6.2 Operating principles
Wärtsilä 46DF engines are usually installed for dual fuel operation meaning the engine can be
run either in gas or diesel operating mode. The operating mode can be changed while the
engine is running, within certain limits, without interruption of power generation. If the gas
supply would fail, the engine will automatically transfer to diesel mode operation (MDF).
6.2.1 Gas mode operation
In gas operating mode the main fuel is natural gas which is injected into the engine at a low
pressure. The gas is ignited by injecting a small amount of pilot diesel fuel (MDF). Gas and
pilot fuel injection are solenoid operated and electronically controlled common rail systems.
Instant transfer from any load is possible to Diesel Mode and Back-up Mode. In case of failure
in pilot fuel system, engine safety system will change operating mode instantly to Back-up
Mode
6.2.2 Diesel mode operation
In diesel operating mode the engine operates only on liquid fuel oil. MDF or HFO is used as
fuel with a conventional fuel injection system. The MDF pilot injection is always active.
Transfer to Gas Mode is possible under 80% engine load. In case of failure in pilot fuel system,
engine safety system will change operating mode instantly to Back-up Mode.
6.2.3 Backup mode operation
The engine control and safety system or the blackout detection system can in some situations
transfer the engine to backup mode operation. In this mode the MDF pilot injection system is
not active and operation longer than 30 minutes (with HFO) or 10 hours (with MDF) may cause
clogging of the pilot fuel injection nozzles.
Transfer to Gas or to Diesel Mode is not possible. If transfer from Backup mode to Diesel or
to Gas mode is desired, the engine must be stopped in order to allow engine to perform pilot
system diagnostic check, which is performed as a part of engine start sequence.
Fig 6-1 Transfer Gas/Diesel
6-10 DBAD209883
Wärtsilä 46DF Product Guide6. Fuel System
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