Properties of Heavy Fuel Oil Used In Marine Diesel Engines
The major properties of heavy fuel oil are as follows;
Density is the relationship between mass and volume at a stated temperature, and the SI unit is Kg/m3. This gives value of 800- 1010 kg/m3 for marine heavy fuel oil.
The density of HFO is limited to 991kg/m3 to facilitate efficient centrifuging. (Centrifuges use centrifugal force to separate water from HFO, so the bigger the difference in density the greater removal of water ). However the density of HFO can be been increased to 1010kg/m3 if clarifiers are used, as water seal can be maintained during clarification. Any higher density than this will inhibit HFO water removal treatment through centrifuging.
Viscosity is a measurement of the resistant of a liquid to shear or flow and is measured in Centistokes (CST) with a quoted reference temperature. Knowing the viscosity of the heavy fuel oil is required the temperature range required for satisfactory injection at the fuel atomizer, and efficient combustion.
3. Flash Point
The flash point of the liquid is the lowest temperature at which sufficient vapor is given to produce a flash on application of a flame under specified test conditions.
The minimum flash point for marine fuels in the machinery space of merchant ship is governed by the IMO; being set at 60o C to minimize fire risk during normal storage and handling.
4. Pour point.
The pour point is the lowest temperature at which a marine fuel oil can be handled without excessive amounts of wax crystals forming out of solution. At a lower temperature the fuel will gel, thereby preventing flow.
5. Carbon Residue.
The carbon residue of a fuel is the tendency to form carbon deposits under high temperature condition in an inert atmosphere, and may be expressed as either Conradson Carbon Residue (CCR) or Micro Carbon Residue (MCR). The maximum limit of carbon residue content in fuel is 22 %.
Normally the level of water in the fuel is very low, since an effort is made by the supplier to deliver the fuel as dry as possible. 0.1% - 0.2 % by volume is typical. However, Water can come from a number of sources on the bunker barge and in ships bunker tanks. These include tank condensation, leakage of steam from heating coils, and bunker tank leakage. The maximum limit of water content in fuel is 1 %.
7. Ash content
The ash content is related to the amount of inorganic material in the fuel. For distillate fuel the ash content is defined as the residue remaining after all the combustible components of the oil have been burned and is negligible. It is the incombustible material which remains after the combustion, which mainly consists of the material such as vanadium, sulphur, silicon, aluminum, nickel, sodium, and iron content present in the fuel. The maximum limit of ash content in the fuel is 0.2% m/m.
8. Calorific Value (CV)
The CV of a fuel is the heat energy given out during combustion. Heavy fuel oil has a net CV of 38.9 MJ/liter and a gross CV of 41.2 MJ/liter; these values being determined by using calorimeter test equipment in a lab.
9. Specific Gravity
The specific gravity of HFO is its ratio to the density of water at a specified temperature. Bunker oil HFO ranges between 0.95-1.03
Sulphur is soluble in water therefore it cannot be removed by centrifuge treatment. However there are chemicals that can be used to lower the sulphur content in HFO.
Sulphur pre-combustion causes corrosion to the pistons and liners and contaminates the lube oil. Post combustion emits SOx to atmosphere in exhaust gases.
11. Calculated Carbon Aromaticity Index (CCAI).
This is a reference index containing a listing of the ignition standard of Heavy fuel oil. Cetane number is the equivalent reference for light fuel oil such as diesel oil.