Marine Diesel Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 163

DC engine

synchronous engine

rectifier propellor

permanently activated
synchronous engine

asynchronous engine

Fig. 11.4 Combination of the diesel-electric engine and propulsion elements

In last decades, new unconventional materials have been being developed, e.g.,
fine grain carbon and titanium alloys for pistons as a substitute for high-temper-
ature steel alloys. However, the cost of alloys is high on average. Expensive
alloyed parts should be partly replaced by steel with a boron or nitrogen bonus and
spherical cast materials.
Synthetic materials are replacing aluminum in many parts such as in the air
intake lines. The advantages of synthetic materials are their low weight and the
almost unlimited possibilities for form and design. In recent years plastics have
become cost competitive with alloys [ 36 ].
For economic reasons, ship construction is decreasing the mass of equipment
on-board. In modern engine design, steel is being replaced by aluminum, mag-
nesium,

and synthetic materials. Apart from mass advantages, light weight

materials must show a positive climate balance and high recycling rate.

11.5.2 Use of Diesel-Electric Systems

A diesel-electric transmission system includes a diesel engine connected to an
electrical generator creating electricity that powers ship's electric traction engine.
The first diesel-electric system was launched in 1903. One advantage of diesel
electric systems is the optimal promotion of space saving. Another advantage is
the possibility of using smaller subsystems instead of one large main engine,
according to the specific tasks and possibilities of the ship's construction (see
Fig. 11.4 )[ 37 ].
The diesel electric propulsion makes the ship far more manageable. Some
modern ships, including chruis ships and icebreakers, use electric motors in pods
to allow for 360 rotation. Gas turbines provides in combination with electric
motors a high speed and a low torque output of a turbine to drive a low speed
propeller, without reduction gearing [ 38 ].