Energy Saving Hybrid Locomotive

Report

“Energy savings with hybrid locomo-

tives on TEN-T corridors”

2

Grant Agreement N°: 2012-EU-94167-S

Project Acronym: SWIFTLY Green

Project Title: Sweden-Italy Freight Transport and Logistics Green Cor-

ridor

Funding Scheme: TEN-T Programme, Collaborative Project

Project Start: 1 October 2013

Project End: 31 December 2015

Status/date of document: Final/31.12.2015

Lead contractor for this document: Lead Partner

CLOSER/Lindholmen Science Park AB

Lindholmspiren 3-5, Box 8077, SE-402 78 Gothenburg,

Sweden

Sub-Activity Leader

Technische Universität Berlin

Straße des 17. Juni 135, 10623 Berlin

Germany

Project Website: http://www.swiftlygreen.eu

3

Involved partners / Version control

The following project partners have been involved in the elaboration of this document:

Partner N° Organisation short name Country Involved experts

7 Berlin University of Technology

(TUB) DE

Markus Hecht, Mirko Leiste, Ger-

noth Götz

The following table gives an overview on elaboration and processed changes of the document:

Date Name / Organisation short name Changes

15/12/2015 Mirko Leiste, Gernoth Götz / TUB First draft

31/12/2015 Markus Hecht /TUB Corrections, Comments

4

Table of Contents

Table of Contents .................................................................................................................................. 4

List of Figures ....................................................................................................................................... 6

List of Tables ......................................................................................................................................... 8

Executive Summary .................................................................................................................... 9

Introduction ............................................................................................................................... 10

2.1. Aims of EU Politics .................................................................................................................. 10

2.2. Green Transport and Railway Innovations ................................................................................ 12

Motivation for this study ........................................................................................................... 13

Technical basis .......................................................................................................................... 14

4.1. Definition and application of hybrid propulsion systems in the automobile and railway

industry ...................................................................................................................................... 14

4.2. Derivation of a new diesel-electric hybrid locomotive for freight trains .................................. 18

4.3. Benefits of hybrid locomotives ................................................................................................. 18

Key performance indicators ...................................................................................................... 19

Freight train configuration ........................................................................................................ 19

6.1. Specification of the conventional diesel locomotive ................................................................. 21

6.2. Specifications of the new hybrid locomotive ............................................................................ 21

Route specifications .................................................................................................................. 23

Scenarios ................................................................................................................................... 24

Calculation model ..................................................................................................................... 26

9.1.1. Drive efficiencies ...................................................................................................................... 26

9.1.2. Traction energy ......................................................................................................................... 30

9.1.3. Electric Energy and fuel consumption ...................................................................................... 31

9.1.4. Key performance indicators ...................................................................................................... 33

Input quantities of the calculation model .................................................................................. 35

Results ....................................................................................................................................... 38

5

11.1. Energy consumption.................................................................................................................. 38

11.1.1. Secondary Energy .................................................................................................................... 38

11.1.2. Primary energy ........................................................................................................................ 41

11.2. Share of fossil and renewable energy ........................................................................................ 43

11.3. CO2 emissions ........................................................................................................................... 44

11.4. Cost for traction resources ........................................................................................................ 46

Summary ................................................................................................................................... 48

List of references ................................................................................................................................. 49

6

List of Figures

Figure 1: Share of electrified routes in the national railway network in selected European countries.. 12

Figure 2: Overview about drive train arrangements of hybrid propulsion systems .............................. 14

Figure 3: Hybrid shunting locomotive “H3” from Alstom Transport ................................................... 15

Figure 4: TRAXX AC3 LM from Bombardier transportation Electric Locomotive with last mile diesel

engine .................................................................................................................................................... 16

Figure 5: ALP-45DP regular service hybrid locomotive of Bombardier Transportation for New York

Transit .................................................................................................................................................... 16

Figure 6: “Class 88 Dual mode” hybrid locomotive from Vossloh ...................................................... 17

Figure 7: Hybrid locomotive "Euro4000 Dual" from Vossloh .............................................................. 17

Figure 8: Tractive-effort diagram of the diesel-hydraulic locomotive Maxima 40 CC with exemplary

driving resistance in tare and laden loading condition µ=0.33 .............................................................. 21

Figure 9: Traction-effort speed Diagram of the hybrid locomotive µ=0.33 .......................................... 22

Figure 10: Trackside speed-profile with 21 stops according to the drive profile (here intermediate stops

are omitted)............................................................................................................................................ 23

Figure 11: Speed-profile of the whole relation for the laden train pulled by the hybrid locomotive with

21 stops .................................................................................................................................................. 35

Figure 12: Exemplary baking and acceleration phase for the laden train pulled by the hybrid locomotive

............................................................................................................................................................... 35

Figure 13: Traction force envelope of the first 150 km for the laden train pulled by the hybrid locomotive

............................................................................................................................................................... 36

Figure 14: Excerpt of the power input along the first 150 km for the laden train pulled by the hybrid

locomotive ............................................................................................................................................. 36

Figure 15: Excerpt of the energy consumption along the first 150 km for the laden train pulled by the

hybrid locomotive.................................................................................................................................. 37

Figure 16: Total energy consumption for laden and tare loading status considering 2 and 21 stops .... 38

Figure 17: Average Energy consumption in total for tare and laden movement considering 2 and 21

stops ....................................................................................................................................................... 39

Figure 18: Specific Energy consumption per tkm average of a tare and laden movement considering 2

and 21 stops ........................................................................................................................................... 40

Figure 19: Primary\secondary energy consumptions of average of a tare and laden movement for 21

Stops ...................................................................................................................................................... 41

7

Figure 20: Primary\secondary energy consumptions of average of a tare and laden movement for 2 Stops

............................................................................................................................................................... 42

Figure 21: Primary and secondary energy demand considering use of green electricity, 21 stops, average

of tare and laden .................................................................................................................................... 42

Figure 22: Consumed primary energy for the scenario of 21 stops (average of a tare and laden movement)

............................................................................................................................................................... 43

Figure 23: Percentage of fossil and renewable primary energy using green electricity (21 Stops, average

of a tare and laden movement) .............................................................................................................. 44

Figure 24: CO2 emissions in total considering the usage of green energy considering 2 and 21 stops

(average of a tare and laden movement) ................................................................................................ 45

Figure 25: Specific CO2 emissions per tkm considering the usage of green energy considering 2 and 21

stops (average of a tare and laden movement) ...................................................................................... 45

Figure 26: Total Costs for traction resources in Euro considering 2 and 21 stops (average of a tare and

laden movement) ................................................................................................................................... 46

Figure 27: Specific Costs for traction resources per tkm (average of a tare and laden movement) ...... 47

8

List of Tables

Table 1: Overview about basic train parameters .................................................................................. 20

Table 2: Overview about the scenario's parameter being investigated in this study ............................. 25

Table 3: Components of the electric propulsion system and their efficiencies ..................................... 27

Table 4: Efficiency of rail electricity grid ............................................................................................. 27

Table 5: Components of the diesel-electric propulsion systems and their efficiencies ......................... 28

Table 6: Components of the diesel-hydraulic propulsion systems and their efficiencies ...................... 29

Table 7: Specific CO2 production for diesel and traction current ......................................................... 33

Table 8: Specific share of fossil and renewable energy of rail traction current mix considering upstream

............................................................................................................................................................... 34

9

Executive Summary

In this study, the Institute of Rail Vehicles of the Technische Universität Berlin investigates the energy

savings of hybrid locomotives being used to pull heavy freight trains. Nowadays diesel locomotives are

used although most of tracks are electrified (typically only first and last parts are not electrified). This

enables the possibility to save a huge amount of CO2 emissions. At the moment, no applicable hybrid

locomotive (diesel-electric) to pull heavy freight trains (up to 4500 t) is available on the market, but

under development.

TU Berlin received information packages about one different practiced freight transports from a Rail-

way company. The package consists of the following information:

Track specifications:

o Track section Röderau to Nüttermoor via Magdeburg, Hannover and Bremen

o Overall track length:548 km

o Electrification rate: 98.2 %

o Regular stops: 21

Train specifications:

o Locomotive Maxima 40 CC (diesel locomotive)

o 46 freight wagons (bulk traffic)

o Overall train weight of 990 t tare and 4230 t laden

Based on these information, TU Berlin derived requirements for a diesel-electric locomotive (dual mode,

powered by external electric supply or on-board diesel engine alternatively, here called catenary hybrid)

which is able to pull the train with the diesel on mainline also, not shunting sides only.

Environmental reduction potential is significant. For today’s operation conditions the demand of sec-

ondary energy (energy from the catenary\tank) decreases about 50 % and the demand of primary energy

by about 16 %. The CO2 production decreases by about 38 %. Additionally a cost reduction for traction

resources about 39 % is expectable.

By using green electricity the primary energy demand is about 65 % lower compared to the diesel loco-

motive and the share of renewable energy increases from 9% to 93 %. Thus the production of CO2

decreases considerably about 97 %.

By reducing the amount of stops it is possible to save about 20 % of secondary energy and CO2. A

switch to a central buffer coupling-system has according to the crucial refitting effort a low effect.

10

Introduction

Railway companies use partly diesel engines to pull freight trains over long distances under the catenary.

The unnecessary CO2 emissions are justified with missing electrified parts (up to 15 km) at the beginning

of the transport and before the final destination. Using electric locomotives would require two additional

powerful diesel locomotives pulling the train on tracks without catenary leading to an increase of the

travel time (for additional shunting operations) and an significant increase of costs (e.g. two diesel lo-

comotives need to be operated and maintained additionally). Instead of the need of two diesel and one

electric locomotive it is cheaper today to operate with one diesel locomotive only. But this leads to the

poor situation that diesel locomotives pull freight trains over 500 km although only few parts are not

electrified resulting in a high CO2 emissions and a high diesel consumption and also high maintenance

costs.

This report compromises an additional agreed best-practice case, namely, the demonstration of the en-

ergy saving potential using powerful hybrid locomotives for freight trains. It contributes to the overall

objective delivering approaches and measures for greening the transport corridors.

2.1. Aims of EU Politics

In the 2011 White paper for transport the European Union describes the current challenges for the Eu-

ropean transport politics as well as the aims to further develop the transport sector. The European Union

describes the transport as the basis of our economy. Society and transport enables economic growth and

creates jobs. Transport concerns almost all areas of our society and plays a major role for the economy

and for the living quality of human beings. Especially in the last decades one further aspect to the ful-

filment of mobility needs of business and society was added: Sustainability. The increasing scarcity of

resources, such as oil, and the continuing pollution of the environment by emissions is the reason that

sustainable transport policy is more important than ever. This is defined by reduction of greenhouse gas

emissions, (Kyoto 1997) or the global warming limits (Paris 2015).

The European Commission has recognised this challenge and set out specific goals by 2050. Regarding

the greenhouse gas emissions, the goal to reduce emissions until 2050 by 80-95 % compared to the

reference year 1990 was formulated. According to estimates by the Commission even greater emission

reductions are possible in other sectors of the economy. For the transport sector the necessary reduction

is 60 % regarding 1990 levels. By 2030, greenhouse gas emissions are to be reduced by 20 % compared

to 2008. By achieving this goal, however, greenhouse gas emissions in the transport sector would still

be 8 % higher than the value from 1990 levels. This problem is due to the substantial increase in emis-

sions since 1990 levels. The persistent increase in traffic within the EU complicates the implementation

of the objectives defined in the White Paper. Therefore, in particular, technological advances for vehi-

cles, but also management systems to reduce emissions in the transport sector, are necessary. At the

opening session of the International Transport Forum (ITF) in Leipzig in May 2014, the German Federal

Transport Minister Alexander Dobrindt described the development of transport infrastructure as insuf-

ficient. To cope with the predicted traffic growth a modern information technology is necessary. At the

same time, the focus is on the efficient use of environmentally friendly energy. In practice this means

the partial shift of freight and passenger traffic on more energy-efficient modes of transport.

According to the EU-whitepaper of transport 2011 by 2030, 30 % of road freight over 300 km shall be

shifted to other modes such as rail or waterborne transport (by 2050, 50 %). Furthermore, until then it

11

is planned to complete the pan-European rail network. The existing length of the rail network will be

tripled by 2030. In addition, the integration of all air and sea ports of the TEN-T core network to the rail

network by 2050 is in the planning. With the following realistic goals, the UIC (International Union of

Railways) and the CER (Community of European Railway and Infrastructure Companies) illustrates the

potential of rail transport to act as an environmentally friendly mode of transport: The organisations

mentioned plan to reduce CO2 emissions in passenger and freight traffic by 30 % per passenger- and

tonne-kilometre by 2020 compared to the base year 1990 levels. Another ten years later, the reference

value from 1990 should be halved. In 2050, a carbon free rail with zero emission is sought. The nitrogen

and particulate matter emissions should by then also completely disappear. Furthermore, a halving of

energy consumption compared to 1990 is sought. The Dutch Railway network will be zero emission

already from 2018 onward.

The challenges of goals mentioned in the White paper will require the railway sector taking on a larger

share of transport demand in the next few decades. The European Commission is working towards the

creation of a single European railway area and has promoted a modal shift from road to rail in order to

achieve a more competitive and resource-efficient European transport system.

The European Commission has also, together with private partners, set up the rail research programme

“Shift2Rail” in 2014. Shift2Rail is a joint undertaking providing a platform for cooperation and innova-

tion in the railway sector. The total budget for Shift2Rail is more than 920 million Euros for the period

2014-2020.

An immediate restructuring of the transport sector is not possible. However, it is necessary to set the

course for a sustainable transport of the future already today. The decisions relating to the transport of

the future were taken by the European Commission in 2011 and ensure that the goals can be achieved

by 2050. To define such goals is important but more important is the work of enforcement. This work

should, in view of the environmental impacts, take place as soon as possible in cooperation with all

European member states. Only with a common interaction in a traffic network, the realisation of the

European Commission's objectives is possible.

12

2.2. Green Transport and Railway Innovations

As transportation systems, railways are linked with several environmental impacts. These impacts result

from transport operations and the necessary energy therefore, but also from infrastructure construction,

land use etc. With the consumption of large quantities of fossil resources, the transport sector emits large

amounts of harmful substances such as carbon dioxide and nitrogen dioxide. Railways are seen as pio-

neers for decades when it comes to the electrification of transport and therefore have the potential to

transport goods completely free of greenhouse gas (GHG) emissions already today. However, the state

of electrification of railways is very different in the countries of Europe (see Figure 1).

Figure 1: Share of electrified routes in the national railway network in selected European countries [1]

As the European main rail corridors are mostly electrified, the reduction of GHG emissions is not the

biggest concern for railway innovations, but could be done quite simple. A much bigger problem today

are the noise emissions. They have a severe impact on the environment and the citizens living close to

railway facilities.

Emissions from rail freight transport can be divided into three categories. [2] Whereas direct impacts

cause an immediate effect on the environment, indirect impacts may occur later and are less apparent.

Third, cumulative impacts derive from the interaction of several other impacts and are often very diffi-

cult to predict.

52,3% 52,4%

58,8% 59,6% 60,2%

68,0%70,7% 71,4%

76,1%

85,5%

99,3%

50,0%

55,0%

60,0%

65,0%

70,0%

75,0%

80,0%

85,0%

90,0%

95,0%

100,0%

13

Having understood the negative impacts of transport on the environment, it is necessary to interpret what

green transport accounts for. Numerous institutions have developed definitions on sustainability or the

greening of transport1. A universally valid definition is for example the one created at the European

Conference of Ministers of Transport (ECMT 2004):

A sustainable transport system is one that is accessible, safe, environmen-

tally-friendly, and affordable.

For the purpose of Swiftly Green, the definition of green transport can be interpreted as one that allows

for the identification of transport measures which:

Support the future needs of freight transport in the European Union,

enable the reduction of environmental impacts deriving from transport at the source of emer-

gence but also in indirectly affected geographic areas,

contribute to a modal shift in towards rail and waterways.

Motivation for this study

Nowadays it is very common that several freight trains are pulled with diesel locomotives since the first

and the last kilometres of the track are without catenary. For railway companies it is much easier to

organize, plan and realize the transport of goods with only one locomotive compared to keeping diesel

locomotives at the first and last parts of the track available and an additional electric locomotive for the

long haul transport. Thus, diesel locomotives pull freight trains hundreds of kilometres under the cate-

nary. There is a lack for diesel-electric hybrid-locomotives being able to pull the freight train with the

diesel engine on tracks without catenary and with the electric system on tracks with catenary. This results

in a huge amount of avoidable CO2 emissions. The aim of this study is to present the advantages of

hybrid locomotives to demonstrate the energy saving potential at the example of a actually used track

provided by a German railway company. The energy consumption and the greenhouse gas emissions

for the run with different operational properties of a modern actual diesel locomotive pulling freight

wagons is compared to a hybrid locomotive pulling the same amount of freight wagons.

1 For a comprehensive overview on the definition of sustainable transportation see [29]

14

Technical basis

In this chapter, the term “hybrid” is defined and current technical solutions for the automobile and rail-

way industry are defined. From this introduction, the need of new hybrid locomotives for freight trains

is derived.

4.1. Definition and application of hybrid propulsion systems in the auto-

mobile and railway industry

Generally a hybrid propulsion system consists of at least two completely independent propulsions. Fol-

lowing this the propulsion systems has to differ from the energy storage (e.g. tank or accumulator) to

the conversion into mechanic energy. Usually the most hybrids are equipped with two propulsion sys-

tems which are using different types of energy (e.g. gasoline and natural gas) and the implementation is

put into practice by sharing assemblies of the drive train. Typically there is one propulsion system which

constitutes the main drive and is primarily used. The other one is used as a supplying drive and used in

particular cases. An exemplary case for passenger trains is the use of the electric propulsion system

instead of the diesel for zero-emission operations in stations. The aim of this technology is to combine

the advantages of both systems and to increase the efficiency.

The automobile industry uses a combination of a combustion engine and an electric generator and bat-

teries in general. The arrangement of the components vary between serial, parallel and power-split-

ted hybrid (see Figure 2). A serial hybrid supplies the electric motor with electric energy directly from

the generator or from an electric energy storage (e.g. a battery). In this case the electric propulsion sys-

tem cannot work independently for long distances in comparison to the combustion engine mode. The

reason is the limited capacity of the energy storages. There are also systems which are working as a

Plug-In Hybrid. An example is an electric car which uses primarily electric energy from accumulators

and for extending the range a small combustion engine with a generator to produce electric energy is

used. [3]

Figure 2: Overview about drive train arrangements of hybrid propulsion systems [3]

15

Besides the automotive industry a few hybrid systems are also existing in the rail sector. Today’s loco-

motives are either equipped with an electric or a diesel drive which are using the catenaries electricity

or the tank’s diesel. Therefore there are two basic possibilities to create a hybrid locomotive concerning

the main propulsion system. On the one hand it is possible to have an electric drive as the main propul-

sion system. On the other hand it also possible to use the diesel motor as the main system. It nearly

depends on the field of application. By the fact that the most diesel locomotives are already using a

diesel-electric propulsion system2, it is only necessary to implement for example energy storages to have

a hybrid locomotive. In general the stored energy is used for supplying the electric motor during accel-

erations. An advantage of this technology is the possibility of recuperation during braking processes or

on slopes. The kinetic energy will be converted into electric energy and stored. Another effect is the

significant wear reduction of the pneumatic brakes. A full electric mode is not possible due to the limi-

tation of the energy storage systems. For storing energy super caps or accumulators are used.

Figure 3: Hybrid shunting locomotive “H3” from Alstom Transport [4]

An exemplary hybrid locomotive with main diesel drive is the shunting locomotive “H3” from Alstom

Transport, see Figure 3. This is a three-axle shunting locomotive with a power output of 700 kW in

which the half is provided by diesel engine and by an electric engine respectively. Alstom advertises an

energy reduction potential of about 50 % compared to conventional diesel shunting locomotives. The

limited power output prevents the locomotive to be used apart from shunting operations. A plain electric

mode is unfortunately not possible. Thus the locomotive can’t be operated completely green although

the track is electrified. [4]

There are also types of hybrid locomotives which have a main electric engine and a small diesel engine.

An example for this type is the “TRAXX AC3 LM” from Bombardier Transportation with a “last mile”

diesel engine, see Figure 4. This enables the locomotive to use electric power to pull the train under the

catenary. Similarly the train can be pulled with the diesel engine over the last mile at very low speed.

The power output in the diesel mode is very limited. Due to this, the maximum speed in diesel mode is

40 km/h at low train weight. The locomotive can’t pull the train over long catenary-less track sections,

only for the last miles of a train movement. [5]

2 More information about the propulsion system provides section 9.1.1.

16

Figure 4: TRAXX AC3 LM from Bombardier transportation Electric Locomotive with last mile diesel engine [5]

Furthermore, Bombardier Transportation developed the “ALP-45DP” locomotive with two fully func-

tional propulsion systems, see Figure 5. The maximum velocity is 200 km/h in electric mode and

160 km/h in diesel mode. The electric mode has a power output of 4000 kW and the diesel mode of

3134 kW (multi engine, two times 1567 kW). The changeover between the modes is done by flipping a

switch. [6] [7] From the high maximum speed it can be concluded that that the locomotive is primarily

designed for passenger transport. The maximum tractive effort is nearly 330 kN and consequently it will

be possible to use the locomotive for light and medium-weight freight trains, too. The locomotive was

designed for northern America and operates inter alia in New Jersey, USA. A usage in Europe is impos-

sible resulting from too high axle loads for European conditions. The “ALP-45DP” weighs about 130.6 t

and has only four axles. This equals with an axle load of 32.65 t (standard value for AAR-mainlines).

The typical maximum axle load for Europe is 22.5 t.

Figure 5: ALP-45DP regular service hybrid locomotive of Bombardier Transportation for New York Transit [7]

Similar to Bombardier Transportation, Vossloh3 launched different types of hybrid locomotives. For

that Vossloh\Stadler develops two platforms, which are both suitable for European freight transport. The

first platform is named “EUROLIGHT” and an exemplary is the four-axle “Class 88 Dual mode” (see

Figure 6). The locomotive has an electric main engine with a power rating of 4000 kW. The second

propulsion system is a diesel engine with a power rating of 700 kW. The maximum speed for the diesel

3Former Vossloh, today Stadler due to a takeover.

17

mode is unknown. Due to the low power rating a maximum speed of less than 50 km/h is assumed,

similar to the “TRAXX AC3 LM”. The nominal speed for the electric mode is 160 km/h. This locomo-

tive exists in a passenger and in a freight version, too. The maximum tractive-effort is for both modes

317 kN. [8] [9]

Figure 6: “Class 88 Dual mode” hybrid locomotive from Vossloh [8]

The second hybrid platform of Vossloh is named “EURO 4000” and an example is the “Euro4000 Dual”,

see Figure 7. The "Euro4000 Dual" is a six-axle locomotive with a power output of 5000 kW (electric

mode) respectively 2.8 MW (diesel mode).4 The maximum velocity for both modes is 120 km/h. With

a maximum tractive-effort of about 475 kN this locomotive is suitable the pull heavy freight trains in

both operation modes. [9] [10]

Figure 7: Hybrid locomotive "Euro4000 Dual" from Vossloh [10]

4 There is also an alternative configuration with a power rate of 1000 kW.

18

4.2. Derivation of a new diesel-electric hybrid locomotive for freight

trains

Nearly all of the mentioned hybrid locomotives, except the “Euro4000 Dual” from Vossloh, are not

conform to the requirements for pulling heavy European freight trains in both modes.

First of all the locomotive has to be suitable for regular service and not only for shunting. Hence a higher

power out is necessary. Secondly the main drive has to be electric (high degree of electrification on

TEN-T corridors lines). These are the reasons why the Alstom “H3” is excluded. Third the locomotive

has also to be able to operate over long distances with adequate velocity with both engines. Due to this

the “TRAXX” with the last mile diesel and the “Class 88 Dual mode” are not suitable. Lastly the loco-

motive has to be able to pull heavy freight trains also on inclines with a gradient of 20 ‰ without need-

ing an additional pushing locomotive. According to this the “ALP-45DP” is not suitable. This locomo-

tive is primarily constructed for passenger transport and not for pulling heavy trains. Additionally this

locomotive does not fulfil the criteria’s for operating in Europe due to its high axle load.

The idea of the new hybrid locomotive is that the locomotive is able to operate in regular service in both

modes, but with a slightly decreased speed in diesel mode. The maximum speed in the electric mode is

set to 120 km/h and the diesel engine will be dimensioned for a maximum speed of 100 km/h. The power

output of the electric engine will be 7000 kW in contrast to the diesel engine with 2000 kW.5 For reduc-

ing the costs of the locomotive the diesel power could be also provided by two smaller diesel engines.

An adequate alternative for the new hybrid locomotive is the “Euro4000 Dual”, which has slightly dif-

ferent specifications. This locomotive is not considered in this report. A significant effect on the results

is not expected.

4.3. Benefits of hybrid locomotives

This section offers the benefits and the reason for using a hybrid instead of a diesel locomotive on

specific relations. In general the degree of electrification is in many European countries higher than

50 %. For example in Sweden, Italy and Austria the degree of electrification ranges between 68 % and

71.4 % for the complete rail network. [11] Whereas the degree of electrification on corridors or main-

lines is significantly higher, the proportion of electrified local tracks with a lower capacity is consider-

ably lower. On these local tracks the senders and receivers of the freight are often situated. Even if only

the last or first kilometres of a train movement are not electrified, the use of electric locomotive is lapsed.

The option of providing additional diesel locomotive for the non-electrified lines is too expensive. That

is why diesel locomotives are operating in general about hundreds of kilometres under a catenary with-

out using the electricity. The option of a 100 % electrified rail network is (because of the high costs) not

expectable within the next years and furthermore typically on less used lines inefficient, too. Addition-

ally there are also areas where an electrification is not possible e.g. in harbours and loading tracks.

5 Proposed by Prof. Markus Hecht

19

By using the hybrid technology the locomotive can use the electricity of the catenary for long distances

and the diesel engine on catenary-less sections. The use of electricity offers a high greening potential,

due to the fact that is possible to use green electricity. The usage of green energy enables a high CO2

reduction potential. Additionally it is also possible to recover the braking energy to reduce the energy

demand and therefore the costs for the traction resources, too. Another important energy and cost reduc-

tion potential offers the improved degree of efficiency of the electric propulsion system.

Considering the fact that the railway transport suffers from high noise emissions the quieter electric

propulsion system can even make an important contribution for a noise reduction.

Key performance indicators

The SWIFTLY Green project has elaborated approaches for greening of transport on corridors. This

includes also approaches to create an environmentally friendly freight corridor being assessed with sev-

eral specific key performance indicators. The following indicators were used for the present research:

Operational costs in € and € per tkm

Emissions of the greenhouse gas CO2 in kg and kg per tkm

Uses of energy (fossil/renewable) in MJ and MJ per tkm

By using these indicators the potential of a hybrid locomotive for the rail freight sector will be evaluated.

Basics, assumptions and calculation methods are set out in the following sections.

Freight train configuration

The modelled train is basing on a real freight train configuration. TU Berlin receives the data from a

German railway company. The freight train consist of a single locomotive and 46 four-axle freight cars

(90 t gross weight). The overall weight amounts 4230 t laden and 990 t empty. Due to that fact that 50 %

of these trains are running their relations tare, both loading conditions are taken into account. At first

the following table offers an overview about the general train configurations as well as some detailed

information like mass factors, friction coefficient and power output. These parameter are necessary for

calculating the energy demand of the locomotive or rather the key performance indicators. Subsequent

to the table the specification of the present used diesel locomotive and the new hybrid locomotive will

be presented.

20

Table 1: Overview about basic train parameters

Parameter Train with Maxima

40 CC

Train with Hybrid

Locomotive

Friction conditions

Wheel Rail friction 𝛍𝐖𝐡𝐞𝐞𝐥−𝐫𝐚𝐢𝐥 𝐜𝐨𝐧𝐭𝐚𝐜𝐭 0.3

Driving Resistance6

𝐜𝟏 1.3

𝐜𝟐𝐭𝐚𝐫𝐞 0.05

𝐜𝟐𝐥𝐚𝐝𝐞𝐧 0.006

Masses

Loco 𝐦𝐥𝐨𝐜 126 t 135 t

Wagons, tare 𝐦𝐰𝐚𝐠𝐨𝐧𝐬,𝐭𝐚𝐫𝐞 990 t

Wagons, laden 𝐦𝐰𝐚𝐠𝐨𝐧𝐬,𝐥𝐚𝐝𝐞𝐧 4230 t

Mass factors

Loco 𝛒𝐥𝐨𝐜 1.37 1.28

Wagons, tare 𝛒𝐰𝐚𝐠𝐨𝐧𝐭𝐚𝐫𝐞 1.15

Wagons, laden 𝛒𝐰𝐚𝐠𝐨𝐧𝐥𝐚𝐝𝐞𝐧 1.06

Power characteristics

Max. electric power output - 7000 kW

Max. Diesel power output 3350 kW [12] 2000 kW

Max. Speed 120 km/h Electric: 120 km/h

Diesel: 100 km/h

Braking characteristics

Max. deceleration -0.51 m/s2

Dynamic Braking

Recuperation No Yes

Degree of efficiency - 0.819

Max. Braking Force - 400 kN

6 The values are fitted in accordance to the information about the Maxima 40 CC provided by the railway

operator.

7 Experienced values

8 Assumed value

9 Considering the grid’s efficiency more information see in section 9.1.1.

21

6.1. Specification of the conventional diesel locomotive

The freight wagons are pulled by the locomotive type “Maxima 40 CC” from “Voith Turbo Lokomo-

tivtechnik GmbH & Co. KG”. The “Maxima 40 CC” is a six-axle diesel-hydraulic regular service loco-

motive and has a maximum power output of 3.600 kW. In case of good adhesion conditions between

wheel and rail (µ=0.33) the maximum tractive effort reaches 408 kN (see Figure 8). The efficiency of

the propulsion system is mentioned in section 9.1.1.

Figure 8: Tractive-effort diagram of the diesel-hydraulic locomotive Maxima 40 CC with exemplary driving re-

sistance in tare and laden loading condition µ=0.33 [Information received TU Berlin from a German railway opera-

tor]

6.2. Specifications of the new hybrid locomotive

As the “Maxima 40 CC”, the new hybrid locomotive shall be able to pull a freight train up to 4500 t for

regular service not only in electric, but also in diesel mode. As consequence the required power output

is set to 7000 kW (electric mode) and 2000 kW (diesel mode). The power requirements and the Euro-

pean track categories implies for the locomotive six axles and a maximum weight of 135 t (6 times 22.5

t). Passenger locomotives mainly need the power for reaching a high maximum speed. In comparison,

freight locomotives need the power for enabling high traction force to pull heavy trains at speeds up to

100 km/h, see Figure 3. Because of that the tractive-effort is set close to the maximum transmittable

traction force and amounts 400 kN.10 Due to the limitations in the rail-wheel contact in transmitting

traction forces it is necessary to have the mentioned high locomotive weight. For operating on tracks in

Europe, a higher weight is impossible for a six axle locomotive. The reason is the limitation of the axle

load, which depends on the specific track category. For European corridors the category D is typical.

10 The Maximum traction force is approximately 30% of the locomotive’s weight forces

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Tra

cti

ve-e

ffo

rt i

n k

N

Speed in km/h

Maxima 40 CC Driving resistance tare 1340 t Driving resistance laden=4230 t

22

The maximum axle load for this category is 22.5 t and therefore the maximum weight of a six axle

locomotive is 135 t.

A characteristic of the traction force is the significant reduction with increasing velocity after reaching

the maximum traction power. Therefore the electric power output is set to 7000 kW and enables a mod-

erate acceleration up to 140 km/h with a significant force reserve even after reaching up to 140 km/h.

Thus it is possible to run on inclines with 20 ‰ without an additional pushing locomotive.

By using the diesel engine, the maximum speed is limited to 100 km/h. The maximum tractive force for

the diesel modes is equal to the electric one. Unlike the electric traction mode, the tractive force de-

creases fast with velocity due to the lower power output.

Figure 9: Traction-effort speed Diagram of the hybrid locomotive µ=0.33

Recuperation ability of the hybrid locomotive

Besides the advantage of using the more efficient electrical propulsion system (see chapter 9.1.1), the

use of recuperation (energy back-feeding to the catenary while braking, equals dynamic braking) is en-

abled with electric locomotives. The use of this technology depends mainly on the European country

itself, because dynamic braking is partly restricted (see chapter 8). The hybrid locomotive’s dynamic

braking force is set to the maximum of the negative traction force, thus, up to 400 kN (Longitudinal

dynamic problems are not considered). It should be mentioned that the dynamic braking force is speed-

dependent. Basically the braking force decreases with velocity. Thus the envelope of the dynamic brake

and the traction force are nearly the same. The only difference exists after reaching velocities lower than

5 km/h. Between 5 km/h and 0 km/h the braking force decreases linear from the maximum to zero in

contrast to the traction force with reaches the maximum at 0 km/h, see Figure 9. The decrease is typical

for the envelope of the dynamic brake. The chosen envelope is assumed.

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Tra

cti

ve

-eff

ort

in

kN

Speed in km/h

Electric mode Diesel mode dyn. Brake F=150 kN

dyn. Brake F=400 kN Driving resistance tare 1340 t Driving resistance laden=4230 t

23

Route specifications

For the present research an exemplary relation was modelled. The relation is a simplification of a real

connection in northern Germany from Röderau to Nüttermoor via Magdeburg, Hannover and Bremen

with an overall length of 548 km. The track has several characteristics that are typical for freight trans-

ports, which are presented firstly. A standard relation of a freight train consists in general of three parts.

In this report these parts are called initial, main and final part. The initial and the final parts are in general

local and non-upgraded rail tracks, in which most of the senders and receivers of the freight are situated.

The characteristics of these sections are inter alia, the absence of an electric catenary and a lower max-

imum speed. Generally local tracks have a small proportion of a train movement in comparison to main

lines. Mainlines are representing the main part of the relation. Main lines are typically equipped with a

catenary. On these sections the track quality is better and thus the trackside speed is significantly higher.

For the present research the track is also dividable into the previous mentioned sections. The length of

the initial and final part is 3 km respectively 7 km. The distance of the electrified main section is about

538 km. Thus, the ratio between electrified and non-electrified track is very high with 98.2 %. Due to

this, the selected relation is suitable for evaluating the benefit of a hybrid locomotive. Although the

degree of electrification is that high, using an electric locomotive is impossible unless the whole relation

is electrified. Because of the significant costs and the low degree of utilization it is not economical to

electrify those routes. Therefore a 100 % electrified network is not expected in future.

Beside the mentioned parameters the amount of stops is important for calculating the key performance

indicators. Referring to the information of a German railway operator the train has to stop 21 times on

every itinerary for crossings and overtaking. Although 18 stops were done under a catenary, the braking

energy is not usable today and is converted into heat.

Figure 10: Trackside speed-profile with 21 stops according to the drive profile (here intermediate stops are omitted)

Whereas the mentioned parameters are based on information of a German railway operator, the maxi-

mum track speed and the speed profile are unknown. Solely the maximum operating speed of 80 km/ is

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250 300 350 400 450 500 550

Tra

ck

sp

ee

d in

in

km

/h

Track distance in km Trackside speed-profile

24

known. Because of that the speed profile is assumed. Beside the stops, the train has to change the veloc-

ity several times per run. Reasons for that are for example switches, passing stations or slow zones. For

visualization the speed-profile for the whole relation is shown in the Figure 10. As a simplification the

track is modelled as a straight track without curves, slopes and inclinations.

Scenarios

For evaluating the benefit of a hybrid locomotive it is possible to examine several parameters. The pre-

sent research concentrates on the following parameters:

Loading status

Share of dynamic and pneumatic breaking force

Number of stops

According to the experiences these parameters are representing the most important ones for evaluating

the benefit of a hybrid locomotive and also in general for all locomotives with regard to saving energy.

Maximum dynamic braking forces

Today the maximum dynamic braking force is restricted to 150 kN (Germany) or 240 kN (for instance

in Switzerland [12]), which depends on each national legislation. These limitations refer in general on

the whole train and are independent from the number of locomotives situated in a trainset. The reason

for the restriction is the maximum allowable longitudinal compression force. High compressions forces

can cause derailments of single screw-coupler freight cars of a trainset, especially in narrow curves or

s-curves Depending on the car type compression forces from 200 kN or 240 kN are able to cause a

derailment by passing a s-curve11. Detailed information for the force restrictions and the limits are pub-

lished in the UIC leaflet 530-2 and EN 15839. [13]

In the present research the maximum dynamic braking force varies between 150 kN and 400 kN. The

scenario with 150 kN represents the limitation in Germany, the second scenario is a more theoretical

scenario and represents the maximum possible value of this technology (considering the 22.5 t axle load

of the six-axle hybrid locomotive). The maximum dynamic braking is physically limited due to the force

transmission in the wheel rail contact. In that way the dynamic braking force is equal with the maximum

traction force – velocity envelope (see Figure 9). With a conventional freight train in Europe it is not

practicable to dimension the dynamic braking forces that high. In the USA for instance, it is already

reality. The main reason is the different coupling system. In contrast to the USA the European trains are

not equipped with a central buffer coupling system, which enables much higher dynamic braking forces.

The reason is that this coupling system causes considerably smaller lateral forces compared to the Eu-

ropean side buffer system, Safety against derailment is not affected by the central buffer coupling sys-

tems.

Additionally the benefit of the dynamic brake is maximized by dynamic braking only and not with the

air brake. In this case nearly the complete kinetic energy will be converted into electric energy. The

11 This applies for conventional freight trains with screw-couplings.

25

challenge of this method is to handle the significantly prolonged braking distance. This will be possible,

if a continuous train monitoring system is used.

Number of stops

The number of stops has one of the greatest influences on the total energy consumption of a freight train.

Because of the train’s high weight12 the required energy for accelerating causes a significant part of the

total consumed energy. In contrast to the total energy consumption the benefit of a hybrid locomotive

in comparison to a diesel locomotive is better if the number of stops (under catenary) is higher.

The present study considers two cases. The first one is in inspired by today’s operation mode on the

present relation. The total number of stops is 21. The second case refers to optimal energy consumption

with just two stops on the complete relation. The first stop is in the middle of the relation and an addi-

tional at the destination point. The following table summarizes the mentioned scenarios.

Table 2: Overview about the scenario's parameter being investigated in this study

Scenario Locomotive Max. regen.

braking force

Braking

method

Number

of stops

Loading condi-

tion

1.1.1/.2 Diesel hydraulic 0 pneumatic 21 Laden\tare

1.2.1/.2 Diesel hydraulic 0 pneumatic 2 Laden\tare

2.1.1/.2 Hybrid 150 pneumatic,

dynamic

21 Laden\tare


dynamic

2 Laden\tare


dynamic

21 Laden\tare


dynamic

2 Laden\tare

4.1.1/.2 Hybrid 400 dynamic 21 Laden\tare

4.2.1/.2 Hybrid 400 dynamic 2 Laden\tare

12 The present train configuration see chapter 16.2

26

Calculation model

The present chapter describes the basic equations which were used for the calculation. Firstly the equa-

tions used for the determination of the drive’s specific efficiencies are shown. The subsequent section

offers the equations for the key performance indicators. Finally the calculation of the total required

traction energy is described.

The results of these equations are influenced by the performance requirements depending on the scenar-

ios’ speed profile. In contrast to the key performance indicators the total energy consumption is calcu-

lated independently from the primary energy source and represents the required energy to the wheels

for every type of train under the present conditions.

9.1.1. Drive efficiencies

Before describing the equations for the indicators and the traction energy, the degrees of efficiency has

to be explained for all three mentioned propulsion systems (see in chapter 9.1.1). This is necessary

because of the significant differences of the drive trains.

Plain electric propulsion

For electric traction by using the electricity of the catenary, the degree of efficiency 𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 com-

poses of the efficiencies of:

pantograph and electricity supply

transformer

power inverters

traction motor

gearbox

auxiliary supply.

Besides the auxiliary supply, the enumeration represents the whole propulsion system in correct order.

Following this the drive efficiency is calculated by multiplying component’s efficiency with each other

(see in Equation 1).

𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 = 𝜂𝑝𝑎𝑛𝑡 ∗ 𝜂𝑡𝑟𝑎𝑛𝑠 ∗ 𝜂𝑔𝑒𝑛 ∗ 𝜂𝑝𝑖 ∗ 𝜂𝑡𝑚 ∗ 𝜂𝑔𝑏 ∗ 𝜂𝑎𝑠 Equation 1

27

The following Table 3 offers an overview about all relevant and even about the calculated total drive

efficiency.

Table 3: Components of the electric propulsion system and their efficiencies [14]

Component Degree of efficiency

Pantograph 𝜼𝒑𝒂𝒏𝒕 0.95

Transformer 𝜼𝒕𝒓𝒂𝒏𝒔 0.95

power inverter 𝜼𝒑𝒊 0.975

traction motor 𝜼𝒕𝒎 0.95

gearbox 𝜼𝒈𝒃 0.96

auxiliary supply 𝜼𝒂𝒔 0.95

Total 𝜼𝒆𝒍𝒆𝒄𝒕𝒓𝒊𝒄,𝒅𝒓𝒊𝒗𝒆 0.76

At last the influence of the grid’s losses has to be considered. Whereas the efficiency of the locomotive

𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 is relevant for calculating the traction costs of the operator, the grids loss is relevant for

the total energy consumption and thus the produced CO2. For calculating the total effi-

ciency 𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑔𝑟𝑖𝑑, the grid’s efficiency 𝜂𝑔𝑟𝑖𝑑 has to be multiplied with the electric drive efficiency

𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 (see Equation 2)

𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑔𝑟𝑖𝑑 = 𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 ∗ 𝜂𝑔𝑟𝑖𝑑 Equation 2

The grid’s efficiency composes of the substation’s 𝜂𝑠𝑢𝑏 and the catenaries’ efficiency 𝜂𝑐𝑎𝑡 (see Equation

3).

𝜂𝑔𝑟𝑖𝑑 = 𝜂𝑠𝑢𝑏 ∗ 𝜂𝑐𝑎𝑡 Equation 3

In the Table 4 values of efficiency are mentioned and the total grid efficiency is already determined.

Table 4: Efficiency of rail electricity grid [15]


substation 𝜼𝒔𝒖𝒃 0.93

Catenary 𝜼𝒄𝒂𝒕 0.97

Total grid 𝜼𝒈𝒓𝒊𝒅 0.9

Finally the efficiency of the plain electric propulsion system 𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑔𝑟𝑖𝑑 including the grids loss

amounts (by using Equation 2) 0.688.

Dynamic brake

28

During braking under a catenary the electric mode of the locomotive enables the use of the dynamic

brake. The degree of efficiency 𝜂𝑑𝑦𝑛 is here assumed to 0.8 without the influence of the grid’s loss.

Diesel-electric propulsion

For the diesel-electric traction mode the drive efficiency composes, with differences, similarly to the

plain electric mode. Instead of catenary, pantograph and transformer, fuel tank, diesel engine and electric

generator are used to provide the power supply for the inverter. [15] The remaining part of the drivetrain

is shared by both traction modes. In that way the drive efficiency 𝜂𝑑𝑖−𝑒𝑙,𝑑𝑟𝑖𝑣𝑒 is calculated by using

following formula and represent the efficiency departing from the tank.

𝜂𝑑𝑖−𝑒𝑙,𝑑𝑟𝑖𝑣𝑒 = 𝜂𝑑𝑒 ∗ 𝜂𝑔𝑒𝑛 ∗ 𝜂𝑝𝑖 ∗ 𝜂𝑡𝑚 ∗ 𝜂𝑔𝑏 ∗ 𝜂𝑎𝑠 Equation 4

The following Table 5 contents the assumed efficiencies of the diesel engine 𝜂𝑑𝑒 and the generator 𝜂𝑔𝑒𝑛.

As well the efficiency of the remaining drivetrain and also the total drive efficiency 𝜂𝑑𝑖−𝑒𝑙,𝑑𝑟𝑖𝑣𝑒 are

mentioned and already calculated. The efficiency of the diesel-electric drivetrain amounts 0.327 in total.

For calculating the fuel demand in total, the efficiency of the diesel engine has to be excluded from the

calculation.13 The efficiency without the combustion engine 𝜂𝑑𝑖−𝑒𝑙,𝑑𝑟𝑖𝑣𝑒,1 is 0.76.

Table 5: Components of the diesel-electric propulsion systems and their efficiencies [15]


Diesel engine 𝜼𝒅𝒆 0.4313

Generator 𝜼𝒈𝒆𝒏 0.9014

Remaining drivetrain15 0.844

Total efficiency 𝜼𝒅𝒊−𝒆𝒍,𝒅𝒓𝒊𝒗𝒆 0.327

Efficiency without Diesel engine 𝜼𝒅𝒊−𝒆𝒍,𝒅𝒓𝒊𝒗𝒆,𝟏 0.76

13 Detailed information see in section 9.1.3

14 Experience value

15 Similar to the electric drivetrain

29

Diesel-hydraulic propulsion

The diesel-hydraulic propulsion system of the locomotive Maxima 40 CC consists of the following

components:

diesel engine,

hydraulic transmission,

drive shafts,

gearbox and

auxiliary supply.

The efficiency is the product of the efficiencies of these components and represents the efficiency from

the tank, too.

Table 6: Components of the diesel-hydraulic propulsion systems and their efficiencies

Number Component Degree of efficiency

1 Diesel engine 𝜂𝑑𝑒 0.43

2 Hydraulic transmission 𝜂ℎ𝑡 0.83 [15]

3 Drive shaft 𝜂𝑑𝑠 0.97 [15]

5 Gearbox 𝜂𝑔𝑏 0.96 [14]

6 Auxiliary supply 𝜂𝑎𝑠 0.94 [15]

Total efficiency 𝜼𝒅𝒊−𝒉𝒚,𝒅𝒓𝒊𝒗𝒆 0.309

Efficiency without Diesel engine 𝜼𝒅𝒊−𝒉𝒚,𝒅𝒓𝒊𝒗𝒆,𝟏 0.719

The total efficiency of these drivetrain 𝜂𝑑𝑖−ℎ𝑦,𝑑𝑟𝑖𝑣𝑒 is 0.309, calculated by means of Equation 5. In

comparison to the diesel-electric locomotive the efficiency is about 2 % lower. In comparison to the

plain electric propulsion the efficiency is nearly 46 % lower.

𝜂𝑑𝑖−ℎ𝑦,𝑑𝑟𝑖𝑣𝑒 = 𝜂𝑑𝑒 ∗ 𝜂ℎ𝑡 ∗ 𝜂𝑑𝑠 ∗ 𝜂𝑔𝑏 ∗ 𝜂𝑎𝑠 Equation 5

The efficiency without the diesel engine 𝜂𝑑𝑖−ℎ𝑦,𝑑𝑟𝑖𝑣𝑒 is 0.72.

30

9.1.2. Traction energy

In this chapter the formulas used to calculate the traction power are presented. In present report the

traction power is the required energy at the wheel without influences of the drive’s efficiency and is

therefore the basis for the, in the previous section mentioned, calculation of the key performance indi-

cators. The determination of the energy is described backward beginning with the power requirements

to necessary traction forces depending on the track’s speed profile.

Following Equation 6, the required power 𝑃𝑡𝑟𝑎𝑐 composes of the multiplication of the total traction force

and the corresponding velocity 𝑣(𝑡). The locomotive’s traction force is the sum of the current accelera-

tion 𝐹𝑎𝑐𝑐 (𝑡) the pneumatic braking force 𝐹𝑏𝑟𝑎𝑘𝑒𝑚𝑒𝑐ℎ (𝑡) and the driving resistance 𝐹𝑟𝑒𝑠𝑖𝑠𝑡 (𝑣).

𝑃𝑡𝑟𝑎𝑐(𝑡) = (𝐹𝑎𝑐𝑐 (𝑡)−𝐹𝑏𝑟𝑎𝑘𝑒𝑚𝑒𝑐ℎ (𝑡) − 𝐹𝑟𝑒𝑠𝑖𝑠𝑡 (𝑣)) ∗ 𝑣(𝑡) Equation 6

The acceleration force 𝐹𝑎𝑐𝑐 and the pneumatic braking force are calculated by the use of the following

Equations:

𝐹𝑎𝑐𝑐 (𝑡) = 𝑚𝑙𝑜𝑐 ∗ 𝑎 ∗ 𝜌𝑙𝑜𝑐 Equation 7

𝐹𝑏𝑟𝑎𝑘𝑒 𝑚𝑒𝑐ℎ (𝑡) = 𝑚𝑙𝑜𝑐 ∗ 𝑏 ∗ 𝜌𝑙𝑜𝑐 Equation 8

The acceleration and deceleration were determined by the help of the traction effort diagram and the

speed profile of the track (see chapter 6).

If the train composition uses a catenary and uses the dynamic brake will be used and the locomotive can

feed electric energy back. Hence the required power is negative. The required dynamic braking power

𝑃𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛(𝑡) is calculated separately due to the deviating degree of efficiency in comparison to the

propulsion system16. The dynamic braking power is calculated similarly as the traction forces by multi-

plying the required force with the corresponding velocity (see Equation 9 ).

𝑃𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛(𝑡) = 𝐹𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛 (𝑡) ∗ 𝑣(𝑡) Equation 9

The dynamic braking forces 𝐹𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛 (𝑡) is calculated like the pneumatic braking force. The maxi-

mum braking force is also limited by the scenario’s specific maximum and by the maximum traction

effort with respect to the rail-wheel contact conditions.

Whereas the dynamic braking is limited due to the mentioned reasons, the pneumatical braking forces

of the whole train is several times higher.The maximum deceleration 𝑏 of the train is limited to 0.51 m/s2.

This matches with a stopping distance of 750 m from a velocity of 100 km/h. The braking capacity of

the dynamic brake and the maximum acceleration capacitiy 𝑎 is limited by the maximum tractive-effort.

16 More information see in Chapter 9.1.1.

31

The driving resistance is calculated by using the equation of Strahl (see Equation 10).

𝐹𝑟𝑒𝑠𝑖𝑠𝑡 (𝑡) = 𝑐1 + (0.007 + 𝑐2) ∗ (𝑣 (𝑡)

10)

2

Equation 10 [16]

The coefficients 𝑐1 and 𝑐2are representing the influence of the starting-up ressistence respectivly the

air and rolling resistance (see Table 2).

9.1.3. Electric Energy and fuel consumption

This section shows equations for calculating the energy the locomotive needs to run the relation. At first

the basics for the electric energy consumption of the hybrid’s locomotive plain electric mode will be

presented. Subsequently the equations for the diesel consumption of the “Maxima” or the diesel mode

of the hybrid locomotive will be presented.

Electric Energy consumption

The electric energy consumption describes the needed electricity of a plain electric propulsion system

of an electric or a hybrid locomotive. For determining the traction costs of the operator and the produc-

tion of CO2 it is necessary to distinguish between the total energy consumption of locomotive 𝐸𝑒𝑙,𝑙𝑜𝑐 and

the energy the grid has to provide 𝐸𝑒𝑙,𝑔𝑟𝑖𝑑. The electric energy consumption 𝐸𝑒𝑙,𝑙𝑜𝑐 is determined by

means of Equation 11. The total required power to the wheel 𝑃𝑡𝑟𝑎𝑐(𝑡) and the dynamic braking power

𝑃𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛(𝑡) will be divided by the specific total degrees of efficiency. 𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 is the efficiency

of the electric propulsion system and 𝜂𝑑𝑦𝑛 the efficiency of the dynamic brake. Both degrees of efficien-

cies do not consider the grid’s deficiency.

𝐸𝑒𝑙,𝑙𝑜𝑐 [𝑘𝑤ℎ] = ∫ (𝑃𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛(𝑡)

𝜂𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐,𝑑𝑟𝑖𝑣𝑒 + 𝑃𝑏𝑟𝑎𝑘𝑒 𝑑𝑦𝑛(𝑡) ∗ 𝜂𝑑𝑦𝑛 ) 𝑑𝑡

𝑡𝑒𝑛𝑑

𝑡𝑏𝑒𝑔𝑖𝑛

Equation 11

The energy consumption including the grid’s loss 𝐸𝑒𝑙,𝑔𝑟𝑖𝑑 is calculated by dividing needed energy of

the locomotive 𝐸𝑒𝑙,𝑙𝑜𝑐 by the grid’s degree of efficiency 𝜂𝑔𝑟𝑖𝑑 .

𝐸𝑒𝑙,𝑔𝑟𝑖𝑑 [𝑘𝑤ℎ] =𝐸𝑒𝑙,𝑙𝑜𝑐

𝜂𝑔𝑟𝑖𝑑 Equation 12

32

Diesel consumption

Before the diesel consumption can be calculated the required energy output of the engine 𝐸𝑑𝑒 has to be

identified. With the help of the Equation 13, this can be done by dividing the traction power with the

drivetrain’s efficiency. In contrast to the previous mentioned calculation the efficiency level of the diesel

engine is not considered, because it is already included in the specific fuel consumption, see Equation

15.

𝐸𝑑𝑒 [𝑘𝑤ℎ] =𝑃𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛(𝑡)

𝜂𝑑𝑖−ℎ𝑦𝑑\𝑑𝑖−𝑒𝑙 𝑑𝑟𝑖𝑣𝑒 Equation 13

The total fuel consumption 𝐷𝑖𝑡𝑜𝑡𝑎𝑙 is calculated by using Equation 14. In that way the amount of the

diesel consumption results from the multiplication of the total required energy 𝐸𝑑𝑖𝑒𝑠𝑒𝑙 𝑒𝑛𝑔𝑖𝑛𝑒 and the

specific fuel consumption 𝑏𝑒𝑓𝑓. For an optimized illustration the fuel consumption is converted from

kilogram into litre by multiplying with the reciprocal of fuel’s density. The density of diesel ranges in

general between 820 kg/m3 and 845 kg/m3 [17]. In the present research the density is converted into

volumetric units and assumed to 0.845 kg/l.

𝐷𝑖𝑡𝑜𝑡𝑎𝑙 [𝑙] = 𝐸𝑑𝑒 ∗ 𝑏𝑒𝑓𝑓 ∗1

𝜌𝐷𝑖𝑒𝑠𝑒𝑙

Equation 14

By applying the Equation 15 it is possible to calculate the specific fuel consumption. According to the

mentioned equation the specific fuel consumption depends mainly on the engine’s degree of effi-

ciency 𝜂𝑑𝑒, although the fuel’s calorific value 𝐻𝑖 has also an influence. Whereas the calorific value is a

fix substance parameter and amounts 42.5 MJ/kg [17] (~11.8 kg/kWh), the degree of efficiency varies

from engine to engine. In general the efficiency of today’s diesel engines with turbo compound ranges

between 0.36 and 0.46. [18] For this research the efficiency 𝜂𝑑𝑒 is set to 0.43

𝑏𝑒𝑓𝑓 =1

𝜂𝑑𝑒[%] ∗ 𝐻𝑖 Equation 15 [18]

33

9.1.4. Key performance indicators

In this section methods and also basic parameters for calculating the key performance indicators will be

presented.

Total CO2 emissions

In this part the equations and the assumptions for the quantification of the CO2 emissions of all scenarios

will be presented. By means of Equation 16 the amount of CO2 is calculated for the plain electric pro-

pulsion. The specific energy 𝐸𝑒𝑙 has to be multiplied with the specific CO2 consumption 𝑐𝑜2,𝑒𝑓𝑓𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 ,

which depends on the rail traction current mix.

𝐶𝑂2,𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 [𝑔] = 𝐸𝑒𝑙,𝑔𝑟𝑖𝑑 ∗ 𝑐𝑜2,𝑒𝑓𝑓𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 Equation 16

Based on the rail traction current mix from 2010 the CO2 emissions are in assumed to 402 g/kWh

(111.681 *103 kg/TJ). [19] By using green electricity (from renewable energy) the emissions per kilo-

watt-hours can be reduced to 5.2 g/kWh (1445 kg/TJ).17 The diesel emissions are determined by multi-

plying the consumed diesel with the specific CO2 production per litre (see Equation 17).

𝐶𝑂2,𝑑𝑖𝑒𝑠𝑒𝑙 [𝑔] = 𝐷𝑖𝑡𝑜𝑡𝑎𝑙 ∗ 𝑐𝑜2,𝑒𝑓𝑓𝑑𝑖𝑒𝑠𝑒𝑙 Equation 17

The combustion of one litre diesel (from the fuel station) produces 3155 g of CO2. [22] The amount of

CO2 per kWh is 621 g (see in Table 7). In comparison to the current mix of the DB the CO2 production

when using diesel is about 54 % higher. Compared to the green electricity the production is nearly 12

times higher.

Table 7: Specific CO2 production for diesel and traction current

Type of Energy C02 [g/l] C02 [g/kWh]

Diesel 3.155 62118

DB Traction current - 402

Green electricity - 5.2 17

In case of the hybrid locomotive the CO2 emissions is calculated by summing up the CO2 produced in

diesel-electric and in pure eletric mode.

17 By using electricity produced by an offshore wind mill. [22]

18 Calculated by the use of Equation 15.

34

Share of fossil and renewable energy consumption

For evaluating the influence on nature it is necessary to determine the need of primary energy or rather

the share of fossil and renewable primary energy. Primary energy includes in contrast to the secondary

energy (traction energy) the energetic investments, which are necessary for providing the electricity of

the catenary of the fuel in tank.

Table 8 offers the values for the need of renewable and fossil energy. The values are expressed as the

specific energy (renewable or fossil) which is necessary for producing 1 TJ of traction energy. The up-

stream of producing energy is considered. Because of this, the energy represents the need of primary

energy.

Table 8: Specific share of fossil and renewable energy of rail traction current mix considering upstream

Type of Energy

Renewable

Energy

TJ/TJ

Renewable

Energy

MJ/kWh

Fossil

Energy

TJ/TJ

Fossil

Energy

MJ/kWh

Electric Energy

DB Current mix 0.21 [23] 0.756 2.19 [23] 7.88

Green electricity 1 [24] 3.6 0.0204 [24] 0.07344

Diesel 0.0924 [25] 0.33 1.09 [25] 3.92

When using the diesel engine, the share of fossil energy is nearly 100 %.19 In the present report the share

of fossil and renewable energy for the electric mode is calculated firstly based on the standard current

mix of the “Deutsche Bahn”. Secondly the option of using green electricity is considered. The need of

fossil energy of the green electricity is nearly 0 %. The share of renewable energy for the DB current

mix is 0.756 MJ/kWh and for fossil energy 7.88 MJ/kWh. [23]

Total Costs

The overall costs for providing the traction power are calculated by multiplying the overall consumed

energy or fuel with the price per kWh of electricity or liter of diesel. The price “from DB Energie” for

one kWh of traction current was 12.5 ct in 2013.20 [26] In contrast to the electric current in recent years

the fuel price is decreasing significantly. The costs are assumed to 1 € per liter of diesel.

19 Referring to the diesel mix of Germany (including green fuel).

20 A lower resale price of the refeeded electric energy is not concidered.

35

Input quantities of the calculation model

This chapter gives an idea about the input quantities of the calculation models, for instance, the calcu-

lated speed profile of the hybrid locomotive along the track, as shown in Figure 11.

Figure 11: Speed-profile of the whole relation for the laden train pulled by the hybrid locomotive with 21 stops

As plotted in Figure 12 the train stops exactly at the stopping point. It represents the ideal train driver.

Because of the braking distance for a velocity of 100 km/h is set to 750 m, the deceleration is about

0.51 m/s2. In contrast to the braking distance the train needs nearly four km for acceleration up to

80 km/h.

Figure 12: Exemplary baking and acceleration phase for the laden train pulled by the hybrid locomotive

Figure 13 displays the traction force along the first 150 km. The peaks of the envelope are representing

accelerations. The speed dependency of the traction force is considerably recognizable.

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250 300 350 400 450 500 550

Sp

eed

in

km

/h

Distance in kmTrain's speed Trackside speed

0

10

20

30

40

50

60

70

80

90

144 145 146 147 148 149 150

Sp

eed

in

km

/h

Distance in km

Train's speed Trackside speed-profile

36

Figure 13: Traction force envelope of the first 150 km for the laden train pulled by the hybrid locomotive

Based on the envelope of the traction force Figure 14 shows the required power input along the first

150 km. The positive values represent acceleration and phases of constant velocity, in which energy is

demanded. Negative values represent braking phases in which the train, if a catenary is available, feeds

energy back into the grid.

Figure 14: Excerpt of the power input along the first 150 km for the laden train pulled by the hybrid locomotive

0

50

100

150

200

250

300

350

400

450

0 50 100 150

Tra

ctio

n f

orc

e in

kN

Distance in km

Traction force

-6000

-4000

-2000

0

2000

4000

6000

8000

10000

0 50 100 150

Tra

ctio

n p

ow

er i

n k

W

Distance in km

Traction power (400 kN dyn. braking force)

37

As a consequence of the demand of traction power the energy consumption increases. As shown in

Figure 15, the energy consumption is increasing nearly about the complete section. The braking phases

are representing an exception, due to the recuperation.

Figure 15: Excerpt of the energy consumption along the first 150 km for the laden train pulled by the hybrid locomotive

0

1000

2000

3000

4000

5000

6000

7000

8000

0 50 100 150

En

ergy c

on

sum

pti

on

in

kW

h

Distance in km

Consumed traction energie (400 kN dyn. braking force)

38

Results

This chapter describes the calculation results for the key performance indicators according to the sce-

narios mentioned in chapter 8. At first the required energy of both locomotives is presented. From this

the need of primary and secondary energy is derived. Secondly the share of used fossil and renewable

primary energy is presented to evaluate the influence on the environment. Afterwards the amount of

produced CO2, which goes along with consumed energy, will be provided. All these key performance

indicators are examined due to their potential in saving the environment by considering the use of green

energy. Finally the costs for traction resources are presented in order to evaluate the possibility of cost

reductions, which is necessary for a comprehensive application of the hybrid technology in the rail

freight market.

If not declared otherwise, the following diagrams represent the arithmetic average of a tare and a laden

movement.

11.1. Energy consumption

At first the demand of secondary energy is presented. This is the energy which is necessary for providing

the traction power. In detail the secondary energy represents the electric current from the pantograph or

the energy content of the fuel. The energy for providing fuel or traction current is called primary energy

and is taken into account in section 11.1.2. The demand of this type of energy is relevant for evaluating

the greening potential of the hybrid locomotive.

11.1.1. Secondary Energy

This section concentrates on the amount of energy the locomotive consumes and the operator has to pay

for (see section 11.4).

Figure 16: Total energy consumption for laden and tare loading status considering 2 and 21 stops

56.84

24.22 23.82

19.46

43.99

18.39 18.34 17.89

28.41

11.46 11.06 10.25

24.63

10.03 9.98 9.90

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Diesel Hybrid (a) Hybrid (b) Hybrid (c)

To

tal E

ne

rgy c

on

su

mp

tio

n in

MW

h

Total energy consumption

Laden,21 Stops

Laden,2 Stops

Tare,21 Stops

Tare,2 Stops

Charge\Count of stops:

Usage of dynamic brake:(a) = 150 kN(b) = 400 kN(c) = 400 kN (dyn. brake solely)

39

Figure 16 gives an overview of all scenarios considering both loading cases. Within the same train con-

figuration the dominating influence on the total energy consumption is the loading status. Independ from

the type of locomotive and the count of stops the demanded energy increases about 100 % from tare to

laden. Considering all aspects the diesel locomotive has always the largest demand of energy. The diesel

locomotive about 5700 litres of diesel needs for pulling the laden train, with 21 stops. This quantity is

equivalent to the energy of 56.84 MWh. Comparing the same scenario the energy consumption of the

hybrid locomotive varies from 24.22 MWh to 19.46 MWh in depending on the used dynamic braking

force. As expected, the hybrid locomotive, which brakes pure dynamic with 400 kN, has the lowest

energy demand. The difference to the diesel locomotive is about 37 MWh. This means that the energy

consumption can be decreased by about 65 % by using the hybrid locomotive instead of the diesel loco-

motive. If also the count of stops is reduced from 21 to two stops, the demand of energy will reduce to

9.90 MWh. This means a reduction potential of 82 % from today’s situation. Rephrased the saved energy

of 46.94 MWh is equivalent to the electric energy demand of more than 10.5 average households21. The

reason for the spread of energy consumption between the diesel and the hybrid locomotive is mainly the

efficiency of the propulsion system. The value of the diesel-hydraulic propulsion system is nearly 0.31.

In contrast to this the efficiency of the electric propulsion system is 0.76. The difference between the

efficiencies of 45 percentage points represents also the energy saving potential of the hybrid locomotive

without recuperating.

Figure 17: Average Energy consumption in total for tare and laden movement considering 2 and 21 stops

Figure 17 also provides the total energy consumption for both locomotive types. In contrast to the pre-

vious figure the energy consumption is the arithmetic average of the laden and tare train movement. The

21According to an average German household with 4 persons and a demand of 4.400 kWh per year.

42.62

17.84 17.44

14.85

34.31

14.21 14.16 13.89

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0


To

tal E

ne

rgy c

on

su

mp

tio

n in

MW

h

Total energy consumption

21 stopps 2 stopps

Count of stops:


40

energy consumption varies from 42.62 MWh to 14.85 MWh, with 21 stops. Thus, the operator can save

65 % of traction energy in average for one movement.

For transferring and comparing the energy consumption with other train configurations, Figure 18 de-

scribes the specific energy consumption per kilometre and ton. The diesel locomotive needs an average

energy of 34.62 Wh/tkm. The need for the hybrid locomotive can be reduced to 12.38 Wh/tkm according

to dynamic braking force.

Beside the effect of changing the propulsion system, a reduction of the count of stops has a significant

effect, too. In that way it is possible to save nearly 20 % of energy, independently from the propulsion

system. The effect of saving energy by increasing the dynamic brake, is reduced from 20 % (Hybrid a)

to 7 % (Hybrid b) for the scenario with 2 stops. The reason for the reduction is that the count of recu-

peration periods reduces with the count of stops. But nevertheless the dynamic brake is still able to save

7 % of energy, although the count of decelerations is significantly reduced.

Figure 18: Specific Energy consumption per tkm average of a tare and laden movement considering 2 and 21 stops

34.62

14.36 13.9512.38

28.91

11.98 11.93 11.77

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0


Sp

ec

ific

En

erg

y c

on

su

mp

tio

n in

W

h\t

km

Specific Energy consumption per tkm

21 stops 2 stopps

Count of stops:

Usage of dynamic brake:(a) = 150 kN(b) = 400 kN

(c) = 400 kN (dyn. brake solely)

41

11.1.2. Primary energy

This section shows the amount of primary energy the train configurations needs for a movement. The

following figure plots the energy demand for the movement with 21 stops. First of all the need of primary

energy is always higher than the need of secondary energy. The difference depends on the propulsion

system or rather on the energy source used for providing the traction power. Two types of energy are

considered in this report. This is the fuel of fuel stations for diesel locomotives on the one hand and the

electric current of the catenary on the other hand.


The energetic investments for providing the energy of 1 MJ are differing considerably. In case of diesel

nearly 1.18 MJ are necessary to provide 1 MJ [27]. For producing the electric traction energy of 1 MJ

the energetic effort of at least 2.4 MJ is necessary [21]. In principle the production of 1 MJ of electric

energy requires twice as much energy compared to diesel.22 In consequence the primary energy con-

sumption of the hybrid locomotive increases steeper than the one of the diesel locomotive. The benefit

reduces. Nevertheless the largest demand of primary energy has also the diesel locomotive with more

than 50 MWh. The difference to the hybrid locomotive ranges between 8 MWh and 15 MWh depending

on the share of the dynamic brake. Thus the advantage of the hybrid technology is reduced to 16 %,

respectively 30 %. According to the scenario with two stops the reduction potential is independently

from the recuperation about 18 %, see Figure 20.

22 Detailed information see chapter 9.1.4.

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

200.00


0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

55.00

En

erg

y c

on

su

mp

tio

n in

GJ

En

erg

y c

on

su

mp

tio

n in

M

Wh

Primary and secondary energy consumption (21 stops)

Primary energy

Secondary energy


Type of energy:

42

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

200.00


0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

55.00E

ne

rgy c

on

su

mp

tio

n in

GJ

En

erg

y c

on

su

mp

tio

n in

M

Wh

Total energy consumption (green electricity, 21 stops)

Primary energy

Secondary energy


Type of energy:


A possibility to decrease the primary energy demand for the hybrid locomotive is changing the current

mix. An electric energy mix, which composes of less energy intensive generating methods, enables to

considerably decrease the demand of primary energy. If a green electricity mix is used, the specific

primary energy demand will be lower than that of diesel. For example an offshore wind mill park needs

1.02 MJ of primary energy for providing one MJ of electric energy. The energy saving potential or rather

the benefit of the hybrid locomotive increases up to 70 % in this case. For the optimized movement with

just two stops the energy saving potential rises about 2 % once again. Today it is possible to save 65 %

of primary energy (Hybrid (a)).

Figure 21: Primary and secondary energy demand considering use of green electricity, 21 stops, average of tare and

laden

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00


0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

En

erg

y c

on

su

mp

tio

n in

GJ

En

erg

y c

on

su

mp

tio

n in

M

Wh

Primary and secondary energy consumption (2 stops)

Primary energy

Secondary energy


Type of energy:

43

11.2. Share of fossil and renewable energy

Besides the consumed primary energy the share of renewable energy is also important for evaluating the

benefit for the environment when using a hybrid locomotive. Therefore this section offers the proportion

of fossil and renewable energy of the total consumed primary energy.

Figure 22: Consumed primary energy for the scenario of 21 stops (average of a tare and laden movement)

Figure 22 plots the total primary energy demand using diesel and the German traction current mix. The

proportion of fossil energy is the larger than the proportion of the renewable energy for every train

configuration. The diesel locomotive with 46.46 MWh has the largest demand. The hybrid locomotive

consumes an amount of fossil energy from 38.15 MWh to 31.73 MWh according to the degree of recu-

peration. The amount of renewable energy is for both locomotives and all dynamic braking mode nearly

the same and ranges between 3 MWh and 4 MWh. Thus, just about 9 % of the consumed energy is

renewable. The change to green electricity move the share of energy considerably. As plotted in Figure

23 the usage of green renewable energy increase to more than 93 %, independently from the dynamic

brake. In total the amount of fossil energy reduces to nearly 1 MWh in case of pure dynamic braking.

50.40

41.80 40.84

34.77

46.46

38.15 37.28

31.73

3.94 3.65 3.56 3.03

0

5

10

15

20

25

30

35

40

45

50

55

Diesel hydraulic Hybrid (a) Hybrid (b) Hybrid (c)

Co

ns

um

ed

pri

ma

ry e

ne

rgy i

n M

Wh

Share of renewable\fossil primary energy (21 Stops)

Total primary energy

fossile

renewable

Type of energy:


44

Figure 23: Percentage of fossil and renewable primary energy using green electricity (21 Stops, average of a tare and

laden movement)

11.3. CO2 emissions

The following section deals with the CO2 emissions. The calculated emissions consider the amount of

CO2 which is produced for providing the traction power (primary energy). Like for the calculation of

the primary energy, the specific amount of emitted CO2 depends on the energy source. In case of using

diesel the consumption of 1 kWh produces nearly 622 g of CO2. In case of using the electricity of the

catenary the production reduces to above one third with 402 g/kWh.23 Due to higher specific emissions

and the even higher secondary energy demand, the emissions are also higher than those for the hybrid

locomotive. 13.49 t of CO2 will be produced for one average movement using the diesel locomotive. By

using the electric current from catenary it is possible to reduce the production to 7.10 t. Referring to the

pure dynamic braking scenario an additional reduction 5.91 t is possible. This equals to CO2 reduction

potentials of 47.4 % respectively 56.2 %.

23 According to the traction current mix of the “Deutsche Bahn.

46.46

1.26 1.25 1.08

3.94

17.08 16.68 14.20

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Sh

are

of

fos

sil

\re

ne

wa

ble

e

ne

rgy i

n %

(M

Wh

)

Share of fossil\renewable energy (21 Stops)

renewable

fossile

Type of energy:


45

Figure 24: CO2 emissions in total considering the usage of green energy considering 2 and 21 stops (average of a tare

and laden movement)

The main benefit of the electric mode is the possibility of using green electricity. By changing from

today’s traction energy mix to green electricity the reduction potential increases significantly to more

than 97 % compared to the diesel locomotive. In consequence the specific productions of C02 decrease

from 11 g/tkm to 0.3 g/tkm respectively 0.2 g/tkm, referring to the scenario with 2 stops (see in Figure

24). Summarizing this, the amount of CO2 can be reduced nearly to zero, for the present train movement.

Figure 25: Specific CO2 emissions per tkm considering the usage of green energy considering 2 and 21 stops (average

of a tare and laden movement)

13.49

7.10 6.94

5.91

10.86

5.67 5.65 5.54

0.35 0.35 0.300.35 0.35 0.30

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0


To

tal C

O2 e

mis

sio

ns

in

t

Total CO2 emissions

21 stops, (DB energy mix\diesel)

2 stops (Db ernergy mix)

21 stops (green)

2 stops (green)

Count of stops (energy type):

Usage of dynamic brake:(a) = 150 kN(b) = 400 kN

(c) = 400 kN (dyn. brake solely)

11

6 6

5

9

5 5 5

0.3 0.3 0.30.2 0.2 0.2

0.0

2.0

4.0

6.0

8.0

10.0

12.0


CO

2p

rod

uc

tio

n in

g\t

km

Specific CO2 emissions per tkm

21 stops, (DB energy mix\diesel)

2 stops (Db ernergy mix)

21 stops (green)

2 stops (green)

Count of stops (energy type:


46

11.4. Cost for traction resources

Besides the mentioned benefits for the environment the costs are important for a comprehensive appli-

cation of the hybrid technology. Therefore this section shows the costs for the operator according to the

energy the locomotive needs. The costs constitutes of the consumed diesel and electric energy. The price

per litre diesel is assumed to 1 €. This equals to a price of 19.7 ct for one kWh of energy.24 The price for

a kilowatt-hour of electric energy from the catenary is assumed to 12.5 ct.

Figure 26: Total Costs for traction resources in Euro considering 2 and 21 stops (average of a tare and laden movement)

Figure 26 and Figure 27 show the costs for the locomotive types and the number of stops for exemplary

movement. Due to fact that the specific energy price and the amount of consumed energy of the hybrid

locomotive is lower than for diesel locomotive, the spread between the costs of locomotives is large.

Costs for the traction resources ranges between 4275 € (0.35 €/tkm) and 2210 € (0.18 €/tkm) or 1839 €

(0.15 €/tkm) for the optimized usage of the dynamic brake. By reducing the count of stops the cost will

decrease once again to 1724 € (0.15 €/tkm), less than the half of the costs of today’s operation condition.

24 Detailed information mentioned in section 9.1.4.

4275

2210 2160

1839

3441

1763 1757 1724

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

3500.0

4000.0

4500.0


Co

st

for

tra

cti

on

re

so

urc

es

in

€

Costs for traction resources

21 stops2 stopps

Count of stops:


47

The financial saving is more than 2065 € (0.17 €/tkm) only by changing the locomotive type. This

amount can be saved under today’s operating conditions, without increasing the dynamic brake and

installing a new train control system to reduce the number of stops or enabling pure dynamic braking.

The cost reduction potential for traction resources is in this case about 48.3 %. If all optimizations are

considered the effect increases to 59.7 %.

Figure 27: Specific Costs for traction resources per tkm (average of a tare and laden movement)

0.35

0.18 0.170.15

0.29

0.15 0.15 0.15

0.0

0.1

0.1

0.2

0.2

0.3

0.3

0.4

0.4


Co

st

for

tra

cti

on

re

so

urc

es

in

c

en

t\tk

m

Costs for traction resources per tkm

21 stops

2 stopps

Count of stops:


48

Summary

The application of a hybrid freight locomotive has a considerably high potential for saving the environ-

ment and the costs for the operator. For today’s situation it is possible to reduce the demand of secondary

energy (from catenary\tank) about 50 %. This goes along with a cost reduction for traction resources by

48 %. The reason for that is primarily the advanced efficiency of the electric propulsion system and

secondary the usage of the dynamic brake.

The reduction of the primary energy demand or rather the share of renewable energy expresses as well

as the CO2 emission the environmental benefit of this technology. Compared to the diesel locomotive it

is possible to minimize the need of primary energy by about 16 %, according to today’s electric energy

mix of the “Deutsche Bahn”. The primary energy saving is lower compared to the savings in secondary

energy demand. This is a consequence of the energy mix, because it constitutes of intensive generation

methods. Nevertheless, the production of CO2 decreases about 47.4 %. The share of renewable energy

increases slightly by using the hybrid locomotive and is about 9 %.

Besides the saving potential of traction energy, the possibility of using green energy is a main benefit of

this technology. The change to green electricity reduces the need of primary energy by about 65 %

compared to the diesel locomotive. The share of renewable energy increases to 93 %. The production of

CO2 decreases considerably by about 97 %, as well. That means that only 3 % are left. In that way it is

possible for the exemplary train movement to drive nearly without using fossil energy and thus without

producing CO2.

Apart from the change of the locomotive it is also possible to save energy by optimizing the operation

mode. By reducing the number of stops it is possible to save approximately 20 % of traction energy

additionally. As a consequence, the reduction of the primary energy demand, the CO2 emission and the

cost reduction is also about 20 %. A switch to a central buffer coupling-system and thus enabled option

of pure dynamic braking has a positive effect to the energy demand, too. But regarding to the crucial

and expensive refitting the effect is too low.

Due to the fact that the results are based on a new hybrid locomotive concept the results are also trans-

ferable to other hybrid locomotives with a similar power rate. An alternative to the new concept is the

“Euro 4000 Dual” from former Vossloh now Stadler, which is also suitable for pulling heavy freight

trains in both operation modes in Europe.

49

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51

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