Fuel Terms

Fuel Terms Description Effects
API Gravity A scale used to measure fuel weight Heavy fuel is hard to burn and has a low API.
Light fuel has less heat and less mpg performances, and has high API
Ash Content Non-Combustible material High ash means increased wear, more smoke, lost fuel
BS & W Bottom Sediment and Water Content Non-usable material in fuel.
BTU The quantity of heat required to raise the temperature of one pound of water by one degree Measure of fuel’s energy output.
Cetane Ignition Quality (Startability) Low cetane means poor starting.
High cetane means good starting.
Cloud Point Wax Formation Temperature
(Crystals form)
Fuel at cloud point will flow but will have paraffin wax crystals suspended in fuel. This may plug filters and lines.
Carbon Residue
On 10% Bottoms
Measure of fuel’s tendency to form injector deposits. High percent means injectors stick, Increase wear, Tip deposits.
Distillation Boiling range/lab test
(Vapor temperatures)
EP End Point Low EP means less horse-power.
High EP means more smoke, more deposits, more wear.
Flash Point Lab test of fuel vapor flame point Low Flash Point means probable blending with lighter products (handling danger).
Hydrogen/Carbon Ratio Measure of fuel’s major components. Hydrogen and carbon content is used to determine the fuels BTU content (fuel economy) Will tell the ultimate MPG the fuel will deliver when used.
IBP Initial Boiling Point Low IBP means lighter fuel.
High IBP means hard to burn
10% Vaporized
50% Vaporized
90% Vaporized
Same as above
Same as above
Same as above
Lubricity Measure of fuel’s lubricity properties Lack of proper lubrication will increase fuel pump and system wear
Microbial Activity
Fungus or Bacteria spores or growth in fuel Microbial activity causes fuel filter plugging, injector fouling, system deposits, tank and line corrosion, loss of usable fuel, lower mpg, more smoke, lower power, poor idling
Oxidation Stability Free Carbon formation in fuel due to incompatibility High test number means unstable fuel, engine deposits, system deposits, increased smoke, low power
Particulate Content
Solid contaminants present in fuel Higher amounts result in fuel system deposits, filter fouling, increased smoke, and loss of usable fuel.
Examples: Rust, Dirt, and other foreign materials.
Pour Point Jell Temperature (Solid Fuel) Fuel at pour point temperatures will not flow through lines or filters.
Solid in tanks
Recovery and Residue A lab test to determine maximum usable fuel content Recovery is a lab measurement of usable fuel. Residue is a lab measurement of unusable fuel.
Sulfur Content Fuel contaminant which is a major element in system corrosion and fuel acidity High sulfur means increased wear, more deposits, oil contamination, more smoke
Trace Metals Contamination of fuel by small amounts of metal particles present in crude oil Higher amounts mean more deposits, increased wear, decreased fuel stability, increased ash.
Viscosity Measure of Fuel Thickness Low viscosity can cause injector leaks
and more wear.
High viscosity is hard to burn and gives poor injector spray.