Some Diesel loks are called Diesel electric loks, while others are called Diesel hydraulic loks, and still others are just called Diesel loks. What is the difference? And what is the "swoop" sound you hear when a diesel starts?
The TEE VT 11.05 on my layout.
(Answers - Paul Berry, Jacques Vuye, Greg Proctor)
Any vehicle has at least three "motion" problems to
1) Energy storage
2) Energy conversion (generally to some sort of motion
in the prime mover)
3) Energy transmission
For example, in your car the fuel tank stores energy
(in the form of chemical energy in the fuel), the
internal combustion engine converts that energy to
rotary mechanical power at the flywheel, and the
transmission/final drive/wheels transmit that power to
In railway Diesel locomotives, the first two parts are
similar across almost all Diesel locos: energy storage
in the Diesel fuel tank and energy conversion in the
Diesel engine. From there, energy transmission varies:
a) Most Diesel locos worldwide use an electrical
transmission: the Diesel engine drives a generator
(nowadays specifically an alternator) and the
electrical power is conducted to traction motors in
the bogies. The locomotive actually moves due to
*electrical* drive. (Since this method of transmission
is so common, a Diesel-electric loco is mostly just
referred to as a Diesel loco.)
b) In Germany, most railway Diesel locos use a
hydraulic transmission, in which the Diesel prime
mover drives a hydraulic transmission (analogous to
your car's automatic trans, but quite different in
detail) which then drives the wheels by means of
shafts and a geared final drive.
BTW, Herr Rudolf Diesel prefers that you
capitalize his name...
Detroit MI (aka Motor City; aka Motown)
The V188 double diesel on my layout.
But not 100% true as far as Europe is concerned.
True, until recently most *DB* diesels and most Diesels *switchers* elsewhere
were indeed diesel hydraulics.
In other countries (France, Belgium, Denmark, Italy, etc.) diesel line locos
were practically always diesel electrics. (e.g the Belgian "potato bug" Class
202 or 204)
With the advent of modern electronics, most are diesel electric (with 3 phase
asynchronous traction) including railcars.
Jacques Vuye AKA Dr. Eisenbahn
Tour de Faure, France
The VT DGR diesel railcar on my layout.
Unlike a manual gearbox motorcar which has a big motor in relation to
the vehicle's weight, a railway locomotive has a miniscule motor when
compared to the total train weight. The motors only work in a restricted
rev range from say 1/3rd maximum to full speed but the vehicle/train has
to make the leap from zero velocity to minimum revs somehow. Your car
does this with a bit of slipage of the clutch (remember those
kangaroo/bunny hops before you mastered the technique) but the clutch
diameter has to be proportional to the vehicle weight, so a locomotive
clutch would be about 100 metres diameter and would require another
locomotive to depress the pedal!
The two normal solutions to the problem are the 'hydraulic' transmission
(like an automobile automatic gearbox and the 'electric' transmission
consisting of a generator, control equipment and electric motors driving
The advanages of each depend on the type of service the loco is used in.
- The hydraulic transmission is lightweight but tends to require
frequent maintenance. It's ideal for high horsepower, high speed
operation where one wants speed.
- the (DC) electric transmission is heavyweight and requires little
maintenance so suits situations where trains are slow but heavy.
The V220 diesel lok on my layout.
That SWOOP sound you hear when a GE starts up is the air powered starter. Since the amount of torque required to start a large displacement diesel engine, like that in just about any diesel locomotive would require an enormous sized electric starter motor and its' requisite battery array, most don't have electric starters.
Most North American railroad diesels are never shut down anyway. Doing so would require that the water to be drained since they have no anti-freeze. Anti-freeze is too expensive when you are talking a coolant system that is about 200 gallons! Then there is the required disposal of anti-freeze since used anti-freeze is classified as a hazardous material.
Diesel yard in Denver. More than 100 Diesels idling.
Visit almost any large Diesel yard in the US and you will hear the sound of all the diesels running. That is what I saw in Union Pacific yard in Denver and in other cities. The Diesels are left idling in the yards with signs that warn that they can start to move without the benefit of an engineer (train driver) since they are capable of being remotely controlled in the yard. (Sean Fanelli)
There is a third type of Diesel lok found primarily in the United States. It is an electric Diesel. Commuter lines into New York City were barred from using steam loks after a 1926 steam lok crash in a tunnel leading into Grand Central Station. The smoke in the tunnel obscured the view of the engineer (United States term for train driver) and the ensuing crash took the lives of 10 persons. As a result all lines into Grand Central and Pennsylvania Station were electrified with a third rail (an outer rail). Electrified tracks for railcar service extended north into Westchester, northeast into Conneticut, and east into Long Island but not to some outlying towns. Initially steam or diesel electric loks would pull the passenger cars to a terminus where they would change to an electric rail car powered by the third rail. Then came the advent of electric-Diesels. These were loks that were Diesel electric to the terminus station - North it was Croton Harmon and on Long Island it was Jamaica. At Croton Harmon ans at Jamaica the shoe (see picture below) would be lowered from the lok to make contact with the third rail. On the New Haven/Amtrak/ConRail FL9's it would be under the third rail (under-running) to avoid ice build-up but for the LIRR it was on top of the third rail (over-running). This sometimes caused problems with ice buiding up on the third rail. The lok would then become an electric lok. The most famous of these was the FL9. These loks were also used by the Long Island Railroad and Metro North. (See pictures below.)