giant machine is really what HowStuffWorks is all about. It
combines some great mechanical technology, including a huge,
diesel engine, with some heavy duty electric
motors and generators, throwing in a little bit of
computer technology for good measure.
General Motors FP59 diesel-electric
This 270,000-pound (122,470-kg) locomotive is designed to
tow passenger-train cars at speeds of up to 110 miles per hour
(177 kph). The diesel engine makes 3,200 horsepower,
and the generator can turn this into almost 4,700 amps of
electrical current. The four drive motors use this electricity
to generate over 64,000 pounds of thrust. There is a
completely separate V-12 engine and generator to provide
electrical power for the rest of the train. This generator is
called the head-end power unit. The one on this train
can make over 560 kilowatts (kW) of electrical power.
This combination of diesel engine and electric generators
and motors makes the locomotive a hybrid
vehicle. In this edition of HowStuffWorks,
we'll start by learning why locomotives are built this way and
why they have steel wheels. Then we'll take a look at the
layout and key components.
Why Hybrid? Why Diesel? The main reason why
diesel locomotives are hybrid is because this eliminates the
need for a mechanical
transmission, as found in cars. Let's start by
understanding why cars have transmissions.
The 3,200-horsepower engine that drives the
Your car needs a transmission because of the physics of the
engine. First, any engine has a redline -- a maximum rpm
(revolutions per minute) value above which the engine cannot
go without exploding. Second, if you have read How
Horsepower Works, then you know that engines have a narrow
rpm range where horsepower and torque are at
their maximum. For example, an engine might produce its
maximum horsepower between 5,200 and 5,500 rpm. The
transmission allows the gear
ratio between the engine and the drive wheels to change as
the car speeds up and slows down. You shift gears so that the
engine can stay below the redline and near the rpm band of its
best performance (maximum power).
The five- or six-speed transmission on most cars allows
them to go 110 mph (177 kph) or faster with an engine-speed
range of 500 to 6,000 rpm. The engine on our diesel locomotive
has a much smaller speed range. Its idle speed is around 269
rpm, and its maximum speed is only 904 rpm. With a speed range
like this, a locomotive would need 20 or 30 gears to make
it up to 110 mph (177 kph).
A gearbox like this would be huge (it would have to handle
3,200 horsepower), complicated and inefficient. It would also
have to provide power to four sets of wheels, which would add
to the complexity.
By going with a hybrid setup, the main diesel engine
can run at a constant speed, turning an electrical generator.
The generator sends electrical power to a traction motor at
each axle, which powers the wheels. The traction motors can
produce adequate torque at any speed, from a full stop to 110
mph (177 kph), without needing to change gears.
Why Diesel? Diesel
engines are more efficient than gasoline engines. A
huge locomotive like this uses an average of 1.5 gallons of
diesel per mile (352 L per 100 km) when towing about five
passenger cars. Locomotives towing hundreds of fully loaded
freight cars use many times more fuel that this, so even a
five or 10 percent decrease in efficiency would quickly add up
to a significant increase in fuel costs.
Steel Wheels Ever wonder why trains have
steel wheels, rather than tires like a
car? It's to reduce rolling friction. When your car is
driving on the freeway, something like 25 percent of the
engine's power is being used to push the tires down the road.
Tires bend and deform a lot as they roll, which uses a lot of
The amount of energy used by the tires is proportional to
the weight that is on them. Since a car is relatively light,
this amount of energy is acceptable (you can buy low
rolling-resistance tires for your car if you want to save a
Since a train weighs thousands of times more than a car,
the rolling resistance is a huge factor in determining how
much force it takes to pull the train. The steel wheels on the
train ride on a tiny contact patch -- the contact area between
each wheel and the track is about the size of a dime.
By using steel wheels on a steel track, the amount of
deformation is minimized, which reduces the rolling
resistance. In fact, a train is about the most efficient way
to move heavy goods.
The downside of using steel wheels is that they don't have
much traction. Traction when going around turns is not
an issue because train wheels have flanges that keep them on
the track. But traction when braking and accelerating is an
This locomotive can generate 64,000 pounds of
thrust. But in order for it to use this thrust
effectively, the eight wheels on the locomotive have to be
able to apply this thrust to the track without slipping. The
locomotive uses a neat trick to increase the traction.
In front of each wheel is a nozzle that uses compressed air
to spray sand, which is stored in two tanks on the
locomotive. The sand dramatically increases the traction of
the drive wheels. The train has an electronic traction-control
system that automatically starts the sand sprayers when the
wheels slip or when the engineer makes an emergency stop. The
system can also reduce the power of any traction motor whose
wheels are slipping.
Now let's check out the layout of the locomotive.
The Layout Nearly every inch of the 54-ft
(16.2-m) locomotive is tightly packed with equipment.
Mouse over the part labels to
see where each is located on the diesel
Main Engine and
Generator The giant two-stroke, turbocharged
V-12 and electrical generator provide the huge amount of power
needed to pull heavy loads at high speeds. The engine alone
weighs over 30,000 pounds (13,608 kg), and the generator
weighs 17,700 pounds (8,029 kg). We'll talk more about the
engine and generator later.
Cab The cab of the
locomotive rides on its own suspension system, which helps
isolate the engineer from bumps. The seats have a suspension
system as well.
The view from the cab of the
Inside the cab there are two seats, one for the engineer
and one for the fireman. The engineer has easy access to all
of the locomotive's controls; the fireman has just a radio and
a brake control. Also inside the car, right in the nose of the
locomotive, is a toilet.
Trucks The trucks are the
complete assembly of two axles with wheels, traction motors,
gearing, suspension and brakes. We'll discuss these components
Head-end Power Unit The
head-end power unit consists of another big diesel
engine, this time a four-stroke, twin-turbocharged Caterpillar
V-12. The engine itself is more powerful than the engine in
almost any semi-truck. It drives a generator that provides
480-volt, 3-phase AC power for the rest of the train. This
engine and generator provide over 560 kW of electrical power
to the rest of the train, to be used by the electric air
conditioners, lights and kitchen facilities. By using a
completely separate engine and generator for these systems,
the train can keep the passengers comfortable even if the main
engine fails. It also decreases the load on the main engine.
Fuel Tank This huge tank
in the underbelly of the locomotive holds 2,200 gallons
(8,328 L) of diesel fuel. The fuel tank is compartmentalized,
so if any compartment is damaged or starts to leak, pumps can
remove the fuel from that compartment.
Batteries The locomotive
operates on a nominal 64-volt electrical system. The
locomotive has eight 8-volt batteries,
each weighing over 300 pounds (136 kg). These batteries
provide the power needed to start the engine (it has a huge
starter motor), as well as to run the electronics in the
locomotive. Once the main engine is running, an alternator
supplies power to the electronics and the batteries.
Let's take a more detailed look at some of the main systems
on the locomotive.
The Engine and Generator The main engine in
this locomotive is a General Motors EMD 710 series engine. The
"710" means that each cylinder in this turbocharged,
two-stroke, diesel V-12 has a displacement of 710 cubic inches
(11.6 L). That's more than double the size of most of the
biggest gasoline V-8 car engines -- and we're only talking
about one of the 12 cylinders in this 3,200-hp engine.
So why two-stroke? Even though this engine is huge,
if it operated on the four-stroke diesel cycle, like most
engines do, it would only make about half the power. This
is because with the two-stroke cycle, there are twice as many
combustion events (which produce the power) per revolution. It
turns out that the diesel two-stoke engine is really much more
elegant and efficient than the two-stroke gasoline engine. See
Diesel Two-Stroke Engines Work for more details.
You might be thinking, if this engine is about 24 times the
size of a big V-8 car engine, and uses a two-stroke instead of
a four-stroke cycle, why does it only make about 10 times the
power? The reason is that this engine is designed to produce
3,200 hp continuously, and it lasts for decades. If you
continuously ran the engine in your car at full power, you'd
be lucky if it lasted a week.
Here are some of the specifications of this engine:
Number of cylinders: 12
Compression ratio: 16:1
Displacement per cylinder: 11.6 L (710
Cylinder bore: 230 mm (9.2 inches)
Cylinder stroke: 279 mm (11.1 inches)
Full speed: 904 rpm
Normal idle speed: 269 rpm
This giant engine is hooked up to an equally impressive
generator. It is about 6 feet (1.8 m) in diameter and
weights about 17,700 pounds (8,029 kg). At peak power, this
generator makes enough electricity to power a neighborhood of
about 1,000 houses!
So where does all this power go? It goes into four, massive
electric motors located in the trucks.
The Trucks The trucks are the heaviest
things on the train -- each one weighs 37,000 pounds
(16,783 kg). The trucks do several jobs. They support the
weight of the locomotive. They provide the propulsion, the
suspensions and the braking. As you can imagine, they are
traction motors provide propulsion power to the wheels.
There is one on each axle. Each motor drives a small gear,
which meshes with a larger gear on the axle shaft. This
provides the gear reduction that allows the motor to drive the
train at speeds of up to 110 mph.
Two of the traction motors removed from a
Each motor weighs 6,000 pounds (2,722 kg) and can draw up
to 1,170 amps of electrical current.
Suspension The trucks
also provide the suspension for the locomotive. The weight of
the locomotive rests on a big, round bearing,
which allows the trucks to pivot so the train can make a turn.
Below the pivot is a huge leaf spring that rests on a
platform. The platform is suspended by four, giant metal
links, which connect to the truck assembly. These links
allow the locomotive to swing from side to side.
The weight of the locomotive rests on the leaf
springs, which compress when it passes over a bump. This
isolates the body of the locomotive from the bump. The links
allow the trucks to move from side to side with fluctuations
in the track. The track is not perfectly straight, and at high
speeds, the small variations in the track would make for a
rough ride if the trucks could not swing laterally. The system
also keeps the amount of weight on each rail relatively equal,
reducing wear on the tracks and wheels.
Braking Braking is
provided by a mechanism that is similar to a car drum
brake. An air-powered piston pushes a pad against
the outer surface of the train wheel.
In conjunction with the mechanical brakes, the locomotive
has dynamic braking. In this mode, each of the four
traction motors acts like a generator, using the wheels of the
train to apply torque to the motors and generate electrical
current. The torque that the wheels apply to turn the motors
slows the train down (instead of the motors turning the
wheels, the wheels turn the motors). The current generated (up
to 760 amps) is routed into a giant resistive mesh that turns
that current into heat. A cooling fan sucks air through the
mesh and blows it out the top of the locomotive -- effectively
the world's most powerful hair dryer.
On the rear truck there is also a hand brake -- yes,
even trains need hand brakes. Since the brakes are air
powered, they can only function while the compressor is
running. If the train has been shut down for a while, there
will be no air pressure to keep the brakes engaged. Without a
hand brake, even a slight slope would be enough to get the
train rolling because of its immense weight and the very low
rolling friction between the wheels and the track.
The hand brake is a crank that pulls a chain. It takes many
turns of the crank to tighten the chain. The chain pulls the
piston out to apply the brakes.
Driving a Locomotive You don't just hop in
the cab, turn the key and drive away in a diesel locomotive.
Starting a train is a little more complicated than starting
The engineer climbs an 8-foot (2.4-m) ladder and enters a
corridor behind the cab. He or she engages a knife
switch (like the ones in old Frankenstein movies) that
connects the batteries to the starter circuit. Then the
engineer flips about a hundred switches on a circuit-breaker
panel, providing power to everything from the lights to the
Next, the engineer walks down a corridor into the engine
room. He turns and holds a switch there, which primes the fuel
system, making sure that all of the air is out of the system.
He then turns the switch the other way and the starter motor
engages. The engine cranks over and starts running.
Next, he goes up to the cab to monitor the gauges and set
the brakes once the compressor has pressurized the brake
system. He can then head to the back of the train to release
the hand brake.
Finally he can head back up to the cab and take over
control from there. Once he has permission from the conductor
of the train to move, he engages the bell, which rings
continuously, and sounds the air horns twice
(indicating forward motion).
The throttle control has eight positions, plus an idle
position. Each of the throttle positions is called a
"notch." Notch 1 is the slowest speed, and notch 8 is
the highest speed. To get the train moving, the engineer
releases the brakes and puts the throttle into notch 1.
This engages a set of contactors (giant electrical
These contactors hook the main generator to the traction
motors. Each notch engages a different combination of
contactors, producing a different voltage. Some combinations
of contactors put certain parts of the generator winding into
a series configuration that results in a higher voltage.
Others put certain parts in parallel, resulting in a lower
voltage. The traction motors produce more power at higher
As the contactors engage, the computerized engine controls
adjust the fuel injectors to start producing more
The brake control varies the air pressure in the
brake cylinders to apply pressure to the brake shoes. At the
same time, it blends in the dynamic braking, using the motors
to slow the train down as well.
The brake and throttle
The engineer also has a host of other controls and
Controls, indicators and the
A computerized readout displays data from sensors all over
the locomotive. It can provide the engineer or mechanics with
information that can help diagnose problems. For instance, if
the pressure in the fuel lines is getting too high, this may
mean that a fuel filter is clogged.
This computerized display can show the status
of systems all over the
Now let's take a look inside the train.
Riding the Train The accommodations inside a
passenger train are quite plush. This train is the
Piedmont, which runs daily from Raleigh to Charlotte,
North Carolina. The seats on this train recline more than
airline seats and have more leg room. They also have
Inside a passenger
The seats on this car can be turned around to
face each other so four people can sit
The train also has a kitchen that serves
mostly sandwiches and light
For first-class passengers on this train,
there is an observation car that has a sunroom upstairs
Although taking the train might be slower than flying, it's
definitely a lot more comfortable. There is plenty of room to
walk around, and you can eat in a dining car or look at the
view from the the top of the lounge car. Some trains even have
private rooms for first-class passengers -- not a bad way to
get from here to there.
For more information on diesel locomotives and related
topics, check out the links on the next page!