)4. Other compounds have varying proportions of methyl radicals (CH3)- and ethyl radicals (C2H5)-. Use of lead compounds in motor gasoline has been phased out for environmental reasons. Beginning with the 1980-model year, all new U.S. and foreign-made cars sold in the U.S. require unleaded gasoline.
LEAD SCAVENGER - See scavenger.
LEAN AND RICH OCTANE NUMBER - expression of the anti-knock value of an aviation gasoline at lean air-fuel mixtures (relatively low concentration of fuel) and rich air-fuel mixtures, respectively. A grade designation of 80/87 means that at lean mixtures the fuel performs like an 80-octane gasoline and at rich mixtures, like an 87-octane gasoline.
LIFTER (STUCK) - one that does not return to its original position by its own force upon removal from the engine.
LIGHT ENDS - low-boiling-point hydrocarbons in gasoline having up to five carbon atoms, e.g., butanes, butenes, pentanes, pentenes, etc. Also, any extraneous low-boiling fraction in a refinery process stream.
LOAD WEAR INDEX (LWI) - measure of the relative ability of a lubricant to prevent wear under applied loads; it is calculated from data obtained from the Four Ball EP Method. Formerly called mean Hertz load.
LPG (LIQUEFIED PETROLEUM GAS) - propane or (less commonly) butane, obtained by extraction from natural gas or from refinery processes. LPG has a vapor pressure sufficiently low to permit compression and storage in a liquid state at moderate pressures and normal ambient temperatures. Pressurized in metal bottles or tanks, LPG is easily handled and readily lends itself to a variety of applications as a fuel, refrigerant, and propellant in packaged aerosols. LPG is also called LP gas and bottled gas. See natural gas liquids.
LUBRICATING OIL - compounded or finished oil consisting of base stocks and the additives necessary for providing the required performance.
LUBRICATION - control of friction and wear by the introduction of a friction-reducing film between moving surfaces in contact. The lubricant used may be a fluid, solid, or plastic substance. For principles of lubrication, see boundary lubrication, full-fluid-film lubrication, ZN/P curve.
LUBRICITY - ability of an oil or grease to lubricate; also, called film strength. Lubricity can be enhanced by additive treatment. See compounded oil.