Fig 6-8 Fuel oil viscosity-temperature diagram for determining the pre-heating
temperatures of fuel oils (4V92G0071b)
Example 1: A fuel oil with a viscosity of 380 cSt (A) at 50°C (B) or 80 cSt at 80°C (C) must be
pre-heated to 115 - 130°C (D-E) before the fuel high pressure pumps, to 98°C (F) at the
separator and to minimum 40°C (G) in the bunker tanks. The fuel oil may not be pumpable
below 36°C (H).
To obtain temperatures for intermediate viscosities, draw a line from the known
viscosity/temperature point in parallel to the nearest viscosity/temperature line in the diagram.
Example 2: Known viscosity 60 cSt at 50°C (K). The following can be read along the dotted
line: viscosity at 80°C = 20 cSt, temperature at fuel high pressure pumps 74 - 87°C, separating
temperature 86°C, minimum bunker tank temperature 28°C.
6.4.3 Fuel tanks
The fuel oil is first transferred from the bunker tanks to settling tanks for initial separation of
sludge and water. After centrifuging the fuel oil is transferred to day tanks, from which fuel is
supplied to the engines.
6.4.3.1 Settling tank, HFO (1T02) and MDF (1T10)
Separate settling tanks for HFO and MDF are recommended.
6-20 DBAE248994
Wärtsilä 31DF Product Guide6. Fuel Oil System
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