Dual fuel engines comply with IMO Tier 3 regulations. In diesel mode dual fuel engines comply with IMO
Tier 2.
The IMO Tier 3 NO
x
enission level corresponds to an 80% reduction from the IMO Tier 1 NOx emission
standard. For diesel engines the reduction can be reached by applying a secondary exhaust gas emission
control system. At present Selective Catalytic Reduction (SCR) is the only efficient way to reach the NOx
reduction needed for the IMO Tier 3 standard.
Sulphur Oxides, SO
x
emissions
Marpol Annex VI has set a maximum global sulphur limit of currently 4,5% (until 1.1.2012) in weight for any
fuel used on board a ship. Annex VI also contains provisions allowing for special SOx Emission Control
Areas (SECA) to be established with more stringent controls on sulphur emissions. In a “SOx Emission
Control Area”, which currently comprises the Baltic Sea, the North Sea and the English Channel, the sulphur
content of fuel oil used onboard a ship must currently not exceed 1% in weight. Alternatively, an exhaust
gas cleaning system can be applied to reduce the total emissions of sulphur oxides from ships, including
both auxiliary and main propulsion engines, calculated as the total weight of sulphur dioxide emissions.
The Marpol Annex VI has undertaken a review with the intention to further reduce emissions from ships. In
the IMO MEPC 12 meeting in April 2008 proposals for new fuel oil sulphur limits were agreed. Final adoption
of the proposed sulphur limits was taken by IMO/MEPC 58 in October 2008. The upcoming limits for future
fuel oil sulphur contents are presented in the following table.
Table 13.3 Fuel sulphur caps
Date of implementation
Area
Fuel sulphur cap
1 July 2010
SECA Areas
Max. 1% S in fuel
1 January 2012
Globally
Max 3.5% S in fuel
1 January 2015
SECA Areas
Max. 0.1% S in fuel
1 January 2020
Globally
Max. 0.5% S in fuel
Abatement technologies including scrubbers are allowed as alternatives to low sulphur fuels.
13.2.2
Other Legislations
There are also other local legislations in force in particular regions.
13.3 Methods to reduce exhaust emissions
All standard Wärtsilä engines meet the NOx emission level set by the IMO (International Maritime Organisation)
and most of the local emission levels without any modifications. Wärtsilä has also developed solutions to
significantly reduce NOx emissions when this is required.
Diesel engine exhaust emissions can be reduced either with primary or secondary methods. The primary
methods limit the formation of specific emissions during the combustion process. The secondary methods
reduce emission components after formation as they pass through the exhaust gas system.
For dual fuel engines same methods as mentioned above can be used to reduce exhaust emissions when
running in diesel mode. In gas mode there is no need for scrubber or SCR.
Refer to the "Wärtsilä Environmental Product Guide" for information about exhaust gas emission control
systems.
Product Guide Wärtsilä 34DF - 3/2012
113
Product Guide
13. Exhaust Emissions
