Gas turbines have been in use in railways for decades, especially outside Europe. In recent times, with pollution standards becoming tougher, gas turbines have returned to discussion as an alternative to diesel traction.

Principle of gas turbines:

A simple gas turbine consists of a compressor, a combustor and a turbine. The gas-turbine runs on a Brayton cycle using a continuous combustion process. Compressed air is mixed with fuel, and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work. Part of this work is spent compressing the air, the rest is available for other work, such as mechanical drive or electric power generation. Recuperator technology exploiting the remaining heat of exhaust gases can be applied in order to improve fuel economy.

Fields of application

Power generation, transportation (aircraft, boats)

Application to automotive

Volvo has developed three pilot vehicles based on a gas turbine / battery hybrid concept: the Environmental Concept Bus, Environmental Concept Truck and the Environmental Concept Car. For example, the Environmental Concept Truck is a hybrid truck designed for gross weights of up to 15 tonnes. Its drive components are:

• gas turbine running on ethanol with integrated high-speed generator.
• NiMH batteries (Nickel-Metal-Hydride).
• Electric motor.

Application to railway traction:

Gas turbines may be used for traction by direct mechanical transmission to the gears or by electric transmission by means of a generator and electric traction motors. For modern stock only electric transmission is relevant. For railway applications the segment of so-called micro gas turbines (small turbines of up to 1000 kW electric power output) is especially interesting for railways. There has been a dynamic process of development towards market introduction of small gas turbines for decentralised power generation. Due to the fact that gas turbines are not fitted for big variation of load (bad efficiency in low load operation), they should be used at constant power. This can be obtained by integrating an on-board energy storage medium to level out variation of traction demand.

Manufacturers:

• Capstone Turbine Corp.
• Bowman/Elliott Energy Systems
• Honeywell/GE
• IR Energy Systems
• Turbomeca