Analysis Definitions & Reference

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Analysis definitions to help identify your fuel testing needs.

API Gravity: (ASTM D1298): API Gravity is the measure of a diesel fuel’s density, or weight per volume. The higher the API Gravity, the less dense the fuel. API Gravity can provide valuable information about the fuel’s compositions and performance characteristics including power economy, low temperature properties and smoking tendencies.

Appearance, (ASTM D4176): It has long been the practice to include in fuel specifications a requirement that the fuel be clear and bright and free of visible particulate matter. However, there has been no standard method for making this determination so that practices have differed. This test method provides standard procedures for the test. This test provides a rapid pass/fail method for contamination in a distillate fuel. It also provides  a gross numerical rating of haze appearance, primarily as a communication tool.

Bio-Blend Verification, FAME,  (ASTM D-7371): By using Infra-Red Spectroscopy, this analysis is designed to verify the specific petrodiesel/biodiesel blend. (FAME).  This is a good way to ensure you are getting the product you pay for and verifying the blend is correct from your supplier.

Cetane Index (ASTM D-4737):  The cetane index measures the ignition quality of the fuel, which affects engine starting and acceleration.  Fuel with a high aromatic content usually has a lower cetane number.  The fuel supplier should know the cetane number or index of each fuel shipment.  Precombustion chamber fuel systems require a minimum cetane number of 35.  Direct injection engines require a minimum cetane number of 40 for good starting characteristics.

Cloud Point (ASTM D-2500):  The cloud point is the temperature at which the smallest observable cluster of hydrocarbon crystals first occurs, which looks like a patch of whitish or milky cloud.  This is caused by the temperature falling below the melting point of waxes or paraffins that occur naturally in petroleum products.  The cloud point of fuels is an index of the lowest temperature of their utility for certain applications, and must be below the lowest outside (ambient) temperature to prevent filters from plugging.

Cold Filter Plugging Point, (ASTM D6371): The CFPP of a fuel is suitable for estimating the lowest temperature at which a fuel will give trouble-free flow in certain fuel systems.

Distillation (ASTM D-86):  The distillation analysis quantitatively determines the boiling range characteristics of fuels, which gives information on fuel composition, properties, and behavior during storage and use. This includes the initial and final boiling points, and percent recovery, loss, and residue. These characteristics have important effects on safety and performance.  Fuel volatility affects starting, warm-up, fuel efficiency, smoke, deposit formation, and engine wear, and is a major determinant of a hydrocarbon mixture to produce potentially explosive vapors.  This analysis will give an indication of the fuel’s ability to start the engine, the power, the fuel economy emissions, and deposit formation, and is also used in calculating the Cetane Index.

Flash Point (ASTM D-93):  The flash point is the lowest temperature at which fuel vapors can be ignited when exposed to a flame, which is determined by the type of fuel and the fuel/air ratio.  It is important for safety reasons – not for engine operating characteristics

Kinematic Viscosity (ASTM D-445):  Viscosity is a measure of a liquid's resistance to flow at a specific temperature; fuels typically are measured at 40°C, and oils at 100°C.  High viscosity means the fuel is thick and does not flow easily.  Fuel with the wrong viscosity can cause engine damage.  High viscosity fuel will increase gear train, cam, and follower wear on the fuel pump assembly due to the higher injection pressure.  High viscosity fuel also atomizes less efficiently making the engine more difficult to start.  Low viscosity fuel may not provide adequate lubricity to plunger, barrels and injectors, causing excessive scuffing and seizure.  

Microbial Presence (Culture Medium):  All water and fuel offer a medium for bacterial growth.  These simple life forms live in the water and feed on the fuel.  Bacteria may be any color but is usually black, green or brown. Bacteria grow in long strings and have a slimy appearance.  Microorganisms or fungi in fuel can cause corrosion and filter plugging.

Particle Count (ISO 4406): Defines the quantity of solid particles that are measured in the fuel by an optical microscope, and the level of contamination is then reported as an ISO Code. The ISO Code simplifies the reporting as it converts the numbers of particles > 4, >6, and > 14 microns (um) into classes, or codes. Each increase into the next higher class, or code, generally indicates the doubling of contamination levels. Particulate contamination interferes with the fuels’ ability to lubricate and has a direct bearing on engine performance and reliability, such as plugging or total failure of fuel pumps, injectors, hosing, filters, and other premature system wear and failure. The higher the ISO Code, the “dirtier” the fuel.

Sulfur Content (ASTM D-5453):  Sulfur is an element, which occurs naturally in all crude oils.  Heavy fuels usually have high sulfur content.  Distillate fuels are usually lower in sulfur content because the sulfur can be reduced or eliminated during the refining process.  When diesel fuel containing sulfur is burned in an engine's combustion chamber, oxides of sulfur form and react with water vapor to form sulfuric acid.  If these acid vapors condense, they chemically attack the metal surfaces of valve guides, cylinder liners, and may affect bearings.  When fuel sulfur damage occurs, there will be very little change in engine power; however, corrosive wear will lead to excessive oil consumption and blow by. Currently in the United States the use of Ultra Low Sulfur fuels is mandatory for on and off highway applications.

Viscosity Index (ASTM D2270) is a widely used and accepted measure of the variation in kinematic viscosity due to changes in the temperature between 40 and 100°C, a higher viscosity index indicates a smaller decrease in viscosity with increasing temperature.

Water and Sediment % Volume  (ASTM D-2709):  Water and Sediment in fuel oils determined by means of centrifuge.  Water and Sediment can cause corrosion of equipment and problems in processing. Sediment can consist of item rust, scale, weld slag, dirt and other debris that often get into fuel tanks.  Settling, straining, filtration, or centrifuging can remove most sediment.  Fuels with a higher viscosity (thicker) and higher specific gravity (heavier) often have more sediment because the settling process is slower.  As sediment increases, the amount of usable energy in the fuel decreases.

Water Content, ppm (ASTM D-1744):  Determines the water content, ppm, using a Karl Fisher titration apparatus.  Water can become a contaminant if it is introduced into the fuel during shipment or is the result of condensation during storage.  There are three types of moisture in fuels: dissolved moisture (moisture in solution), free and dispersed moisture in the fuel, and free and settled moisture at the bottom of the tank.  Excessive water in fuel will cause fuel pump and injector damage in most modern fuel systems which use fuel to lubricate the pump or unit injectors.

Wear Metal Analysis, (ASTM D7455): Wear metal analysis is used as a tool to determine certain contaminates in diesel fuel including but not limited to corrosion, waste oil and gycol.

Total Acid Number, (ASTM D-974): A titration method known as potentiometric titration.  It is designed to give you the relative acidity in a feedstock. This is a good indicator of the free fatty acids present in BioDiesel as well as the presence of process acids. High acid number in fuels can have a strong solvency effect in your engine’s fuel system.


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