D6 is a type of residual fuel, mainly used in
power plants and larger ships. The fuel requires
to be preheated before it can be used. It is not
possible to use it in smaller engines or
vessels/vehicles where it is not possible to
pre-heat it. D6 is its name in the USA. In other
parts of the world it has other names.
Residual means the material remaining after the
more valuable cuts of crude oil have boiled off.
The residue may contain various undesirable
impurities including 2 percent water and
one-half percent mineral soil. D6 fuel is also
known as residual fuel oil (RFO), by the Navy
specification of Bunker C, or by the Pacific
Specification of PS-400.
Recent changes in fuel quality regulation now
require further refining of the D6 in order to
remove the sulfur, which leads to a higher cost.
Despite this recent change, D6 is still less
useful because of its viscosity as well as that
it needs to be pre-heated before it can be used
and contains high amounts of pollutants, such as
sulfur. Since it requires pre-heating, it cannot
be used in small ships or boats or cars. However
large ships and power plants can use the
residual fuel oil.