Marine Diesel Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 157

50
40
20
50
10
0
-10
-20
-30
-40

two-stroke

four-stroke

-8 -5 -4 -2 0 2 4 6 8 10

change of fuel consumption [%]

Fig. 11.2 Impact of changing fuel consumption on NO x emissions at constant rpm

11.2.1 Slow Speed Two-Stroke Marine Diesel Engines

Slow speed, high capacity marine diesel engines are the largest engines in the
world which operate with a crosshead principle at a maximum of 300 rpm. Most
large two-stroke, slow speed diesel engines operate below 120 rpm, even between
60 and 70 rpm. Two-stroke marine diesel engines have the best SFC among
internal combustion engines. Their construction and operational characteristics are
presented in Table 11.1 [ 8 ].
Slow speed marine diesel engines usually work with gate, valve, and port
control as well as with a combination of them. In the largest engines only the valve
and the port control are used.
NO x emissions are directly related to the combustion temperature. Decreasing the
amount of fuel injected into the combustion chamber usually requires more intensive
mixing which increases the temperature in the burning zone and lead to locally higher
NO x emissions at a constant number of revolutions (see Fig. 11.2 ).

11.2.2 Medium Speed Four-Stroke Marine Diesel Engines

Medium speed marine diesel engines are widely used as main and auxiliary
engines. They operate on diesel fuel or heavy fuel oil by direct injection in the
same manner as low speed engines. There are natural gas fueled versions, which
operate on the Otto cycle and also dual fuel versions (Table 11.2 )[ 14 ].

11.2.3 High Speed Four-Stroke Marine Diesel Engines

High speed marine diesel engines are usually used to provide high specific power,
low weight, and small volume. They are special engines and have a maximum