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MAN B&W 7.01
Pressur<strong>is</strong>ed Fuel Oil System
The system <strong>is</strong> so arranged that both diesel oil and
heavy fuel oil can be used, see figure 7.0 .0 .
From the service tank the fuel <strong>is</strong> led to an electrically
driven supply pump by means of which a
pressure of approximately 4 bar can be maintained
in the low pressure part of the fuel circulating
system, thus avoiding gasification of the fuel
in the venting box in the temperature ranges applied.
The venting box <strong>is</strong> connected to the service tank
via an automatic deaerating valve, which will release
any gases present, but will retain liquids.
From the low pressure part of the fuel system the
fuel oil <strong>is</strong> led to an electrically�driven circulating
pump, which pumps the fuel oil through a heater
and a full flow filter situated immediately before
the inlet to the engine.
The fuel injection <strong>is</strong> performed by the electronically
controlled pressure booster located on the
Hydraulic Cylinder Unit (HCU), one per cylinder,
which also contains the actuator for the electronic
exhaust valve activation.
The Cylinder Control Units (CCU) of the Engine
Control System (described in Chapter 6.0 ) calculate
the timing of the fuel injection and the exhaust
valve activation.
To ensure ample filling of the HCU, the capacity of
the electrically�driven circulating pump <strong>is</strong> higher
than the amount of fuel consumed by the diesel
engine. Surplus fuel oil <strong>is</strong> recirculated from the engine
through the venting box.
To ensure a constant fuel pressure to the fuel
injection pumps during all engine loads, a spring
loaded overflow valve <strong>is</strong> inserted in the fuel oil
system on the engine.
The fuel oil pressure measured on the engine (at
fuel pump level) should be 7�8 bar, equivalent to a
circulating pump pressure of 0 bar.
Fuel considerations
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When the engine <strong>is</strong> stopped, the circulating
pump will continue to circulate heated heavy fuel
through the fuel oil system on the engine, thereby
keeping the fuel pumps heated and the fuel valves
deaerated. <strong>Th<strong>is</strong></strong> automatic circulation of preheated
fuel during engine standstill <strong>is</strong> the background for
our recommendation:
Constant operation on heavy fuel
In addition, if th<strong>is</strong> recommendation was not followed,
there would be a latent r<strong>is</strong>k of diesel oil
and heavy fuels of marginal quality forming incompatible
blends during fuel change over or
when operating in areas with restrictions on sulpher
content in fuel oil due to exhaust gas em<strong>is</strong>sion
control.
In special circumstances a change�over to diesel
oil may become necessary – and th<strong>is</strong> can be performed
at any time, even when the engine <strong>is</strong> not
running. Such a change�over may become necessary
if, for instance, the vessel <strong>is</strong> expected to be
inactive for a prolonged period with cold engine
e.g. due to:
• docking
• stop for more than five days
• major repairs of the fuel system, etc.
The built�on overflow valves, if any, at the supply
pumps are to be adjusted to 5 bar, whereas the
external bypass valve <strong>is</strong> adjusted to 4 bar. The
pipes between the tanks and the supply pumps
shall have minimum 50% larger passage area
than the pipe between the supply pump and the
circulating pump.
If the fuel oil pipe ‘X’ at inlet to engine <strong>is</strong> made as
a straight line immediately at the end of the engine,
it will be necessary to mount an expansion
joint. If the connection <strong>is</strong> made as indicated, with
a bend immediately at the end of the engine, no
expansion joint <strong>is</strong> required.
MAN B&W ME/ME-B/ME�C/ME�GI engines 198 42 28�2.6
MAN Diesel