Wartsila ?31DF Series, Product Manual, Page: 102 / 216

Value Unit Property
Bar(g) 8 ± 1.75 Pressure before
purging value
The following guidelines apply for purging the fuel gas pipe between GVU and engine:
Required inert gas amount: 5 times the total volume of gas pipes that are to be purged 1.
Flow: Standard purging time is 20 seconds; thus flow should be 5 times the gas pipe volume
per 20 seconds 2.
The following guidelines apply for flushing the engine crankcase with inert gas:
Max filling flow: 100l/min/cylinder 1.
A sniffer is recommended to be installed in the crankcase breather pipe in order to indicate
when the crankcase have been flushed from toxic gases. 2.
Crankcase size: 0.9 m3/crank (v-engine) 3.
6.3.1.8 Gas feed pressure
The required fuel gas feed pressure depends on the expected minimum lower heating value
(LHV) of the fuel gas, as well as the pressure losses in the feed system to the engine. The LHV
of the fuel gas has to be above 28 MJ/m
3
at 0°C and 101.3 kPa. For pressure requirements,
see section "Technical Data" and chapter "1.3.2 Output limitations due to gas feed pressure
and lower heating value"
For pressure requirements, see chapters Technical Data and Output limitations due to methane
number.
●
The pressure losses in the gas feed system to engine has to be added to get the required
gas pressure.
●
A pressure drop of 120 kPa over the GVU is a typical value that can be used as guidance.
●
The required gas pressure to the engine depends on the engine load. This is regulated by
the GVU.
6.4 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 high pressure 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 dimensioning 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.
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.
6-18 DBAE248994
Wärtsilä 31DF Product Guide 6. Fuel Oil System