Umair Gaines
Trains can run on diesel, electricity, or a combination of both. Diesel-electric trains use a diesel engine to generate electricity, which then powers the electric motors that drive the train's axles. This type of train is particularly efficient for railways due to its ability to handle the stop-start nature of the tracks and the need to move heavy loads. Electric motors are more efficient than internal combustion engines in generating mechanical energy, and they don't require mechanical transmissions, clutches, or other parts that can fail or wear out prematurely. Diesel-electric trains are also more flexible and affordable than purely electric trains, as they don't rely on power lines and can be refueled quickly almost anywhere. However, electric trains are more efficient in terms of energy transfer, with lower long-term fuel costs and reduced greenhouse gas emissions.
| Characteristics | Values |
|---|---|
| Types of trains | Diesel-electric, diesel-hydraulic, diesel mechanic |
| Efficiency | Electric motors are more efficient than internal combustion engines |
| Power output | Diesel-electric locomotive's power output is independent of road speed |
| Usage | Diesel-powered trains are used on less than 1% of US railroad tracks |
| Cost | It is 50% less expensive to power a train by electricity than by diesel |
| Maintenance | Maintenance costs for electric trains are 25-35% less than for diesel trains |
| Fuel | Diesel fuel prices are predicted to increase in the long term |
| Environmental impact | Switching from diesel to electricity would help lower greenhouse gas emissions |
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What You'll Learn
Modern diesel-electric trains
Diesel-electric locomotives come in three main varieties, depending on the period in which they were designed: DC-DC, AC-DC, and AC-DC-AC. The DC-DC type has a generator that supplies DC traction motors through a resistance control system. The AC-DC type uses an alternator to produce AC current, which is then rectified to DC before being supplied to the DC traction motors. The most modern variation, the AC-DC-AC, takes the AC current produced by the alternator, rectifies it to DC, and then inverts it back to 3-phase AC power for the traction motors.
These modern diesel-electric trains can produce impressive amounts of power. For example, the AC6000CW, built between 1995 and 2001, is a 6,000-horsepower locomotive, making it one of the world's most powerful single-engined diesel locomotives. On the other hand, Siemens' modern engines can generate up to 4,200 horsepower, which can be converted into nearly 4,700 amps of electrical current. This power enables these trains to tow passenger train cars at speeds of up to 125 miles per hour (200 km/h).
The head-end power unit (HEP) is another crucial aspect of modern diesel-electric trains. It consists of a separate diesel engine capable of producing 3,000-4,000 horsepower. The HEP engine typically spins at a slower rate than the main engine, reaching a maximum of about 1,000 rpm. It drives a generator that provides 480-volt, 3-phase AC power for various systems on the train, such as electric air conditioners, lights, and kitchen facilities. By having a separate engine and generator for these systems, the train can maintain passenger comfort even if the main engine encounters issues. Additionally, modern locomotives have electronic systems that allow for flexible power distribution between the main engine and the HEP, depending on the current energy requirements.
In terms of aesthetics, identifying modern diesel locomotives can be challenging due to the evolution of designs into families of similar-looking variants. However, comparing scale models to photographs and referencing construction methods and fittings can aid in distinguishing between different locomotives. For example, Electro-Motive Diesel and its predecessors are known for their distinctive low nose, rectangular cab, and flat roof construction with angled corners.
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Advantages of diesel-electric trains
Trains can run on diesel, electricity, or a combination of both. Diesel-electric trains have a diesel engine that acts as a generator for the electric motor. There are several advantages to using diesel-electric trains.
Firstly, diesel-electric trains are highly efficient. Electric motors are more efficient than internal combustion engines when creating mechanical energy, which is particularly beneficial for trains due to their stop-start nature and the need to move heavy loads. Electric motors do not require mechanical transmission, clutches, or other parts that can fail or wear out prematurely. The diesel engine can run at a constant load, unaffected by challenging operating conditions, resulting in increased efficiency, lower fuel consumption, and reduced emissions.
Secondly, diesel-electric trains are versatile and can operate in areas where electric power lines are not available. They do not rely on batteries, which would add weight, reduce speed and cargo capacity, and increase downtime for charging. Diesel engines are a relatively affordable, flexible, and easily maintained solution, as they require little space and can be refueled quickly almost anywhere.
Thirdly, diesel-electric trains have better acceleration and braking capabilities than traditional diesel locomotives. The power output of a diesel-electric locomotive is independent of road speed, allowing for smooth modulation of power and avoiding sudden changes in train loading. This results in improved schedule times and performance, making them ideal for passenger services.
Finally, diesel-electric trains offer significant operating advantages over steam locomotives. They are safer, quieter, fully weatherproof, and do not produce the dirt and heat associated with steam locomotives. Diesel locomotives can be operated by a single person, making them suitable for switching/shunting duties, and multiple locomotives can be controlled by a single crew, increasing efficiency.
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Diesel-electric trains vs fully electric trains
The longstanding debate between diesel-electric and fully electric trains continues to rage on, with both sides presenting compelling arguments. This comparison will outline the key differences, advantages, and considerations between the two types of trains.
Diesel-electric trains combine a diesel engine with an electric transmission, offering unique benefits. Firstly, they are highly efficient, as the diesel engine powers an electric generator, which then drives the electric motors that move the train. This setup allows the diesel engine to run at a constant load, reducing fuel consumption and emissions. Additionally, diesel-electric trains are versatile, capable of operating on any railway, including areas without electrified rails. They are also relatively affordable, requiring a small engine compartment and easy maintenance by experienced technicians.
However, diesel-electric trains do have certain drawbacks. They require more maintenance overall and are heavier, leading to increased wear and tear on the tracks. The diesel engine also needs to be powerful enough to generate sufficient voltage for the electric motors, which can be challenging.
On the other hand, fully electric trains offer their own set of advantages. They are generally cleaner and more environmentally friendly, especially in places where renewable energy sources, such as nuclear, hydro, or renewables, are predominantly used for electricity generation. Electric trains are also more powerful and forgiving, making them suitable for handling big loads without the risk of breaking transmissions.
Yet, fully electric trains also come with their own set of considerations. They require electrified rails, which can be costly to install and maintain. This limits their feasibility in areas with low train frequency or lacking the infrastructure for electrification.
In conclusion, the choice between diesel-electric and fully electric trains depends on various factors, including the frequency of train traffic, the availability of electrification infrastructure, and environmental considerations. Both types of trains have their strengths and weaknesses, and the optimal solution may lie in a combination of both, as seen in the growing interest in hybrid designs and dual-mode locomotives.
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Dual-mode diesel-electric trains
Trains can run on diesel, electricity, or a combination of both. The latter are known as dual-mode diesel-electric trains, which can switch between diesel and electric power sources depending on the availability of electric power lines.
History
The first diesel-electric locomotives were introduced in 1924 by the Soviet Railways. These early models hauled trains between Moscow and Kursk and in the Caucasus region from 1925 to 1927. In the 1930s, American railroads began adopting diesel-electric locomotives, with the Winton Engine Corporation and General Motors leading the way.
Functionality
Examples
Several examples of dual-mode diesel-electric trains are in operation worldwide. The Long Island Rail Road, Metro-North Railroad, and New Jersey Transit Rail Operations use these trains between non-electrified territories and New York City due to a ban on diesel-powered locomotives in Manhattan tunnels. Amtrak also operates a fleet of dual-mode locomotives in the New York area.
In Europe, the British Rail Class 73 and 74 are examples of dual-mode trains, while the Stadler Flirt trains in Norway and the Newag Impuls in Poland are more recent additions. The Chinese CR200J-SG Fuxing high-speed train is another instance of a dual-mode train, specifically designed for plateau operation.
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Diesel-hydraulic trains
Trains can run on diesel, electricity, or a combination of both. Diesel-electric trains are the most common type of diesel locomotive, but diesel-hydraulic trains are also used.
One advantage of diesel-hydraulic trains is that they can operate at very low controlled speeds, making them suitable for certain tasks such as hauling cane in the sugar industry. They also tend to perform better in wet conditions as they don't have electric motors close to the ground. However, they require special technical attention and can be prone to overheating. The setup and starting torque can also be issues, often requiring the inclusion of a gearbox.
The use of diesel-hydraulic trains has some drawbacks. For example, they are often oil-dripping, requiring crews to continuously add transmission oil while driving. The hydrostatic drive system, which uses pumps, pistons, motors, and hoses, demands exacting setup and cleanliness. If the system fails, oil can spread down the track, causing environmental issues and potentially lunching the entire system.
Diesel-Electric Trains
Diesel-electric trains, on the other hand, use a diesel engine to generate power for electric motors, which then drive the train. This type of train is advantageous because it doesn't require a mechanical transmission, clutches, or other parts that can fail or wear out prematurely. The diesel engine can run at a constant load and is less affected by challenging operating conditions, resulting in increased efficiency, lower fuel consumption, and reduced emissions. Additionally, diesel-electric trains can go where electric power lines are not available.
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Frequently asked questions
Diesel-electric trains are more efficient than trains powered solely by diesel fuel. Electric motors are more efficient than internal combustion engines when creating mechanical energy, which is particularly relevant for trains due to their stop-start nature. Electric motors also don't require mechanical transmissions, clutches or other parts that can fail or wear out prematurely.
They require both an engine and electric motors, which adds complexity and cost.
Trains can run on either diesel or electricity.
Examples of diesel-electric trains include the Alstom Coradia Lint Family and the Stadler GTW family.
Electric trains have more torque than diesel trains. An electric motor can transmit the torque required to move a 40,000-ton freight train with minimal parts, whereas any other form of transmission would need to be overbuilt and complicated with too many points of failure.
