The diesel fuel you buy is always changing in both chemical content and quality. Since October 1993, the refining process for diesel fuel was changed to include a process called Hydrotreating. This process significantly reduces the sulfur and aromatic content of the fuel, making the product we buy far less stable than the fuel we bought a decade ago. It also can introduce potentially harmful amounts of water into the diesel fuel that may end up in users’ tanks across the country.

Since October 15, 2006, the government has required Ultra Low Diesel for *on-road use. This means the hydrotreating process has been further intensified to remove the equivalent of another 80 percent of the sulfur. This has further exacerbated an already serious water problem and resulted in fuel with reduced lubricity. The benefits of a cleaner environment are achieved but with additional costs to the diesel user as today’s fuels are more susceptible to water and do not provide the traditionally high level of lubrication to critical engine components such as injectors and fuel pumps.

Water in fuel can be in several forms: free water or heavy water is usually found at the bottom of tanks. Emulsified or suspended water gives the fuel a cloudy appearance. In addition to higher water content at the pump, additional water is formed by year round condensation. Water separators help with the heavy water but fall short of solving the problem of emulsion.

Each time a diesel engine operates, regardless of the time the year, condensation forms. When the water reaches the diesel fuel injection system, the effects can be ruinous. The injectors depend on the diesel fuel for lubrication. Water further reduces lubricity as it washes away the thin oily film coating the injectors’ Micro-Machined surfaces, causing enlargements of the spray holes, eroding the injector tips, and destruction of the spray pattern. In a precision part like a fuel injection pump, this damage can be enormously expensive and result in equipment downtime waiting for repair.

* Does not yet apply to train locomotives, marine, or off road uses until December 1, 2010. In 2010, the sulfur concentrations allowed in diesel fuel for generators and other non-highway applications will migrate to the current on road standard for diesel fuel. This is considered ultra low sulfur diesel (ULSD) and has an allowable concentration of 15 ppm sulfur.