Abrasion
Material removal caused by hard particles or rough surfaces moving against a component.
Open related article →Working Glossary
Concise definitions that link directly to full technical articles and diagnostic context.
Acid number
A titration result expressing acidic constituents as potassium-hydroxide equivalence per gram of sample.
Open related article →Additive depletion
Reduction or chemical alteration of a fluid’s functional additive system during service.
Open related article →AdBlue
A commercial name for AUS 32, an aqueous urea solution used by selective catalytic reduction systems.
Open related article →Analytical ferrography
Microscopic examination of magnetically separated wear particles to evaluate morphology and wear mode.
Open related article →AUS 32
A standardised aqueous urea solution concept used as a NOx reduction agent in SCR-equipped diesel systems.
Open related article →Base number
A titration result expressing alkaline reserve, commonly used to trend engine-oil neutralising capacity.
Open related article →Boundary lubrication
A regime where surface films and additives carry much of the load because full fluid-film separation is absent.
Open related article →Cavitation
Formation and collapse of vapour cavities that can create noise, erosion and unstable fluid-system performance.
Open related article →Cetane index
A calculated estimate of diesel ignition quality derived from specified physical-property data.
Open related article →Cetane number
A standardised measure of diesel ignition quality obtained using a prescribed engine or accepted derived method.
Open related article →Cloud point
The temperature at which visible wax crystals first appear under the specified test conditions.
Open related article →Coolant inhibitor
A chemical constituent intended to reduce corrosion, cavitation, scale or related cooling-system damage.
Open related article →Demulsibility
A fluid’s ability to separate from water under specified test conditions.
Open related article →Dissolved gas analysis
Measurement and interpretation of gases dissolved in insulating oil to support transformer condition assessment.
Open related article →Elemental spectroscopy
Measurement of element-specific signals to estimate wear, contamination and additive concentrations.
Open related article →Flash point
The lowest test temperature at which vapour flashes under a specified apparatus and procedure.
Open related article →Fluid cleanliness
The concentration and size distribution of particulate contamination in a fluid.
Open related article →Fourier-transform infrared spectroscopy
Infrared measurement used to identify molecular absorption patterns and trend fluid-condition changes.
Open related article →Fuel dilution
Unburned or partially burned fuel entering lubricating oil and altering its properties.
Open related article →Glycol
Ethylene- or propylene-glycol compounds used in coolants and detectable as lubricant contaminants.
Open related article →Hydrodynamic lubrication
A regime in which a pressure-supported fluid film separates moving surfaces.
Open related article →ISO cleanliness code
A three-number code representing particle populations at specified size thresholds.
Open related article →Kinematic viscosity
A fluid’s dynamic viscosity divided by density, commonly reported in square millimetres per second.
Open related article →Lubricity
Ability of a fuel or lubricant to reduce friction and wear under defined boundary conditions.
Open related article →Membrane patch
A membrane carrying captured contamination for visual or instrumental deposit assessment.
Open related article →Nitration
Formation of nitrogen-containing oxidation products, commonly trended in some engine oils by FTIR.
Open related article →Oxidation
Chemical reaction with oxygen that can increase acidity, viscosity, deposits and varnish tendency.
Open related article →PQ index
A relative magnetic response to ferromagnetic debris, including particles larger than typical ICP response.
Open related article →Pour point
The lowest temperature at which movement is observed under a prescribed cooling test.
Open related article →Reserve alkalinity
A coolant titration measure related to acid-neutralising reserve; it is not equivalent to pH.
Open related article →Sulfation
Formation or accumulation of sulfate-related species, sometimes trended in engine-oil infrared analysis.
Open related article →Tribology
The science and engineering of interacting surfaces in relative motion, including friction, wear and lubrication.
Open related article →Urea concentration
The mass fraction of urea in AUS 32, central to SCR dosing quality.
Open related article →Varnish
Thin, adherent deposits formed from degraded lubricant products on system surfaces.
Open related article →Viscosity
Resistance of a fluid to deformation or flow under specified conditions.
Open related article →Viscosity index
An empirical index describing how lubricant viscosity changes with temperature.
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