The Power Plant Laboratory Viscometer reports viscosity in cSt at 40, 50 and 100°C.
Viscosity is usually expressed as kinematic viscosity, which is measured in Stokes. Kinematic viscosity is the quotient of the dynamic or absolute viscosity divided by the density, with both expressed at the same temperature.
As one Stoke is a large unit, kinematic viscosity is usually measured in - (cSt) - (one cSt = 1mm 2 /s). Sometimes viscosity is quoted in Engler, Saybolt or even Redwood and the conversion is shown in the appendices.
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Info Centre >> Fuel and Lube Oil Technical Manual >> 2. Fuel Oil - Characteristics >> 2.3 Viscosity
Dynamic Viscosity
Dynamic viscosity is a property of the internal resistance of a fluid that opposes the motion of adjacent layers.
The unit of measure of this resistance in SI units is a Pascal.s. Frequently the unit of a Poise is used, where 1 Pascal.s = 10 Poise. It should be noted that dynamic viscosity is also referred to as absolute viscosity.
For distillate fuels the reference temperature used is 40°C. However for residual fuels 50°C is still commonly used, even though the most common specification (ISO 8217) has a reference temperature of 100°C.
Temperature and Viscosity Relationship
Each fuel has its own temperature / viscosity relationship and this is shown for a typical oil.
Oil suppliers publish temperature / viscosity charts, however it should be appreciated that these charts are based on average data of a large number of representative fuels. As the relationship depends on its crude oil source and the refinery processes employed, estimations made from the charts cannot be regarded as precise. In general the difference is small for the lower viscosity fuels but it becomes wider as the viscosity of the fuel increases.
The viscosity determines the storage and handling temperature if the pour point of the fuel is low. Typical maximum fuel viscosity for transfer is 800 - 1000 cSt. The temperature for atomisation of the fuel also depends on viscosity.
Below: Viscosity Temperature Chart
