A steam turbine locomotive
is a steam locomotive
which transmits steam power to the wheels via a steam turbine
. Numerous attempts at this type of locomotive were made, mostly without success. In the 1930s this type of locomotive was seen as a way both to revitalize steam power and challenge the diesel locomotives then being introduced.
Advantages of steam turbines
- High efficiency at high speed.
- Far fewer moving parts, hence potentially greater reliability.
- Conventional piston steam locomotives give a varying, sinusoidal torque, making wheelslip much more likely when starting.
- The side rods and valve gear of conventional steam locomotives create horizontal forces that cannot be fully balanced without substantially increasing the vertical forces on the track, known as hammer blow.
Disadvantages of steam turbines
- High efficiency is ordinarily obtained only at high speed (though some Swedish and UK locomotives were designed and built to operate with an efficiency equal to or better than that of piston engines under customary operating conditions). Gas turbine locomotives had similar problems, together with a range of other difficulties.
- Peak efficiency can be reached only if the turbine exhausts into a near vacuum, generated by a surface condenser. These devices are heavy and cumbersome.
- Turbines can rotate in only one direction. A reverse turbine must also be fitted for a direct-drive steam turbine locomotive to be able to move backwards.
There are two ways to drive the wheels: either directly via gears, or using generator-driven traction motors.
The Pennsylvania Railroad
used the largest direct-drive steam turbine locomotive in the world. Built by Baldwin Locomotive Works, the S2 Turbine, c/n 70900, was delivered to Pennsylvania Railroad in September 1944. It was originally designed as a 4-8-4, but due to shortages of lightweight materials during World War II, the S2 became the only locomotive ever built with a 6-8-6 wheel arrangement
. PRR #6200, the S2
turbine, had a maximum power output of 6,900 HP (5.1 MW) and was capable of speeds over 100mph. With the tender, the unit was approximately 123 feet long. The steam turbine was a modified marine unit. While the gearing system was simpler than a generator, it had a fatal flaw: the turbine was inefficient at slow speeds. Below about 40 mph (64 km/h) the turbine used enormous amounts of steam and fuel. At high speeds, however, the S2 could propel heavy trains almost effortlessly and efficiently. The smooth turbine drive put far less stress on the track than a normal piston-driven locomotive. However, poor efficiency at slow speeds doomed this turbine, and with diesel-electrics
being introduced, no more S2s were built. The locomotive was retired in 1949 and scrapped in May, 1952.
One of the more successful turbines operated in the United Kingdom
. The LMS Turbomotive
was a 4-6-2
locomotive with no condenser. Despite this, it had greater thermal efficiency than conventional locomotives. The high efficiency mainly resulted from the fact that there were six steam nozzles directed into the turbine which could be turned on and off individually. A certain amount of inspiration appears to have come from Fredrik Ljungström's turbines in Sweden. The main turbine failed after eleven years in heavy service. The Turbomotive was converted to piston drive in 1949 and withdrawn after the deadly Harrow and Wealdstone railway accident
One locomotive was built by Beyer-Peacock and used a turbine from Ljungström. Like one of Ljungström's early designs, the driving wheels were under the tender. Performance was disappointing, partly because of poor heating of the boiler.
Another unit was rebuilt by the North British Locomotive Company. In its first incarnation (described below) it had an electrical transmission. Only a few tests were done before it was abandoned due to mechanical failures.
Multiple attempts at this type were made by German
locomotive builders. In 1928 Krupp
built a geared steam turbine locomotive. The output of the turbine was fed to a condenser
which both conserved water and increased the thermal efficiency of the turbine. Draft for the fire was provided by a steam-driven fan in the smokebox
. In 1940 this locomotive was hit by a bomb. It was withdrawn from service and not repaired.
A similar machine was built by Maffei in 1929. Despite having a higher-pressure boiler, it was less efficient than the Krupp-Zoelly locomotive. It was hit by a bomb in 1943 and removed from service.
Henschel converted a normal steam locomotive to use a steam turbine in 1927. Additional driving wheels under the tender were driven by the turbine. The exhaust from the cylinders was fed to the turbine, and the turbine exhaust was fed into a condenser. A smokebox fan provided draft for the fire. Performance was disappointing, and the tender turbine was later removed.
Two attempts were made in France
. One effort, the Nord Turbine, resembled the LMS Turbomotive
in both appearance and mechanical layout. The project was canceled and the locomotive was built as a compound piston steam locomotive instead. The second attempt, SNCF 232Q1
, was built in 1939. It was unusual in that its driving wheels
were not connected by side rods
. Each of its three driving axles had its own turbine. It was heavily damaged by German troops in World War II
and was scrapped in 1946.
built a turbine locomotive in 1919. It was a 4-6-0
locomotive fitted with a condenser. It was fitted with a cold-air blower feeding into the firebox
grate rather than a suction fan in the smokebox. This avoided the complexity of building a fan that could withstand hot, corrosive gases, but introduced a new problem. The firebox was at positive pressure
, and hot gases and cinders could be blown out the firebox doors if they were opened while the blower was operating. This potentially dangerous arrangement was eventually replaced with a smokebox fan.
designed a number of experimental turbine locomotives. None were ever tested on main lines. His first was a small locomotive with four wheels, each fitted with its own small turbine. Reverse movement was accomplished by feeding steam into the turbines via a backwards-facing inlet. Steam turbines are designed to rotate in only one direction, making this method very inefficient. No one else appears to have attempted it.
Belluzzo contributed to the design of a 2-8-2 locomotive built by Ernesto Breda in 1931. It used four turbines in a multiple expansion arrangement.
In 1933, an FS 2-6-2 locomotive was rebuilt with turbines. It made a test run from Florence to Pistoia and then was never seen again.
engineer Fredrik Ljungström
designed a number of steam turbine locomotives, some of which were highly successful. His first attempt in 1921 was a rather odd-looking machine. Its three driving axles were located under the tender, and the cab and boiler sat on unpowered wheels. As a result, only a small portion of the locomotive's weight contributed to traction
The second design was a 2-8-0 similar to a successful freight design. Built in 1930 and 1936 by Nydqvist and Holm, these locomotives replaced conventional ones on the Grängesberg-Oxelösund Railway. No condenser was fitted, as its complexity outweighed its thermodynamic advantages. The wheels were driven by a jackshaft. These engines were not retired until the 1950s when the line was electrified. Two examples of this type have been preserved and can be seen in Grängesberg, Sweden.
The route from Tucumán
to Santa Fe
goes through mountainous terrain with few opportunities to take on water. In 1925 the Swedish firm NOHAB
built a turbine locomotive similar to Ljungström's first design. The condenser worked quite well - only 3 or 4% of the water was lost en route and due only to leakage from the tank. The locomotive had reliability problems and was later replaced by a condenser-equipped piston steam locomotive.
built two steam turbine-electric locomotives with a 2-C+C-2
) wheel arrangement for the Union Pacific Railroad
in 1938. These locomotives were essentially mobile power plants
and were correspondingly complex. They were the only condensing steam locomotives ever used in the United States. A Babcock and Wilcox
boiler provided steam, and an electric generator was fitted in the front of the locomotive to provide head-end power
, a concept that would not catch on until the creation of Amtrak
. Boiler control was largely automatic, and the two locomotives could be MUed
together, both controlled by one engineer. The fuel was Bunker C oil, the same fuel that was later used in Union Pacific's gas turbine-electric locomotives
. Union Pacific accepted the locomotives in 1939, but returned them later that year, citing unsatisfactory results. The GE turbines were used during a motive power shortage on the Great Northern Railway
in 1943, and appear to have performed quite well.
In the waning years of steam, the Baldwin Locomotive Works undertook several attempts at alternative technologies to diesel power. In 1944, Baldwin outshopped an S2 class 6-8-6 direct-drive steam turbine locomotive for the Pennsylvania Railroad (see above).
Between 1947–1948, Baldwin built three unique coal-fired steam turbine-electric locomotives, designed for passenger service on the Chesapeake and Ohio Railway (C&O). Their official designation was M1, but because of their expense and poor performance they acquired the nickname "Sacred Cow". The 6,000-horsepower units, which were equipped with Westinghouse electrical systems, had a 2-C1+2-C1-2 wheel arrangement. They were 106 feet (32 m) long, making them the longest locomotives ever built for passenger service. The cab was mounted in the center, with a coal bunker ahead of it and a backwards-mounted conventional boiler behind it (the tender only carried water). These locomotives were intended for a route from Washington, D.C. to Cincinnati, Ohio but could never travel the whole route without some sort of failure. Coal dust and water frequently got into the traction motors. While these problems could have been fixed given enough time, it was obvious that these locomotives would always be expensive to maintain, and all three were scrapped in 1950.
In May, 1954 Baldwin built a 4,500-horsepower steam turbine-electric locomotive for freight service on the Norfolk and Western Railway (N&W), nicknamed the Jawn Henry after the legend of John Henry, a track layer who famously raced against a steam drill and won, only to die immediately after. The unit was similar in appearance to the C&O turbines but very different mechanically; it had a C+C-C+C wheel arrangement, and a Babcock and Wilcox water-tube boiler which was fitted with automatic controls. Unfortunately, the boiler controls were sometimes problematic, and (as with the C&O turbines) coal dust and water got into the motors. The Jawn Henry was retired from the N&W roster on January 4, 1958.
The Reid-Ramsey turbine, built by the North British Locomotive Company
in 1910, had a 2-B+B-2
) wheel arrangement. Little is known about it, though it appears to have been unsuccessful. It was later rebuilt as a direct-drive turbine locomotive as seen above.
The Armstrong-Whitworth turbine, built in 1922, had a 1-C+C-1 (2-6-6-2) wheel arrangement. It was fitted with a rotary evaporative condenser, in which the steam was condensed by passing it through a rotating set of tubes. The tubes were dampened and cooled by the evaporation of water. The loss of water from evaporation was far less than what it would have been with no condenser at all. The airflow in the condenser had to take a convoluted path, reducing the condenser's efficiency. The locomotive was overweight and a poor performer. It was returned in 1923 and scrapped.