Properties of Light Diesel Oil

by Tammie Painter
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Boilers, ladders and pipes at a power plant, image by Andrei Merkulov from

Light diesel oil, or LDO, is a blend of components from the distillation process of diesel. It is used in engines with an rpm less than 750, such as boilers and furnaces. LDO is also referred to as distillate fuel or marked oil since it is marked with a coloring substance. A number of properties must meet standard requirements for a fuel to be classified as light diesel oil.

Water Content, Flash Point and Viscosity

The water content of LDO must not exceed 0.25 percent of volume. The flash point (the lowest temperature of ignition) is 66 degrees Celsius. The viscosity of LDO at 40 degrees Celsius must be a minimum of 2.5 centistrokes and a maximum of 15.7 centistrokes.

Sulfur, Sediment, Carbon Residue and Ash Content

LDO is required to have a sulphur content of less than 1.8 percent by weight. Sediment levels must be below 0.1 percent by weight. Ash content must be less than 0.02 percent by weight. LDO must contain less than 1.5 percent carbon residue.

Cetane Number

The cetane number of LDO is 45. This measure of combustion quality can be up to 100 but most premium diesels are around 60. A higher cetane number means the fuel is of higher quality.

Pour Point

The pour point is the lowest temperature that the fuel will flow. This quality is important for continued performance in the cold. The pour point for LDO is 12 degrees Celsius from November to February and 21 degrees Celsius for the rest of the year.

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