Napthene -- hydrocarbon characterized by saturated carbon atoms
in a ring structure, having the general formula CnH2n;
also called cycloparaffin or cycloalkane.
Naphthenic -- a type of petroleum fluid derived from naphthenic
crude oil. Characterized by low pour point (due to low wax content), and good
solvency properties.
Neutralization number -- a measure of the total acidity or
basicity of an oil; this includes organic or inorganic acids or bases or a
combination thereof.
Newtonian fluid -- a fluid whose viscosity does not change with
the rate of flow / shear. So-called multigrade oils are non-Newtonian because
viscosity varies with shear rate.
Nitration -- specific to internal combustion engines, the
formation of nitrogen oxides (NOx) during fuel combustion. NOx escapes the
combustion area via ring blowby and reacts with water in the crankcase to form
nitrous acid (HNO2), which can degrade the oil and increase oil
viscosity. Nitration is a particular problem in gas engines due to relatively
high combustion chamber temperatures.
NLGI number -- one of a series of numbers classifying the
consistency range of lubricating greases, based on the ASTM cone penetration
number. The National Lubricating Grease Institute (NLGI) grades are in order of
increasing consistency (hardness).
Noble metal – a metal with marked resistance to chemical
reaction, particularly to oxidation and to solution by inorganic acids.
Contrast with active metal.
Nominal filtration rating -- filter rating indicating the
approximate particle size for which the majority will not pass through a
given filter. It is generally interpreted as meaning that 85% of the
particles of size equal to the nominal filter rating will be retained by
the filter. Due to unreproducibility and lack of precision with respect
to true upstream vs. downstream contamination loads, this rating is
discouraged as a means of assessing a filter's performance.
Non-Newtonian fluid -- fluid, such as a grease or a
polymer-containing oil (e.g., multi-grade oil), in which shear stress is not
proportional to shear rate.
