In a diesel engine, the fuel provides the lubrication for moving parts. Diesel fuel naturally contains compounds that provide lubricity, but hydrotreatment of diesel fuel to remove sulfur also removes the compounds that provide lubricity.
D 6079 is a standard method used to measure the lubricity properties of diesel fuel. This test is called HFFR (High-Frequency Reciprocating Rig). It is measured in micrometer. The test consists of submerging a contact point between a steel ball and a flat steel disc into a sample of fuel. The ball placed under slight weight moves back and forth for a specific period of time. The extent of wear is measured in µm (microns) and is called WSD (Wear Scar Dia). Its normal value is 460~520 µm.