Bunker fuel or bunker crude is technically any type of fuel oil used aboard vessels. Named from the tanks on ships and in ports that it is stored in; they are bunker fuel tanks.
Since the 1980s the International Organization for Standardization (ISO) has been the accepted standard for marine fuels (bunkers). The standard is listed under number 8217, with recent updates in 2005 and 2010. The standard divides fuels into residual and distillate fuels.
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CCAI and CII are two indexes which describe the ignition quality of residual fuel oil, and CCAI is especially often calculated for marine fuels.
Despite this marine fuels are still 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 d6 fuel most frequently quoted are listed below in order of cost, the least expensive first-
* IFO 380 – Intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes
* IFO 180 – Intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes
* LS 380 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes
* LS 180 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes
* MDO – Marine diesel oil.
* MGO – Marine gasoil.