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Challenges in Fuel Filtration

Challenges in the fuel filtration industry continue to grow. Changes in fuel and increased fuel efficiency demands persist complicating an
already difficult task. Fuel cleanliness demands are not being met. We all want cleaner air and more efficient engines, but the consequences require developing higher performance filtration equipment and fuel quality management systems that address the complex nature of the problems.

HDS removes sulfur from petroleum products as well as lowering oxidation stability. As a result, fuels tend to have a shorter shelf life. They are also dryer requiring special additives. This is especially true of diesel fuel. In order to meet the lubricity requirements and protect equipment, additives are blended with diesel. These additives increase the surfactancy of the product changing the stability of water suspended in the fuel or interfacial tension (IFT). IFT is the relationship between water and fuel. The lower the IFT, the more difficult it is to remove water from fuel. The lower the IFT, the smaller the water droplets suspended in the fuel become. The higher the IFT, the larger the water droplets become. Larger droplets are easier to remove from fuel. If the IFT is too lower, water separation can be almost impossible.

Lubricity additives are not the only surfactants creating problems. Many of the aftermarket products sold have surfactant properties. If added to fuel, filtration becomes more difficult. This includes a host of biocides and fuel quality additives. Emulsifiers encapsulate water droplets and allow them to pass through the fuel system while demulsifiers cause water to fall out of fuel and make separation easier. If there is a need to correct for fuel quality issues, it is always best to introduce additives after filtration is completed and testing confirms the need.

Biofuels introduce unique challenges to fuel filtration. Both ethanol and biodiesel require special treatment. Because they are more water soluble than conventional fuels, water problems are prevalent and more difficult to correct. Water droplets in biodiesel are believed to be smaller and better distributed because of the surfactant nature of the fuel. Ethanol actually forms a bond with water and will draw the water into the fuel until it reaches saturation at which point the water and most of the ethanol drop out of the fuel to form a separate layer in the bottom of the tank. This phase separation renders the fuel out of spec requiring additional actions after water removal and filtration have been completed.

In many areas, up to 5% biodiesel can be added to ULSD without notice to the end user. Cross contamination is also a problem. Ethanol is often found in diesel fuel as a result of switch loading. The combination of these when water is present make filtration a more difficult task. Understanding the challenges helps to identify the potential pitfalls in filtration. Creating new and better methods of filtration to address the issues require integrated features and flexible approaches in the field. Innovative technologies and designs to meet the demand for clean fuel will continue to be a priority.