Marine diesel oil

Marine Diesel Oil (MDO) is a type of fuel oil and is a blend of gasoil and heavy fuel oil, with less gasoil than intermediate fuel oil used in the maritime field. Marine Diesel Oil is also called "Distillate Marine Diesel". MDO is widely used by medium speed and medium/high speed marine diesel engines. It is also used in the larger slow speed and medium speed propulsion engine which normally burn residual fuel. Those fuels resulting from a catalytic cracking/visbreaking refinery. Marine diesel oil has been condemned for its nimiety of sulfur, so many countries and organizations established regulations and laws on MDO use. Due to its lower price compared to more refined fuel, MDO is favored particularly by shipping industry.

ISO 8217 of the International Standards Organization (ISO) is the primary standard of MDO.

Marine fuels range in viscosity from less than one centistoke (see viscosity) (cSt) to about 700 cSt at 50°C (122°F). (1 cSt = 1 mm2/s.) And higher viscosity grades are preheated during use to bring their viscosity into the range suitable for fuel injection (8 to 27 cSt). But MDO does not need to be preheated before using. According to Chevron, MDO has a sulfur limit varies from 1 to 4.5 percent by mass for different grades and Sulfur Emission Control Areas (SECAs).

MDO is made from a catalytic cracking/visbreaking refinery. The catalytic cracking operation breaks large molecules into small molecules. It happens in high temperature and with appropriate catalyst.Visbreaking is a process that turn the bottom product of the vacuum unit, which has extremely high viscosity, into lower viscosity, marketable product. In visbreaking, a relatively mild thermal cracking operation is performed. And the amount of cracking is limited by the overruling requirement to safeguard the heavy fuel stability.

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