DIESEL LOCOMOTIVE:

The loco is generally divided into following divisions:

Short Hood Long Hood

Nose Driver Alternator Engine Expresser Radiator
Compartment Cab Room Room Room Room

Important parts of the railway engine locomotive:

1. Diesel engine
2. Turbo charger
3. Radiator fan
4. Radiator
5. Sand box
6. Air compressor
7. Truck frame
8. Drive shaft
9. Gear box
10. Fuel tank
11. Air reservoirs
12. Main alternator
13. Auxiliary alternator
14. Motor blower
15. Air intakes
16. Rectifiers/inverters
17. Electronic controls
18. Cab
19. Traction motor
20. Pinion & gear
21. Wheel
22. Batteries
The Diesel Locomotive:

• The modern diesel locomotive is a self contained version of the electric locomotive.
• Like the electric locomotive, it has electric drive, in the form of traction motors
driving the axles and controlled with electronic controls.
• It also has many of the same auxiliary systems for cooling, lighting, heating, braking
and hotel power (if required) for the train.
• It can operate over the same routes (usually) and can be operated by the same
drivers.
• It differs principally in that it carries its own generating station around with it,
instead of being connected to a remote generating station through overhead wires
or a third rail.
• The generating station consists of a large diesel engine coupled to an alternator
producing the necessary electricity.
• A fuel tank is also essential.

Diesel Engine:

• This is the main power source for the locomotive.

• It comprises a large cylinder block, with cylinders arranged in a straight line or in a V.
• The engine rotates the drive shaft at up to 1,000 rpm and this drives the various
items needed to power the locomotive.

Main Alternator:

• The diesel engine drives the main alternator which provides the power to move the
train.
• The alternator generates AC electricity which is used to provide power for the
traction motors mounted on the trucks (bogies).
• In older locomotives, the alternator was a DC machine, called a generator.
• It produced direct current which was used to provide power for DC traction motors.
• Many of these machines are still in regular use.
• The next development was the replacement of the generator by the alternator but
still using DC traction motors.
• The AC output is rectified to give the DC required for the motors.

Auxiliary Alternator:

• Locomotives used to operate passenger trains are equipped with an auxiliary

alternator.
• This provides AC power for lighting, heating, air conditioning, dining facilities etc. on
the train.
• The output is transmitted along the train through an auxiliary power line. It is known
as "head end power" or "hotel power".
• Air conditioned passenger coaches’ get what is called electric train supply (ETS) from
the auxiliary alternator.
Motor Blower:

• The diesel engine also drives a motor blower.

• As its name suggests, the motor blower provides air which is blown over the traction
motors to keep them cool during periods of heavy work.
• The blower is mounted inside the locomotive body but the motors are on the trucks,
so the blower output is connected to each of the motors through flexible ducting.
• The blower output also cools the alternators.
• Some designs have separate blowers for the group of motors on each truck and
others for the alternators.
• Whatever the arrangement, a modern locomotive has a complex air management
system which monitors the temperature of the various rotating machines in the
locomotive and adjusts the flow of air accordingly.

Air Intakes:

• The air for cooling the locomotive's motors is drawn in from outside the locomotive.
• It has to be filtered to remove dust and other impurities and its flow regulated by
temperature, both inside and outside the locomotive.
• The air management system has to take account of the wide range of temperatures
from the possible +40°C of summer to the possible -40°C of winter.

Rectifiers/Inverters:

• The output from the main alternator is AC but it can be used in a locomotive with
either DC or AC traction motors.
• DC motors were the traditional type used for many years but, in the last 10 years, AC
motors have become standard for new locomotives.
• They are cheaper to build and cost less to maintain and, with electronic
management can be very finely controlled.
• To convert the AC output from the main alternator to DC, rectifiers are required.
• If the motors are DC, the output from the rectifiers is used directly.
• If the motors are AC, the DC output from the rectifiers is converted to 3-phase AC for
the traction motors.

Electronic Controls:

• Almost every part of the modern locomotive's equipment has some form of
electronic control.
• These are usually collected in a control cubicle near the cab for easy access.
• The controls will usually include a maintenance management system of some sort
which can be used to download data to a portable or hand-held computer.
Control Stand:

• This is the principal man-machine interface, known as a control desk or control

stand.
• The common of stand is positioned at an angle on the left side of the driving position
and, it is said, is much preferred by drivers to the modern desk type of control
layout.

Cab:

• The standard configuration of locomotives is to have a cab at one end of the

locomotive only.
• Since most structure gauge is large enough to allow the locomotive to have a
walkway on either side, there is enough visibility for the locomotive to be worked in
reverse.
• However, it is normal for the locomotive to operate with the cab forwards.
• In many countries, locomotives are full width to the structure gauge and cabs are
therefore provided at both ends.

Batteries:

Just like an automobile, the diesel engine needs a battery to start it and to provide electrical
power for lights and controls when the engine is switched off and the alternator is not
running.

Traction Motor:

• Since the diesel-electric locomotive uses electric transmission, traction motors are
provided on the axles to give the final drive.
• These motors were traditionally DC but the development of modern power and
control electronics has led to the introduction of 3-phase AC motors.
• There are between four and six motors on most diesel-electric locomotives.
• A modern AC motor with air blowing can provide up to 1,000 hp.

Pinion/Gear - The traction motor drives the axle through a reduction gear.

Fuel Tank:

• A diesel locomotive has to carry its own fuel around with it and there has to be
enough for a reasonable length of trip.
• The fuel tank is normally under the loco frame and will have a capacity of say 1,000
imperial gallons.
• In addition to fuel, the locomotive will carry around, typically about 300 US gallons of
cooling water and 250 gallons of lubricating oil for the diesel engine.
Air Reservoirs:

• Air reservoirs containing compressed air at high pressure are required for the train
braking and some other systems on the locomotive.
• These are often mounted next to the fuel tank under the floor of the locomotive.

Air Compressor:

The air compressor is required to provide a constant supply of compressed air for the
locomotive and train brakes.

Drive Shaft:

The main output from the diesel engine is transmitted by the drive shaft to the alternators
at one end and the radiator fans and compressor at the other end.

Gear Box:

• The radiator and its cooling fan is often located in the roof of the locomotive.
• Drive to the fan is therefore through a gearbox to change the direction of the drive
upwards.

Radiator and Radiator Fan:

• The radiator works the same way as in an automobile.

• Water is distributed around the engine block to keep the temperature within the
most efficient range for the engine.
• The water is cooled by passing it through a radiator blown by a fan driven by the
diesel engine.

Turbo Charging:

• The amount of power obtained from a cylinder in a diesel engine depends on how
much fuel can be burnt in it.
• The amount of fuel which can be burnt depends on the amount of air available in the
cylinder.
• So, if you can get more air into the cylinder, more fuel will be burnt and you will get
more power out of your ignition.
• Turbo charging is used to increase the amount of air pushed into each cylinder.
• The turbocharger is driven by exhaust gas from the engine.
• This gas drives a fan which, in turn, drives a small compressor which pushes the
additional air into the cylinder.
• Turbo charging gives a 50% increase in engine power.
• The main advantage of the turbocharger is that it gives more power with no increase
in fuel costs because it uses exhaust gas as drive power.
• It does need additional maintenance, however, so there are some types of lower
power locomotives which are built without it.
Sand Box:

• Locomotives always carry sand to assist adhesion in bad rail conditions.

• Sand is not often provided on multiple unit trains because the adhesion
requirements are lower and there are normally more driven axles.

Truck Frame:

This is the part (called the bogie) carrying the wheels and traction motors of the
locomotive.

Wheel:

• Wheels are driven by the power from the engine block.

• The wheels are connected to a traction motor by bull gears that transmit power to
the wheels.

Mechanical Transmission:

• A diesel-mechanical locomotive is the simplest type of diesel locomotive.

• As the name suggests, a mechanical transmission on a diesel locomotive consists a
direct mechanical link between the diesel engine and the wheels.

Fluid Coupling:

• In a diesel-mechanical transmission, the main drive shaft is coupled to the engine by

a fluid coupling.
• This is a hydraulic clutch, consisting of a case filled with oil, a rotating disc with
curved blades driven by the engine and another connected to the road wheels.
• As the engine turns the fan, the oil is driven by one disc towards the other.
• This turns under the force of the oil and thus turns the drive shaft. Of course, the
start up is gradual until the fan speed is almost matched by the blades.
• The whole system acts like an automatic clutch to allow a graduated start for the
locomotive.

Gearbox:

• This does the same job as that on an automobile.

• It varies the gear ratio between the engine and the road wheels so that the
appropriate level of power can be applied to the wheels.
• Gear change is manual.
• There is no need for a separate clutch because the functions of a clutch are already
provided in the fluid coupling.
Final Drive:

• The diesel-mechanical locomotive uses a final drive similar to that of a steam

engine.
• The wheels are coupled to each other to provide more adhesion.
• The output from the 4-speed gearbox is coupled to a final drive and reversing
gearbox which is provided with a transverse drive shaft and balance weights.
• This is connected to the driving wheels by connecting rods.

Hydraulic Transmission:

• Hydraulic transmission works on the same principal as the fluid coupling but it allows
a wider range of "slip" between the engine and wheels. It is known as a "torque
converter".
• When the train speed has increased sufficiently to match the engine speed, the fluid
is drained out of the torque converter so that the engine is virtually coupled directly
to the locomotive wheels.
• It is virtually direct because the coupling is usually a fluid coupling, to give some
"slip".
• Higher speed locomotives use two or three torque converters in a sequence similar
to gear changing in a mechanical transmission and some have used a combination of
torque converters and gears.

Diesel Multiple Units (DMUs)

• The diesel engines used in DMUs work on exactly the same principles as those used
in locomotives, except that the transmission is normally mechanical with some form
of gear change system.
• DMU engines are smaller and several are used on a train, depending on the
configuration.
• The diesel engine is often mounted under the car floor and on its side because of the
restricted space available.
• Vibration being transmitted into the passenger saloon has always been a problem
but some of the newer designs are very good in this respect.
• There are some diesel-electric DMUs around and these normally have a separate
engine compartment containing the engine and the generator or alternator.
• The reason for using one type or the other is really a question of preference.
However, it can be said that the 2-stroke design is simpler than the 4-stroke but the
4-stroke engine is more fuel efficient.
Diesel-Electric Types:

Diesel-electric locomotives come in three varieties, according to the period in which they
were designed. These three are:

• DC - DC (DC generator supplying DC traction motors);

AC - DC (AC alternator output rectified to supply DC motors) and
AC-DC-AC(AC alternator output rectified to DC and then inverted to 3-phase AC for
the traction motors).
• The DC - DC type has a generator supplying the DC traction motors through a
resistance control system, the AC - DC type has an alternator producing AC current
which is rectified to DC and then supplied to the DC traction motors and, finally, the
most modern has the AC alternator output being rectified to DC and then converted
to AC (3-phase) so that it can power the 3-phase AC traction motors.
• Although this last system might seem the most complex, the gains from using AC
motors far outweigh the apparent complexity of the system.
• There is one traction alternator (or generator) per diesel engine in a locomotive.

Transmissions:

• Like an automobile, a diesel locomotive cannot start itself directly from a stand.
• It will not develop maximum power at idling speed, so it needs some form of
transmission system to multiply torque when starting.
• It will also be necessary to vary the power applied according to the train weight or
the line gradient.
• There are three methods of doing this: mechanical, hydraulic or electric.
• Most diesel locomotives use electric transmission called "diesel-electric" locomotive.
• Mechanical and hydraulic transmissions are still used but are more common on
multiple unit trains or lighter locomotives.

Governor

• Once a diesel engine is running, the engine speed is monitored and controlled
through a governor.
• The governor ensures that the engine speed stays high enough to idle at the right
speed and the engine speed will not raise too high when full power is demanded.
• The governor consists of a rotating shaft, which is driven by the diesel engine.
• A pair of flyweights is linked to the shaft and they rotate as it rotates.
• The centrifugal force caused by the rotation causes the weights to be thrown
outwards as the speed of the shaft rises.
• If the speed falls the weights move inwards.
• The flyweights are linked to a collar fitted around the shaft by a pair of arms.
• As the weights move out, so the collar rises on the shaft.
• If the weights move inwards, the collar moves down the shaft.
• The movement of the collar is used to operate the fuel rack lever controlling the
amount of fuel supplied to the engine by the injectors.
Fuel Injection

• Ignition is a diesel engine is achieved by compressing air inside a cylinder until it gets
very hot (say 400°C, almost 800°F) and then injecting a fine spray of fuel oil to cause
a miniature explosion.
• The explosion forces down the piston in the cylinder and this turns the crankshaft.
• To get the fine spray needed for successful ignition the fuel has to be pumped into
the cylinder at high pressure.
• The fuel pump is operated by a cam driven off the engine.
• The fuel is pumped into an injector, which gives the fine spray of fuel required in the
cylinder for combustion.

Starting

• A diesel engine is started (like an automobile) by turning over the crankshaft until
the cylinders "fire" or begin combustion.
• The starting can be done electrically or pneumatically.
• Pneumatic starting was used for some engines.
• Compressed air was pumped into the cylinders of the engine until it gained sufficient
speed to allow ignition, then fuel was applied to fire the engine.
• The compressed air was supplied by a small auxiliary engine or by high pressure air
cylinders carried by the locomotive.
• Electric starting is now standard.
• It works the same way as for an automobile, with batteries providing the power to
turn a starter motor which turns over the main engine.
• In older locomotives fitted with DC generators instead of AC alternators, the
generator was used as a starter motor by applying battery power to it.

Engine Control Development

• The systems used by most locomotives in service today are more sophisticated.
• To begin with, the drivers control was combined with the governor and hydraulic
control was introduced.
• One type of governor uses oil to control the fuel racks hydraulically and another uses
the fuel oil pumped by a gear pump driven by the engine.
• Some governors are also linked to the turbo charging system to ensure that fuel does
not increase before enough turbocharged air is available.
• In the most modern systems, the governor is electronic and is part of a complete
engine management system.
Tractive Effort, Pull and Power

• The definition of tractive effort (TE) is simply the force exerted at the wheel rim of
the locomotive and is usually expressed in pounds (lbs) or kilo Newtons (kN).
• By the time the tractive effort is transmitted to the coupling between the locomotive
and the train, the drawbar pull, as it is called will have reduced because of the
friction of the mechanical parts of the drive and some wind resistance.
• Power is expressed as horsepower (hp) or kilo Watts (kW) and is actually a rate of
doing work.
• A unit of horsepower is defined as the work involved by a horse lifting 33,000 lbs one
foot in one minute.
• In the metric system it is calculated as the power (Watts) needed when one Newton
of force is moved one metre in one second.
• The relationship between power and drawbar pull is that a low speed and a high
drawbar pull can produce the same power as high speed and low drawbar pull.
• If you need to increase higher tractive effort and high speed, you need to increase
the power.
• To get the variations needed by a locomotive to operate on the railway, you need to
have a suitable means of transmission between the diesel engine and the wheels.
• One thing worth remembering is that the power produced by the diesel engine is not
all available for traction.
• In a 2,580 hp diesel electric locomotive, some 450 hp is lost to on-board equipment
like blowers, radiator fans, air compressors and "hotel power" for the train.

Power Control

• The diesel engine in a diesel-electric locomotive provides the drive for the main
alternator which, in turn, provides the power required for the traction motors.
• We can see from this therefore, that the power required from the diesel engine is
related to the power required by the motors.
• So, if we want more power from the motors, we must get more current from the
alternator so the engine needs to run faster to generate it.
• Therefore, to get the optimum performance from the locomotive, we must link the
control of the diesel engine to the power demands being made on the alternator.
• In the days of generators, a complex electro-mechanical system was developed to
achieve the feedback required to regulate engine speed according to generator
demand.
• The core of the system was a load regulator, basically a variable resistor which was
used to vary the excitation of the generator so that its output matched engine
speed.
The control sequence (simplified) was as follows:

• Driver moves the power controller to the full power position.

• An air operated piston actuated by the controller moves a lever, which closes a
switch to supply a low voltage to the load regulator motor.
• The load regulator motor moves the variable resistor to increase the main generator
field strength and therefore its output.
• The load on the engine increases so its speed falls and the governor detects the
reduced speed.
• The governor weights drop and cause the fuel rack servo system to actuate.
• The fuel rack moves to increase the fuel supplied to the injectors and therefore the
power from the engine.
• The lever (mentioned above) is used to reduce the pressure of the governor spring.
• When the engine has responded to the new control and governor settings, it and the
generator will be producing more power.
• On locomotives with an alternator, the load regulation is done electronically.
• Engine speed is measured like modern speedometers, by counting the frequency of
the gear teeth driven by the engine, in this case, the starter motor gearwheel.
• Electrical control of the fuel injection is another improvement now adopted for
modern engines.
• Overheating can be controlled by electronic monitoring of coolant temperature and
regulating the engine power accordingly.
• Oil pressure can be monitored and used to regulate the engine power in a similar
way.