Marine fuels were traditionally classified after their kinematic viscosity. This is a mostly valid criteria for the quality of the oil as long as the oil is made only from atmospheric distillation. Marine fuels are quoted on the international bunker markets with their maximum viscosity (which is set by the ISO 8217 standard – see below) due to the fact that marine engines are designed to use different viscosities of fuel. The unit of viscosity used is the Centistoke and the fuels most frequently quoted are listed below in order of cost, the least expensive first-
- IFO 380: Intermediate fuel oil with a maximum viscosity of 380 Centistokes/500 C
- IFO 180: Intermediate fuel oil with a maximum viscosity of 180 Centistokes/500 C
- LS 380: Low-sulphur (<1.5%) intermediate fuel oil with a maximum viscosity of 380 Centistokes/500 C
- LS 180: Low-sulphur (<1.5%) intermediate fuel oil with a maximum viscosity of 180 Centistokes/500 C
- MDO: Marine diesel oil.
- MGO: Marine gasoil.
The density is also an important parameter for fuel oils since marine fuels are cleaned by centrifugal type separators before use to remove water and dirt from the oil. Since the separators use centrifugal force, the oil must have a density which is sufficiently different from water. Conventional type separators of purifier type have a maximum density limit of 991 kg/m3/150 C ; with modern High Density type separators it’s possible to clean fuel oils with a maximum density of 1010 kg/m3/150 C.
Please find below the ISO specifications of Marine Fuel (Distillates and Residual)
MARINE DISTILLATE FUELS
| Parameter | Unit | Limit | DMX | DMA | DMZ | DMB |
| Viscosity at 40°C | mm²/s | Max | 5.500 | 6.000 | 6.000 | 11.00 |
| Viscosity at 40°C | mm²/s | Min | 1.400 | 2.000 | 3.000 | 2.000 |
| Micro Carbon Residue at 10% Residue | % m/m | Max | 0.30 | 0.30 | 0.30 | – |
| Density at 15°C | kg/m3 | Max | – | 890.0 | 890.0 | 900.0 |
| Micro Carbon Residue | % m/m | Max | – | – | – | 0.30 |
| Sulphur a | % m/m | Max | 1.00 | 1.50 | 1.50 | 2.00 |
| Water | % V/V | Max | – | – | – | 0.30b |
| Total sediment by hot filtration | % m/m | Max | – | – | – | 0.10b |
| Ash | % m/m | Max | 0.010 | 0.010 | 0.010 | 0.010 |
| Flash point | 0°C | Min | 43.0 | 60.0 | 60.0 | 60.0 |
| Pour point, Summer | 0°C | Max | 0 | 0 | 0 | 6 |
| Pour point, Winter | °C | Max | -6 | -6 | -6 | 0 |
| Cloud point | °C | Max | -16 | – | – | – |
| Calculated Cetane Index | Min | 45 | 40 | 40 | 35 | |
| Acid Number | mgKOH/g | Max | 0.5 | 0.5 | 0.5 | 0.5 |
| Oxidation stability | g/m3 | Max | 25 | 25 | 25 | 25 c |
| Lubricity, corrected wear scar diameter (wsd 1.4 at 60°C d | um | Max | 520 | 520 | 520 | 520 c |
| Hydrogen sulphide e | mg/kg | Max | 2.00 | 2.00 | 2.00 | 2.00 |
| Appearance | Clear & Bright f | b, c | ||||
| a | A sulphur limit of 1.00% m/m applies in the Emission Control Areas designated by the International Maritime Organization. As there may be local variations, the purchaser shall define the maximum sulphur content according to the relevant statutory requirements, notwithstanding the limits given in this table. | |||||
| b | If the sample is not clear and bright, total sediment by hot filtration and water test shall be required. | |||||
| c | Oxidation stability and lubricity tests are not applicable if the sample is not clear and bright. | |||||
| d | Applicable if sulphur is less than 0.050% m/m. | |||||
| e | Effective only from 1 July 2012. | |||||
| f | If the sample is dyed and not transparent, water test shall be required. The water content shall not exceed 200 mg/kg (0.02% m/m). | |||||
MARINE RESIDUAL FUELS
| Parameter | Unit | Limit | RMAa | RMB | RMD | RME | RMG | RMK | |||||
| 10 | 30 | 80 | 180 | 180 | 380 | 500 | 700 | 380 | 500 | 700 | |||
| Viscosity at 50°C | mm²/s | Max | 10.00 | 30.00 | 80.00 | 180.0 | 180.0 | 380.0 | 500.0 | 700.0 | 380.0 | 500.0 | 700.0 |
| Density at 15°C | kg/m3 | Max | 920.0 | 960.0 | 975.0 | 991.0 | 991.0 | 1010.0 | |||||
| Micro Carbon Residue | % m/m | Max | 2.50 | 10.00 | 14.00 | 15.00 | 18.00 | 20.00 | |||||
| Aluminium + Silicon | mg/kg | Max | 25 | 40 | 50 | 60 | |||||||
| Sodium | mg/kg | Max | 50 | 100 | 50 | 100 | |||||||
| Ash | % m/m | Max | 0.040 | 0.070 | 0.100 | 0.150 | |||||||
| Vanadium | mg/kg | Max | 50 | 150 | 350 | 450 | |||||||
| CCAI | – | Max | 850 | 860 | 870 | ||||||||
| Water | % V/V | Max | 0.30 | 0.50 | |||||||||
| Pour point (upper) b, Summer | °C | Max | 6 | 30 | |||||||||
| Pour point (upper) b, Winter | °C | Max | 0 | 30 | |||||||||
| Flash point | °C | Min | 60.0 | ||||||||||
| Sulphur c | % m/m | Max | Statutory requirements | ||||||||||
| Total Sediment, aged | % m/m | Max | 0.10 | ||||||||||
| Acid Number e | mgKOH/g | Max | 2.5 | ||||||||||
| Used lubricating oils (ULO):Calcium and Zinc; or Calcium and Phosphorus | mg/kg | – | The fuel shall be free from ULO, and shall be considered to contain ULO when either one of the following conditions is met:Calcium > 30 and zinc >15; or Calcium > 30 and phosphorus > 15. | ||||||||||
| Hydrogen sulphide d | mg/kg | Max | 2.00 | ||||||||||
| a | This residual marine fuel grade is formerly DMC distillate under ISO 8217:2005. | ||||||||||||
| b | Purchasers shall ensure that this pour point is suitable for the equipment on board, especially in cold climates. | ||||||||||||
| c | The purchaser shall define the maximum sulphur content according to the relevant statutory requirements. | ||||||||||||
| d | Effective only from 1 July 2012. | ||||||||||||
| e | Strong acids are not acceptable, even at levels not detectable by the standard test methods for SAN. As acid numbers below the values stated in the table do not guarantee that the fuels are free from problems associated with the presence of acidic compounds, it is the responsibility of the supplier and the purchaser to agree upon an acceptable acid number. | ||||||||||||