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BASE - any of a broad class of compounds, including alkalis, that react with acids to form salts, plus water. Also known as hydroxides. Hydroxides ionize in solution to form hydroxyl ions (OH-); the higher the concentration of these ions, the stronger the base. Bases are used extensively in petroleum refining in caustic washing of process streams to remove acidic impurities, and are components in certain additives that neutralize weak acids formed during oxidation.

BASE NUMBER - See neutralization number.

BASE OIL CREDIT - the value of the base fluid displaced by the additive dosage.

BASE STOCK - crude oil fractions of suitable viscosities and volatilities, generally refined to remove unstable and waxy components, and classified as Neutrals and Bright Stocks. See distillation.

BEVEL GEAR - See gears.

BHP - brake horsepower, the effective or available power of an engine or turbine, measured at the output shaft. It is equivalent to the calculated horsepower, less the power lost in friction.

BLOW-BY - that portion of the combustion reactants and unburned air-fuel mixture which leaks into the engine crankcase during engine operation. See positive crankcase ventilation.

BORE POLISHING - an action between rings and cylinder walls that produces a glazed surface finish and can result in poor compression sealing.

BMEP - brake mean effective pressure, the theoretical average pressure that would have to be imposed on the pistons of a frictionless engine (of the same dimensions and speed) to produce the same power output as the engine under consideration; a measure of how effectively an engine utilizes its piston displacement to do work.

BORDERLINE PUMPING TEMPERATURE - See pumpability and mini-rotary viscometer.

BOUNDARY LUBRICATION - form of lubrication between two rubbing surfaces without development of a full-fluid lubricating film. See full-fluid lubrication, ZN/P curve. Boundary lubrication can be made more effective by including additives in the lubricating oil that provide a stronger oil film, thus preventing excessive friction and possible scoring. There are varying degrees of boundary lubrication, depending on the severity of service. For mild conditions, oiliness agents may be used; these are polar compounds that have exceptionally high affinity for metal surfaces. By plating out on these surfaces in a thin but durable film, oiliness agents prevent scoring under some conditions that are too severe for a straight mineral oil. Compounded oils, which are formulated with polar fatty oils, are sometimes used for this purpose. Anti-wear additives are commonly used in more severe boundary lubrication applications. High quality motor oils contain anti-wear additives to protect heavily loaded engine components, such as the valve train. The more severe the cases of boundary lubrication are defined as extreme pressure conditions; they are met with lubricants containing EP additives that prevent sliding surfaces from fusing together at high local temperatures and pressures.

BRIGHT STOCK - high viscosity oil, highly refined and dewaxed, produced from residual stocks or bottoms. Named for their SUS viscosity at 210°F, having viscosities ranging from about 500 to 1100 cSt at 40°C. They are HVI oils refined to clear products of good color. Used for blending with lower viscosity oils.

BROOKFIELD VISCOSITY - apparent viscosity of an oil, as determined under test method ASTM D 2983. Since the apparent viscosity of a non-Newtonian fluid holds only for the shear rate (as well as temperature) at which it is determined, the Brookfield viscometer provides a known rate of shear by means of a spindle of specified configuration that rotates at a known constant speed in the fluid. The torque imposed by fluid friction can be converted to absolute viscosity units (centipoises) by a multiplication factor. See viscosity, shear stress. The viscosities of certain petroleum waxes and wax-polymer blends in the molten state can also be determined by the Brookfield test method ASTM D 2669.

BTU (BRITISH THERMAL UNIT) - quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit, at sixty degrees Fahrenheit and at a pressure of one atmosphere. See energy.