The following information describes the basic fuel characteristics and their relation to engine performance.
– Cetane Number: Index of ignition quality determined by comparing with fuels used as standards
for high and low cetane numbers. The higher the cetane number is the shorter the ignition delay
period which affects warm-up, combustion, cold start and exhaust smoke density.
– Sulfur: Sulfur is an element that occurs naturally in all crude oils, and when burned in the
combustion chamber, can form oxides of sulfur. These can react with water vapor to create
sulfuric acid, which can cause severe engine damage. High sulfur content requires usage of high
Total Base Number (TBN) oils or shortening of the oil change periods.
– Gravity: An index of weight of a measured volume of fuel. Lower American Petroleum Institute
(API) ratings indicate heavier fuel containing greater heat content.
– Viscosity: A time measure to resistance of flow. High viscosities cause poor fuel atomization
thereby decreasing combustion efficiency. Low viscosity may not provide adequate lubrication to
fuel system components.
– Distillation: This involves heating crude to relatively high temperatures. Vapor drawn at
various temperatures produce fuels of different types. Lighter fuels, such as gasoline, are
drawn off first and heavier fuels last. It has an influence on viscosity of the fuel and the
BTU content, which affects exhaust and smoke, starting and power output.
– Flash Point: Lowest temperature at which fuel will give off sufficient vapor to ignite when
flame is applied.
– Pour Point: Is the temperature which is 3ยฐC (5ยฐF) above the temperature where the fuel just
fails to flow or turns solid.
– Cloud Point: The temperature at which a cloud or a haze appears in the fuel. This will happen
when the temperature falls below the melting point of waxes or paraffins that occur naturally
in petroleum products.
– Water and Sediment: Percentage by volume of water and foreign material removed by centrifuging.
– Carbon Residue: Percentage by weight of dry carbon remaining when fuel is burned until no
liquid remains.
– Ash: Percentage by weight of dirt, dust, sand, and other foreign matter remaining after
combustion.
– Corrosion: A polished copper strip is immersed in fuel for three hours at 50ยฐC (122ยฐF).
Fuel imparting more than slight discoloration is rejected.