Fuel System and Fuel Measurement - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 71

In the preparation chain, foreign matter such as liquids and solids are removed
from the fuel. For HFO and IFO fuels, a two-step preparation chain is necessary,
while for distillate fuels such as MDO and MGO, a single-step preparation chain is
sufficient. MDO and MGO are used for maneuvering in harbors or to navigate in
protected sea areas. It is usually stored in MDO and MGO bunker tanks.
4.3.2 Fuel Measurement on Ships
On ships the fuel is stored in tanks, which are arranged in the double bottom.
According to the IMO Convention ''Safety of Life at Sea'' (SOLAS), a minimum
quantity must be stored in tanks, which are not directly endangered in case of
running aground or a collision [ 48 ].
In the settling tanks, water and impurities are separated from the fuel and
drained off. The level sensors in these tanks must be robust and have high dura-
bility. From the settling tank, transfer pumps move the fuel through a pre-heater to
a daily tank to preheat the fuel. Temperature and pressure sensors control the
process and maintain a temperature in the supply tanks which is always inde-
pendent of the ambient conditions. If the fuel is too cold it must be warmed before
withdrawal from the tank. The temperature of the fuel should be adjusted in the
daily tank with a final pre-heater. The heat flow density is approximately
1Wcm -2 (3.413 BTU h -1 cm -2 , i.e., 22.014 BTU h -1 in -2 )[ 49 ].
From the pre-heater, the fuel is led to a separator to purify the fuel at the second
cleaning level. The surplus quantity is led back from the overflow of the daily tank
into the settling tank. The level in the overflow tank is continuously monitored and
attached to an alarm system. In the most cases piezoelectric sensors are used to
measure the changing fuel level [ 50 ].
From the separator, the fuel enters the two daily service tanks. One tank may be
used while the other is being filled. From the daily service tank the fuel is pumped
to the second heater by the pressure fuel pump. From the heater the HFO and IFO
fuels are passed through a viscosity meter and a regulator to the fuel filter, the flow
counter, and the engine [ 51 ].
Engines or boilers, which are operated with different fuel qualities, should be
equipped with a viscosity regulation via magnetic coupling. A connected electric
pump saves a constant volume flow independently on fuel viscosity [ 52 ].
On modern ships, there is a flow counter in the transfer pipe which is a propeller
or an oval wheel counter to determine the volume flow similar to the impeller
system. The axis of the rotation must always be installed underneath the pipe axis,
so that the analyzer chambers can be filled with fuel by gravity, depending upon
the kind of fuel. The temperature has to be high enough to guarantee optimal flow
for the continuous measurement of consumption [ 53 ].
Figure 4.10 shows the scheme of the fuel store, the pump, and the measuring
system of a ship for MDO and IFO fuels [ 54 ].