We as human kind have always aimed at achieving something better, something bigger. This led to the research on gas turbines, which was mainly inspired due to the immediate requirement in the aerospace and power generation industry, to also look beyond the scope of aeronautics.
Today gas turbine technology is often used when dealing with aerospace and power generation industries, but believe it or not, gas turbine technology has been used in ground transportation too; notably locomotives.
The Early Applications
After the first world war, several countries had the expertise and the finances to invest in achieving the technological edge in the new post war era. The gas turbine technology was one such technological endeavor, and by the mid-20th century the gas turbine could be found in several applications. Birth of gas turbine locomotives can be credited to two distinct characteristics of these locomotives versus the contemporary diesel locomotives. First, there are fewer moving parts in a gas turbine, decreasing the need for lubrication. This can also potentially reduce the maintenance costs. Second, the power-to-weight ratio is much higher for such locomotives which makes a turbine of a given power output physically smaller than an equally powerful piston engine, allowing a locomotive to be powerful enough without being too bulky.
Early Types of Gas Turbine Locomotives
Gas turbine locomotives are broadly classified in two types: 1) gas turbine-mechanical locomotives, and 2) gas turbine-electric locomotives. The first type uses a mechanical transmission to deliver the power output of gas turbines to the wheels. The second uses the gas turbine to drive an electric generator or alternator, which in turn powers traction motors. Marc Antoine Francois Mennons received the first patented design for a gas turbine locomotive in 1861. The design included all essential features of gas turbine locomotives built later in the 20th century, including compressor, combustion chamber, turbine and air pre-heater.
High fuel consumption was a major factor in the reluctance towards gas-turbine locomotives which delayed the application of first gas turbine locomotives. At the time, a piston engine with a gas generator could give better fuel economy than a turbine-type compressor, especially when running at less than a full load.
The first gas turbine-mechanical locomotive was the 1000 hp Class 040-GA-1, built by Renault in 1952. The Pescara gas generator in 040-GA-1 consisted of a horizontal, single cylinder, two-stroke diesel engine with opposed pistons. The exhaust from the diesel engine powered the gas-turbine which drove the wheels through a two-speed gearbox and propeller shafts. The diesel engine had no crankshaft and the pistons were returned after each power stroke by compression and expansion of air in a separate cylinder. The design is called the free piston engine, and it was patented by Raúl Pateras Pescara in 1934.
The development was simultaneously going on in Czechoslovakia, France, Sweden, UK USSR, and USA. In the 1940s and 1950s, research in both the USA and UK focused on building gas turbine locomotives which could run on pulverized coal.
Gas Turbine-Electric Locomotives
Experiments with gas turbine-electric locomotives (GTELs) started during the Second World War, and reached its peak during the 1950s and 1960s. In 1939, the Swiss Federal Railways commissioned Brown Boveri to deliver a GTEL with a 1,620 kW (2,170 hp) of maximum engine power. The first GTEL was delivered in 1941. After successfully passing all the tests “Am 4/6” finally entered regular service later that year. It became the world's first gas turbine-electric locomotive. The main role of Am 4/6 was to work light, fast, passenger trains on routes which normally handle insufficient traffic to justify electrification.
Union Pacific, in the USA, ran the largest fleet of GTELs of any railroad in the world. It was the only railroad to use them for hauling freight. At their peak, Union Pacific estimated that they powered about 10% of its freight trains, a much wider use than any other example of this class. They were widely used on long-haul routes, and proved cost-effective despite their poor fuel economy due to their use of "leftover" fuels from the petroleum industry.
GTELs used heavier petroleum byproducts for fuel. As other uses for these leftover fuels were found, notably for plastics, the cost of the Bunker C fuel increased until the units became too expensive to operate. Union Pacific retired CTELs from service by 1969.
Most GTELs were built based on the requirements of small passenger trains, and only a few met with success. In April 1950, Westinghouse produced an experimental 4000 hp (3000 kW) turbine locomotive, known as the Blue Goose. The locomotive consisted two 2000 hp (1500 kW) turbine engines, and was equipped for passenger train heating with a steam generator that utilized the waste exhaust heat of one of the turbines. It was geared for 100 miles per hour (160 km/h). It was demonstrated successfully in both freight and passenger services, but no production orders followed. The project was scrapped in 1953.
In the 1960s, United Aircraft built the Turbo passenger train, which was first tested by the Pennsylvania Railroad and later used by Amtrak and Via Rail. Via's engines remained in service till as late as into the 1980s and showed an excellent maintenance record during the operating period. They were eventually replaced by the LRCs in 1982.
In the Soviet Union, two gas turbine-electric locomotive projects were experimented. The test program, called G1-01 freight GTEL, began in 1959 and lasted into the early 1970s. The other project “GP1” was a similar design and was introduced in 1964. Two units were built, GP1-0001 and GP1-0002, which were also used in regular service.
Russian Railways demonstrated the GEM-10 switcher GTELin 2006, which runs on liquefied natural gas. 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). In a test run conducted in September 2011, the locomotive pulled 170 freight cars weighing 16,000 metric tons. This makes the GT1-001, the most powerful gas turbine locomotive ever produced till date.
The first TGV prototype if France, the TGV 001, was powered by a gas turbine. However, steep oil prices prompted the change to overhead electric lines for power delivery. 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 the year 2000. SNCF (French National Railways) used a number of gas-turbine train sets, called the Turbo-trains, in non-electrified territory. These typically consisted of a power car at each end with three cars between them. Turbotrains were in use up until 2005.
The Fall of Gas Turbine Locomotives
One thing that can be fathomed from this history of gas turbine locomotives is that there have been a few success stories. However, it is still hard to find gas turbine locomotives in common use in railways throughout the world. The development prompted by the advantages of the gas turbine locomotives did not replicate exponentially and eventually efforts in this field ceased.
The biggest disadvantage of gas turbines as prime movers in locomotives is fuel efficiency at low output (high turndown). Diesel engines are the preferred prime movers because of relatively high efficiency at all output levels, especially if the prime mover speed is allowed to vary with power output (true in most locomotive applications). A turbine's power output and efficiency both drop significantly with rotational speed, unlike a piston engine, which has a comparatively flat power curve. This renders GTEL systems useful primarily for long-distance high-speed runs. In the post war era, there was no comparison between the efficiencies of gas turbines and the conventional diesel engines. After many years of development, some simple cycle gas turbines of today come closer or may surpass the efficiency of a 1950's era diesel engine at full output.
Efficiency aside, there were additional problems with gas turbine-electric locomotives. They were very noisy. Also, the exhaust gases produced were so extremely hot that the exhaust would melt asphalt if the locomotive was parked under a paved overpass. The gas-turbine engine must keep running when the locomotive is stopped.
These technical aspects would have improved if the research in this sector had flourished. However, the biggest road block in the path of gas turbine locomotive research was not technical but rather economical. 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. At the time, it was more economically viable to improve the existing, proven technology of diesel and electric locomotives rather than invest in developing and improving a promising technology.
The Resurgence of the Gas Turbine Locomotive
The development of gas turbines continued for aerospace and industrial purposes for entirely different reasons. With these advances in technology, the shortcomings of those earlier generations of gas turbine locomotives are not relevant today.
In fact, the development of cycle technology can turn many of those limitations in to advantage.
For example, the higher exhaust temperature is beneficial if a suitable bottoming cycle is designed. This can improve the overall cycle efficiency while providing auxiliary power for passenger compartments or freight cooling.
Efficiency has been improved by a factor of two, thanks to advances in turbine materials, to allow higher turbine inlet temperatures, and computational fluid dynamics, to improve compressor design. This efficiency can be increased further by using combined cycle gas turbines. This configuration would match or even surpass contemporary locomotives.
Another good option could be to use a gas turbine battery hybrid, where the lighter weight of the gas turbine would allow for a much larger battery than possible with a diesel engine of equivalent power. Ideally the battery should be large enough to store at least 1 to 2 hours of the gas turbine's power allowing the turbine to run at full power (most efficient) when the turbine is required to work under part load or idle condition. This could achieve more efficient turbine cycles, and reduce the number of starts (extends the life of the turbine).
The Future of Gas Turbines
Gas turbines, following aerospace designs, are better suited to portable use owing to their distinct characteristics like easy start and stop, lighter weight, etc. Despite the many advantages to a gas turbine engine, fuel costs are still a limiting factor. The well-established technique of recuperation goes a long way in solving this problem. Natural gas also has potential to reduce fuel costs and emissions. A new locomotive design can be much lighter in weight than the earlier counterparts, saving more fuel. The easy start configuration could save fuel by allowing the power turbines to shut down while descending a long slope, using auxiliary power for dynamic brake excitation.
These concepts are feasible. The practicality is in doubt because, locomotive builders have little incentive to abandon a fully amortized design. Government or industry incentive to reduce oil consumption and emission limitations could re-awake this sleeping giant and reignite the flame that started burning in the last century. The upper hand we have today is the advantage of computational technology that was not available back then.
Advanced cycle design tools of today, such as AxCYCLETM , provide great freedom to simulate various configurations for engine preliminary performance output and detailed off design analysis without consuming a lot of time and effort. The best part in these digital design methods is that there is no real monetary investment involved. Everything from the concept to economic analysis can be streamlined and a complete report can be made available in no time.
Today finally, we have everything we need to resurrect the promising technology. We have the resources. We have the ideas, and the methodologies to implement those ides. With a little push in the right direction and a bunch of intent to achieve what has been long delayed, we can get to the future of locomotives very quickly.