Tier II fuel optimisation
NO
x
regulations place a limit on the SFOC on
two-stroke engines. In general, NO
x
emissions will
increase if SFOC is decreased and vice versa. In
the standard configuration, MAN B&W engines are
optimised close to the IMO NO
x
limit and, there-
fore, NO
x
emissions may not be further increased.
The IMO NO
x
limit is given as a weighted average
of the NO
x
emission at 25, 50, 75 and 100% load.
This relationship can be utilised to tilt the SFOC
profile over the load range. This means that SFOC
can be reduced at part load or low load at the
expense of a higher SFOC in the high-load range
without exceeding the IMO NO
x
limit.
Optimisation of SFOC in the part-load (50-85%)
or low-load (25-70%) range requires selection of a
tuning method:
• ECT: Engine Control Tuning
• VT: Variable Turbine Area
• EGB: Exhaust Gas Bypass
• HPT: High Pressure Tuning (only for ME-C)
Each tuning method makes it possible to optimise
the fuel consumption when normally operating at
low loads, while maintaining the possibility of op-
erating at high load when needed.
The tuning methods are available for all SMCR in
the specific engine layout diagram but they can-
not be combined. The specific SFOC reduction
potential of each tuning method together with
full rated (L
1
/L
3
) and maximum derated (L
2
/L
4
) is
shown in Section 1.03.
For engine types 40 and smaller, as well as for
larger types with conventional turbochargers, only
high-load optimisation is applicable.
In general, data in this project guide is based on
high-load optimisation unless explicitly noted. For
part- and low-load optimisation, calculations can
be made in the CEAS application described in
Section 20.02.
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