Why diesel electric trains?

Question

why isnt it just straight diesel to power the train, why is electricty involved?

Answer 1

The diesel engine in a diesel-electric locomotive is only used as the motive power for an electric generator which, obviously, creates electricity which is then used to power the locomotive's traction motors; gearing found/housed within the truck assembly (where the wheels are).  So, essentially, diesel-electrics (although commonly called just diesels) are an electric locomotive that essentially carries its own power plant on board.

As the above poster stated, electricity is much more efficient than simply using a diesel engine and generates much more tractive effort and overall power for a locomotive (for instance,  overhead electric locomotives are the most efficient form of motive power, whereby they actually work harder as tonnage/grades increase).

Answer 2

Yup, they are right, and one other thing to ponder, it is not uncommon to have 2, 3, or more locomotives hooked together, just no way for a mechanical link to make all the locomotives work together, electric is the only practical way.

In the steam days when two locomotives were needed on a train they were "doubleheaded" meaning there was an engineer and fireman on each locomotive.

It worked, but not always very good. One or the other would always be working harder than the other.

Good question by the way.

Answer 3

They have found that it is the most efficient way to move the train  The electric motors will help keep an even load on the diesel engines to make them run at a constant speed.  Also the batteries will assist the motor to provide power to turn the wheels.  good luck.

Answer 4

They tried diesel-elastic, but it took forever to wind the rubber band.

Diesel-electric was the next power source, in alphabetical order.

Thus it was decided a diesel prime mover would run various electricity producing alternators and generators.

Primary amongst these is the tractive system.  Though powerful, the diesel motors work on mechanical principle, which is clumsy and the power is hard to direct, so it connects right to the main alternator.

The electricity the alternator produces, which is easy to manage and transmit, is fed to traction motors mounted on the locomotive trucks.  This is a very simple and efficient way of converting the mechanical energy into tractive effort, or torque.  When electricity is provided, in controlled amounts, the wheel is forced to turn, and the locomotive is under way.

Answer 5

The other guys got here ahead of me, and they are correct. (Except there is no battery power involved.) One other point is that there isn't a clutch in the world that could hold up to such slow starts pulling so much weight. It would simply burn up. The electric traction motors can run slow all day with no mechanical wear. The diesel electric concept was first put to practice and proven in U.S. submarines during World War II. The German submarines, although very effective in the war, were a pair of diesel engines with a clutch to the propeller shafts. The system worked alright, but the subs had to be smaller with this system. The U.S. subs were larger, with more fire power, and fuel because the electric motors provided more power at the propellers.

Answer 6

A diesel - electric train works as follows. The diesel engine is attached to a generator and electric wires transfer the power to the wheel motors. There are no mechanical parts that move back and forth (like a clutch) and no gears to change for mechanical power transmission. Electric motors have the advantage of all their torque being available right from a standing stop. A diesel engine attached to a transmission would have to build-up RPM to reach its peak torque.

Without clutches or gearboxes, they are mechanically simple and reliable. Trains have several thousand horsepower engines. Could you imagine how large, heavy, and tough a conventional transmission would have to be in order to handle that much power? In addition, it would be hard to drive smoothly.

Using electricity, the diesel engine can drive the generator at maximum speed and the wheel motors can be running slowly. There is no direct mechanical connection between engine and drive. It is modulated with a device like a dimmer switch.

Answer 7

Whilst not wishing to argue with preceding answers,there are, of course, diesel-mechanical locos which use transmission similiar to a road vehicle (see, for example, the many Class 03  shunting locos built for British Railways). German Railways (DB) built many diesel locos which used a diesel-hydraulic system of transmission which system was adopted by the Western Region of British Rail in the late 1950s/early 1960s in the 'Warship' and 'Western' classes of locos