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 34DF
are 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. In the following table
there are some examples of the typical emissions levels of a 34DF engine.
Table 13.1 Typical emissions for Wärtsilä 34DF engine in gas operating mode
75 % load
100% load
Typical emission levels*
1.4
1.3
NO
x
(g/kWh)
469
460
CO
2
(g/kWh)
Note
:
* the CO
2
emissions are depending on the quality of the gas used as a fuel. For a specific project value,
please ask for information based on the actual gas specification.
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.
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.
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.
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.
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
110
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
13. Exhaust Emissions
