Gas turbine locomotive

A Gas turbine locomotive is a locomotive powered by a gas turbine. The majority of gas turbine locomotives have had electric transmission but mechanical transmission has also been used, particularly in the early days. The advantage of using gas turbines is that they have very high power-to-bulk and power-to-weight ratios. The disadvantage is that gas turbines generally have lower thermal efficiency than diesel engines, especially when running at less than full load.

Overview

Where electric transmission is used, the engine is usually a single-shaft machine in which one turbine drives both the compressor and the output shaft.

With mechanical transmission, the power turbine must be capable of starting from rest, so a more complex arrangement is necessary. One option is a two-shaft machine, with separate turbines to drive the compressor and the output shaft. Another is to use a separate gas generator, which may be of either rotary or piston type.

Examples

Examples of gas turbine-mechanical locomotives:

* 1933 Nydqvist and Holm, Sweden, 1-B-1
* 1951 Renault, France, B-B, 1,000 hp
* 1954 Gotaverken, Sweden, 1-C-1, 1,300 hp
* 1958 Renault, France, C-C, 2,000 hp
* 1958 Škoda, Czechoslovakia, 3,200 hp
* 1959 British Rail GT3, 2-C-0, 2,700 hp

History

See Gas turbine for the early history of gas turbine development.

Work leading to the emergence of the gas turbine locomotive began in France and Sweden in the 1920s but the first locomotive did not appear until 1933. These early experiments used piston engines as gas generators. This idea has not been widely adopted, but it might be worth re-visiting. High fuel consumption was a major factor in the decline of conventional gas-turbine locomotives and the use of a piston engine as a gas generator would probably give better fuel economy than a turbine-type compressor, especially when running at less than full load.

France

The locomotives were built by Renault and had Pescara free-piston engines as gas generators. Each gas generator consisted of a horizontal, single cylinder, two-stroke diesel engine with opposed pistons. It had no crankshaft and the pistons were returned after each power stroke by compression and expansion of air in a separate cylinder. The exhaust from the diesel engine powered the gas-turbine which drove the wheels through a two-speed gearbox and propeller shafts.

weden

The Power gas locomotive was built by Gotaverken. It had a vertical, five cylinder, two-stroke diesel engine with opposed pistons. There was a single crankshaft connected to both upper and lower pistons. The exhaust from the diesel engine powered the gas turbine which drove the wheels through reduction gearing, jack shaft and side rods.

Free-piston engine

The free-piston engine was patented in 1934 by Raul Pateras Pescara (1890-1966). He was an Argentinian, who worked in Spain and France, and was prominent in Helicopter development in the 1919s.

Coal-firing

In the 1940s and 1950s research was done, in both the USA and UK, aimed at building gas turbine locomotives which could run on pulverized coal. The main problem was to avoid erosion of the turbine blades by particles of ash. Some bench testing was done but the projects were abandoned before any complete locomotives were built. The sources for the following information are Robertson [Robertson, K. "The Great Western Railway Gas Turbines", published by Alan Sutton, 1989, ISBN 0 86299 541 8] and Sampson [Sampson, H. (editor), "The Dumpy Book of Railways of the World", published by Sampson Low, London, date circa 1960] .

USA

In the USA, the plan was to use a gas turbine similar to an oil-fuelled one and to remove ash particles with filters. Details of the US research (done in 1946) were passed to Britain's London, Midland and Scottish Railway.

UK

On 23 December 1952 the UK Ministry of Fuel and Power placed an order for a coal-fired gas turbine locomotive to be used on British Railways. The locomotive was to be built by the North British Locomotive Company and the turbine would be supplied by C. A. Parsons and Company.

According to Sampson, the plan was to use indirect heating. The pulverized coal would be burned in a combustion chamber and the hot gases passed to a heat exchanger. Here, the heat would be transferred to a separate body of compressed air which would power the turbine. Essentially, it would have been a hot air engine using a turbine instead of a piston.

Robertson shows a diagram which confirms Sampson's information but also refers to problems with erosion of turbine blades by ash. This is strange because, with a conventional shell and tube heat exchanger, there would be no risk of ash entering the turbine circuit.

Working cycle

There were two separate, but linked, circuits - the combustion circuit and the turbine circuit.

# Combustion circuit. Pulverized coal and air were mixed and burned in a combustion chamber and the hot gases passed to a heat exchanger where heat was transferred to the compressed air in the turbine circuit. After leaving the heat exchanger the combustion gases entered a boiler to generate steam for train heating.
# Turbine circuit. Air entered the compressor and was compressed. The compressed air passed to the heat exchanger where it was heated by the combustion gases. The heated compressed air drove two turbines - one to drive the compressor and the other to power the locomotive. The turbine exhaust (which was hot air) then entered the combustion chamber to support the combustion.

Specification

The locomotive was never built but the specification was as follows:
* Wheel arrangement: C-C, later changed to 1A1A-A1A1
* Horsepower: 1,800, later reduced to 1,500
* Weight: 117 tons, later increased to 150 tons

The projected output was:
* Tractive effort,
** 30,000 lbf at 72 mph
** 45,000 lbf at 50 mph
* Thermal efficiency,
** 10% at 1/10th load
** 16% at half load
** 19% at full load

The transmission was to be mechanical, via a two-speed gearbox, giving a high speed for passenger working and a lower speed for freight. The tractive effort figures, quoted above, look suspiciously high for the specified speeds. It seems more likely that the figures quoted are for starting tractive effort and maximum speed in high gear and low gear respectively.

There is a model of the proposed locomotive at Glasgow Museum of Transport and some records are held at the National Railway Museum.

References

ources

* "The Gas Turbine in Railway Traction" by M. C. Duffy, Transactions of the Newcomen Society 70 (1998-99), pp 27-58.

External links

* [http://web.telia.com/~u30207596/gotaverkenmotor.htm Gotaverken Motor AB]

* [http://fr.wikipedia.org/wiki/Les_g%C3%A9n%C3%A9rateurs_%C3%A0_pistons_libres_Pescara French Wikipedia article on the Pescara system]

* [http://belph80001.free.fr/Belph_section/060GA.html Diagram of a Renault/Pescara locomotive]