The Future of Diesel Engines

Research Programme

Engineering The future of the diesel engine

THE FUTURE OF THE DIESEL ENGINE

AUTHOR : IAN SILVER DATE : 1 JUNE 2007

Copyright 2007 Rail Safety and Standards Board Ltd. This publication may be reproduced free of charge for research, private study or for internal circulation within an organisation. This is subject to it being reproduced and referenced accurately and not being used in a misleading context. The material must be acknowledged as the copyright of Rail Safety and Standards Board and the title of the publication specified accordingly. For any other use of the material please apply to RSSB's Head of Research and Development for permission. Any additional queries can be directed to [email protected]. This publication can be accessed via the RSSB website www.rssb.co.uk

THE FUTURE OF THE DIESEL ENGINE Page No. 1 of 121

CONTENTS PAGE

1 EXECUTIVE SUMMARY..................................................................... 7 2 INTRODUCTION ............................................................................. 11 3 ABBREVIATIONS USED................................................................... 11 4 USEFUL DEFINITIONS ...................................................................... 13 5 UIC RESEARCH INTO LOCAL AIR POLLUTION .............................. 15

5.1 BACKGROUND .................................................................................................. 15 5.2 METHODOLOGY OF UIC WP3 REVIEW ................................................................. 15 5.3 REVIEW OF RESULTS FROM WP3 ........................................................................... 16

6 CURRENT EXHAUST EMISSIONS STANDARDS ............................... 18 6.1 BACKGROUND .................................................................................................. 18 6.2 EUROPEAN DIRECTIVE 2004/26/EC.................................................................... 18 6.3 UIC GUIDELINES ................................................................................................ 21 6.4 EURO LIMITS ...................................................................................................... 23 6.5 US EPA REGULATIONS........................................................................................ 23 6.6 LEVEL OF COMPLIANCE OF UK TRACTION FLEET..................................................... 24

7 CURRENT GOVERNMENT ENVIRONMENTAL POLICY................... 24 7.1 UK LEGISLATION ................................................................................................ 24 7.2 FUTURE POLICY .................................................................................................. 25 7.3 SUMMARY OF LIKELY FUTURE GOVERNMENT DIRECTION.......................................... 26

8 CURRENT INDUSTRIES POLICIES AND ACTIONS ........................... 26 8.1 NOTIFICATION TO TRAIN OPERATORS ................................................................... 26 8.2 ENGINE MANUFACTURER EMISSIONS STATEMENTS .................................................. 27 8.3 ENGINE TECHNOLOGY FOR EMISSIONS ABATEMENT GENERAL .............................. 27 8.4 NOX REDUCTION TECHNIQUES ............................................................................ 28 8.5 PM REDUCTION TECHNIQUES .............................................................................. 30 8.6 CO2 REDUCTION TECHNIQUES............................................................................ 31 8.7 RE-ENGINING.................................................................................................... 31 8.8 MULTIPLE ENGINES ............................................................................................. 33 8.9 FUTURE DEVELOPMENTS....................................................................................... 33

9 LEGISLATIVE DEVELOPMENTS ....................................................... 35 9.1 NRMM DIRECTIVE ............................................................................................. 35 9.2 EU DIRECTIVE 2003/17/EC ............................................................................... 35 9.3 EU DIRECTIVE 2003/30/EC ............................................................................... 36 9.4 EU DIRECTIVE 96/62/EC ................................................................................... 37 9.5 RENEWABLE TRANSPORT FUEL OBLIGATION............................................................ 37


10 COMMERCIAL DEVELOPMENTS IN OTHER SECTORS ................... 37 10.1 GENERAL .......................................................................................................... 37 10.2 FUEL AVAILABILITY ............................................................................................. 37 10.3 FUEL MANUFACTURING COST.............................................................................. 38 10.4 FUEL DUTY......................................................................................................... 39 10.5 ALTERNATIVE POWER SOURCES............................................................................ 40

11 FUEL DEVELOPMENT ...................................................................... 41 11.1 GAS OIL AND DIESEL FUEL .................................................................................. 41 11.2 BIOFUELS........................................................................................................... 41 11.3 WATER DIESEL EMULSION .................................................................................... 43 11.4 NATURAL GAS................................................................................................... 44 11.5 BIOGAS ............................................................................................................ 45 11.6 FUEL ADDITIVES.................................................................................................. 45

12 REDUCED SULPHUR FUEL PROJECT ............................................... 47 12.1 BACKGROUND .................................................................................................. 47 12.2 ENGINE TESTING PROGRAMME ............................................................................ 48 12.3 IN-SERVICE TRIALS.............................................................................................. 51 12.4 CONCLUSIONS FROM PROJECT............................................................................ 51

13 EXHAUST AFTER TREATMENT OPTIONS.......................................... 52 13.1 DIESEL OXIDATION CATALYSTS ............................................................................ 52 13.2 DIESEL PARTICULATE FILTERS ................................................................................ 52 13.3 CONTINUOUSLY REGENERATING TRAP .................................................................. 53 13.4 SELECTIVE CATALYTIC REDUCTION ....................................................................... 56 13.5 COMBINED (SCR + DPF) OR (SCR + CRT). ........................................................ 56 13.6 NOX ADSORBERS .............................................................................................. 57 13.7 SUMMARY OF SYSTEM EFFECTS............................................................................. 57 13.8 RAIL OPERATING EXPERIENCE.............................................................................. 58 13.9 INSTALLATION DIFFICULTIES.................................................................................. 59 13.10 FUTURE DEVELOPMENTS....................................................................................... 59

14 DIESEL ELECTRIC HYBIRDS ............................................................. 60 14.1 BACKGROUND AND DESCRIPTION........................................................................ 60 14.2 OPERATING EXPERIENCE..................................................................................... 62 14.3 FUTURE DEVELOPMENTS....................................................................................... 64 14.4 APPLICABILITY FOR UK OPERATION...................................................................... 65

15 INVESTMENT PROGRAMME........................................................... 66 15.1 LEASING COMPANY INVESTMENT......................................................................... 66 15.2 GOVERNMENT INVESTMENT ................................................................................. 67


16 KNOWLEDGE GAPS....................................................................... 67 16.1 GENERAL .......................................................................................................... 67 16.2 FUEL CELLS DESCRIPTION.................................................................................. 67 16.3 FUEL CELL RAILWAY PROJECTS............................................................................. 68 16.4 SUMMARY OF FUEL CELL ISSUES FOR RAIL APPLICATIONS ........................................ 70 16.5 SUPERCAPACITORS............................................................................................. 70 16.6 VEHICLE IMPORTS GM LOCOMOTIVES............................................................... 71 16.7 VEHICLE IMPORTS CHINESE DMUS .................................................................... 71

17 POTENTIAL FOR IMPROVEMENTS TO EXISTING FLEET................... 72 17.1 SURVEY OF CURRENT UK DIESEL FLEET................................................................... 72 17.2 ENGINE DUTY AND USAGE FACTORS .................................................................... 75 17.3 OPTIONS FOR RETROFITTING OF TECHNOLOGY....................................................... 76 17.4 POTENTIAL SAVINGS FROM NEW ENGINES OR ASSOCIATED TECHNOLOGY................ 77 17.5 OPPORTUNITIES FOR REDUCED ENGINE IDLING....................................................... 80 17.6 OVERVIEW OF FUTURE TRENDS ............................................................................. 86 17.7 FUEL CONSUMPTION TRENDS ............................................................................... 89 17.8 QUICK AND EASY SOLUTIONS............................................................................ 92

18 AREAS FOR POLICY ACTION ........................................................ 93 18.1 GENERAL .......................................................................................................... 93 18.2 CATEGORY 1 .................................................................................................... 93 18.3 CATEGORY 2 .................................................................................................... 94 18.4 CATEGORY 3 .................................................................................................... 95

19 AREAS FOR INVESTMENT ACTION ................................................ 95 19.1 GENERAL .......................................................................................................... 95 19.2 CATEGORY 1 .................................................................................................... 95 19.3 CATEGORY 2 .................................................................................................... 96 19.4 CATEGORY 3 .................................................................................................... 97

20 CONCLUSIONS.............................................................................. 97 21 REFERENCES................................................................................. 102 22 APPENDICES ................................................................................ 105


1 EXECUTIVE SUMMARY

With significant work having been carried out recently by the rail industry into exhaust emissions and alternative fuels, RSSB has commissioned a wider investigation into the current position and future of diesel traction. Specifically, the objectives of this work are: Identify the current position regarding rail emissions and the likely future

sustainable development path. Review rails contribution to local air quality issues. Identify areas where the economic and/or environmental performance of

rail can be improved by simple solutions. Consider the future use of the diesel engine in rail traction, against the

background of a more stringent environmental approach and the development of alternative power technologies.

This information would feed into the industrys rail strategy work and provide appropriate briefing material. As background, descriptions have been provided of the principal diesel pollutants, namely oxides of nitrogen (NOx), hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) and particulate matter (PM), their causes and effects. The UIC rail diesel study into local air quality concluded that engine idling was a principal generator of nitrogen dioxide and PM emissions, particularly around terminal stations. However, this was a modelling approach and emissions measurements around a terminal station are now recommended to better map the local air quality. A review has been carried out of the current EU, UIC, Euro and US EPA rail diesel emissions standards, with comparisons made between these where practicable. For the current UK traction fleet, some engines are complaint with UIC II, but none comply with Stage IIIA levels of the EU Non-Road Mobile Machinery (NRMM) Directive. The Government has enacted the NRMM into national legislation, and via its Climate Change Programme, has stated its intention to encourage the rail industry to pursue measures to reduce emissions. Approaches to engine manufacturers for their formal statement on emissions compliance of their rail engines and technologies under development met with very limited success (only one direct response). However, a review has been carried out of the principal engine technologies for emissions abatement. In general terms, mechanisms to reduce NOx often increase PM, and vice-versa. Principal available technologies for NOx reduction are retarded injection timing, charge air cooling and exhaust gas recirculation. Integration of air/fuel control can control combustion and reduce peak temperatures to control NOx formation. Principal available technologies for PM reduction are centred on increased injection pressures (common rail), injector system and combustion chamber


design, variable valve timing, increases in compression ratio and oil consumption control. Single-bank idling for vee-engines is also an option. Future developments for emissions reductions will concentrate on combustion modelling and shaping methods, such as Homogeneous Charge Compression Ignition (HCCI), oxygen enrichment and low temperature combustion. These technologies are all at an early development stage. Compliance with the NRMM Stage IIIB emissions limits planned for 2011-12 will require the use of exhaust after-treatment devices, of which a survey of available types has been carried out. The principal designs are: - Diesel Oxidation Catalysts (DOC) (for CO/HC/PM) Diesel Particulate Filters (DPF) (for PM) Continuously Regenerating Trap (CRT) (for CO/HC/PM) Selective Catalytic Reduction (SCR) (for NOx) NOx adsorber Testing of a CRT on two different engine types has shown reductions of between 83 and 98.5% in HC, CO and PM. The optimum emissions reductions are achieved by a combination of technologies; the limited rail experience within Europe to date has generally been with DPF/CRT systems. There are significant issues of weight, size and cost for the installation of after-treatment equipment in new rail vehicles, and even more so for retro-fit installations (although emissions legislation is not currently retrospective). Future developments will eventually make after-treatment systems lighter, smaller and more efficient. Despite international pressure on reducing greenhouse gases, carbon dioxide is currently unregulated by any of the standards reviewed. It is often noted as an increased by-product of exhaust after-treatment. Conventional crude oil reserves are expected to last for well over 30 years, although costs may increase as the diminishing of the higher quality North Sea stocks requires additional refining of lower quality oil stocks from other areas. The industry change from the current gas oil to sulphur-free diesel (SFD) is expected to result in a manufacturing cost increase of 2 to 2.5 pence per litre. The exact specification of the low sulphur fuel (gas oil or diesel) is being examined by the industrys fuel strategy development group. The Governments Renewable Transport Fuels Obligation (RTFO) requires increasing percentages of transport fuels to be from renewable sources starting in 2008, with a figure of 5% by 2010. A 5% level of biodiesel can already be included in standard diesel fuels without identification, and the RTFO is likely to expedite its inclusion. The production of biodiesel creates minimal CO2 emissions and also reduces other pollutants (except NOx) during its combustion. Its use as a blend with either gas oil or SFD will increase, once testing has established what mix ratios are acceptable with minimal impact on engine performance and reliability, and once fuel duty issues relating to this blending have been resolved.


Engine testing as part of the ATOC/RSSB-sponsored low sulphur fuel project showed that some engines exhibited both power reductions and fuel consumption increases, as a result of the fuels lower energy content. Allowing for longer periods at lower power output, it is anticipated that an overall fuel consumption increase of up to 3% could be experienced across the fleet. Generally, NOx reductions of up to 10% and PM reductions of more than 10% were noted from the test results. Fleet trials with ULSD/SFD are have been completed. No significant adverse performance or reliability effects have been noted. Overall fuel consumption effects have been difficult to quantify precisely due to gaps and discrepancies in the returned data, but no significant detrimental effects in service have been identified. Diesel-electric hybrid systems are particularly suited to shunting and similar duties, and international experience with new or converted locomotives is growing. A diesel-hybrid railcar has also been produced for evaluation, and one of the Network Rail HST power cars has also been adapted for hybrid operation. This represents a growth area for the UK for suitable applications. Supercapacitors could substitute for the battery power pack required in the future, or could be used in an all-electric installation. Fuel cell development is not yet at a stage where its power output, size and weight make it suitable for rail application. However, various international rail projects are in progress and their progress should be monitored, with further feasibility work carried out at an appropriate point. A review of the likely investment into the railways has not identified any major projects within the next few years, notwithstanding current and future re-engining programmes. The DfTs Rail group has produced a strategy document, parts of whose remit is to consider developing technologies for potential adoption by UK railways. A full survey of the current UK diesel fleet has been carried out, categorising stock by size, power output, age, quantity and estimated remaining life, establishing a useful database. Whereas there are few DMUs older than 22 years, nearly 25% of the locomotive fleet is over 40 years old. An efficiency profile of the fleet has also been constructed, based on relative fuel consumption. Eight utilisation categories for the fleet have been established, each of which defines a particular no load/full load duty cycle, and estimated hours/miles. Although simplistic, this can indicate under-utilised vehicles, and should serve as a basis for further discussion. Limited options are considered to be available for easy retro-fitting of suitable technology to existing engines, except for some consideration of single-bank idling for vee or twin-bank locomotive engines. However, opportunities exist for effective re-engining of appropriate vehicles, which can produce significant fuel and emissions savings, as well as other benefits.


Operational measures have been identified that can reduce fuel consumption and emissions without disproportionate effort. Various mechanisms could be employed ro reduce the amount of time spent with the engine idling, such as enforced shutdowns, shore supplies, auxiliary power units and selective control of individual engines. Energy-efficient driving techniques have been shown to be effective by other overseas operators, and could be implemented by straightforward driver training or using a range of increasingly sophisticated aids. The effect of any altered driving profile on timetabling needs to be seriously considered. An attempt has been made to summarise much of the detail of this study in order to predict a possible development path for the rail traction fleet up to 2030. It should be emphasised that this is one view only, and should be considered as the basis for further discussion and development. Areas for policy action have been suggested as follows: - Category 1 fuel additives and energy-efficient driving techniques. Category 2 reduction of engine idling, re-engining of rolling stock before NRMM Stage IIIA and review of new rolling stock requirements. Category 3 retrofit of exhaust after-treatment equipment and biodiesel evaluation. Areas for investment action have been suggested as follows: - Category 1 evaluation of fuel additives Category 2 auxiliary power units, re-engining of rolling stock and hybrid development. Category 3 biodiesel testing and fuel cell prototyping. The reasoning for each of these proposals is identified. This study has covered a complex and wide-ranging subject. There are many areas of discussion where opinions may differ or new facts emerge that affect previous comments. In addition, recipients may require particular areas examined in more detail. The author therefore requests feedback on any aspect of this work, so that it is tailored to suit expectations and can be considered as being as representative as it is possible to be.


2 INTRODUCTION

There has been a significant body of work carried out by the UK rail industry recently into the subject of exhaust emissions and the use of alternative fuels, much of it having been sponsored by the Rail Safety and Standards Board (RSSB). RSSB now wishes to extend this area into a wider remit, investigating the short-term issues on emissions compliance and the longer-term development of diesel engines, fuels and exhaust after-treatment. The principal objectives of this work have been established as: - Definition of the current position of the UK rail network regarding emissions

and the likely sustainable development path, for use as industry briefing material.

Identification of the relative contribution of rail to local air quality issues. Identification of any areas where simple fixes (quick wins) can be

implemented to improve the economic and/or environmental performance of rail.

Consideration of the future of the diesel engine, to be referenced against continuing developments in electrification and alternative energy sources. This information would feed into the industrys rail strategy work.

The methodology employed for this investigation has been to consider specific areas of relevance, generally identified as section headings within this report. Particularly for technical descriptions, it has not been the intention to detail excessively methods of construction, operation or the range of options available; rather an overall summary is provided to put the subject into context as part of the principal remit of this investigation. The intention has been to enable conclusions to be drawn on areas where policy and investment action can be planned and taken to improve the environmental performance and image of the rail network in a feasible and cost-effective manner.

3 ABBREVIATIONS USED

ADMS Atmospheric Dispersion Modelling System APU Auxiliary power unit CARB California Air Resources Board CCP Climate Change Programme CH4 Methane CNG Compressed Natural Gas CO Carbon monoxide CO2 Carbon dioxide CRT Continuously Regenerating Trap DDHS Diesel Driven Heating System DfT Department for Transport DOC Diesel Oxidation Catalyst DPF Diesel Particulate Filter EAC Environmental Audit Committee EGR Exhaust Gas Recirculation ELR European Load Response


EMA Engine Manufacturers Association ESC European Stationary Cycle ETC European Transient Cycle ETS Electric Train Supply Euromot European Association of Internal Combustion Engine

Manufacturers fie Fuel Injection Equipment GPS Global Positioning System HCCI Homogenous Charge Compression Ignition H2SO4 Sulphuric acid ICE Internal Combustion Engine IEA International Energy Agency LNG Liquefied Natural Gas (NH2)2CO Urea NH3 Ammonia NMHC Non-methane hydrocarbons NMT New Measurement Train NO Nitric oxide NOx Nitrogen oxide NO2 Nitrogen dioxide N2O Nitrous Oxide nPAH Nitrated Polycyclic Aromatic Hydrocarbons NRMM Non-Road Mobile Machinery OEM Original Equipment Manufacturer ORR Office of the Rail Regulator PAH Polynuclear Aromatic Hydrocarbons PEM Proton Exchange Membrane PM Particulate Matter PM10 Particulate Matter with a size of less than 10 micrometres PM0.1 Particulate Matter with a size of less than 0.1 micrometres (ultra

fine particles) ppm Parts per million RTFO Renewable Transport Fuels Obligation SCR Selective Catalytic Reduction SCRT Selective Catalytic Reduction with Continuously Regenerating

Trap SFC Specific Fuel Consumption SFD Sulphur Free Diesel SID Split Injection Device SOF Solid Organic Fraction (of PM) SOFC Solid Oxide Fuel Cell SOL Solid Fraction (of PM) SO2 Sulphur dioxide SO3 Sulphur trioxide SO4 Sulphate Particulates SULEV Super Ultra Low Emissions Vehicle THC Total hydrocarbons (or HC) UIC Union Internationale de Chemins de Fer (International Union of

Railways) UKPIA United Kingdom Petroleum Industry Association ULEL Ultra Low Emission Locomotive ULSD Ultra Low Sulphur Diesel


ULSGO Ultra Low Sulphur Gas Oil UNIFE Association of European Railway Industries VOF Volatile organic fraction (of PM)

4 USEFUL DEFINITIONS

Exhaust emissions are an inherent part of this report, and it is therefore considered appropriate to include for reference definitions of the various emissions parameters. These are not intended to be comprehensive descriptions, rather a useful overview. Carbon Monoxide Carbon monoxide (CO) is an odourless, colourless and highly toxic gas, with a similar density to air. It results from incomplete combustion within the engine cylinder. Emissions from diesel engines are relatively low, around 10 to 500 ppm. Carbon Dioxide At elevated cylinder temperatures, CO can be oxidised to form carbon dioxide (CO2), and is characteristic of more complete combustion. CO2 is a greenhouse gas, meaning that it absorbs heat reflected from the Earths surface, rather than permitting the heat to radiate back out into space. This causes atmospheric warming, creating the greenhouse effect. Hydrocarbons Hydrocarbons consist of many hydrocarbon species derived from diesel fuel and lubricating oil. In engine emissions standards, hydrocarbons are regulated as either total hydrocarbon (THC) or non-methane hydrocarbons (NMHC). The latter categorisation excludes the simplest hydrocarbon methane (CH4), due to its different atmospheric reactivity. CH4 accounts for only around 2% of THC. Most hydrocarbons are toxic and/or carcinogenic. In the atmosphere, hydrocarbons undergo photochemical reactions with NOx to form smog and ground level ozone. CH4 does not react, which is why it is sometimes excluded from assessments. Typical levels of THC in diesel exhaust are between 20 and 300 ppm. Nitrogen Oxides Oxides of nitrogen (NOx) as defined in emissions regulations include nitric oxide (NO) and nitrogen dioxide (NO2). NO is a colourless, odourless gas and is formed within the combustion chamber from nitrogen and oxygen under high temperature and pressure. When discharged into the atmosphere, NO can be easily oxidised into NO2 at ambient conditions. NOx gases are toxic, cause acid rain and contribute to smog formation. Methods to reduce NOx formation tend to concentrate on reducing the peak flame temperature and/or reducing the oxygen concentration. This often leads to increased PM levels, with mechanisms to reduce PM leading to increased NOx. In general terms, considering the split of NO and NO2 in diesel exhaust, older technology engines would be approximately 95% NO and 5% NO2, whereas more recent engine designs would be approximately 85% NO and 15% NO2.


Nitrous oxide (N2O) is an unregulated pollutant, mainly due to its very low emissions level, typically 0.03 g/kWh (or 3 ppm). It is however a strong greenhouse gas and attacks stratospheric ozone. Although it remains unregulated, there is a general consensus within the engine industry that emission control technologies should not increase the amount of N2O present by any means. Typical levels of NOx in diesel exhaust are between 50 and 1000 ppm. Sulphur Dioxide Sulphur dioxide (SO2) is an unregulated pollutant, originating principally from the sulphur content of the fuel. It is a colourless gas with a distinctive, generally unpleasant odour. During combustion, SO2 can be oxidised to form sulphur trioxide (SO3) (approximately 2-4% of SO2), which can lead to the formation of sulphuric acid (H2SO4). With reducing fuel sulphur levels, the dominant SO2 emission will become from lubricating oil, which contains sulphur as part of anti-wear and detergent additives. Particulate Matter Particulate matter (PM) represents all small particles (solid and liquid material) within the exhaust including carbon. Despite considerable research, neither the formation of PM in the engine cylinder, nor its physical and chemical properties or human health effects are fully understood. It is responsible for visible black smoke. PM is generally divided into three main fractions: - - Solid fraction (SOL) (carbon, metallic ash). As newer engines produce less

carbon from combustion, the relative importance of metallic ash increases, to around 10% or more.

- Soluble Organic Fraction (SOF) (organic material from fuel or lubricating oil). This is sometimes referred to as the Volatile Organic Fraction (VOF). PM with low SOF is referred to as dry (10% or less of total PM), high SOF as wet (50% or more of total PM). SOF is strongly dependent upon operating conditions, and is highest at light engine loads.

- Sulphate Particulates (SO4) (sulphuric acid, water). This requires an interaction between H2SO4 and H2O, and depends principally upon the fuel sulphur level.

PM10 is airborne particulate matter with a size of less than 10 micrometres. This includes most airborne particles in the UK atmosphere, and most particles capable of penetrating into and depositing within the human respiratory system. PM0.1 (ultra fine particles) can also be a hazard. Most diesel particulates are in this size. Methods of diesel engine combustion control to reduce PM often tend to increase NOx levels, and vice-versa.


Polycyclic Aromatic Hydrocarbons Polycyclic Aromatic Hydrocarbons (PAH) constitute part of the SOF fraction of PM. The aromatics content of the fuel defines the number of fuel molecules that contain at least one benzene ring (a closed chain of six carbon atoms with hydrogen atoms attached, from which benzene compounds are formed by replacement of the hydrogen atoms). These beneficially affect combustion, but form PAHs. They are of interest due to their mutagenic and, in some cases, carcinogenic nature, but are not separately regulated.

5 UIC RESEARCH INTO LOCAL AIR POLLUTION

5.1 BACKGROUND

In October 2003, the Union Internationale de Chemins de Fer (UIC) initiated their Diesel Action Plan, advocating pro-active measures to reduce diesel engine exhaust emissions. Part of this plan was the Rail Diesel Study 1, which was carried out by UIC, the Association of European Railway Industries (UNIFE), the European Association of Internal Combustion Engine Manufacturers (Euromot) and AEA Technology to assess possible measures by which nitrogen oxides (NOx) and Particulate Matter (PM) from the European rail diesel fleet could be reduced. The Rail Diesel Study was published in March 2006, and comprised four work packages (WP), as follows: - WP1 Status and future development of the diesel fleet. WP2 Technical and operational measures to improve the emissions performance of rail diesel. WP3 The contribution of rail diesel exhaust emissions to local air quality. WP4 Possible emission reduction strategies that could be applied to diesel traction units across the EU Railway 27. WPs 1, 2 and 4 are not reviewed specifically in this section, but are referenced where appropriate in other parts of this report. WP3 examined the impact of emissions from the rail sector in terms of their significance to local air quality, and the location of hotspots. The findings from this work package are reviewed here.

5.2 METHODOLOGY OF UIC WP3 REVIEW

EU Framework Directive 96/62/EC 2 revised air quality standards for pollutants previously covered by legislation and also introduced new standards for previously unregulated pollutants. The UIC approach has been to consider nitrogen dioxide (NO2) and PM10 emissions principally, since these are the pollutants of most concern from the rail sector. The requirements for these particular pollutants are covered by a daughter Directive to 96/62/EC, namely 99/30/EC 3. The study was concerned with identifying air quality problems on the EU Railway 27 (defined as being the 15 EU countries, plus the 8 new member states, plus Norway, Switzerland, Bulgaria and Romania). A questionnaire was therefore sent to the UIC members in the 27 countries, plus environment ministries and other organisations responsible for reporting data on air pollution


(a total of 100 organisations referenced), requesting information on complaints received and identification where possible of emissions hotspots. In addition to the questionnaire, a dispersion modelling technique (Atmospheric Dispersion Modelling System, or ADMS) was employed to assess the impact of railway emissions on the different pollutant concentrations, for a busy line section, a shunting yard (three sites considered) and an idling train. The first two of these were modelled using base data from a Deutsche Bahn (DB) study, whereas the idling study utilised UK data. The line section results were compared with NOx and PM10 emissions from both a major motorway and a minor road, and to predicted UK background concentrations from WP1 for a locomotive, for metropolitan, urban and rural areas. For shunting yards, the NO2 and PM10 concentrations were plotted for 200 metres in each direction, and comparisons made with predicted UK background concentrations from WP1 for a shunting locomotive, again for metropolitan, urban and rural areas. For the idling condition, it was concluded that modelling of a covered and enclosed terminal station area would be extremely complex, so the assumption was made of an open station area. The modelling also assumed a 12-platform station with inter-city trains left idling for approximately 40% of the day. Pollutant concentrations were plotted over a 220 by 140 metre area, centred on the station platforms. This analysis was then repeated using two idling trains, rather than 12.

5.3 REVIEW OF RESULTS FROM WP3

Based on the interpretation that the 100 organisations listed were all contacted, the percentage level of responses overall was not identified. However, responses were received from 22 of the EU railway 27 countries. Of these 22 countries, 10 reported receiving complaints from the public concerning poor air quality, with an average of between one and ten complaints per annum. The maximum number of complaints received over one year was 20. Engine idling and shunting yards were suggested as the principal causes for complaint. Some comment was made concerning stations with restricted air exchange also being a susceptible area. The study therefore concluded that air quality complaints overall are not a major issue within European railways. An important point noted by the study was the percentage of gross tkm (tonne-kilometre) hauled (passenger and freight) attributed to diesel operation by country; for reference, the UK figure was 43%. The validity of these results seems reasonable. With regard to the methodology, Interfleet has been involved with previous surveys to obtain information from a wide range of organisations within Europe, and it is always difficult to motivate the recipients to provide prompt and useful information, or indeed any response at all. Under these circumstances, the UIC survey has achieved a good response, obviously assisted by the good standing of the organisation.


Although the number of complaints received will always only represent the formal complaints registered, the survey established the principal locations where complaints could be expected. Dispersion modelling of busy line sections clearly showed that NO2 and PM10 concentrations from rail would be minor compared with defined background concentrations. Given the relative numbers determined from this analysis, this conclusion cannot readily be disputed. The modelling of three shunting yards of differing size and utilisation concluded that even the worst case combination of the maximum number of shunting movements using the shunting locomotive with the highest emissions factor would not lead to an exceedance of the defined NO2 air quality limit values. Similarly, PM10 levels do not contribute significantly to ambient concentrations. This conclusion seems slightly at odds with the reported complaints from shunting yard locations, but complaints do tend to be more subjective. Engine idling was determined to be the worst situation for emissions hotspots, with the conclusion that engine idling at terminal stations could significantly affect concentrations in these locations. The main analysis with 12 idling trains was based on a UK terminal station (Paddington), which was concluded to not be representative of other European mainline stations this point is made within the report and was also re-iterated by a UIC representative at the presentation of the rail study in Paris. However, this project is primarily concerned with the UK situation, so the maximum number of idling trains becomes of greater relevance. The recommendation is made that measurements should be taken of emissions at terminal stations, and that use of this data should supersede the modelling data once available. This is clearly a sensible and pragmatic approach, and enables mapping of these measurements to establish any pollution concentrations around a terminal station area, which will have potentially significant variations between different locations within the station boundaries. The author is familiar with the layout of Paddington station and the historic practices of engines at the country end of the platforms being left on train supply operation. Initially, this would indicate that the emissions from these engines would be away from the more densely populated areas of the station, although the effects on adjacent premises and open spaces need to be considered. The level of emissions at the city end of the station when the train arrives and before the leading engine is shut down needs to be assessed, and equally importantly when the engine is restarted prior to departure, with a significant burst of black smoke as the engine fires. For information, the recent re-engining of the HST power car with the MTU engine (discussed later in this report) has shown some significant visible improvements in emitted smoke levels. A programme of measurements could readily be compiled for a location such as Paddington station, which must represent the densest diesel traction population for a UK station. Accepting that the London termini will incur the most train movements, the only other all-diesel operation is the Midland Mainline fleet at St Pancras station, which does not approach Paddingtons


service levels (only one operator using electric traction on two dedicated platforms). This review has focused on exhaust emissions, but the issue of noise levels should not be overlooked. Although much of this is generated from other activities such as tannoy announcements and train dispatch whistles, noise from diesel engines and their associated equipment can be a significant contributor, particularly from the older and larger engine types. This can also be a driver towards environmental action.

6 CURRENT EXHAUST EMISSIONS STANDARDS

6.1 BACKGROUND

In contrast to the road industry, European diesel rail traction has not had any legislative requirements to reduce exhaust emissions until the advent of EU Directive 2004/26/EC (see section 6.2). The UIC has been active in publishing guidelines for its members (see section 6.3), but these have not been binding (although the UIC would have expected its members to comply). With the inclusion of rail traction into the emissions legislation, continuing pressure will be applied in future years to further reduce exhaust emissions. Ultimately, this may apply retrospectively to existing rolling stock, although this would have major cost implications for compliance (discussed later in this report). The UIC has initiated formal investigations into potential retrospective modifications in its Rail Diesel Study 1.

6.2 EUROPEAN DIRECTIVE 2004/26/EC

EU Directive 97/68/EC issued in December 1997 established limits for gaseous and particulate emissions from internal combustion engines installed in non-road mobile machinery. This original Directive specifically excluded railway locomotives or railcars (DMUs). In line with the general tightening of emissions limits worldwide, the Directive has been reviewed and was reissued as Directive 2004/26/EC 4 in April 2004. Rail traction engines are now included, with separate categories for railcars and locomotives. The Directive is commonly referred to as the NRMM Directive. The legislated pollutants are NOx, THC, CO and PM, with CO2 excluded. Weighted emissions values are determined according to ISO 8178-4 Test Cycle F defined for a rail traction duty cycle. The Directive has introduced two staged sets of limit values, Stage IIIA (effective over the period 2005 to 2009) and Stage IIIB (effective over the period 2011 to 2012). The first set of limit values is expected to be able to be achieved using on-engine technology, whereas Stage IIIB limits will require the use of exhaust after-treatment devices in order to comply. Stage IIIA sub-divides the locomotive limits into power-dependent categories. Table 1 details the various categories and limits. For each category, there is a Type Approval date and a Placing on the Market date. The Type Approval date is the date by which the engine manufacturer must have certified that his engine is compliant, with UK



legislation (see section 7) based on this Directive requiring certification to be carried out by the Department of Trade and Industry. The Placing on the Market date is generally one year later (with one exception for category RC A, which is six months). A review date of 31st December 2007 is identified within the Directive for the Stage IIIB limits to be reviewed. This is intended to review the available technology necessary to satisfy these limits, and to determine whether there is a need for additional flexibilities, exemptions or later introduction dates for certain engines. It also identifies the possibility of further reductions for locomotive engines in view of the application of NOx after-treatment technology.


Stage

Category Propulsionby:

Type Approvalfrom:

Placing on the Market from:

CO g/kWh

HC g/kWh

NOx g/kWh

PM g/kWh

IIIA RC A P>130 kW Railcar 01/07/2005 01/01/2006 3.5 4.0 0.2 RL A 130 kW < P < 560

kW Locomotive 01/01/2006 01/01/2007 3.5 4.0 0.2

RH A P > 560 kW Locomotive 01/01/2008 01/01/2009 3.5 0.5 6.0 0.2 RH A P > 2000 kW &

SV > 5 l/cylinder Locomotive 01/01/2008 01/01/2009 3.5 0.4 7.4 0.2

IIIB RC B P > 130 kW Railcar 01/01/2011 01/01/2012 3.5 0.19 2.0 0.025 P > 130 kW Locomotiv

e 01/01/2011 01/01/2012 3.5 4.0 0.025

Key P = Power Output SV = Swept Volume (of engine cylinder) CO = Carbon Monoxide HC = Hydrocarbons NOx = Nitrogen Oxides PM = Particulate Matter

Table 1 EU Directive 2004/26/EC Emissions Limits


There are a number of areas of the Directive that require some additional emphasis or clarification, as follows. The Directive applies solely to engines, not vehicles. Therefore, re-engining

of a locomotive or DMU is the same as supplying a new engine for a new locomotive or DMU for the emissions requirement.

The Directive does not apply to overhauled engines, which can continue to be repaired indefinitely, replacing individual components as necessary. This can include such core engine components as the crankcase.

Placing on the market means when an engine has completed assembly and is available for use, even if it remains within the manufacturers stock. In other words, older design engines for existing rolling stock will be subject to the Directives requirements if they are assembled after the implementation date, potentially affecting spares holdings.

Where a contract has been entered into to purchase engines before the date of entry into force of the Directive, there is an exemption that permits the engine to be placed on the market up to two years after the relevant implementation date without having to comply with the Directives requirements.

Although the principal areas of interest for the rail industry are for propulsion engines, further categories within the Directive cover other engine types and duties, for example auxiliary constant speed generating sets of relatively low power output.

6.3 UIC GUIDELINES

Prior to the introduction of the NRMM Directive, the UIC had produced its own set of emissions guidelines. The most recent of these are the UIC III limits, which have been aligned with the Stage IIIA limits of EU Directive 2004/26/EC. Since some of the compliance dates are in the future, UIC II limits are still current. All UIC limits are summarised in table 2. Again, values are weighted according to ISO 8178-4 Cycle F. Two UIC leaflets define the process of testing and authorising engines to the UIC limits. UIC leaflet 623 5 6 7 (in three parts) defines the requirements for an acceptance test for rail traction diesel engines, with UIC leaflet 624 8 specifying the limit values for exhaust gas emissions and how an emissions test is organised and reported. Leaflet 624 also refers to an online reference for approved engines (see section 6.6). UIC leaflet 345 Environmental specifications for new rolling stock has also recently been published, which includes reference to diesel exhaust emissions amongst its tender assessment criteria.


Stage Category Propulsionby:

Effective from: CO g/kWh

HC g/kWh

NOx g/kWh

PM g/kWh

Comments

UIC I 3.0 0.8 12 - a) UIC II P< 560 kW 01/01/2003 2.5 0.6 6.0 0.25

P> 560 kW n< 1000 rpm

01/01/2003 3.0 0.8 9.9 0.25

P > 560 kW n> 1000 rpm

01/01/2003 3.0 0.8 9.5 0.25

UIC IIIA P> 130 kW Railcar 01/02006 3.5 4.0 0.2 As NRMM Stage IIIA RC A

130 kW < P < 560 kW

Locomotive 01/01/2007 3.5 4.0 0.2 As NRMM Stage IIIA RL A

P > 560 kW Locomotive 01/01/2009 3.5 0.5 6.0 0.2 As NRMM Stage IIIA RH A

P > 2000 kW & SV > 5 l/cylinder

Locomotive

01/01/2009 3.5 0.4 7.4 0.2 As NRMM Stage IIIA RH A

Key a) PM not included in UIC I. Exhaust smoke level range of 1.6 - 2.5 Bosch defined, dependent upon mass air flow rate. P = Power Output SV = Swept Volume (of engine cylinder) CO = Carbon Monoxide HC = Hydrocarbons NOx = Nitrogen Oxides PM = Particulate Matter

Table 2 UIC II and IIIA Emissions Limits.

6.4 EURO LIMITS

For the road industry, the first emissions standards were effective from 1992, with separate categories for cars/light trucks and heavy duty truck/bus engines. Although these standards are not applicable to rail, some manufacturers of DMU engines often refer to them since this engine size is also compatible with truck applications. The previous Euro II and III levels, plus the current Euro IV and future Euro V are therefore included in table 3 for reference purposes.

Date CO g/kWh

HC g/kWh

NOx g/kWh

PM g/kWh

Smoke (m-1)

Euro II 10/1998 4.0 1.1 7.0 0.15 - Euro III 10/2000 2.1 0.66 5.0 0.1 0.8 Euro IV 10/2005 1.5 0.46 3.5 0.02 0.5 Euro V 10/2008 1.5 0.46 2.0 0.02 0.5

Table 3 Euro II to IV Emissions Limits for Heavy-duty Road Diesel Engines

The above limits are based upon a defined European Stationary Cycle (ESC), with smoke opacity being measured during a European Load Response test (ELR). In addition, Euro III limits and above have required approval under the European Transient Cycle (ETC) test these limits are not detailed here, as they do not make a sensible comparison with the rail stationary cycle limits.

6.5 US EPA REGULATIONS

The USA has a wider range of emissions categories for diesel engine applications than Europe, including some specific to the state of California. Part of the reasoning behind the NRMM Directive was to harmonise emissions legislation between the US and Europe, so it is considered appropriate to include the relevant limits here. Harmonisation has not quite been achieved, since there are a number of important differences between the US locomotive legislation and the NRMM, as follows. US regulations sub-divide rail vehicles into line haul (main line) and switch

(shunter), rather than locomotives and railcars. Locomotive regulations only apply to engines with power outputs greater

than 750 kW, with vehicles below this level having to comply with the off-road regulations, which is again sub-divided into power bands.

A 10-mode locomotive test cycle is used, rather than the 3-mode European cycle.

For reference, the US EPA Tier 1 and 2 Locomotive standards are reproduced in table 4 below, converted from the original quoted g/bhp-hr to g/kWh to facilitate comparison with EU limits. It is understood that a current EPA review is considering the introduction of rail traction legislation comparable to the NRMM IIIB limits, but with significantly lower NOx levels, although this had not been announced by the end of May 2007.


Category Manufacturing

date CO g/kWh

HC g/kWh

NOx g/kWh

PM g/kWh

Tier 1 Line haul 2002 - 2004 2.9 0.74 9.9 0.6 Switch 3.3 1.61 14.7 0.72

Tier 2 Line haul From 2005 2.0 0.4 7.4 0.27 Switch 3.2 0.8 10.9 0.32

Table 4 US EPA Locomotive Emissions Standards

6.6 LEVEL OF COMPLIANCE OF UK TRACTION FLEET

When considering the likely level of compliance of the existing UK diesel traction fleet with the NRMM and UIC levels in particular, it should be remembered that the bulk of the current engine design ages predate the requirement for compliance with the standards of either body. General comments are provided below, with additional specific comments provided by the OEMs included within section 8. Considering first the UIC requirements which, although not mandatory, have been established since the late-90s. Generally, most of the existing DMU engines would be compliant (just) with UIC I levels, whereas only one is known to satisfy UIC II (the Cummins QSK19 engine). Certain engines, such as variants of the NT855, would comply with some of the UIC II pollutant levels, but not all. For locomotives, none of the older design engines would be expected to comply with UIC I, with the MAN VP185 complying with this limit, but not UIC II. Of the other current production engines, both the MTU 16V4000 series, and the low emissions version of the EMD 12N-710G3B engine now being fitted to Class 66 locomotives comply with UIC II. It is understood that EMD has now received type approval for Stage IIIA compliance of this engine. For the NRMM Stage IIIA legislation, only the RC A limits are currently in force, covering railcar (DMU) engines, with power outputs greater than 130 kW. The principal current production DMU engine, the QSK19, would not meet these limits. None of the Stage IIIA locomotive requirements are yet in force, and it can reasonably be concluded that none of the current engines in service would comply in their current form.

7 CURRENT GOVERNMENT ENVIRONMENTAL POLICY

7.1 UK LEGISLATION

The provisions of the NRMM Directive have been enacted into UK legislation by Statutory Instrument 2006 No. 29 9, effective from 17th February 2006. A regulatory impact assessment carried out before this transposition estimated that the total benefit per annum would amount to 27 - 31 ktonnes reduction in annual NOx emissions and 2.3 - 4.4 ktonnes annual reduction in PM emissions 10.


In addition to the NRMM legislation, the Clean Air Act has been in place for a number of years, with the most recent update in 1993 11. This deals with smoke, dust and fume emissions generally, but has a specific clause (clause 43) for railway engines, which requires the owner of any locomotive engine to use any practicable means there may be for minimising the emission of smoke from the chimney of the engine. This is with particular reference to adjacent buildings, and it is believed that the act has been referenced in the past relating to smoke emission from stationary idling locomotive engines.

7.2 FUTURE POLICY

The UK NRMM Directive now takes into account the progressive tightening of the regulated pollutants, namely CO, HC, NOx and PM, and it is reasonable to presume that future developments in this area by the EU will be subsequently incorporated into UK legislation. CO2 greenhouse gas emissions remain unlegislated, although a key feature of recent international agreements such as the Kyoto Protocol. The Government issued its 2006 Climate Change Programme (CCP) 12 in March 2006. This followed on from the previous CCP in 2000 and outlined in general terms the actions necessary to achieve the declared emissions reduction targets. The greater part of the transport section of the programme concerned road transport, but a statement was included that the Government will consider how new technologies can improve energy efficiency and reduce fuel consumption to get even more environmental benefits from rail. No other significant reference to rail was incorporated, save for the general requirement under the Renewable Transport Fuels Obligation (RTFO) for 5% of all UK fuel sales to come from renewable sources by 2010-11 (see section 9.5). A statement issued by DfT in April 2006 13 outlined their view of rails contribution to the energy review, identifying their intention to encourage the industry to pursue a range of operational and technical measures to ensure that trains are operated as efficiently as possible. Longer term developments in hybrid and fuel cell technology were also referenced. A recent report by the House of Commons Environmental Audit Committee (EAC) 14 considered carbon emissions from transport further, as part of its continuing remit to examine climate change, but also to respond specifically to the CCP 2006. Whilst much of the document is again concerned with road developments, relevant conclusions from this work were: - The DfT should accelerate its efforts to reduce carbon emissions from

transport, which is the only sector in the UK economy in which carbon emissions are increasing.

The committee supported the construction of new high speed rail links, to encourage a modal shift from air to rail and to free up capacity on the existing network.

Local rail services are vital in reducing demand for car journeys. The rail industry could make a significant contribution to expanding

renewable energy generation, and the Government should act to enable it to do so.


Transport is the most technically and politically difficult sector in which to reduce carbon emissions, requiring widespread behavioural change.

UK Government estimates are for conventional crude oil reserves to last until 2030 14, with the possibility of improved technology and unconventional reserves extending this by a further 30 years.

7.3 SUMMARY OF LIKELY FUTURE GOVERNMENT DIRECTION

An approach was made to the Cleaner Fuels and Vehicles Division of the DfT for further comment on potential future Government intentions for rail transport in particular, but no response had been received by the completion date of this report. From the above, it is clear that the UK Government will encourage technical and operational measures to reduce diesel exhaust emissions and improve the environmental performance of the railways. One approach to this objective will no doubt be continued pressure from legislation, particularly in the area of renewable fuels. In this context, as with emissions generally, the Government is following the lead of the EU decision making. Assuming that no major change in the structure of UK railways is effected (for example, renationalisation), it is difficult to determine whether there would be any financial support in future years, in the form of emissions credits, reduced fuel duty or similar measures. This may be required to significantly affect the rate of improvement in environmental performance.

8 CURRENT INDUSTRIES POLICIES AND ACTIONS

8.1 NOTIFICATION TO TRAIN OPERATORS

The original intention as part of this work was to advise all diesel train operators of the project, and to request them to participate by contributing information on any relevant initiatives that they may have either in progress or planned. This was to be achieved via a letter from RSSB sent to the Engineering Director or equivalent position of each operator. The letter would also have advised recipients that they would be informed of the investigations outcome and conclusions. As the project progressed, further consideration by RSSB resulted in this letter not being sent, with the intention being to raise awareness of the project at a Fuel Strategy Workshop to be facilitated by RSSB during October 2006. Some useful feedback from this forum on the industrys views and strategy on future fuels was obtained, which has been incorporated into the relevant part of this review. Similarly, under advice from RSSB, the author has refrained from making direct formal contact with train operators. As such, additional relevant and useful information that may have been forthcoming is not available, and commentary in this area is therefore limited.


8.2 ENGINE MANUFACTURER EMISSIONS STATEMENTS

Each OEM with engine types in service with UK fleets was contacted to ascertain the official position of the company regarding emissions compliance of these engines, together with their projected technological developments in this area. Minimal feedback was obtained, despite re-contacting all companies (this is often the case with this type of enquiry). Only limited comment is therefore included here regarding stated compliance levels. MTU was the only engine manufacturer to respond directly to this enquiry. From their response, and from previous discussions with the company, the following are the stated compliance levels for their engines. 6R183 (Class 170) Euro II 6H1800 (one example now fitted in a Class170) Euro III / UIC II 16V4000 R41 (Class 43) UIC II MTU has also made the comment that all its Euro III rail derivative horizontal engines (principally the 6H1800) will migrate to NRMM Stage IIIA compliance. When fitted with a particulate filter in place of a silencer, MTU claim that the 6H1800 will be Stage IIIB-compliant. The 16V4000 R43 engine was announced in September 2006 which will comply with the NRMM Stage IIIA limits. Perkins is now under the ownership of Caterpillar, and in September 2006, Caterpillar announced a new range of low-emission, horizontal engines, the C18 ACERT (see section 8.4 for a description of the ACERT system). The engine is claimed to have a competitive power density (mass per kilowatt), with a power output close (>90%) to that of the Cummins QSK19, and to be compliant with NRMM Stage IIIA.

8.3 ENGINE TECHNOLOGY FOR EMISSIONS ABATEMENT GENERAL

With the moves to reduce emissions since the fuel crises of the mid-1970s, the initial focus has been on engine modifications and developments to reduce the generation of emissions at their source. This section reviews the principal areas that have been or are being considered by engine manufacturers. In general terms, design modifications to reduce emissions form part of the design of a new engine; where it is possible to apply such technology retrospectively to existing engines, this is discussed further in section 17. Only on-engine or in-engine technology is covered in this section. Exhaust after-treatment is considered in more detail in section 13. As noted in section 4, combustion modifications to reduce NOx usually result in an increase in PM emissions. With emissions of HC and CO from diesel engines at relatively low levels by comparison, the challenge has been to reduce the formation of NOx and PM. Mechanisms for reducing each of these pollutants are outlined below. With many of these techniques, the addition of more complexity into the design and operation of the engine could have a negative impact on the vehicles overall reliability.


8.4 NOX REDUCTION TECHNIQUES

Retarded Fuel Injection Timing One of the most basic measures to reduce NOx formation has been to retard the injection timing of the fuel, which reduces the peak cylinder pressure and peak flame temperature, and hence restricts NOx formation. The precise effect will vary dependent upon engine type and design, but typically a 2 degree retard of the injection timing would reduce NOx levels by approximately 10%. Unfortunately, this retard increases HC and PM levels, as well as having an adverse effect on fuel consumption, which limits the degree of retard practically achievable. The fuel penalty can be mitigated to a degree by other engine adjustments (see below). Charge Air Cooling Reducing the temperature of the intake air has a similar effect to retarding the injection timing, by reducing peak temperature and cylinder pressure, albeit at a reduced level. In general terms, a 100C reduction in charge air temperature can be expected to reduce NOx emissions by approximately 5-6%. The two modifications can be combined to maximise the effect figure 1 below illustrates the effects of varying both parameters, based upon engine test work carried out in the USA 15.

ASME

Figure 1 Effect on NOx emissions of varying injection timing and charge air temperature.

Both of these techniques increase fuel consumption, which can be offset by increased injection pressure. This is commonly applied to diesel engines, either by increased rate cam profiles or more recently by unit injectors. This can also reduce PM and smoke levels see section 8.5. Exhaust Gas Recirculation (EGR) If a controlled level of exhaust gas is re-admitted to the combustion chamber via the air inlet manifold, this dilutes the oxygen available to mix with nitrogen to form NOx. If this recirculated exhaust gas is cooled, then the peak combustion temperature is also reduced, further reducing NOx emissions. This process is a very effective NOx reduction strategy. However, in addition to increased HC, CO and PM emissions, there are potential engine wear and durability issues. Operation of the system is usually via an electronically-controlled valve operating on the exhaust back pressure, or via a waste gate fitted to the


turbocharger, permitting exhaust gas to be admitted to the intake manifold. Combined EGR and particulate filter systems are commonly fitted to heavy duty road vehicles. For a fixed mix ratio of exhaust gas to air, the magnitude of the NOx reduction will depend upon the engine load. Typically, at full load, there will be a linear relationship between NOx reduction and mix ratio. A small fuel consumption penalty is likely, of perhaps 2-3%. PM emissions may also increase, which can be moderated by combustion system optimisation, for example high pressure fuel injection (see section 8.5). The temperature within the air/exhaust delivery system needs to be controlled such that there is no condensation of sulphuric acid within it. This becomes more of a problem with fuels having higher sulphur content. One advantage of using cooled EGR rather than an exhaust after-treatment device (see section 13) is that it does not significantly increase the space required for the system. Pilot Injection If a small pilot quantity of fuel (typically a few per cent of the main injection volume) is injected at a relatively low rate ahead of the primary injection, this will ignite first and reduce the ignition delay of the main injection. This considerably reduces the volume of lean, oxygen-rich fuel mixture, leading to potentially significant (around 30%) NOx reduction. Such mechanisms are often referred to as split-injection devices (SID). Water Injection Water injection through the fuel spray nozzle reduces the peak cycle temperature as a result of water evaporation. The water may be emulsified before pumping to the engine, directly injected at the injector, or injected into the air manifold. Water addition systems using emulsified fuels have also shown PM reductions. Maintenance of the fuel-water emulsion consistency and potential system corrosion are obvious issues. Water injection is considered here separately from water-diesel emulsion, which is discussed under Fuel Development in section 11.3. ACERTTM Technology To reduce NOx emissions, Caterpillar has introduced its ACERTTM Technology to its latest engines. This is essentially a systems integration approach for combustion control. The electronic control system regulates both the volume of charge air required at various speeds and loads, and the fuel injection quantity and timing. It is claimed that this not only improves emissions, but also provides improved engine response and better performance. A final part of the ACERTTM Technology is a diesel oxidation catalyst (see section 13.1), which reduces the particulate matter.


8.5 PM REDUCTION TECHNIQUES

Increased Fuel Injection Pressure Diesel engine development has seen gradually increasing injection pressures, which has the effect of improved atomisation of the fuel to optimise fuel-air mixing. This also results in improved fuel economy and smoke levels. Increasing the injection pressure has a further effect on combustion beyond just the improved atomisation. Other parameters such as the injection rate, duration and spray penetration are also affected. As high speed direct injection engines have developed, more of the energy for fuel-air mixing comes from the momentum of the injected fuel, rather than the engine design features for air mixing. This has required high pressure injection systems, with the current optimum system for delivering this high pressure being a Common Rail System. This utilises a common fuel manifold (accumulator or rail) maintained at high pressure (for example, 1400 bar) from an engine-driven pump, but with the rail pressure being independent of engine speed. Each injector feeds from this rail, with injection timing and duration being controlled electronically. The system provides good spray penetration and subsequent mixing for PM reductions, and can also incorporate further electronic control for pilot injections to reduce NOx. One disadvantage of the Common Rail system is the potential for fuel leaks, given that the injector connections to the rail are permanently at high pressure. To counteract this, fuel leakage detection can be incorporated, either as a straight forward flow limiting device for each cylinder, or as a more complex in-cylinder knock detector linked to the electronic controller. Injector Design Features Features of the injector design can affect combustion and PM formation. Specifically, the number and diameter of the spray holes, the included spray angle and the spray hole length can all affect the resultant fuel spray and ignition. Spray angle in particular must be matched to the profile of the piston bowl to ensure that good fuel-air mixing is achieved. Reduced Injector Sac Volume The sac on the end of the injector nozzle contains the volume of fuel which is injected into the cylinder via the injector spray holes. A smaller sac volume will reduce the amount of fuel drawn out of the injector late in the cycle by air motion, and can reduce both PM and HC emissions. Increased Compression Ratio Increasing the compression ratio reduces particulate formation and improves fuel consumption, but generates increased NOx, due to the higher pressures and temperatures. The ability of the engine components (particularly the piston) to withstand the increased firing pressure needs to be considered. Combustion Chamber Design Efficient combustion is achieved by ensuring that there is sufficient air motion within the cylinder (swirl) to promote good fuel-air mixing. Re-entrant piston bowls with a profiled central recess can assist this process. Inlet port profiling


can also ensure that the charge air enters the cylinder at the right angle for efficient mixing. Oil Consumption Control Lubricating oil within the combustion chamber contributes to PM emissions, therefore a reduction in oil consumption will reduce particulates. This can be achieved by changes to the sealing mechanism between the oil supply and the combustion chamber, i.e. the liner and piston rings. Liner surface finish definition is intricate, with the honed surface defined by a variety of topographical parameters of the peaks and troughs profile. Piston ring design is even more complex, with engine testing still an essential part of the development of any new design, even with current computer modelling techniques. Although the piston/ring interface is the primary source of oil entry, other sources can also be addressed, for example, leakage past the valve guides, carry-over of oil from the turbocharger and blow-back from the exhaust. Single-bank Idling Engine idling is an inherent part of the rail traction duty cycle. Under idling conditions, the fuel injected into all cylinders of the engine does not combust efficiently or effectively, resulting in unburnt fuel contaminating the lubricating oil. For a V-engine, a mechanical/electrical control system can be incorporated to cut out one complete bank of cylinders when idling, resulting in improved combustion efficiency of the operational bank. The control system can be arranged so that either the same bank of cylinders is always isolated, or the active bank is changed after a set time to the opposite set of cylinders. Variable valve timing (VVT) By controlling the timing and rate of the engine inlet and/or exhaust valves, improvements in fuel economy and emissions can be obtained, as well as benefits in low speed torque and transient performance. Valve timing variations can be achieved in several ways, for example by switching from one set of cam lobes to another at a set engine speed.

8.6 CO2 REDUCTION TECHNIQUES

Since the formation of CO2 is representative of more complete combustion as a result of higher cylinder temperatures, mechanisms to reduce CO2 can be considered to be complementary to those for reducing NOx. Therefore, at the expense of combustion efficiency, many of the techniques outlined in section 8.4 above apply.

8.7 RE-ENGINING

Whilst not strictly an engine modification, one of the most effective ways technically to reduce emissions from older engines is to re-engine the vehicle with an engine to a more modern design. This can not only reduce the specific emissions levels, but also reduce the total pollutant output by virtue of superior fuel consumption. Replacing a 20 or 30-year old engine with a current design can readily reduce the overall fuel consumption by around 8-12%, with reductions in all exhaust emissions. It can also facilitate compliance with known future emissions legislation, assuming that suitable engines are available.


For the UK rail traction fleet, two successful examples of re-engining over the past ten years or so have been with the Class 43 HST power car and the Class 47 locomotive. For the HST, replacing the existing Paxman Valenta with the Paxman (now MAN) VP185 engine was proven to give an equivalent 8% overall fuel consumption reduction when measured in service over the typical rail traction duty cycle. Emissions reductions between the Valenta and VP185 engines are shown in table 5 below.

Pollutant / Fuel consumption Valenta VP185 NOx 12 11.2 CO 3.3 1 HC 1.3 1.4 PM 0.5 No data

SFC (full load) 222 202

Table 5 Comparison of Valenta and VP185 Exhaust Emissions (All data in g/kWh)

Note that the NOx reductions are not significant, since this version of the engine was the low fuel consumption specification. Later engine modifications to reduce NOx further erode the fuel benefit defined above (see comments in section 17.4). A recent DMU re-engining exercise has been the replacement of the existing MTU 6R183 engine with the current MTU 6H1800 engine, with one example having been fitted for evaluation on a Class 170 Turbostar. Note that the NRMM Stage IIIA limits for railcars are now in place, so that any DMU re-engining will have to be with compliant engines (which the 6H1800 is).

Re-engining should also have the benefit of improving maintenance, reliability and time between overhauls. For the VP185, the overhaul period extended initially to four years, with a further subsequent gradual increase to five years (approximately 24,000 hours) as operating experience was gained, from the preceding 18/36-month periodicity of the Valenta engine. The HST power car has been re-engined a total of three times. The very first of these, with the Mirrlees-Blackstone MB190 engine in the late-80s, also offered an increase in power output of around 8-10%. In 2005, two First Great Western power cars were re-engined with the MTU 16V4000 engine, with further vehicles now being similarly re-engined. The second example of re-engining has seen the installation of remanufactured EMD 645-12E3C engines into the Class 47 locomotive, replacing the ageing Sulzer 12LDA28C engine. This has formed the basis of the Thunderbird rescue locomotives operated by Virgin Trains. Table 6 below compares emissions levels of the original and replacement engines. In this particular instance, there is no major improvement in emissions, since the design age of the replacement engine is not the latest available, although assessment of visible smoke tends to substantiate a likely improvement in PM levels. Fuel consumption improves by over 6% at full load, for an increased power output of the EMD engine of 2050 kW compared with 1924 kW for the Sulzer.


Pollutant Sulzer EMD NOx 14.4 13.02 CO 4.7 5.81 HC 0.92 0.5 PM No data 0.61

SFC (full load) 228 214

Table 6 Comparison of Sulzer and EMD Exhaust Emissions (All data in g/kWh)

8.8 MULTIPLE ENGINES

A variation on traditional re-engining is the possibility of replacing a single large engine with two or more smaller units, with a suitable control system arranged to operate one or more units as appropriate to the load demand. This concept has been promoted recently by Cummins, with a number of installations worldwide. Alternatively, one unit could be dedicated for auxiliary loads, effectively an auxiliary power unit (APU) see section 17.5 for more comments in this area. By definition, this concept is best applied to a locomotive, rather than a DMU, at least if the engine output is being used for traction power. Additional space would be required for such installations and weight may also be an issue. Individual engine overhaul costs would not be reduced pro-rata in line with the number of engines.

8.9 FUTURE DEVELOPMENTS

Homogenous Charge Compression Ignition (HCCI) In petrol engines, the fuel and air for combustion is premixed before entering the combustion chamber, creating a homogenous, or uniform, mixture, which is then ignited by an electric spark. Diesel engines inject fuel into the cylinder to mix with compressed air already present, with combustion initiated by the increased heat from the pressure of the piston compression stroke. Although the diesel cycle is inherently more efficient than spark ignition, the characteristics of this process are that combustion starts at the fuel boundary and propagates through the fuel-air mixture, i.e. it is not homogenous. HCCI combines characteristics from both processes, with a pre-mixed homogenous fuel-air mixture ignited by compression. This creates cleaner near-simultaneous combustion throughout the mixture, with no flame propagation. Peak temperatures are lower, resulting in very low NOx emissions. PM emissions are also reduced as a result of the more complete combustion. The HCCI process remains under development due to difficulties in controlling the start of combustion. Both spark ignition and compression ignition engines have defined parameters that can control the point at which combustion is initiated, whereas for HCCI combustion, this occurs whenever the appropriate conditions are reached within the cylinder, making variable load operation particularly difficult. Control technologies will have to consider variable compression ratio, intake temperature, valve timing or EGR.


Additionally, although peak temperatures are low, cylinder pressures are high, requiring sufficient strength of cylinder components. High HC and CO emissions are also produced, due to incomplete burning at the boundaries of the chamber. Despite the disadvantages, HCCI is likely to be incorporated in future diesel engine designs once practical control mechanisms have been evolved, probably within the next 5-10 years. Premixed Controlled Compression Ignition (PCCI) can be considered to be a variation of HCCI, where the fuel-air mixture may be partially stratified at the moment of injection. This stratification may be used for lengthening the burn duration, allowing the engine to operate at higher specific power. Oxygen Enrichment By increasing the amount of oxygen-rich air in the cylinder, the fuel burns more completely, reducing PM emissions and increasing available power. However, the resultant higher combustion temperature creates an increase in NOx emissions. This can be mitigated by adjustments to fuel injection timing and flow rates. A permeable membrane inserted into the air flow to the engine separates out the ambient air into oxygen-rich and nitrogen-rich segments, with the former being fed into the engine at ratios of up to 25% by volume. Current development work is concentrating on reducing the size and power requirement of the membrane to acceptable levels. Low temperature combustion Research work by the US Department of Energy 16 with very high levels of EGR in combination with fuel timing and flow rate changes has created a lower temperature combustion regime where emissions of NOx and PM were both reduced, by around 90% and 45% respectively, with no reduction in fuel efficiency. This situation with significant percentage reductions of both these pollutants from a single technology is unusual. Toyota has also been examining this system as a means to enrich the exhaust gas stream to facilitate the regeneration of a NOx adsorber (see section 13.6). Plasma-assisted Combustion The Los Alamos National Laboratory in the USA has been developing plasma-assisted combustion, whereby an electrical voltage is applied to the atomised fuel stream from an existing fuel injector. This generates a plasma in the fuel, which breaks down the long chain hydrocarbon molecules into smaller constituents, creating more complete combustion. Ricardo Developments Ricardo is a major UK independent engine development and consultancy company. In August 2006, a press release 17 was issued stating that Ricardo are collaborating with a global manufacturer to develop advanced diesel technology capable of achieving the US Super Ultra-Low Emission Vehicle (SULEV) and Tier 2 Bin 2 requirements (these limits have not been stated in section 6.4 due to their not being directly relevant to rail applications, however, the quoted NOx level for the Tier 2 Bin 2 requirements is 12.4 mg/km, compared


with the 250 mg/km limit of the current Euro 4 legislation for cars and light vehicles). A combination of technologies will be required for this objective, which are unsurprisingly not identified in any detail, but will include advanced air handling systems, two-stage turbocharging, advanced EGR and closed-loop cylinder pressure-based engine controls. Ricardo has also been active in the area of hybrid technology (section 14.2).

9 LEGISLATIVE DEVELOPMENTS

9.1 NRMM DIRECTIVE

European Directive 2004/26/EC (see section 6.2) defines Stage IIIB emissions limits to be introduced from 2011 onwards. Inherent within the Directive is the requirement for a technical review by the end of 2007 to establish whether the defined emissions limits will be achievable. Contact with a representative of the UKs Department for Transport established that the UK Government was not expecting to be actively involved with the review of this Directive. The UK rail industry is represented by two of the rolling stock leasing companies. Other bodies represented in the review include Euromot, UNIFE, UIC and EMA, plus vehicle and engine builders. The review process is currently collecting data on engine duty cycles and operation within Europe.

9.2 EU DIRECTIVE 2003/17/EC

European Directive 2003/17/EC relates to the quality of petrol and diesel fuels, amending previous Directive 98/70/EC. With particular reference to the sulphur content of diesel fuels, Directive 2003/17/EC comments on both road diesel and gas oil (as currently used by the railway industry). Existing road diesel supplies are required to satisfy BS EN 590:2004, for which a maximum sulphur content of 50 ppm is defined. The Directive requires that from 1st January 2005, fuel with a maximum sulphur content of 10 ppm should be marketed on an appropriately balanced geographical basis, and that by 1st January 2009, all diesel fuel shall be no greater than this limit. Existing gas oil supplies are required to satisfy BS 2869:2006 Class A2, for which a maximum sulphur content of 2000 ppm is defined (in reality, the sulphur levels of a typical gas oil used on the railways will usually be in the range 1000-1500 ppm sulphur). The Directive requires that by 1st January 2008 at the latest, this level shall be reduced to 1000 ppm. In January 2007, amendments to Directive 2003/17/EC proposed a further reduction in the maximum sulphur content of gas oil to 10 ppm from the end of 2009. This is currently under consideration the implications of reducing fuel sulphur content are discussed in detail in a separate RSSB report 18.


With the need to satisfy the NRMM Stage IIIB limits requiring the use of exhaust after-treatment devices, the rail industry will have to move to low sulphur fuels before the Stage IIIB implementation dates. Thus, it is likely that a complete change from gas oil to SFD (or sulphur-free gas oil) will occur before 2010, subject to resolution of fuel duty issues (see section 10.4).


European Directive 2003/30/EC 19 covers the use of biofuels or other renewable fuels for transport. The Directive came into force on 8th May 2003, with the requirement for member states to enact its provisions into national legislation by 31st December 2004. The main requirements of the Directive were as follows: - Reference value of 2% biofuel use (petrol and diesel) for transport purposes

on the basis of energy content by 31st December 2005. Reference value of 5.75% biofuel use (petrol and diesel) for transport

purposes on the basis of energy content by 31st December 2010. Member States to set national indicative targets for their share of biofuels.

These were to be defined in 2004 (for 2005) and 2007 (for 2010). Monitoring of the effects on the use of biodiesel blends greater than 5% by

non-adapted vehicles. Annual report by Member States to the Commission detailing the progress

made on the Directive objectives. Detailed evaluation report by the Commission by 31st December 2006, and

every two years thereafter. Between April and July 2006, a public consultation exercise was carried out, inviting comments from both industry and private individuals, as part of a review process of this Directive scheduled for completion by the end of 2006. With biofuels able to be made from a variety of sources, it has been important to establish an accepted fuel specification. For biodiesel, the required fuel standard is BS EN 14214: 2003. EU Directive 2003/87/EC 20 introduced the concept of the GHG Emissions Trading Scheme (ETS), whereby companies are allocated an allowance of total CO2 emissions per annum. If this allowance is exceeded, companies have to buy further allocations; conversely, if the allowance is not used, it can be sold. The Directive was amended by Linking Directive 2004/101/EC 20 which enabled operators to use emissions credits to comply with their obligations under the scheme. The system commenced at the start of 2005, initially for a 3-year period. Reports on the operation of the scheme are expected during 2006. The UK Government is complying with Directive 2003/30/EC, and has issued the required progress reports for the last three years. The 2006 report introduced the RTFO (see section 9.5) as a primary means of advancing the use of renewable fuels.



European Directive 96/62/EC 2

Documents

The Future of Diesel Engines