Lubricity Impact of Low and Ultra-Low Sulfur Fuels
Sep 25th, 2006
When the low and ultra-low sulfur program was introduced questions were not raised regarding the adequacy of lubricity, "naturally", present in traditionally manufactured diesel fuel.
This previous, unrestricted diesel fuel manufacturing method, which contained a higher sulfur content, resulted in providing sufficient levels of lubricity. This natural level of lubricity prevented and reduced engine wear on fuel surface components, such as, fuel tanks, lines, fuel pumps, injectors, valve train, cylinder liners, rings, and other combustion chamber components. This type of lubricity is believed to be a polar compound absorbed into alloys resulting in the formation of a protective, "film"? coating and therefore reducing excessive friction.
When diesel fuel is produced using more intensive hydrotreating processes, as those used in the production of low and ultra-low sulfur fuel, a large portion of the lubricating, polar compound is "removed". It is believed that the sulfur present in the feedstock, the liquid blend components prior to hydroprocessing, "binds" itself to the polar compound. This binding process removes sulfur from the fuel while also removing a substantial portion of the lubricating properties of the fuel. A similar "separation"? is also believed to take place during the process which reduces the aromatics content of diesel.
In other words, reducing the sulfur and aromatics content of diesel and jet fuel components will "automatically" reduce the quality of lubricity in the finished products. In all diesel and jet applications, including stationary power plants, lubricity is crucial. Adequate lubricity allows for less maintenance, long-term operation, extended engine life, and added safety of machinery. Therefore, any process, mechanical or chemical, that removes the natural lubricity of fuel will undoubtedly cause an increase in; premature fuel system failure, reduction in engine life, and an increase in the risk of "unexpected" equipment malfunction. Sufficient lubricity decreases maintenance cost but can also be crucial to proper operating safety, especially in airline, shipping, and military applications.
Tests conducted by a major oil company, on two types of fuels with ultra-low sulfur and low-aromatics, demonstrated destructive mechanical malfunctions and loss of performance at 2,000-8,000 miles. When the first type of fuel was tested, having a sulfur content of 0.001% and aromatics content of 5%, engine problems developed at 3,000-19,000 miles. When the second type of fuel was tested, with sulfur content of 0.005% and aromatics contents of 20% the results were similar to that of the first.
As of October 15, 2006, all diesel fuel on the market will have .0015% sulfur and 10% aromatic content. When comparing this new requirement to the results of the major oil company's study it is possible to see its future effects. However, when looking at the performance of unrestricted diesel fuel, having an aromatics content of 25-35% and sulfur content of about 0.20 - 0.25%, engine problems did not develop until about 100,000 miles or higher. Even at that high mileage only a slight loss of performance and wear could be seen. The tests only further supported the adverse impact of the lack of lubricity when reducing the sulfur and aromatics content in EPA PHASE III diesel fuels.