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110 Third IMO GHG Study 2014
Table 50 – Specific fuel oil consumption (SFOC baseline ) of gas turbines, boiler and auxiliary engines used in
this study as the basis to estimate dependency of SFOC as a function of load. Unit is grams of fuel used per
power unit (g/kWh) (IVL, 2004)
Engine type HFO MDO/MGO HSD
Gas turbine 305 300 225
Steam boiler 305 300 205
Auxiliary
engine
225 225 195
The values in Table 49 and Table 50 represent the lowest point in the SFOC/load curve illustrated in Figure 72.
In this study each MDO engine is assumed to maintain a parabolic dependency on engine load, which has
been applied to SSD/MSD/HSD engines. This approach is described further in Jalkanen et al. (2012). The
changes of SFOC as a function of engine load are computed using the base values in Table 49 and a parabolic
representation of changes over the whole engine load range.
SFOC(load) = SFOC base × (0.455 × load 2 - 0.71 × load + 1.28) eq. (3)
In equation (3), engine load range (0–1) adjusts the base value of SFOC and describes the SFOC as a function
of the engine load. This provides a mechanism that will increase SFOC on low engine loads (see Table 49)
and allow the energy-based (grams of emissions per grams of fuel) and power-based (grams of emissions per
kWh used) emissions factors to be linked. Different curves are used for SSD, MSD and HSD, depending on the
values in Table 49, but all diesel engines use identical load dependency across the whole load range (0–100%)
in this study. The default engine tuning is assumed (SFOC lowest at 80% engine load) for all diesel engines
because it was not possible to determine the low load optimizations from the IHS Fairplay data.
Figure 73: Impact of engine load on brake-specific fuel consumption of various selected SSD,
MSD and HSD engines (emissions factors by engine type)
Figure 73 illustrates the change of SFOC as a function of engine load for a large two-stroke engine (31,620 kW,
MAN 6S90MC-C8), two medium-size four-stroke engines (6,000 kW, Wärtsilä 6L46; 6,000 kW, MaK M43C)
and a small four-stroke engine (1,700 kW, CAT 3512C HD). The methodology used in this study allows SFOC
changes of approximately 28% above the optimum engine load range.
Load dependency of SFOC in the case of a gas turbine
There is only a limited amount of information available about the load dependency and fuel economy of gas
turbines. In this study, gas turbine SFOC load dependency was not modelled.
SFOC of auxiliary boilers
In this study, a constant value of 305 g/kWh SFOC was used for auxiliary boilers.