Marine Diesel Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 156

Table 11.1 Characteristics of large, slow speed, two stroke marine diesel engine

Engine
characteristics

Physical properties

Operation
parameters

Two-stroke crosshead engines have piston diameters from 350 mm (13.82 in)
to 1,080 mm (42.66 in) and strokes of up to 3,200 mm (126.4 in). The
average cylinder volume is 600-650 l (21.2-23.0 ft 3 ) with a middle
cylinder bore of 600 mm (23.6 in). The piston speed is between 4.0 m s -1
and 6.0 m s -1 , i.e. between 13.2 and 19.7 ft s -1 . Fast engines run at about
8.0 m s -1

(26.2 ft s -1 ). The ignition pressure ranges from 140 9 10 5

Pa

to 160 9 10 5 Pa, i.e., from 2.92 9 10 5 lbf ft -2 to 3.34 9 10 5 lbf ft -2

or

from 2,030 to 2,320 psi [ 9 ]

Dimensions Currently, the dimensions are up to 29 9 15.5 9 11.5 m or 95.1 9 50.8 9

37.7 ft, i.e., length x width x height and the weight is up to 2,300 t
(5,066,079 lb) (Wärtsila 14RT-flex96C). The wave output ranges up to
84,420 kW (114 811 HP), (Wärtsila RT-flex/RTA96C) at 102 rpm.
However, development is very fast and new engines will be larger and
heavier [ 10 ]

Control system Fully electronic engine control makes it possible to separately regulate the

fuel injection, the exhaust-valve opening and closing, the cylinder
lubrication and the compressed air starting the engine operation after
interruption. Sensors monitor pressures, temperatures, number of
revolutions and other fuel management parameters, such as fuel
consumption [ 11 ]

Fuel Two-stroke marine diesel engines can burn a variety of fuels, even biogenic

and synthetic fuels or CNG and hydrogen [ 12 ]

Efficiency The two-stroke engine theoretically would produce twice the power of an

equal sized four-stroke engine. However, due to losses from the lower
operating efficiency only approximately 60% of the theoretical efficiency
can be reached. Two-stroke engines guarantee low fuel consumption and
high reliability, optimal durability and extremely long lifespan also with
low viscosity and variable quality of fuels [ 13 ]

Fuel consumption and exhaust gas emissions can be reduced by approximately
20% with better exhaust gas recirculation and by pre-heating the engine before the
cold start. Further measures are:

• Reduction of mechanical and thermal losses in the complete chain of air and fuel
injection and in the exhaust gas after treatment system;
• Use of a two-step load of the turbocharger to improve the stationary performance; and
• Application of an electric driven exhaust gas turbocharger with less inertia [ 7 ].

11.2 Engine Operation

Engine operation mainly depends on the principle of operation, the size and the
number of revolutions, often called the speed of the engine. There are slow,
medium, and high speed diesel engines.