Diesel-electric
A number of vehicles use a
diesel-electric powerplant for providing
locomotion. A diesel-electric powerplant includes a
diesel engine connected to an
electrical generator, creating
electricity that powers
electric traction motors.
This kind of
power transmission is used by
locomotives (see that article for details), used for pulling or pushing
trains. Diesel-electric powerplants have also been used in
submarines and surface
ships and some land vehicles. Vehicles using diesel-electric power system can be considered as a class of
hybrid electric vehicle, especially, if the electric energy is also coming from
rechargeable batteries.
When the diesel engine was first installed in submarines before the
First World War, it revolutionized submarine tactics because its range (or operating time) far surpassed that of the
gasoline engine, and leaked vapors of its fuel were far less prone to explode within a submarine cabin. The fuel was also easier to stow. In submarines, the engine is connected to generators to produce electric energy that is stored in
batteries for running underwater where
oxygen is not available to feed the engines. It had been standard for them to use a driveshaft directly connecting the diesel engine, generator and
propellers. There were a variety of
clutch mechanisms for various connections as well. However, the long driveshaft has often been a source of trouble, also producing
noise and
vibration.
Some Soviet submarines had three propellers, and could be used in a variety of ways: each running on its diesel engine; either the central one or the outer two could each be connected to a diesel engine with or without the other propeller running on electric; or the engines could via snorkel be recharging the batteries while the central propeller was quietly running on its electric motor; or all three could be running on electric motors.
The performance of its diesel engine was critical for a conventional submarine, and not easy to ensure. Navies imported and copied successful designs. Although the Germans had some excellent diesels for their U-boats, they also had some which were not so good. The Americans had a similar history; their last diesel engine design was radial in form, its driveshaft axis angled vertically. To replace this unreliable but space-efficient engine, submarines had to be sawn in half through the engine room and proven engines installed in a lengthened hull section. Since then, European submarine diesels have shown advances.
Modern diesel-electric submarines don't have a direct connection of the diesel engine to the propeller anymore: The usually single propeller is driven directly by an electric motor. Two or more diesel-generators provide electric energy for loading the batteries and/or driving the electric motor. This allows to mechanically insulate the noisy engine compartement from the outer pressure hull. reducing the acoustic signature of the submarine. Even some
nuclear submarines decouple their reactor room this way, e.g. all
French classes, like the
Rubis and
Redoutable and the
Chinese Type 093 class, have
turbo-electric propulsion.
Even though diesel-powered
motor ships have been in use since
1912 (e.g. with the
Selandia) andsteam-turbine/electric propulsion at least since the
1920s (
Tennessee class battleships), the practice of using diesel-electric powerplants in surface ships has been a more recent development. The
Finnish "
coastal battleship "
Ilmarinen, laid down in
1929, was among the first surface ships to use diesel-electric transmission. Later the technology was used in diesel powered
icebreakers.
Some modern ships, including
cruise ships and icebreakers, use electric motors in pods called
azimuth thrusters underneath to allow for 360° rotation, meaning that the ships are far more maneuverable.
Some vehicles also use
gas turbines in the same way. In fact, some use a combination: the
Queen Mary 2 has a set of diesel engines in the bottom of the ship plus a gas turbine near the top
exhaust tower. All are used for generating electrical power, and none of the ship's propellers are directly connected to any engines.
One example of a sucsessful conversion from steam to diesel electric was in the
AT&SF tugboats
Hastings and
Engle, operated on
San Francisco Bay to move barges of railroad cars in a side-towing arrangement between specialized
barge slips The
Hastings was originally built as a wartime ocean going rescue tugboat using tube steam boilers and a uniflow
steam engine, and a similar powerplant was used in the postwar
Engle, built specifically for this use. Conventional diesel engines were unsuitable for this application, owing to the time that it took to reverse the engine and produce power, while a steam engine had the responsiveness to bring the barge safely into the slip (even though operated through an engine room telegraph to an operator). The engine room crew consisted of one engineer and two firemen, a substantial proportion of the total crew of eight. By replacing the steam engine with a diesel electric unit (with parts commonality with a locomotive), maintenance was both simplified and reduced, several crew members could be eliminated, and the responsiveness to throttle operation (now directly controlled from the bridge) was substantially improved.
In the
1920s, diesel-electric technology first saw limited use in
switchers (or
shunters), locomotives used for moving trains around in railroad yards and assembling and disassembling them. One of the first companies to offer "Oil-Electric" locomotives was the
American Locomotive Company. The
ALCO HH series of diesel-electric switcher entered series production in
1931. In the
1930s, the system was adapted for
streamliners, the fastest trains of their day. Diesel-electric powerplants became popular because they greatly simplified the way motive power
was transmitted to the wheels and because they were both more
efficient and had greatly reduced maintenance requirements. Direct-drive
transmissions can become very complex, considering that a typical locomotive has four or more
axles. Some attempts were made at using
hydraulic fluid as a transmission medium, and it proved to be somewhat more efficient than diesel-electric technology. However, the complexity of both the direct-drive and hydraulic systems meant that breakdowns were more common.
|
The diesel-electric powerd Liebherr T282 dumper |
Diesel-electric propulsion was tried on some
military vehicles, such as
tanks. One example was the ill-fated
Maus tank. Currently no tank uses this principle for movement, but it's quite common to train the turret and/or guns with electric motors powered by diesel or turbine
APUs.
More success had diesel-electric propulsion on the civilian market: Big mining machines like the
Liebherr T282B dump truck or
LeTourneau L-2350
wheel loader are powered that way. Also
NASA's huge
Crawler-Transporters are propelled diesel-electrically.
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