I always find the sulfur debates interesting. Sulfur is a natural component of crude oil. It is extremely difficult to remove the sulfur from gasoline and diesel fuel. The latent sulfur in gasoline is what causes the rotten eggs smell, and the tear inspiring acid smell from cars with catalytic converters. The latent sulfur in diesel fuel is what eats the bearing shells out of a diesel engine, and shreds exhaust pipes and mufflers... (turbos too! ) and makes your eyes water when you follow a misadjusted diesel truck.
Sulfur has never been added to any fuel. Not gasoline, not diesel. The engine manufacturers have spent years studying the effects of sulfur on internal combustion engines, and have concluded that as long as you keep the sulfur very low (0.1%), and keep the oil changed it can be tolerated. The oil companies plead and cry whenever you ask them to limit the sulfur in fuels. They sponsor studies that try to show benefits of sulfur, and completely forget to mention the extreme harm sulfur causes to engines, and the environment.
Here is a quote out of an engineering text I used in school, "Internal Combustion Engines", by Obert (p274):
SULFUR. Hydrocarbon fuels may contain free sulfur, hydrogen sulfide, and other sulfur compounds. The sulfur content is determined by measuring the amount of sulfur dioxide formed by combustion and translating this into an equivalent mass of free sulfur (although the sulfur in the fuel may exist in a number of various compounds). Sulfur or sulfur compounds are objectionable for several reasons. In some forms, notably free sulfur and hydrogen sulfide, the sulfur is a corrosive element of the fuel that can corrode fuel lines, carburetors, and injection pumps. In all forms, the sulfur will unite with oxygen to form sulfur dioxide that, in the presence of water at low temperatures, may form sulfurous acid. However, the exhaust gases of the engine usually leave the engine and the exhaust pipe at high temperatures and therefore formation of acid does not occur. On the other hand, the gases remaining in the cylinder or in the exhaust line on shutdown are exposed to the necessary conditions for forming an acid: low temperature and water. The same comments can be made for winter operation and for blow by products in the crankcase. It is also entirely possible for the sulfur dioxide to unite with other substances to form products that could cause engine wear even though temperatures are high. Since sulfur has a low ignition temperature, the presence of sulfur can reduce the self-ignition temperature, thus promoting knock in the SI (spark ignition) engine and tending to decrease knock in the CI (compression ignition) engine. It is found that the response of the SI fuel to tetra-ethyl lead is reduced by the presence of sulfur....
In every case where sulfur is mentioned in this fine engineering textbook, it is in terms of maximums to limit the corrosive tendencies of sulfur. Never as a lubricant for the injectors, bearings, or any other part of the engine.
Lubrication of the injectors is entirely done by the fuel. Gasoline, and diesel are both light weight mineral oils. They are very slippery. As is typical of alkane series, of which they belong, the longer the molecule, the thicker and more lubricious it is... diesel fuels (hexadecane, aka cetane) are slipperier than gasolines (octane). Mineral oils are slipperier still.
If you are worried about injector lubrication, add some oil to your fuel. Low sulfur fuel is better for your engine in every way.
-Chuck
