Technologies        
  Hauptmenu
 
    Introduction
    Database
    -  Technologies
  -  Projects
    Calendar
    Discussions
    Contact & Links
    Imprint & Disclaimer
    Sitemap
 
 


     
 
Content
 
back to list go back to technology list      previous previous technology  next technology  next

   Diesel-electric vehicles with energy storage  evaluated  
Modern energy storage devices permit the storage of braking energy on-board for use in the subsequent acceleration phase. This offers the possibility of an effective brake energy recovery in diesel-electric vehicles. Furthermore the peak demands on the diesel engines are reduced allowing for both downsizing of engine layout and better load management of diesel engines.
Technology field: Regenerative braking and energy management
close main section General information
  close sub-section Description
   

Principle

Modern energy storage devices permit the storage of braking energy on-board for use in the subsequent acceleration phase. This offers the possibility of an effective brake energy recovery in diesel-electric vehicles.

Furthermore the peak demands on the diesel engines are reduced allowing for both downsizing of engine layout and better load management of diesel engines.

Energy storage in the driving cycle

Figure 1 shows the use of energy storage in a typical driving cycle consisting of the phases acceleration – constant speed – braking – standstill.

Figure 1: Driving Cycle and Storage Cycle. Line 1: Speed v, tractive effort T. Line 2: Power P, Energy E. Line 3: Voltage U, current i of a supercapacitor for energy storage

Driving-cycle.gif

Source: Hentschel et al. 2000

During braking phases the kinetic energy of the vehicle is transformed into another form of energy (e.g. electrostatic energy in the case of a capacitor) and stored in the storage device. When the vehicle stands still the energy storage device should be fully charged to be able to deliver energy during the subsequent acceleration phase. The power supply during acceleration is supported by the stored energy. The energy management system should be designed in such a way that the external energy supply never needs to deliver the full accelerating power (important condition to downsize energy supply!). When driving at maximum speed the storage device should be completely discharged.

Table 1 shows the operating modes discussed at DB AG for trains equipped with an on-board energy storage.

Table 1: Operating modes for dieselelectric vehicles with energy storage

No. Operating modes Cost savings

Improvement of the environmental compatibility

1 Reduction of the fuel consumption by recuperating the braking energy

x

x

2 Increased power during acceleration (booster operation)

x

 
3 Noise reduction during starting in stations  

x

4 Emission-free operation on short sections of line (e.g. tunnel stations)  

x

5 Auxiliary supply when standing with the diesel engine stopped

x

x

6 Reduction of the fuel consumption by operation  of the diesel units in low-consumption operating areas

x

x

Source: Witthuhn, Hoerl 2001

 

Integration into drive system

Figure 2: Integration into drive system

Storage-system_dieselelectr.gif

Source: IZT

Choice of energy storage device

The best choice of an energy storage device heavily depends on the individual vehicle and service type. The following table shows the main characteristics to be looked at in an individual application context and the corresponding storage parameters. 

Characteristics of application context Corresponding parameter of storage device
Braking time Charging time / power density
Braking energy Energy density
Drive cycles in lifetime Product life / reliability
Source: IZT

Table 2 gives the relevant characteristics for a DMU.

Table 2: Relevant characteristics of a DMU in local service

Mass of train (brutto) 116 tons
Top speed 120 km/h
Drive power 875 kW
Maximum tractive effort 122 kN
Braking power 875 kW
Maximum braking effort 56 kN
Stored kinetic energy 18 kWh
Braking time 70 s
Drive cycles per year 5000
Drive cycles in lifetime 106
Source: Hentschel, Müller et al. 2000

The Ragone diagram plotting energy density against power density is a convenient means to compare different storage technologies and assess their suitability for different vehicles. Figure 3 shows the position of relevant storage technologies in the Ragone diagram and the corresponding charging times. They are labelled by train types with corresponding braking times. Since most diesel-electric vehicles are used in the regional or local range but hardly as LRVs, it is clear from the Ragone diagram that fly-wheels and in some cases double-layer capacitors are the first choice for energy storage.

Figure 3: Ragone diagram and charging times (corresponding to braking times of different trains)

Ragone-diagram_trains.gif

Source: IZT, data mainly from: Hentschel, Müller et al. 2000.

close main section General criteria
  close sub-section Status of development: test series
    For the Alstom LIREX (Light Innovative Regional Express) a version featuring a fly-wheel storage system is planned. However, the implementation had to be delayed recently since the development of the 6 kWh fly-wheel ran into difficulties (cf. fly-wheel).
  Time horizon for broad application: in > 10 years
   

A wide-spread integration of on-board storage systems into diesel-electric vehicles seems doubtful since payback is critical for regional service with relatively long distances between stations.

  Expected technological development: highly dynamic
    Technological developments will come mainly from storage technologies (cf. flywheel, double-layer capacitors).
    Motivation:
    Energy savings
  Benefits (other than environmental): medium
   

Downsizing of energy supply

The load of the supply system (diesel engine) is equalized and thus reduced, which allows for a smaller layout of the diesel engine/generator system.

  Barriers: medium
   

Technological

Storage technologies are starting to become mature but lifespans are often still a problem.

Vehicle mass

The storage system increases vehicle mass.

Costs

High investment costs and long payback periods.

Complexity

Operators are reluctant to purchase trains with higher complexity, since this could decrease availability and reliability and always requires additional know-how.

    Success factors:
    An important factor is the cost of diesel fuel serving as a reference parameter. In the predictable future the diesel price is more likely to rise than fall, thus improving the perspectives for energy storage on diesel-electric vehicles.
  Applicability for railway segments: medium
    Type of traction:  diesel
    Type of transportation:  passenger - main lines, passenger - regional lines, passenger - suburban lines
    It is evident, that energy storage shows best benefits and payback for local and regional trains with frequent stops (many storage cycles!). The system described here is fitted to diesel-electric stock, but storage systems are also discussed for DC systems (cf. On-board energy storage in DC systems).
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): medium
    (no details available)
    Example:
    Alstom LIREX (in the near future a version featuring a fly-wheel storage system will be built)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: > 10%
  Energy efficiency potential throughout fleet: (no data)
   

In principle, there are two energy efficiency effects obtainable through energy storage in diesel-electric vehicles:

  • recovery and reuse of brake energy
  • demand equalizing in order to operate diesel engine only at the operation point of highest efficiency

Various simulations of brake energy recovery on diesel-electric vehicles exist giving a quite heterogeneous picture. Anything between 10 and 35 % saving potential can be found in literature.

It is estimated that a saving potential between 10 and 15 % for regional service and up to 30 % for DMUs in some suburban networks with very frequent stops could be realistic.

DB Simulations of LIREX

The Research Center of Deutsche Bahn AG carried out simulations of the operation of the LIREX with energy storage, showing an energy saving potential of about 11% for a vehicle with storage fly-wheels compared with a similar vehicle without storage fly-wheels. As can be expected, the simulations showed that the use of storage flywheels in vehicles produced the greatest saving effects on routes with short distances between stops.

The simulation was carried out for the German line Magdeburg - Halberstadt - Thale having a total length of 87 km and 8 stations. It was based on operating mode 1 ("reduction of the fuel consumption by recovering the braking energy", cf. table 1). The simulations allowed for the power losses of the storage flywheel as well as the maximum available coefficient of adhesion between wheel and rail. The optimum driving style was assumed.

DB Simulations of Shunting Locomotive

Earlier calculations by the DB environmental center simulating a shunting locomotive with brake energy recovery yielded 14%. If in addition, an idle speed cut-off and fuel supply cut-off during slow down phases are assumed, energy consumption can be reduced by up to 35% compared to a reference vehicle.

Other estimates

Hentschel, Müller et al. (DaimlerChrysler / Adtranz) give a saving potential of 35 % for a suburban DMU. Even if this is too optimistic in a practical context, it hints at the huge theoretical saving potential offered by energy storage in diesel-electric vehicles.

  Other environmental impacts: neutral
    Less toxic emissions through reduced diesel consumption.
close main section Economic criteria
  close sub-section Vehicle - fix costs: high
    Investment costs depend on the storage technology and the system layout chosen but are generally high.
  Vehicle - running costs: significant reduction
    (no details available)
  Infrastructure - fix costs: none
    (no details available)
  Infrastructure - running costs: unchanged
    (no details available)
  Scale effects: high
    Scale effects for storage technologies.
  Amortisation: 2 - 5 years
    Payback of energy storage systems is in the range of 10 to 30% of the vehicle lifetime, that is 3 to 10 years, depending on the vehicle and the storage type. It is highly dependent not only on price for storage technologies (potentially reduced by scale effects!) but also on the diesel reference price.
no data available Application outside railway sector (this technology is railway specific)
close main section Overall rating
  close sub-section Overall potential: promising
  Time horizon: mid-term
    Storage systems for diesel-electric regional and suburban trains are an interesting option for energy efficiency. However, payback times for present storage technologies are critical, especially in regional operation with large distances between stops. This may improve in the future if scale effects can be realized in storage technologies.
References / Links:  Hentschel et al. 2000;  Hesse et al. 1997;  Witthuhn, Hoerl 2001
Attachments:
Related projects:  Flytrain
Contact persons:
 date created: 2002-10-09
 
 
© UIC - International Union of Railways 2003
 
Aktionmenu
 
 Your contribution
   add technology
 Views of this page
   show overview
   show evaluation
   show details
 Print options
   print data sheet
   print screen
 Help
   Evaluation briefing
   Technology list
    French - German