Beatrice Lang
The diesel engine in a diesel-electric locomotive drives a generator that produces electricity to run electric motors mounted on the locomotive's axles. The diesel engine drives either a DC generator or an AC alternator-rectifier, and the output power is then used to power the traction motors that drive the locomotive. This combination of diesel engine and electric generators and motors makes the locomotive a hybrid vehicle. The engine rotates the drive shaft at up to 1,000 rpm, which drives the various components needed to power the locomotive. The radiator and its cooling fan are often located on the roof of the locomotive, with drive to the fan provided through a gearbox that changes the direction of the drive upwards.
Characteristics and Values of Diesel-Electric Locomotives
| Characteristics | Values |
|---|---|
| Power Output | Independent of road speed |
| Prime Mover | Diesel Engine |
| Generator | DC or AC |
| Traction Motors | 4 or 6 axles |
| Speed | Up to 125 mph |
| Weight | 100-200 tons |
| Horsepower | 3,000-6,600 HP |
| Control System | Adjusts power output, monitors performance, diagnoses issues |
| Efficiency | 20% more efficient than gasoline engines |
| Energy | Hybrid of electrical and mechanical energy |
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What You'll Learn
The diesel engine drives a generator or alternator-rectifier
In a diesel–electric locomotive, the diesel engine drives either a DC generator or an AC alternator-rectifier. The output of which provides power to the traction motors that drive the locomotive. There is no mechanical connection between the diesel engine and the wheels. The main components of diesel–electric propulsion are the diesel engine (also known as the prime mover), the main generator/alternator-rectifier, traction motors (usually with four or six axles), and a control system consisting of the engine governor and electrical or electronic components.
The electrical current that is generated in the stator is an alternating current (AC). The AC voltage that is produced by the alternator is determined by the speed of the rotor and the number of coils in the stator. The AC current is then converted into DC current by the rectifier, which is used to power the electrical loads. The rectifier plays a crucial role in converting the AC output of the alternator into DC, which is required by vehicles and most electronic devices.
The control panel is another important component in the system, allowing users to control and monitor the diesel generator. It contains switches, gauges, and indicators for starting and stopping the generator, monitoring its performance, and protecting it from overloading or faults. The crankshaft is also essential, converting the reciprocating motion of the pistons into rotational motion to drive the alternator.
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Power output is independent of road speed
The power output of a diesel-electric locomotive is independent of road speed, as long as the generator's current and voltage limits are not exceeded. This means that the locomotive's ability to develop tractive effort, or drawbar pull, will vary inversely with speed within these limits. The prime mover's power output is determined by its rotational speed (RPM) and fuel rate, which are controlled by a governor or similar mechanism.
The governor is designed to respond to the throttle setting, as set by the engine driver, and the speed at which the prime mover is running. The engine driver uses a stepped or "notched" throttle that produces binary-like electrical signals corresponding to the throttle position. This design is well-suited for multiple unit (MU) operation, as it ensures that all units in a consist respond in the same way to the throttle position. Binary encoding also helps to minimize the number of trainlines (electrical connections) needed to transmit signals between units. For instance, only four trainlines are required to encode all possible throttle positions for up to 14 throttling stages.
The diesel engine in a diesel-electric locomotive drives either a DC generator or an AC alternator-rectifier, providing power to the traction motors that drive the locomotive. There is no mechanical connection between the diesel engine and the wheels. The key components of diesel-electric propulsion include the diesel engine (also known as the prime mover), the main generator/alternator-rectifier, traction motors (typically with four or six axles), and a control system that includes the engine governor and electrical or electronic components.
The hybrid nature of diesel-electric locomotives eliminates the need for a mechanical transmission, as found in cars. In a car, the transmission allows the gear ratio between the engine and the drive wheels to change as the vehicle speeds up or slows down. However, in a diesel-electric locomotive, the traction motors can produce adequate torque at any speed, from a standstill to high velocities, without the need to change gears. This efficiency is crucial when transporting massive amounts of cargo or passengers.
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Diesel-electric locomotives are hybrid vehicles
Diesel-electric locomotives are considered hybrid because they use two different energy sources and converters to generate power. The diesel engine turns a shaft that drives the generator, which then produces electricity. This electrical energy is used to power the large electric motors at the wheels, known as traction motors. The use of electricity in the propulsion system provides several advantages, including the ability to independently control each axle, improving adhesion and traction.
The hybrid nature of diesel-electric locomotives offers environmental and economic benefits. For example, regenerative braking can be used to convert the train's kinetic energy into electrical energy, which can then be stored and used to power the locomotive, reducing energy consumption and fuel costs. Additionally, the use of dynamic braking can further enhance the efficiency of the braking system.
Some examples of diesel-electric hybrid trains include the Hitachi-developed system used on the British Rail Class 139 railcars and the Railpower Technologies' Green Goat shunting locomotives. These trains are expected to significantly reduce emissions and fuel consumption compared to conventional diesel-powered locomotives.
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The engine spins torque through the driveshaft
In a diesel–electric locomotive, a large diesel engine turns a shaft that drives a generator to produce electricity. This electrical energy powers electric motors at the wheels, known as 'traction motors'. The diesel engine, or prime mover, spins torque through the driveshaft, which is then transferred through the engine mounts to the car frame. This torque is met with an "equal and opposite" reaction, which makes the differential want to spin in the reverse direction. This is similar to how a cyclist "pops a wheelie", with the bicycle lifting in the opposite direction to the turn of the wheel.
The driveshaft spins at the same speed as the engine if the transmission is in a gear with a 1:1 ratio, slower than the engine in reduction gears, and faster than the engine if the transmission is in overdrive. It is important that the driveshaft is dynamically balanced to avoid vibration. The driveshaft also needs to be able to transfer power through a multitude of different angles, as there is rarely a straight line from the transmission to the rear end. This transfer of power is achieved through universal joints, or U-joints, which are usually found at each end of the driveshaft.
The engine driver controls the power output and speed of the locomotive using a stepped or "notched" throttle that produces binary-like electrical signals corresponding to the throttle position. This throttle design lends itself well to multiple unit (MU) operation, as it assures that all units in a consist respond in the same way to throttle position. Binary encoding also helps to minimize the number of trainlines (electrical connections) required to pass signals from unit to unit.
The driveshaft's universal joint allows relative motion between the two ends of the driveshaft. In most applications, a single universal joint is used, which can cause speed fluctuations in the driveshaft when the shaft is not straight. However, the Hotchkiss drive uses two universal joints, which eliminates speed fluctuations and provides a constant speed even when the shaft is no longer straight.
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The engine is used as the power source for the alternator
A diesel locomotive is a type of railway locomotive that uses a diesel engine as its power source. The most common types are diesel-electric and diesel-hydraulic. The former uses electricity to drive forward motion, despite the name "diesel".
In older locomotives, the alternator was a DC machine called a generator. It produced direct current, which was used to power 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 locomotive operates on a nominal 64-volt electrical system. The locomotive has eight 8-volt batteries, each weighing over 300 pounds (136 kilograms). These batteries provide the power needed to start the engine and run the electronics in the locomotive. Once the main engine is running, an alternator supplies power to the electronics and the batteries.
The diesel-electric system is five times more efficient than the old steam engine locomotives, which is why diesel entirely replaced steam in the early 20th century.
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Frequently asked questions
Yes, diesel-electric locomotives have output shafts. The diesel engine rotates the drive shaft at up to 1,000 rpm, which powers the various components needed to drive the locomotive.
Diesel-electric locomotives use a combination of diesel engines and electric generators and motors, making them hybrid vehicles. The diesel engine drives a generator or alternator-rectifier, which produces electricity to power the traction motors that drive the locomotive.
Diesel-electric locomotives combine mechanical and electrical energy to provide better power output. They are more efficient than traditional locomotives as they eliminate the need for a mechanical transmission. Additionally, they have improved adhesion and traction, making them suitable for heavier loads.
