WÄRTSILÄ WARTSILA 34DF, Product Manual

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13. Exhaust Emissions
Exhaust emissions from the dual fuel engine mainly consist of nitrogen, carbon dioxide (CO2)
and water vapour with smaller quantities of carbon monoxide (CO), sulphur oxides (SOx) and
nitrogen oxides (NOx), partially reacted and non-combusted hydrocarbons and particulates.
13.1 Dual fuel engine exhaust components
Due to the high efficiency and the clean fuel used in a dual fuel engine in gas mode, the exhaust
gas emissions when running on gas are extremely low. In a dual fuel engine, the air-fuel ratio
is very high, and uniform throughout the cylinders. Maximum temperatures and subsequent
NOx formation are therefore low, since the same specific heat quantity released to combustion
is used to heat up a large mass of air. Benefitting from this unique feature of the lean-burn
principle, the NOx emissions from the Wärtsilä DF engine is very low, complying with most
existing legislation. In gas mode most stringent emissions of IMO, EPA and SECA are met,
while in diesel mode the dual fuel engine is a normal diesel engine.
To reach low emissions in gas operation, it is essential that the amount of injected diesel fuel
is very small. The Wärtsilä DF engines therefore use a "micro-pilot" with less than 1% diesel
fuel injected at nominal load. Thus the emissions of SOx from the dual fuel engine are
negligable. When the engine is in diesel operating mode, the emissions are in the same range
as for any ordinary diesel engine, and the engine will be delivered with an EIAPP certificate to
show compliance with the MARPOL Annex VI.
13.2 Marine exhaust emissions legislation
13.2.1 International Maritime Organization (IMO)
The increasing concern over the air pollution has resulted in the introduction of exhaust
emission controls to the marine industry. To avoid the growth of uncoordinated regulations,
the IMO (International Maritime Organization) has developed the Annex VI of MARPOL 73/78,
which represents the first set of regulations on the marine exhaust emissions.
13.2.1.1 MARPOL Annex VI - Air Pollution
The MARPOL 73/78 Annex VI entered into force 19 May 2005. The Annex VI sets limits on
Nitrogen Oxides, Sulphur Oxides and Volatile Organic Compounds emissions from ship
exhausts and prohibits deliberate emissions of ozone depleting substances.
13.2.1.1.1 Nitrogen Oxides, NO
x
Emissions
The MARPOL 73/78 Annex VI regulation 13, Nitrogen Oxides, applies to diesel engines over
130 kW installed on ships built (defined as date of keel laying or similar stage of construction)
on or after January 1, 2000 and different levels (Tiers) of NOx control apply based on the ship
construction date. The NO
x
emissions limit is expressed as dependent on engine speed. IMO
has developed a detailed NO
x
Technical Code which regulates the enforcement of these rules.
13.2.1.1.1.1 EIAPP Certification
An EIAPP (Engine International Air Pollution Prevention) Certificate is issued for each engine
showing that the engine complies with the NO
x
regulations set by the IMO.
When testing the engine for NO
x
emissions, the reference fuel is Marine Diesel Oil (distillate)
and the test is performed according to ISO 8178 test cycles. Subsequently, the NO
x
value has
to be calculated using different weighting factors for different loads that have been corrected
to ISO 8178 conditions. The used ISO 8178 test cycles are presented in the following table.
Wärtsilä 34DF Product Guide - a16 - 23 September 2016 13-1
13. Exhaust Emissions Wärtsilä 34DF Product Guide