Third IMO Greenhouse Gas Study 2014

Inventories of emissions of GHGs and other relevant substances 111
SFOC of auxiliary engines
A constant value for auxiliary engine SFOC was used (indicated in Table 50). The load/SFOC dependency was
not used for auxiliary engines, because the engine load of operational auxiliary engines is usually adjusted by
switching multiple engines on or off. The optimum working range of auxiliary engines is thus maintained by
the crew and it is not expected to have large variability, in contrast to the main engine load.
CO 2
The power-based CO 2 emissions factors for main, auxiliary and boiler engines at slow, medium and high
speeds were taken from either ENTEC (2002) or IVL (2004) and were converted to mass-based factors using
the corresponding SFOC.
NO x
The NO x emissions factors for main and auxiliary engines at slow, medium and high speeds were assigned
according to the three IMO NO x emission Tiers defined in MARPOL Annex VI. Emissions for Tier 0 engines
(constructed before 2000) were modelled in accordance with Starcrest (2013). This approach will give an
energy-based emissions factor as a function of engine RPM. The SFOC corresponding to the energy-based
emissions factor provided a link between the energy- and fuel-based emissions factors. NO x EF for boilers
remains the same, as there are no emissions standards that apply to boiler emissions.
SO x
For all three emissions sources, SO x emissions are directly linked to the sulphur content of the fuel consumed.
For emissions estimating purposes, the typical fuel types (based on ISO 8217 definitions) include HFO, IFO,
MDO and MGO.
The emissions factor for SO x was determined directly from fuel sulphur content by assuming conversion of fuel
sulphur to gaseous SO 2 according to
EF(SO x ) = SFOC × 2 × 0.97753 × fuel_sulphur_content eq. (4)
Equation (4) includes a constant indicating that approximately 98% of the fuel sulphur will be converted to
gaseous SO 2 and that about 2% of the sulphur can be found in particulate matter (SO 4 ) (IVL, 2004). In order
to obtain the mass-based emissions factors from the power-based factors given by equation (4), division with
SFOC was made. The SFOC was obtained from the SFOC baseline after adjusting with the load dependency
(Eq. (3)).
The global sulphur content of marine fuel oils was modelled according to IMO global sulphur fuel oil monitoring
reports, as shown in Table 51. For regional variations driven by regulation (ECAs), the fuel sulphur content is
assumed to be equivalent to the minimum regulatory requirement (see the description in Section 1.2 of how
shipping activity is attributed to different global regions).
Table 51 – Annual fuel oil sulphur worldwide averages
Fuel type 2007 2008 2009 2010 2011 2012
HFO/IFO 2.42 2.37 2.60 2.61 2.65 2.51
MDO/MGO 0.15 0.15 0.15 0.15 0.14 0.14
PM
The current literature contains a large range of PM emissions factors, which vary significantly between studies
because of differences in methodology, sampling and analysis techniques. Again, the approach taken in
the current study is compatible with the Second IMO GHG Study 2009, which defined PM as substances
including sulphate, water associated with sulphate ash and organic carbons, measured by dilution method.
Therefore, the model can accommodate changes in fuel sulphur content. This reflects the changes in PM
emissions factors arising from ECAs as defined in MARPOL Annex VI. For main engines, PM was adjusted for
low engine loads (