Sulphur (or Sulfur if you like, but not Sulpher) is not a lubricant. Early on, the sulphur removal process affected lubricity as well but that has been corrected.

The big impact of ULSD is that the air we all have to breath is less foul.

 

That's true, to what degree I don't know. But being in a machine shop for 20 years, I can tell you that all of the good, heavy duty cutting fluids had a high sulpher content. If you were tapping a super high temp stainless alloy without sulpher and moly, you were going to gall a tap. Could be coincidence I guess.

 

Sulfur is not a lubricant in of itself, but it can combine with the nickel content in many metal alloys to form a low melting point eutectic alloy that can increase lubricity. The process used to reduce the sulfur also reduces the fuel's lubricating properties. Lubricity is a measure of the fuel's ability to lubricate and protect the various parts of the engine's fuel injection system from wear. The processing required to reduce sulfur to 15 ppm also removes naturally-occurring lubricity agents in diesel fuel. -- Info provided by Wiki

 

Both the reduction of sulfur and the process to remove sulfur are why ULSD has lower lubricity. The low lubricity of ULSD is rectified thru addivies that are added after the fuel is processed.

Sulfur is an extreme pressure lubricant, so it acts as a lubricant for the injection pump and injectors, but does nothing before the fuel is pressurized.