Definition
Lubricity is the ability of a fluid to reduce friction and wear between sliding surfaces in boundary or mixed lubrication conditions. In lubricant formulation, lubricity is primarily a property of the additive package rather than the base oil.
Lubricity is particularly critical in:
- Diesel fuel — ultra-low sulfur diesel (ULSD) has poor inherent lubricity; lubricity additives (fatty acid methyl esters, dimer acids) are required to protect fuel injection systems
- Metalworking fluids — lubricity additives reduce tool wear and improve surface finish in cutting and grinding operations
- ATF and CVT fluids — precise friction characteristics must be maintained over the fluid’s service life
Standard test: HFRR (High-Frequency Reciprocating Rig) — ISO 12156. The wear scar diameter (WSD) is measured; ULSD diesel fuel must achieve WSD ≤ 460 µm at 60°C to meet European and US specifications.