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Ultra Low Sulfur Diesel: Great for Emissions - Here’s What's Missing!

Posted by: Erik Bjornstad

ultra low sulfur diesel additiveToday, guest blogger Joe Fazio of Bell Performance tackles some information on ultra-low sulfur diesel fuel.  When you think of diesel engine emissions, the two elements that come to mind are soot and sulfur.  Both of these have negative impacts on our environment. Sulfur is a natural part of the crude oil from which diesel fuel is refined, and is one of the key causes of acid rain pollution. Soot is the main component of diesel engines' noxious black exhaust fumes, and is among the prime contributors to air pollution. The move towardultra-low sulfur diesel (ULSD) use, started around 2006, is aimed at lowering diesel engines' harmful exhaust emissions and improving air quality.

Petroleum-based ULSD is produced by removing sulfur during the oil refining process, through the process of hydrotreating. In this process, a heated mixture of petroleum feedstock (diesel) and hydrogen passes through a reactor with catalysts—substances that facilitate chemical reactions without being consumed by the reaction—to separate sulfur from hydrocarbon molecules.

Though it’s great for emissions, here are 3 essential things that ULSD is missing:

1) Biocide properties -- Sulfur is a natural biocide - it helps to prevent the growth of bacteria and fungus in stored diesel fuel. Microbes simply don't like to be around sulfur (then again, neither would we).  Removing 98% of the sulfur as they do, takes away much of what prevents or slows the growth of existing microbes who otherwise would love to grow and thrive and feed off parts of the diesel fuel, provided there's water present in the tank (which there usually is).  Water itself is another issue for diesel fuel. It acts differently in ULSD than in higher-sulfur version of diesel, causing greater problems in the engine, damaging injectors, and, of course, helps the fuel harbor microbes.

2) It lacks lubricity. ULSD is a very dry fuel, which means that it has a very low amount of lubricating properties. Removing the sulfur contributes to this, as hydrotreating destroys some of the essential organic parts of the diesel that otherwise would provide lubrication in the fuel. This lack of lubricity can cause premature failure of fuel pumps and injectors that normally rely on the diesel fuel for lubrication.

3) Poor Cold Flow properties—the process that refineries use to remove sulfur from diesel not only raises the fuel cloud point (the temperature at which the paraffin in the fuel changes from a liquid to a solid wax), but also can significantly lower the aromatic content of the fuel. As a result, when the paraffin changes to solid wax, the crystals are less likely to remain suspended or dissolved in the fuel. Instead, the wax crystals tend to precipitate out (they drop out faster the colder it gets) and accumulate in the fuel and in the bottom of the tank. As more crystals drop out, they stick together and get bigger. The solid wax crystals are then drawn into the fuel filter as soon as the pump system is activated, quickly plugging the fuel filter and shutting down the engine.

All of these issues can be addressed through cost-effective additization. For more information on supplementing your ULSD fuel to offset these down sides, please contact us.

Check out this related post:

Most Common Diesel Fuel Problems

This post was published on October 24, 2012 and was updated on January 22, 2016.

Topics: Lubrication, Diesel, Heavy Trucks and Equipment