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   Gas turbine  evaluated  
Gas turbines have been in use in railways for decades, especially outside Europe. In recent times, with pollution standards becoming tougher and modern micro gas turbines arriving on the market, gas turbines have returned to discussion as an alternative to diesel traction.
Technology field: Innovative traction concepts and energy sources
close main section General information
  close sub-section Description
   

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
close main section General criteria
  close sub-section Status of development: in use
    Gas turbine powered rail vehicles have been in use for decades in some isolated railway sectors (in USA, Egypt and Iran). New high performance micro gas turbines offer new potential. Railway industry claims it can produce a prototype with high tech micro turbines within 2-3 years (if turbine manufacturers co-operate in development)
  Time horizon for broad application: 5 - 10 years
    (no details available)
  Expected technological development: highly dynamic
    Micro gas turbines may constitute a quantum leap in gas turbine driven propulsion.
    Motivation:
   
  • Weight and volume reduction (compared to diesel-electric system).
  • LCC reduction (low maintenance).
  Benefits (other than environmental): big
   

Weight

Low weight and volume compared to diesel-electric system: two diesel engines are replaced by one turbine. Interesting for high speed trains.

LCC

Low maintenance requirements of the turbine-driven system as compared to diesel-electric traction are low (the rotor of the turbine being the only moving part).

Noise and vibration

Low noise and vibration levels

Fuel variability

The gas turbine can be driven by virtually any gas or liquid fuel.
  Barriers: medium
   

Initial costs

High manufacturing costs (complicated design).

Operation

Strength of gas turbines lies in constant high load operation (e.g. for base load). For low load operation efficiency is low. Furthermore, a turbine engine responds slowly to changes in speed request.
    Success factors:
   

Legislation

Environmental legislation (emission standards)

Technological development

Railways depend on innovation dynamics of gas turbines in other fields, especially power generation.
  Applicability for railway segments: medium
    Type of traction:  diesel
    Type of transportation:  passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines, freight
    Gas turbines are an alternative to today’s diesel traction. They are especially interesting for high speeds (high load operation!).
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: < 5%
  Share of newly purchased stock: < 20%
    (no details available)
  Market potential (railways): highly uncertain
    Potential could be especially high in USA where currently diesel locos are used for high speeds. In Europe the potential is somewhat smaller, since European diesel fleets are mainly used at lower speed operation.
    Example:
    (no details available)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: not applicable
  Energy efficiency potential throughout fleet: not applicable
    Turbomeca claims that since the 60s when first gas turbine driven rail vehicles were developed, fuel economy has improved from 420 g/kWh to 250 g/kWh. In long-term perspective, 210 g/kWh seems possible on the basis of modern recuperator technology. Modern diesel engines reach values of around 200 g/kWh. Modern gas turbines may reach efficiencies of up to 28 %. On board energy storage could level out demand variations of traction motors to ensure that gas turbine always operates at maximum power (where efficiency is best). According to experts, gas turbines will at best reach energy efficiency of diesel technology but hardly beat it.
  Other environmental impacts: positive
   

Emission

Turbomeca claims that gas turbines running on liquid diesel fuel meet EURO V requirements. New combustor allows very low levels of NOx, much lower than modern diesel combustion engines.

Noise

Low noise levels compared to diesel traction.
close main section Economic criteria
  close sub-section Vehicle - fix costs: high
    Turbomeca is trying to reach price level of diesel engines by lowering complexity and simplifying design.
  Vehicle - running costs: (no data)
    Manufacturers claim very high reliability and low maintenance costs.
  Infrastructure - fix costs: none
    (no details available)
  Infrastructure - running costs: unchanged
    (no details available)
  Scale effects: medium
    A successful introduction of micro gas turbines into European power generation market would certainly produce scale effects for turbine prices. However scale effects are limited by different specifications for railway application.
  Amortisation: (no data)
    (no details available)
close main section Application outside railway sector
  close sub-section Status of development outside railway sector: in use
   
  • Micro gas turbines for decentralised power generation are available on the market.
  • Automotive applications such as the Volvo Environmental Concept Truck (cf. Description) are at a pilot stage.
  Time horizon for broad application outside railway sector: in 5 - 10 years
   
  • In decentralised power generation, gas turbines are expected to diffuse into the market in this decade (cf. market potential).
  • In automotive sector, the wide-spread use of gas turbines is doubtful and would take over ten years.
  Expected technological development outside railway sector: dynamic
    The developments in the field of micro gas turbines in recent years show that gas turbines still offer considerable innovation dynamics. This concerns among other things efficiency and fuel economy.
  Market potential outside railway sector: high
    Especially in the field of industrial gas turbines for power generation market potential is seen as very promising. According to a study by the consultancy Frost&Sullivan the European market for micro gas turbines is considerable since many energy suppliers will use the technology for decentralised power generation. Frost&Sullivan predict that the number of sold microturbine decentralised power plants will grow from presently a few dozens to more than 5000 by 2010. This concerns especially gas turbines in the power class between 100 and 500 kW. This assumption could however conflict with existing over-capacities in European electricity markets.
close main section Overall rating
  close sub-section Overall potential: interesting
  Time horizon: long-term
    Modern micro gas turbines could offer certain constructive and maintenance advantages. With regard to energy efficiency gas turbines will at best reach but not beat diesel-electric traction but there are some emission and noise advantages. The potential of gas turbines for railways appears limited, but technological developments in other markets, especially decentralised power generation, could improve the perspective should be closely observed.
References / Links:  Roger, Watier 1997;  Turbomeca 2001;  www.ott.doe.gov;  www.bhkw-infozentrum.de;  www.truck.volvo.se;  www-3.abb.de
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 date created: 2002-10-09
 
© UIC - International Union of Railways 2003