There are separate pipe connections for the main fuel oil and pilot fuel oil. Main fuel oil can be Marine
Diesel Fuel (MDF) or Heavy Fuel Oil (HFO). Pilot fuel oil is always MDF and the pilot fuel system is in operation
in both gas- and diesel mode operation.
A pressure control valve in the main fuel oil return line on the engine maintains desired pressure before the
injection pumps.
Leak fuel system
Clean leak fuel from the injection valves and the injection pumps is collected on the engine and drained by
gravity through a clean leak fuel connection. The clean leak fuel can be re-used without separation. The
quantity of clean leak fuel is given in chapter Technical data.
Other possible leak fuel and spilled water and oil is separately drained from the hot-box through dirty fuel
oil connections and it shall be led to a sludge tank.
6.4.2 External fuel oil system
The design of the external fuel system may vary from ship to ship, but every system should provide well
cleaned fuel of correct viscosity and pressure to each engine. Temperature control is required to maintain
stable and correct viscosity of the fuel before the injection pumps (see Technical data). Sufficient circulation
through every engine connected to the same circuit must be ensured in all operating conditions.
The fuel treatment system should comprise at least one settling tank and two separators. Correct dimen-
sioning of HFO separators is of greatest importance, and therefore the recommendations of the separator
manufacturer must be closely followed. Poorly centrifuged fuel is harmful to the engine and a high content
of water may also damage the fuel feed system.
Injection pumps generate pressure pulses into the fuel feed and return piping. The fuel pipes between the
feed unit and the engine must be properly clamped to rigid structures. The distance between the fixing
points should be at close distance next to the engine. See chapter Piping design, treatment and installation.
A connection for compressed air should be provided before the engine, together with a drain from the fuel
return line to the clean leakage fuel or overflow tank. With this arrangement it is possible to blow out fuel
from the engine prior to maintenance work, to avoid spilling.
NOTE!
In multiple engine installations, where several engines are connected to the same fuel feed circuit,
it must be possible to close the fuel supply and return lines connected to the engine individually.
This is a SOLAS requirement. It is further stipulated that the means of isolation shall not affect
the operation of the other engines, and it shall be possible to close the fuel lines from a position
that is not rendered inaccessible due to fire on any of the engines.
Fuel heating requirements HFO
Heating is required for:
•
Bunker tanks, settling tanks, day tanks
•
Pipes (trace heating)
•
Separators
•
Fuel feeder/booster units
To enable pumping the temperature of bunker tanks must always be maintained 5...10°C above the pour
point, typically at 40...50°C. The heating coils can be designed for a temperature of 60°C.
The tank heating capacity is determined by the heat loss from the bunker tank and the desired temperature
increase rate.
Product Guide Wärtsilä 34DF - 3/2012
51
Product Guide
6. Fuel System
