Future Transportation Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 281

30

20

14% for IFO

10

7% for MDO

0

emulsion
with 20% H O
2

emulsion and
late injection

exhaust gas
recirculation 10%

water injection
with 50% H O
2

SRC

Fig. 17.13 Changes in fuel consumption with fuel preparation and exhaust gas after treatment

The highest rates of reductions, of up to 95%, can be reached by the use of SCR
technology. In a two-stroke marine diesel engine the SCR reactor nury advanta-
geously be put in front of the exhaust gas turbocharger because of the optimal
temperatures in the area [ 47 ].
Furthermore, there are several other methods for decreasing emissions. How-
ever, these methods usually have individual side effects which are disadvanta-
geous. Humid air engines require less water, but need large humidification towers.
Emulsified fuels require large quantities of water from freshwater production
plants. Fuel-Water Emulsions (FWE) have lower heating values and higher vis-
cosities than pure HFO. Emulsified fuels require an increased injection pump
capacity and a bigger final heater [ 48 ].
FWE requires increased preheating temperature and higher feeder pump pres-
sure to avoid water evaporation. Parallel to decreasing the exhaust gas emissions
all these methods cause higher fuel consumption; see Fig. 17.13 [ 49 ].
Further aims for improvement of exhaust gas quality in marine technology are:

• Reduction of NO x concentrations in the exhaust gas by 40-50% at sea and up to
80% in coastal waters, i.e., 50-200 nmi or 92.6-370.4 km off shore [ 50 ];
• Reconstruction of existing engine technology on ships built before 2000 to be in
compliance with the current NO x emission limits; and [ 51 ]
• Lowering the operating costs and space requirements of exhaust gas after
treatment systems for broad ranged applications [ 52 ].

17.3.1.2 Reduction of SO x Emissions

The average sulfur content of marine diesel fuel is 3.0-4.0% by weight. Operation
with a standard HFO with sulfur content higher than 1% may lead to clogging the
catalyst because the exhaust gas temperature of marine diesel engines is too low to
avoid deposits under most operating conditions. The best results can be reached
through the combined use of low sulfur fuel and SCR technology [ 53 ].