Lubricicity and ULSD. A Problem?



Emissions regulations in most of Europe and North America have mandated the use of Ultra Low Sulfur Diesel (“ULSD”) in diesel engines. How does this requirement impact the operation of your diesel engine?

All modern diesel engines are designed to use ULSD without any problems. The problems arise in older engines that may still be in operation.

First off, ULSD is diesel that is refined to include no more than 15 ppm of sulfur. When the fuel is refined, other contaminants and components of fuel are also removed. ULSD is, therefore, refined to a much higher degree than the older versions of diesel that often had 1,000 ppm or more of sulfur. This additional refining, of course, results in a higher fuel cost.

Why is sulfur considered “bad” from an emissions standpoint? Quite simply, sulfur, when combined with water vapor, forms sulfuric acid, a primary component of acid rain. This sulfuric acid also impacts the performance of your engine. Excessive sulfur can score and pit the inside of cylinder walls.

So, on older mechanical engines, how could they burn high sulphur fuel without any damage?

The answer is a question of the lubricicity of the fuel.

When the ULSD is refined, not just the sulfur is removed. Carbon and other contaminants are also removed. In older fuel grades, these “contaminants” performed an important function in lubricating the pistons and cylinders. Now that these components are removed by statute, older engines sometimes experience higher wear and tear when using ULSD. This wear and tear is not as pronounced on common rail engines that were designed to used ULSD.

So, if you are using an older engine, what can you do? The answer is that the lubricicity of the fuel needs to be replaced, through fuel additives. This is where caution comes in. The additive chosen must be certified to replace the lubricicity without adding contaminants to the fuel system or leading to incomplete combustion.