A GTEL uses a turbo-electric drivetrain in which a turboshaft engine drives an electrical generator or alternator via a system of gears. The electrical power is distributed to power the traction motors that drive the locomotive. In overall terms the system is very similar to a conventional diesel-electric, with the large diesel engine replaced with a smaller gas turbine of similar power.
A gas turbine offers some advantages over a piston engine. There are few moving parts, decreasing the need for lubrication and potentially reducing maintenance costs, and the power-to-weight ratio is much higher. A turbine of a given power output is also physically smaller than an equally powerful piston engine, allowing a locomotive to be very powerful without being inordinately large. However, a turbine's power output and efficiency both drop dramatically with rotational speed, unlike a piston engine, which has a comparatively flat power curve. This makes GTEL systems useful primarily for long-distance high-speed runs.
Union Pacific operated the largest fleet of such locomotives of any railroad in the world, and was the only railroad to use them for hauling freight. Most other GTELs have been built for small passenger trains, and only a few have seen any real success in that role. With a rise in fuel costs (eventually leading to the 1973 oil crisis), gas turbine locomotives became uneconomical to operate, and many were taken out of service. Additionally, Union Pacific's locomotives required more maintenance than originally anticipated, due to fouling of the turbine blades by the Bunker C oil used as fuel.
Additional problems with gas turbine-electric locomotives included that they were very noisy, and they produced such extremely hot exhaust that if the locomotive were parked under an overpass paved with asphalt, it could melt the asphalt.
In 1939 the Swiss Federal Railways ordered a GTEL with a 1,620 kW (2,170 hp) of maximum engine power from Brown Boveri. It was completed in 1941, and then underwent testing before entering regular service. The Am 4/6 was the first gas turbine - electric locomotive. It was intended primarily to work light, fast, passenger trains on routes which normally handle insufficient traffic to justify electrification.
Two gas turbine locomotives of different design, 18000 and 18100 were ordered by the Great Western Railway, but completed for the newly nationalised British Railways.
18000 was built by Brown Boveri and delivered in 1949. It was a 1840 kW (2470 hp) GTEL, ordered by the GWR and used for express passenger services.
18100 was built by Metropolitan-Vickers and delivered in 1951. It had an aircraft-type gas turbine of 2.2 MW (3,000 hp). Maximum speed was 90 miles per hour (140 km/h).
The British Rail APT-E, prototype of the Advanced Passenger Train, was turbine-powered. Like the French TGV, later models were electric instead. This choice was made because British Leyland, the turbine supplier, ceased production of the model used in the APT-E.
SNCF In 1952, Renault delivered a prototype four-axle 1150 hp gas-turbine-mechanical locomotive fitted with the Pescara "free turbine" gas- and compressed-air producing system, rather than a co-axial multi-stage compressor integral to the turbine. This model was succeeded by a pair of six-axle 2400 hp locomotives with two turbines and Pescara feeds in 1959. However, these complex locomotives were not a complete success and meanwhile Renault decided to exit the railway equipment business. About a decade later, the first TGV prototype, TGV 001, was powered by a gas turbine, but steep oil prices prompted the change to overhead electric lines for power delivery. However, two large classes of gas-turbine powered intercity railcars were constructed in the early 1970s (ETG and RTG) and were used extensively up to about 2000.
Union Pacific ran a large fleet of turbine-powered freight locomotives starting in the 1950s. These were widely used on long-haul routes, and were cost-effective despite their poor fuel economy due to their use of "leftover" fuels from the petroleum industry. At their height the railroad estimated that they powered about 10% of Union Pacific's freight trains, a much wider use than any other example of this class. As other uses were found for these heavier petroleum byproducts, notably for plastics, the cost of the Bunker C fuel increased until the units became too expensive to operate and they were retired from service by 1969.
In April 1950, Westinghouse completed an experimental 4,000 hp (3,000 kW) turbine locomotive, #4000, known as the Blue Goose, with a B-B-B-B wheel arrangement. The locomotive used two 2,000 hp (1,500 kW) turbine engines, was equipped for passenger train heating with a steam generator that utilized the waste exhaust heat of the right hand turbine, and was geared for 100 miles per hour (160 km/h) While it was demonstrated successfully in both freight and passenger service on the PRR, MKT, and CNW, no production orders followed, and it was scrapped in 1953.
In 1997 the Federal Railroad Administration (FRA) solicited proposals to develop high speed locomotives for routes outside the Northeast Corridor where electrification was not economical. Bombardier Ltd, at the Plattsburg, N.Y. plant where the Acela was produced, developed a prototype (JetTrain) which combined a Pratt & Whitney Canada PW100 gas turbine and a diesel engine with a single gearbox powering four traction motors identical to those in Acela. The diesel provided head end power and low speed traction, with the turbine not being started until after leaving stations. The prototype was completed in June 2000, and safety testing was done at the FRA's Pueblo, CO test track beginning in the summer of 2001. A maximum speed of 156 miles per hour (251 km/h) was reached. The prototype was then taken on a tour of potential sites for high speed service, but no service has yet begun.
In 2002, Bombardier Transportation announced the launch of the JetTrain, a high-speed trainset consisting of tilting carriages and a locomotive powered by a Pratt & Whitney turboshaft engine. Proposals were made to use the trains for Quebec City-Windsor, Orlando-Miami, and in Alberta, Texas, Nevada and the UK.
However, nothing ever came of any of these proposals, and the JetTrain essentially disappeared, being superseded by the Bombardier Zefiro line of conventionally powered high speed and very high speed trains. The JetTrain no longer appears on any of Bombardier's current web sites or promotional materials, although it can still be found on older web sites bearing the Canadair logos.
Two gas turbine-electric locomotive types underwent testing in the Soviet Union. The G1-01 freight GTEL was intended to consist of two locomotives of a C-C wheel arrangement, but only one section was built. The test program began in 1959 and lasted into the early 1970s. The GP1 was a similar design, also with a C-C wheel arrangement, introduced in 1964. Two units were built, GP1-0001 and GP1-0002, which were also used in regular service. Both types had a maximum power output of 2,600 kW (3,500 hp).
In 2006, Russian Railways introduced the GEM-10 switcher GTEL. The turbine's maximum power output is 1,000 kW (1,300 hp) and it runs on liquefied natural gas. The GEM-10 has a C-C wheel arrangement. The TGEM10-0001 is a two-unit (cow-calf) switcher GTEL, with a B-B+B-B wheel arrangement, and uses the same turbine and fuel as the GEM-10.
The GT1-001 freight GTEL, introduced in 2007, runs on liquefied natural gas and has a maximum power output of 8,300 kW (11,100 hp). The locomotive has a B-B-B+B-B-B wheel arrangement, and up to three GT1s can be coupled. On January 23, 2009, the locomotive conducted a test run with a 159 car train weighing 15,000 metric tons (14,800 long tons; 16,500 short tons). Further heavy-haul tests were conducted in December 2010. In a test run conducted in September 2011 the locomotive pulled 170 freight cars weighing 16,000 metric tons (15,700 long tons; 17,600 short tons).