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Fuel Specifications

Unfortunately out of spec fuel is not uncommon. The most common cause is water contamination. Other causes include cross contamination, aging and sediment. Sometimes fuel arrives to the end user out of spec due to a refining, storage or transportation problems. There can be many variables contributing to bad fuel. Therefore it is important to identify when it is out of spec. With fuel markets in over 150 countries and numerous fuel grades and specifications, it would be a voluminous task to repeat them here. However, knowing your specific market and the requirements set for each fuel grade is very important.

There are some measurable factors that help narrow down fuel quality standards regardless of where you might live.

  • Octane in gasoline, while not the most important factor to fuel quality, it does have a lot to do with how an engine runs. The octane number of gasoline determines how capable a gasoline engine is able to resist knocking during combustion. If the octane is too low, an engine will knock or ping and if frequent enough, damage can happen over time. Generally, retail gasoline octane ranges from 87 to 94. Octane effects the performance of an engine. Using the engine manufacturers specified octane fuel is advisable.

  • Cetane in diesel fuel is akin to octane in gasoline. It is an indicator of combustion. If the cetane is too low then ignition may be impaired. Typically cetane ranges between 40 and 60. Over 110 countries specify a cetane of 48 or greater. Low cetane can result in poor engine power and performance. Continued use can result in engine damage.

  • Water is possibly the most damaging contaminant in fuel. Measuring fuel quality includes identifying contaminants and adulterations. While it is impossible to be 100% perfect, free water should always be removed. When water reaches its saturation point in fuel, it becomes free water. If the fuel is ethanol free or ULSD then the water drops out of the fuel and settles to the bottom where is can be removed. If the biofuel is present, a considerable amount of water could remain in suspension and damage the engine or keep it from running.

  • Acid Number of fuel is significant. Acidity in petroleum can come from organic sulfur and naphthenic acids. Acids are also a byproduct of microbial infection. A high acid level will always indicate a problem warranting further investigation.

  • Oxidation Stability concerns the stability of the fuel composition. All fuel degrade over time, however FAME degrades faster due to its lower oxidation stability. Heat, water and contaminants accelerate degradation and reduce the oxidation stability of fuel. As gasoline degrades, gums form that leave a residue fouling filters and damaging engine components. As diesel fuel breaks down it leaves solid deposits and Asphaltenes to coat and damage systems.

  • Microbial Contamination in fuel is not always evident. Once it is visibly identifiable in fuel immediate action should be taken. System and engine corrosion is a primary result of microbial contamination. Because most fuel eating microbes create acidic byproducts, acids that accelerate corrosion, microbial influenced corrosion (MIC) is an industry wide problem.