Future Transportation Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 283

air
cleaner

pipes and
nozzles

oxidation
catalyst

reduction
catalyst

air intake exhaust system

single
filter

PM-Cat
filter

engine
brake

turbocharger

Fig. 17.14 Common air intake and exhaust gas after treatment system

effectively reduce common NO, NO 2 , and particle emissions. Systems must be
suitable for both retrofitting and for new engines. The required separation rate is
approximately 70% [ 56 ].
Figure 17.14 shows the elements of the common air intake and exhaust gas
after treatment system.
SCR and connected filter technology offers the largest future potential for the
improvement of the exhaust gas treatment on ships. This procedure can be combined
with exhaust gas recirculating and the catalyst can be integrated into the muffler. SCR
technology in ships can only be used when ships combust low sulfur bunker fuels.
Filter on ships have to operate under raw conditions. The pressure difference in
the filter between the entrance and the exhaust side can be measured with pressure
sensors. A blocked filter leads to an increased pressure difference between the
sensors. The filter must be regenerated before high counter pressure can seriously
increase fuel consumption or stop the engine. In ships, the filter is heated by a
burner to 600C (1,112F). Starting at 550C (1,022F), the deposited soot burns
away and leaves the filter as CO 2 . If the filter is frequently clogged with ash, the
regeneration requires longer time interval or higher temperatures. In critical cases,
it cannot be regenerated anymore [ 57 ].

17.3.2 Far Future Phases of Development

17.3.2.1 Use of Biogenic and Synthetic Fuels in Ships

Future development will need cooperation between refineries and manufacturers of
combustion engines. New generations of biogenic and synthetic fuels could be
added to recent navy fuels in ratios of up to 20-25%. Liquid biogenic and synthetic
fuels do not need a new distribution system and can be bunkered, and used in the
existing fuel system.
However, new regulations are in the starting phase. Although CNG is a new
fuel in road vehicles, with clear environmental advantages in comparison to oil
products, CNG has been forbidden as a marine fuel by the IMO in international
sea-going shipping for safety reasons up to now. According to SOLAS, only fuels