Education Part 6
Motive Power
Introduction
This section is devoted to a discussion of powered railroad cars that are called locomotives. We begin with the basic idea of tractive effort, review the basics of steam, diesel-electric and electric locomotives and conclude with recent and possible future developments in motive power.
Pulling Power or Tractive Effort
Motive power amounts to the energy needed to move a train. This power may be called pulling power or (better) tractive effort. Tractive effort is the energy needed to overcome friction, which arises from several points. For one, there is the friction of the bearings that facilitate the turning of the axels of the rolling stock. While the object of the bearings is to minimize this friction, it cannot be reduced to zero. On a long train with many axels, bearing friction is significant.
Another source of friction is that of the wheels against the rails. Such friction is absolutely necessary if the train is to be moved or stopped. But it is also a cost in tractive effort necessary to overcome wheel/rail friction. A related source of friction is called truck hunting (bogie hunting) in which an oscillation occurs as the wheels of the truck "hunt" for lateral equilibrium. This oscillation manifests itself as swaying of rolling stock and as a cost in tractive effort.
Another source of friction is the air through which a train must pass. Aerodynamic friction is meaningless when the train is stationary, but it increases as the square of the velocity of the train in motion.
Finally, there is a friction due to gravity. On a grade of 0° the friction due to gravity is a constant that provides the adhesion (wheel/rail friction) necessary for a train to move. But if the grade is greater than 0° there will be a cost in tractive effort necessary to overcome the force of gravity. If the grade is less than 0°, then the force of gravity contributes to the tractive effort.
Measuring Tractive Effort
Tractive effort is determined by the equation
Fmax = coefficient of friction × weight on drive wheel
where the coefficient of friction for steel on steel typically ranges between about 0.35 to 0.5. Fmax will have the dimension Newtons (N) which is a measure of acceleration such that 1N = 1 kg⋅m/s/s. In words, one Newton is the acceleration of one kilogram of mass 1 meter/second per second. For motive power, consider a locomotive with mass 50 tons (45359 kg) operating under a coefficient of friction of 0.4. Weight on drive wheel will be 45359 kg x 0.4 = 18143 N or 18.143 kN.
For practical purposes, there are two types of tractive effort, starting tractive effort and continuous tractive effort. It takes more effort to start a train from stand-sill than it does to keep a train moving once started thanks to momentum. There is also a point at which, if acceleration continues, the train will eventually reach a velocity at which the available tractive force of the locomotive(s) will exactly offset the total drag (sum of friction components), causing acceleration to cease and the train will run at a constant velocity as long at the tractive effort remains constant.
For modern motive power, a different approach to measurement of pulling power may be used. Railways now use dynamometer cars to measure tractive force at speed in actual road testing. This provides a more accurate and realistic measure of a locomotive's ability to move a train. Today, motive power can be expressed in kiloNewtons (kN), watts or horsepower (see table below).
Types of Motive Power
For all practical purposes, there are three types of motive power, namely steam, diesel and electric. The fuel for steam locomotives can be anything that burns at a high enough temperature to convert water into steam. Although coal has been most common, wood, oil and other fuels have been used.
Fuel for diesel locomotives is diesel oil. While there have been constructed diesel locomotives in which the diesel engine directly drives the axels of a locomotive, virtually all diesel locomotives today are actually diesel-electric. In such locomotives, the diesel engine drives a generator or alternator that provides electrical energy to the axels through electric motors. For our purposes, only diesel-electric locomotives will be considered.
Fuel for electric locomotives may be fossil fuels (coal, oil, gas), nuclear energy, hydropower, hydrogen fuel cells, wind power, or solar power. Batteries have been used in situations where wired electrical transmission is unavailable such as in maintenance of overhead catenary lines (when they must not be powered) or in situations where other power would be hazardous (e.g., mines). Battery-powered trains may become more important as storage and charging capacities improve and as environmental concerns are taken more seriously (see Other Motive Power, a bit later).
The following table gives the motive power of selected locomotives.
Pulling Power or Tractive Effort
Motive power amounts to the energy needed to move a train. This power may be called pulling power or (better) tractive effort. Tractive effort is the energy needed to overcome friction, which arises from several points. For one, there is the friction of the bearings that facilitate the turning of the axels of the rolling stock. While the object of the bearings is to minimize this friction, it cannot be reduced to zero. On a long train with many axels, bearing friction is significant.
Another source of friction is that of the wheels against the rails. Such friction is absolutely necessary if the train is to be moved or stopped. But it is also a cost in tractive effort necessary to overcome wheel/rail friction. A related source of friction is called truck hunting (bogie hunting) in which an oscillation occurs as the wheels of the truck "hunt" for lateral equilibrium. This oscillation manifests itself as swaying of rolling stock and as a cost in tractive effort.
Another source of friction is the air through which a train must pass. Aerodynamic friction is meaningless when the train is stationary, but it increases as the square of the velocity of the train in motion.
Finally, there is a friction due to gravity. On a grade of 0° the friction due to gravity is a constant that provides the adhesion (wheel/rail friction) necessary for a train to move. But if the grade is greater than 0° there will be a cost in tractive effort necessary to overcome the force of gravity. If the grade is less than 0°, then the force of gravity contributes to the tractive effort.
Measuring Tractive Effort
Tractive effort is determined by the equation
Fmax = coefficient of friction × weight on drive wheel
where the coefficient of friction for steel on steel typically ranges between about 0.35 to 0.5. Fmax will have the dimension Newtons (N) which is a measure of acceleration such that 1N = 1 kg⋅m/s/s. In words, one Newton is the acceleration of one kilogram of mass 1 meter/second per second. For motive power, consider a locomotive with mass 50 tons (45359 kg) operating under a coefficient of friction of 0.4. Weight on drive wheel will be 45359 kg x 0.4 = 18143 N or 18.143 kN.
For practical purposes, there are two types of tractive effort, starting tractive effort and continuous tractive effort. It takes more effort to start a train from stand-sill than it does to keep a train moving once started thanks to momentum. There is also a point at which, if acceleration continues, the train will eventually reach a velocity at which the available tractive force of the locomotive(s) will exactly offset the total drag (sum of friction components), causing acceleration to cease and the train will run at a constant velocity as long at the tractive effort remains constant.
For modern motive power, a different approach to measurement of pulling power may be used. Railways now use dynamometer cars to measure tractive force at speed in actual road testing. This provides a more accurate and realistic measure of a locomotive's ability to move a train. Today, motive power can be expressed in kiloNewtons (kN), watts or horsepower (see table below).
Types of Motive Power
For all practical purposes, there are three types of motive power, namely steam, diesel and electric. The fuel for steam locomotives can be anything that burns at a high enough temperature to convert water into steam. Although coal has been most common, wood, oil and other fuels have been used.
Fuel for diesel locomotives is diesel oil. While there have been constructed diesel locomotives in which the diesel engine directly drives the axels of a locomotive, virtually all diesel locomotives today are actually diesel-electric. In such locomotives, the diesel engine drives a generator or alternator that provides electrical energy to the axels through electric motors. For our purposes, only diesel-electric locomotives will be considered.
Fuel for electric locomotives may be fossil fuels (coal, oil, gas), nuclear energy, hydropower, hydrogen fuel cells, wind power, or solar power. Batteries have been used in situations where wired electrical transmission is unavailable such as in maintenance of overhead catenary lines (when they must not be powered) or in situations where other power would be hazardous (e.g., mines). Battery-powered trains may become more important as storage and charging capacities improve and as environmental concerns are taken more seriously (see Other Motive Power, a bit later).
The following table gives the motive power of selected locomotives.
Selected locomotive weight and power
Other Classifications of Locomotives
We just discussed one method of locomotive classification: power source. Two other methods of classification are perhaps more important.
Wheel or Axel Arrangement Denotation Systems
Different systems for denoting wheel or axel arrangements have been developed in various countries. We describe the two most common systems.
We just discussed one method of locomotive classification: power source. Two other methods of classification are perhaps more important.
Wheel or Axel Arrangement Denotation Systems
Different systems for denoting wheel or axel arrangements have been developed in various countries. We describe the two most common systems.
The Whyte System of Classification of Locomotives
In the United States (US) and United Kingdom (UK) it is common to refer to a steam locomotive wheel arrangement numerically, first by the leading carrying wheels, then the coupled wheels (including the driving wheels) and finally the trailing carrying wheels, in a system invented by Frederick Methvan Whyte in the US in 1900. Examples are given in the following table.
In the United States (US) and United Kingdom (UK) it is common to refer to a steam locomotive wheel arrangement numerically, first by the leading carrying wheels, then the coupled wheels (including the driving wheels) and finally the trailing carrying wheels, in a system invented by Frederick Methvan Whyte in the US in 1900. Examples are given in the following table.
Table Illustrating the Whyte Wheel Classification system
A list of US wheel arrangements is available here on the Wes Barris US Steam locomotive site.
Some European railways used the Whyte system except that the number of axles was used rather than the number of wheels, 4-6-2 becoming 231. This was further developed by the French who used numbers for non-driven axles and letters for driven axles, thus 2C1. Today, axel arrangement is specified using the UIC System.
Some European railways used the Whyte system except that the number of axles was used rather than the number of wheels, 4-6-2 becoming 231. This was further developed by the French who used numbers for non-driven axles and letters for driven axles, thus 2C1. Today, axel arrangement is specified using the UIC System.
The UIC System of Classification of Locomotives
The UIC system of classification of railroad locomotives is managed by the International Union of Railways (UIC: Union Internationale des Chemins de fer). There are two UIC systems to consider.
The UIC Classification of Locomotive Axle Arrangements
This classification scheme describes the axel arrangement of locomotives, multiple units and trams. Note that an axel in this context always implies two wheels. The UIC axel classification system is widely used world-wide, with notable exceptions being the United Kingdom, which uses a slightly simplified form of UIC (except for steam locomotives and small diesel shunters, where Whyte notation is used), and in North America, where the Association of American Railroads (AAR) wheel arrangement system (essentially another simplification of the UIC system) is used to describe diesel and electric locomotives; Whyte notation is used in North America only for steam locomotives.
The UIC axel classification scheme uses the structure defined in the following table.
The UIC system of classification of railroad locomotives is managed by the International Union of Railways (UIC: Union Internationale des Chemins de fer). There are two UIC systems to consider.
The UIC Classification of Locomotive Axle Arrangements
This classification scheme describes the axel arrangement of locomotives, multiple units and trams. Note that an axel in this context always implies two wheels. The UIC axel classification system is widely used world-wide, with notable exceptions being the United Kingdom, which uses a slightly simplified form of UIC (except for steam locomotives and small diesel shunters, where Whyte notation is used), and in North America, where the Association of American Railroads (AAR) wheel arrangement system (essentially another simplification of the UIC system) is used to describe diesel and electric locomotives; Whyte notation is used in North America only for steam locomotives.
The UIC axel classification scheme uses the structure defined in the following table.
Specification and Examples of the UIC Axel Classification Scheme
The following suffixes may be used with the above scheme to further refine a classification:
- h: superheated steam
- n: saturated steam
- v: compound
- Turb: turbine
- number: number of cylinders
- t: tank locomotive
- tr: tram (urban) locomotive
- E: Engerth-type locomotive
- G: freight
- P: passenger
- S: fast passenger
The UIC System of Identifying Locomotives
In addition to axel arrangement, the UIC system is used to identify a locomotive irrespective of axel arrangement. This system provides a unique identifier for every locomotive within its sphere of influence. The system is called the UIC Identification Marking for Tractive Stock (UIC ID Mark).
The UIC locomotive identifier is a 12-digit number that may be displayed as plain text, as a barcode or as a Quick Response (QR) Code.
The UIC locomotive identifier is structured as shown in the flowing illustration:
Structure of the UIC Locomotive Identifier
The International Block consists of two parts, a type code and a country code. The type codes, ranging from 90 to 99, specify a type of locomotive (e.g., 91 = electric locomotive; 92 = diesel locomotive). The country code is a two-digit number that specifies the country to which the identifier pertains. Spain, for example, has the country code 71.
The National Block consists of two parts, a series number and an order number. The series number (4 digits) is assigned by the country of ownership and thus varies by country. The order number (3 digits) is a serial number within a series, also assigned by the country of ownership. The country code distinguishes otherwise duplicate numbers.
The final digit is a check digit used to insure uniqueness of the complete identification mark. It is computed via an algorithm developed by H. P. Luhn.
An example UIC locomotive identification mark is shown and parsed below. The precise format of the number is immaterial so long as the order of digits is not altered.
The National Block consists of two parts, a series number and an order number. The series number (4 digits) is assigned by the country of ownership and thus varies by country. The order number (3 digits) is a serial number within a series, also assigned by the country of ownership. The country code distinguishes otherwise duplicate numbers.
The final digit is a check digit used to insure uniqueness of the complete identification mark. It is computed via an algorithm developed by H. P. Luhn.
An example UIC locomotive identification mark is shown and parsed below. The precise format of the number is immaterial so long as the order of digits is not altered.
Parse of a UIC Locomotive Identifier
A reporting mark or Vehicle Keeper Marking (VKM) is also assigned to every piece of rolling stock to identify the owner or leesee, as appropriate. In North America, the VKM or Reporting Mark is assigned by Railinc Corporation. Examples of such identifying marks may be found in the tables of Class I and Class II railroads presented earlier. In the United States, rolling stock is identified by the Reporting Mark, followed by a number of 1-6 digits. For example, UP 23452 identifies an un-powered car owned by Union Pacific Railroad (UP). The number does not necessarily represent the total number of cars owned or leased by a Reporting Mark.
We turn next to a discussion of the major types of locomotives based on type of motive power: steam, diesel fuel and electric energy.
Steam Locomotive
The steam locomotive is a marvel of engineering. Although very largely historical at this point in time, it is instructive to study the basics of steam locomotives.
Steam-powered locomotives convert steam energy to mechanical energy by boiling water to produce steam. Liquid water increases in volume by about 1700 times at standard temperature and pressure (STP) when it changes to the gaseous state and it is this change in volume that creates a mechanical advantage.
Steam (gaseous water) produced in a boiler is piped to a cylinder containing a piston. This forces the piston to move. By linking the piston to an axel, the movement of the piston is translated into a movement of the axel. If the axel is fitted with wheels at opposite ends, the wheels will rotate, thus achieving motion along a predetermined path. If the cylinder containing the piston can be fed steam at either end, a continuous forward movement of the linked wheels can be achieved. That is the essence of operation of a steam-powered locomotive. Examples of steam-powered locomotives on the Shannondell Model Railroad may be found here.
Every steam locomotive consisted of a frame upon which to support a fire box that heated water to steam in a boiler, a cab in which the driver and support staff worked, a set of wheels upon which these components rested, plumbing, control mechanisms and other components. The following illustration identifies 48 different but integrated components of a steam locomotive.
The steam locomotive is a marvel of engineering. Although very largely historical at this point in time, it is instructive to study the basics of steam locomotives.
Steam-powered locomotives convert steam energy to mechanical energy by boiling water to produce steam. Liquid water increases in volume by about 1700 times at standard temperature and pressure (STP) when it changes to the gaseous state and it is this change in volume that creates a mechanical advantage.
Steam (gaseous water) produced in a boiler is piped to a cylinder containing a piston. This forces the piston to move. By linking the piston to an axel, the movement of the piston is translated into a movement of the axel. If the axel is fitted with wheels at opposite ends, the wheels will rotate, thus achieving motion along a predetermined path. If the cylinder containing the piston can be fed steam at either end, a continuous forward movement of the linked wheels can be achieved. That is the essence of operation of a steam-powered locomotive. Examples of steam-powered locomotives on the Shannondell Model Railroad may be found here.
Every steam locomotive consisted of a frame upon which to support a fire box that heated water to steam in a boiler, a cab in which the driver and support staff worked, a set of wheels upon which these components rested, plumbing, control mechanisms and other components. The following illustration identifies 48 different but integrated components of a steam locomotive.
Main components of a typical steam locomotive
A description of the numbered components (above) is given in the following table.
Description of the keyed components in the above illustration
Although steam-powered locomotives were used for many years, the only remaining operating examples are used in tourist applications (e.g., excursion trains) giving people a chance to experience them once again. Some can also be found in museums.
No steam-powered locomotive could meet the current regulations for environmental care and probably not safety and health regulations either. There is an instructive video (17:16 minutes) showing how a steam locomotive was built in 1935. It is well worth watching.
The following image is of a steam locomotive built by Climax Manufacturing Co. in Curry, PA in 1923.
No steam-powered locomotive could meet the current regulations for environmental care and probably not safety and health regulations either. There is an instructive video (17:16 minutes) showing how a steam locomotive was built in 1935. It is well worth watching.
The following image is of a steam locomotive built by Climax Manufacturing Co. in Curry, PA in 1923.
Photo of Climax No. 1653 housed at The Tasmanian Transport Museum in Glenorchy, Tasmania, Australia. It worked in the logging industry in Australia
Diesel-Electric Locomotive
The workhorse of the railroad industry today is the diesel-electric locomotive, especially in North America. These locomotives are electric because it is electric traction motors that drive the axels. They are diesel because it is a large diesel-powered engine that drives either a generator or alternator that produces the electricity upon which the traction motors depend. Gone are the massive drive wheels of the steam era, replaced by two or more trucks (bogies) of two or three axels (trucks will be described in more detail a bit later). A tender is replaced by a diesel fuel tank suspended from the locomotive frame.
Within the body of the locomotive there is a diesel engine, the drive-shaft of which is coupled to either a generator (producing direct current or DC electric power) or an alternator (producing alternating current or AC electric power). Various other devices in the locomotive are also electrically powered, such as the operating controls, an air compressor for air brakes and other applications, a traction motor blower to help maintain the correct traction motor operating temperature and radiator fans to maintain the correct operating temperature of the diesel engine. These various devices, although essential, do not contribute to tractive effort and are thus called parasitic loads (an electrical load is anything energized by a source of electricity; in essence a consumer of electrical energy).
The following diagram illustrates the main components of a diesel-electric locomotive.
A simple diagram illustrating the main components of a diesel-electric locomotive
In this illustration, the diesel engine drives an alternator that produces alternating current (AC) at some desired voltage. This AC supply then passes through a rectifier that not only converts the AC to DC, it is also designed to smooth the current flow to yield a steady voltage. Once a steady voltage is achieved, the current passes through an inverter to produce AC once again. This power source drives the traction motors that move the locomotive. In the above illustration, the locomotive has two trucks (bogies) each with three axels (6 wheels). Each axel is rotated by means of gears turned by the traction motors that mesh with the gears on the axels. The trucks also carry a braking mechanism to slow or stop the locomotive.
Diesel-electric locomotives are much more efficient and environmentally friendly than steam-powered locomotives. The Environmental Protection Agency established Tier 4 performance standards for diesel-electric locomotives in 2015. General Electric Transportation (now part of Wabtec) began delivering a new line of such locomotives beginning in Autumn 2015. Today, the addition of battery-powered locomotives (see Other Motive Power below) further improves both environmental performance and overall fuel efficiency. The following photo shows an example of a diesel-electric locomotive.
BNSF No. 8013 seen in Dallas, Texas, 2014 May 20. This is a GE ES44C4 4,000 HP locomotive with two 3-axel trucks, driven by 4 traction motors.
Electric Locomotive
Unlike the diesel-electric locomotive, an electric locomotive does not produce its own power but derives it from some external source (however, see Other Motive Power later on). The following illustration identifies the main components of an electric locomotive.
Unlike the diesel-electric locomotive, an electric locomotive does not produce its own power but derives it from some external source (however, see Other Motive Power later on). The following illustration identifies the main components of an electric locomotive.
Schematic diagram of an electric locomotive
A description of the numbered components of the above diagram is given in the following table.
Key to electric locomotive diagram
Electric locomotives usually obtain electric power from overhead catenary lines or from a third rail. It is also possible to use batteries, but the technology is not quite ready for very long runs at present. We here limit the discussion to supply of electricity power to a locomotive via overhead catenary lines. These lines operate at various voltages in different parts of the world, but an increasingly popular standard is 25,000 volts (25 kV) at 60 Hertz. Nevertheless, voltage ranges from about 600 V to 25 kV. Some lines are DC, but the higher voltage lines are AC.
Needless to say, the electric locomotive must be designed to operate on the lines available (or the railroad must generate the electric energy itself). The incoming electric power passes through a transformer that either steps down or steps up the voltage as needed. The current at the proper voltage then passes through a rectifier that converts alternating current to direct current so that the voltage can be smoothed and steadied. An inverter is then used to convert back to alternating current since the traction motors run on AC (as do other functional elements such as blowers, fans, compressors and controls). A battery back-up system may need to be charged via DC, necessitating an auxiliary rectifier. The battery back-up enables critical control systems to operate in the event of loss of main power.
The locomotive is moved using traction motors connected to axels in the leading and trailing trucks (bogies). We will have more to say about trucks later. In the illustration above, the locomotive has two trucks of three axels each. All are shown as powered in the illustration, but sometimes the middle axel in each truck is unpowered. The choice depends on the purpose of the locomotive. The traction motors may be of different designs. At present, they are likely to be 3-phase AC motors. Other designs have been used, including one in which the axel served as the rotating shaft of the motor. Today, most traction motors are geared to the axel, one motor to each axel. An electric locomotive is illustrated below.
Needless to say, the electric locomotive must be designed to operate on the lines available (or the railroad must generate the electric energy itself). The incoming electric power passes through a transformer that either steps down or steps up the voltage as needed. The current at the proper voltage then passes through a rectifier that converts alternating current to direct current so that the voltage can be smoothed and steadied. An inverter is then used to convert back to alternating current since the traction motors run on AC (as do other functional elements such as blowers, fans, compressors and controls). A battery back-up system may need to be charged via DC, necessitating an auxiliary rectifier. The battery back-up enables critical control systems to operate in the event of loss of main power.
The locomotive is moved using traction motors connected to axels in the leading and trailing trucks (bogies). We will have more to say about trucks later. In the illustration above, the locomotive has two trucks of three axels each. All are shown as powered in the illustration, but sometimes the middle axel in each truck is unpowered. The choice depends on the purpose of the locomotive. The traction motors may be of different designs. At present, they are likely to be 3-phase AC motors. Other designs have been used, including one in which the axel served as the rotating shaft of the motor. Today, most traction motors are geared to the axel, one motor to each axel. An electric locomotive is illustrated below.
Amtrak 627 electric locomotive pulling a Northeast Regional in Madison, Connecticut, April 2015.
What we have described is a locomotive entirely dependent upon an external source of power. Take away the catenary line or third rail and the locomotive comes to a halt. However, use of battery storage of electric potential (like the fuel tank of a diesel-electric locomotive) renders an electric locomotive semi-independent of external sources of power.
Speaking of independence, the following table compares the three major sources of motive power. Obviously, none are independent of fuel source, but both steam and diesel or diesel-electric are more nearly independent compared with electric employing either overhead catenary or third rail delivery of electric energy. Nevertheless, continued research and development may soon permit electric locomotives to replace diesel-electric (see Other Motive Power, below).
Speaking of independence, the following table compares the three major sources of motive power. Obviously, none are independent of fuel source, but both steam and diesel or diesel-electric are more nearly independent compared with electric employing either overhead catenary or third rail delivery of electric energy. Nevertheless, continued research and development may soon permit electric locomotives to replace diesel-electric (see Other Motive Power, below).
Comparison of three major sources of motive power on four dimensions
Electric locomotives are more likely to be used on freight routes that have consistently high traffic volumes, or in areas with advanced rail networks. Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines. The power can also come from low-carbon or renewable sources, including geothermal power, hydroelectric power, biomass, solar power, nuclear power, hydrogen and wind turbines. Electric locomotives usually cost 20% less than diesel locomotives, their maintenance costs are 25-35% lower, and cost up to 50% less to operate. In addition, they are the most environmentally sound locomotives in operation.
Other Motive Power
There are other sources of power to move trains beside the three, steam, diesel-electric or electric, that we have described. These newer power sources all yield electric energy that drives a locomotive. We consider electrical energy storage where the electrical energy is generated away from the locomotive and electrical energy generation within the locomotive.
Batteries are devices that store electrical potential for later use. We are all familiar with lead/acid batteries used in automobiles, trucks and the like. The problem with this type of battery is that they are heavy and have a low specific energy (energy per unit mass). They also pose an environmental hazard due to the lead used.
However, there are many other types of battery with varying performance characteristics depending on the chemistry used (e.g., lithium ion), packaging, etc. There are two broad classes of battery for electrical energy storage, primary and secondary. Primary batteries are designed for use until exhausted and then discarded (think of the common AA alkaline battery). Secondary batteries are designed to be recharged and reused (Ni-Cd batteries, Li-ion batteries and many others). It is this type of battery of main interest to railroads.
Wabtec Corporation has introduced a battery-powered locomotive called FLXdrive. This locomotive carries enough power to operate as a freight locomotive or switching locomotive, using a battery pack containing some 20,000 lithium ion cells that collectively produce 2,400 kilowatt hours of electricity to power four traction motors (two on each 3-axel truck). The locomotive is designed to work together with standard diesel-electric units to reduce environmentally hazardous emissions, reduce diesel fuel consumption and pull a train over considerable distance once operating momentum has been achieved. The locomotive can produce a full 4,400 horse-power output for 30-40 minutes. The photo below shows such a locomotive being "fueled" from track side. Regenerative braking is also employed to recharge batteries during operation (see also Wabtec).
Other Motive Power
There are other sources of power to move trains beside the three, steam, diesel-electric or electric, that we have described. These newer power sources all yield electric energy that drives a locomotive. We consider electrical energy storage where the electrical energy is generated away from the locomotive and electrical energy generation within the locomotive.
Batteries are devices that store electrical potential for later use. We are all familiar with lead/acid batteries used in automobiles, trucks and the like. The problem with this type of battery is that they are heavy and have a low specific energy (energy per unit mass). They also pose an environmental hazard due to the lead used.
However, there are many other types of battery with varying performance characteristics depending on the chemistry used (e.g., lithium ion), packaging, etc. There are two broad classes of battery for electrical energy storage, primary and secondary. Primary batteries are designed for use until exhausted and then discarded (think of the common AA alkaline battery). Secondary batteries are designed to be recharged and reused (Ni-Cd batteries, Li-ion batteries and many others). It is this type of battery of main interest to railroads.
Wabtec Corporation has introduced a battery-powered locomotive called FLXdrive. This locomotive carries enough power to operate as a freight locomotive or switching locomotive, using a battery pack containing some 20,000 lithium ion cells that collectively produce 2,400 kilowatt hours of electricity to power four traction motors (two on each 3-axel truck). The locomotive is designed to work together with standard diesel-electric units to reduce environmentally hazardous emissions, reduce diesel fuel consumption and pull a train over considerable distance once operating momentum has been achieved. The locomotive can produce a full 4,400 horse-power output for 30-40 minutes. The photo below shows such a locomotive being "fueled" from track side. Regenerative braking is also employed to recharge batteries during operation (see also Wabtec).
"Fueling" a Wabtec FLXdrive battery-electric locomotive
Other manufacturers have produced, or are developing, battery-electric locomotives, including Progress Rail (U.S.A.), Alstom (France), Deutsche Bahn (Germany), JR Group (Japan) and Wabtec-India (India) among others.
As progress is made in battery storage of electric power, it may soon be possible to operate electric locomotives over quite long distances (see Environmental and Energy Study Institute). In the meantime, hybrid schemes in which a combination of battery power and diesel-electric power or battery-electric-multiple-unit (BEMU) motive power has been developed and is being installed by various railroads, including BNSF Railway (BNSF), Union Pacific Railroad (UP), Société Nationale des Chemins de fer Français (SNCF), Chiltern Railway (CH), and others. These BEMUs will improve operating efficiency and reduce environmental degradation while proving the use of battery-electric locomotives.
As progress is made in battery storage of electric power, it may soon be possible to operate electric locomotives over quite long distances (see Environmental and Energy Study Institute). In the meantime, hybrid schemes in which a combination of battery power and diesel-electric power or battery-electric-multiple-unit (BEMU) motive power has been developed and is being installed by various railroads, including BNSF Railway (BNSF), Union Pacific Railroad (UP), Société Nationale des Chemins de fer Français (SNCF), Chiltern Railway (CH), and others. These BEMUs will improve operating efficiency and reduce environmental degradation while proving the use of battery-electric locomotives.
In addition to battery storage of electric energy, hydrogen fuel cells are being used to generate electricity on board a locomotive as is done in diesel-electric locomotives. The hydrogen fuel cell produces electric energy by removing electrons from hydrogen atoms and combining the resulting hydrogen ion (proton) with oxygen to yield water. The image below gives an elementary view of how a hydrogen fuel cell works. The flow of electrons (electric energy) from the anode energizes a load (e.g., a traction motor) and then returns to the cathode, completing a circuit.
Simplified schematic of a hydrogen fuel cell
More detail on fuel cells may be found at Ballard (using batteries to store the power generated), Chiltern Railways (converting diesel-electric locomotives to fuel-cell power) and Railway Age (using batteries to store the power generated). See also Green Car Congress.
There are several advantages to either battery-electric or hydrogen fuel-cell electric motive power, including much less pollution, lower installation costs (no overhead catenary lines or third rails), lower maintenance costs and lower operating costs.
Two hydrogen-powered units are shown in the following figures, one manufactured by Alstom and one by Siemens. There are a number of other similar products on the market.
There are several advantages to either battery-electric or hydrogen fuel-cell electric motive power, including much less pollution, lower installation costs (no overhead catenary lines or third rails), lower maintenance costs and lower operating costs.
Two hydrogen-powered units are shown in the following figures, one manufactured by Alstom and one by Siemens. There are a number of other similar products on the market.
Alstom Coradia iLint hydrogen-fueled train
Siemens Mobility Mireo Plus H hydrogen-fueled train
Nuclear power has also been considered for use on railroads. An article in Life magazine (June 21, 1954, pp. 78-79) described in some detail a nuclear-powered locomotive (never built) that could improve operating efficiency and require refueling much less often than conventional locomotives of the day.
A U.S. patent was issued to one L. B. Borst (University of Utah) on March 31, 1964, titled Nuclear Reactor for a Railway Vehicle, U.S. Patent 3,127,321. No further development has been reported. A more recent U.S. Patent (US20090283007A1) issued to W. G. Taylor, "Nuclear Locomotive", describes the use of nuclear energy to power a maglev (magnetic levitation) locomotive. No further work has been described based on this patent.
Russia is reported to have designed a nuclear-powered locomotive, but this too has evidently not produced anything operational.
Bill Lee has written a piece (November, 2013) taking a very pragmatic view of nuclear-powered locomotives and concludes they are quite impractical. A more recent review of "atomic trains" provides a good summary of the pros and cons of the idea. In short, the weight of necessary shielding, cooling mechanisms and other issues makes nuclear-powered locomotives unrealistic at present. Nevertheless, fusion (rather than fission) nuclear power may one day change this view.
Locomotive Manufacturers
We have mentioned a number of companies that have manufactured or are manufacturing locomotives in the United States. World-wide, hundreds of companies have built locomotives of various types and sizes (see Locomotive Builders). Well-known U.S.A. companies included Baldwin Locomotive Works, American Locomotive Company (ALCO), Lima Locomotive Works, and Altoona Works, all of which built locomotives not only for domestic applications but for use in other countries as well. Several specialty manufacturers, such as Climax Manufacturing Company of Corry, Pennsylvania and Lima Locomotive Works, built locomotives for logging, mining and other applications. These and many other locomotive builders are now all defunct.
Among U.S.A. companies still in operation are NS Juniata Locomotive Shop, Wabtec, Fairbanks-Morse, Electro-Motive Diesel (EMD) and Progress Rail. The following table presents a selected list of locomotive manufacturers around the world.
Selected Locomotive Manufacturers
Famous Locomotives
From the historical point of view, several locomotives have become famous for various reasons. Among them are the following:
Tom Thumb, designed and constructed in 1829 by Peter Cooper, was the first American-built steam locomotive to operate on a common-carrier, the Baltimore and Ohio Railroad (B&O). It was intended to replace B&O's use of horse-drawn trains.
New York Central and Hudson River Railroad No. 999, a 4-4-0 “American” type steam locomotive, was built for the railroad in 1893, by New York Central West Albany Shops.
Pennsylvania Railroad 1361 is a 4-6-2 "Pacific"-type steam locomotive built in 1918 by the Pennsylvania Railroad's Altoona Works. See also "Pacific K4" under Railroad History.
From the historical point of view, several locomotives have become famous for various reasons. Among them are the following:
Tom Thumb, designed and constructed in 1829 by Peter Cooper, was the first American-built steam locomotive to operate on a common-carrier, the Baltimore and Ohio Railroad (B&O). It was intended to replace B&O's use of horse-drawn trains.
New York Central and Hudson River Railroad No. 999, a 4-4-0 “American” type steam locomotive, was built for the railroad in 1893, by New York Central West Albany Shops.
Pennsylvania Railroad 1361 is a 4-6-2 "Pacific"-type steam locomotive built in 1918 by the Pennsylvania Railroad's Altoona Works. See also "Pacific K4" under Railroad History.
An HO-scale model of Pennsylvania Railroad 1361 on the Shannondell Model Railroad
LNER Class A3 4472 Flying Scotsman is a 4-6-2 "Pacific" steam locomotive built in 1923 for the London and North Eastern Railway (LNER) at Doncaster Works. It was employed on long-distance express service between London, UK and Edinburgh, Scotland.
London and Northeastern Railway (LNER) Flying Scotsman locomotive No. 4472 at Doncaster, England
Japan Railways Shinkansen 1964. Starting with the Tōkaidō Shinkansen (515.4 km, 320.3 mi) in 1964, Japan introduced the era of fast trains (trains routinely operating at velocities of 125 mph (200 kmh or more). The Shinkansen is actually a train set, because all cars are built to operate as an integral unit. Trains of up to 16 cars may be used to handle the high volume of passenger traffic experienced (over 5.6 billion paying customers since inception). Today there are many Shinkansen running on five interconnected routes. These trains operate with extreme precision, allowing trains on a given line to be spaced as closely as 3 minutes apart.
Photo of Japan's Shinkansen train about 1967