Third IMO Greenhouse Gas Study 2014

108 Third IMO GHG Study 2014
N 2 O baseline
Emissions factors for N 2 O and LNG were taken from the EPA 2014 report on GHGs and Kunz & Gorse
(2013), respectively. The LNG N 2 O EF baseline was converted from g/mmBTU to g/kWh assuming 38% engine
efficiency, and then converted to grams of N 2 O per gram of fuel using an SFOC of 166g fuel/kWh. From these
sources, the N 2 O EF baseline factors presented in Table 47 were used.
Table 47 – N 2 O baseline emissions factors
Eng speed/type Fuel type ME EF baseline (kg/tonne fuel) Aux eng EF baseline (kg/tonne fuel) Reference
SSD
MSD
HSD
HFO
HFO
HFO
0.16
0.16
na
na
0.16
0.16
EPA, 2014
EPA, 2014
EPA, 2014
Otto LNG 0.11 0.11 Kunz & Gorse, 2013
GT HFO 0.16 na EPA, 2014
STM HFO 0.16 na EPA, 2014
It should be noted that, similar to NO x , N 2 O emissions are unaffected by fuel sulphur content but do change
slightly between HFO and distillate fuels. For further information on specific emissions factors, FCFs and
references, see Annex 6.
NMVOC baseline
Emissions factors for non-methane volatile organic compounds (NMVOC) were taken from ENTEC (2002)
study and for LNG from Kristensen (2012) report. The LNG NMVOC emissions factor was conservatively
assumed to be the same as the hydrocarbon emissions factor. From these sources, the NMVOC EF baseline
factors presented in Table 48 were used for this study. It should be noted that NMVOCs and non-methane
hydrocarbons have the same emissions factors.
Table 48 – NMVOC baseline emissions factors
Eng speed/type Fuel type ME EF baseline (kg/tonne fuel) Aux eng EF baseline (kg/tonne fuel) Reference
SSD
MSD
HSD
HFO
HFO
HFO
3.08
2.33
na
na
1.76
1.76
ENTEC, 2002
ENTEC, 2002
ENTEC, 2002
Otto LNG 3.01 3.01 Kristensen, 2012
GT HFO 0.33 na ENTEC, 2002
STM HFO 0.33 na ENTEC, 2002
NMVOC emissions are also unaffected by the sulphur content of the fuel burned and are the same for HFO
and distillates. For further information on specific emissions factors and references, see Annex 6.
SFOC variability with load
Marine diesel engines have been optimized to work within a designated load range, in which fuel economy
and engine emissions are balanced. Optimizing for fuel economy will lead to higher NO x emissions and
vice versa; MARPOL Annex VI NO x emission Tiers thus indirectly regulate the specific fuel oil consumption
(SFOC) range of the engine. Using an MDO outside the optimum load range (usually 85%–100% MCR) will
lead to higher specific fuel oil consumption per power unit (g/kWh) unless the electronic engine control unit
can adjust the engine accordingly (valve timing, fuel injection). This is possible to achieve with modern smart
engine control units by changing the engine control programming, but for older mechanical set-ups greater
effort may be required from the engine manufacturer. For slow steaming purposes, the optimum working load
range of a diesel engine can be adjusted to be lower than the default load range.