Preface
This report finalises the official part of the large-scale project with particulate filters in Odense. In several ways the activities of the project will continue. Odense Municipality will continue to purchase vehicles with particulate filters. Work is still being carried out to ensure a more efficient operation and other transport companies will continuously be encouraged to purchase filters. We hope that the large-scale project will contribute to promote the use of particulate filters. Especially during the first year, the project was characterised by a number of running-in and teething problems for some of the filters in the project. However, after two years the filters are still in working order on the majority of the vehicles. And much improved knowledge of what is required to become satisfied with a retrofitted filter has been obtained.
The steering group would like to thank all the employees at the three operational departments in Odense, namely Odense Public Bus Transportation (Odense Bybusser), Odense Parks and Roads Management (Park- og Vej Service) and Odense Waste Management Ltd. (Odense Renova-tionsselskab A/S) for their competent and committed participation in the project.
Contents
1 Summary...5
2 The background of the project...9
2.1 Regulation of air pollution in general... 9
2.2 Particulate pollution ... 10
2.3 Regulation of motor vehicle emissions, EU legislation ... 13
2.4 Health conditions... 14
2.5 Effects of particulate filters ... 15
2.6 Filter technology and filter types... 16
2.7 The large-scale project in Odense ... 20
3 Measurements of the effects of the project...23
3.1 Cleaning efficiency of the particulate filters ... 23
3.2 Measurements in the street canyon... 34
3.3 Interview with citizens who frequent the city centre... 35
3.4 Questionnaire completed by employees... 38
4 Experience...43
4.1 General overview of operational experience ... 43
4.2 Requirements to the vehicle and evaluation of its suitability for retrofitting of particulate filters... 50
4.3 Fitting ... 51
4.4 Servicing of filters, handling of additives ... 51
4.5 Monitoring of filters in operation ... 53
4.6 Health and safety at work ... 54
4.7 Teething troubles... 54
4.8 Operational problems ... 55
4.9 Co-operation with manufacturers and distributors ... 57
4.10 Fuel consumption and additives ... 57
4.11 The environmental plan of Odense Municipality ... 58
5 Conclusions from the project...59
5.1 Filter efficiency ... 59
5.2 Prerequisites for filter operation without substantial problems... 59
6 References ...63
Enclosure 1: Course of the project...65
Enclosure 2: Members of steering group, working group and technician group ...77
Enclosure 3: Overview of filters and vehicles...79
Enclosure 4: Exhaust gas measurements Odense public buses...83
1 Summary
BackgroundThe emission of particulates from heavy-duty diesel vehicles contributes to one of the most substantial environmental problems in cities. In a number of investigations a connection has been ascertained between particulate pollution and life-shortening lung and cardiovascular diseases. In a number of directives, the EU has implemented regulations concerning emissions from heavy-duty diesel vehicles. In the directive containing the requirements to emissions from heavy-heavy-duty diesel vehicles which are effective from 1 October 2006 (Euro 4) sharpened particulate emission requirements also appear. In order to meet the emission requirements stated in this directive new heavy-duty diesel vehicles will presumably have to be equipped with particulate filters from that date (1 October 2006).
In 1998, the Danish Road Safety and Transport Agency decided to promote an early use of particulate filters on existing heavy-duty diesel vehicles and in 1999 the Agency started a co-operation with Odense Municipality to test and demonstrate filter technology on a large scale. The main objective of the project has been to investigate the efficiency as well as the possibilities of particulate filter retrofitting on heavy-duty diesel vehicles. The project has run over nearly 3 years with a working period of two years and was finalised in the first quarter of 2002.
This report describes the course of the project and the results that were obtained.
Course of the project
As part of the project, particulate filters were fitted on the heavy-duty diesel vehicles owned by Odense Municipality that were suited for retrofitting. In addition, other transport companies in Odense have been able to apply for support for partial payment of expenses connected with the purchase of filters and three transport companies have made use of the offer. As part of Odense Municipality's environmental plan other initiatives have been implemented to disseminate
environmentally friendly vehicle technology with the objective to improve the air quality in the city. All in all, particulate filters were fitted on approximately 120 vehicles. 8 of the vehicles were
privately owned. Four different types of filters were purchased. Furthermore, additional testing of systems that also reduce the emission of NOx has taken place.
The project had a budget of DKK 11 million, which was financed by the Danish Ministry of Transport through funds for traffic measures. Beyond that budget, Odense Municipality financed a considerable workload in connection with fitting, operation and maintenance of filters and the collection of experience in connection with the preparation of the final report.
During the project data has been collected about operational and environmental conditions that apply to the different types of filters. In addition, measurements have been made of the filter efficiency as well of the air quality in the selected street canyons and analyses concerning citizen and employee reactions have been carried out.
Project results
In general it can be ascertained that the filters function well and they have proved to be operational during the entire two-year project period. On the basis of the measurements it can be documented that all filters after some time have had a particulate emission of 0.03 – 0.08 g/kWh.
Measurement of particulate size distribution shows that the filters have efficiency on particulates in all sizes. The measurements also show that the CRT type filters under a very heavy load (and thus high temperatures) emit a considerable number of particulates in sizes between 10 and 100 nm (nanoparticles) – which presumably consist of condensed sulphate compounds.
Among the 120 filters that were fitted at the beginning of the project or during the first 6 months more than 80% worked well or were acceptable. However, the remaining filters had operational problems. Problems especially arose in connection with the just under 10% buses1 that had too low exhaust temperature and too high particulate emissions for the filters to function properly. In the light of the current knowledge it must be assumed that it will be possible to obtain satisfactory operation also on the service buses. It is considered that 10% of the remaining vehicles had engines that had not been maintained satisfactorily and would be disproportionately expensive to repair.
The project has given essential knowledge of the requirements to vehicles and filters during retrofitting of particulate filters. It has been possible to obtain satisfactory filter operation for all filter types fitted on vehicles with a driving profile that gives high exhaust temperatures. However, it is essential that the vehicle has been satisfactorily maintained - otherwise, considerable require-ments to maintenance might arise. If a filter is used in connection with lower exhaust temperatures and if it is well-suited for these temperatures, then satisfactory operation can be obtained. It might be a question of filters based on additives being added to the engine fuel or of filters with electric regeneration.
During the first year of the project a lot of effort was put into operational problems of which some were mechanical teething troubles and others were running-in problems. That resulted in quite a few filter replacements. Most of the problems were solved within the first working year, which seems to suggest that filter technology at the beginning had not been sufficiently developed for retrofitting. The second year of the project went much smoother and it was possible to arrive at the conclusion that particulate filter retrofitting can be carried out on most heavy-duty diesel vehicles in Denmark.
During the project, knowledge has been collected about the demands to fitting, maintenance and operation. Special demands are made to the working environment when filters are handled. In order to obtain good particulate filter operation it is necessary to check the condition of the filter and to ensure that the filters are maintained on a regular basis. The condition of the filters has been checked by means of pressure and opacity measurements and in the case of too high back-pressure the filters are cleaned on a specially developed filter cleaner and afterwards they are reversed. In connection with vehicles that are in good repair the service intervals prescribed by the suppliers seem to be correct. A smaller group of vehicles that were poorly maintained will require more frequent maintenance of the filter.
Parallel with the project, back-pressure alarms have been developed and they can contribute to im-proved monitoring. It has been ascertained that if the risk of filter core melt down has to be reduced then a back-pressure alarm should be installed. Back-pressure alarms have not been tested during this project.
The experience gained during the project has been passed on to the suppliers and in that connection subjects such as working environment and filter monitoring have been discussed.
As part of the project, citizens from Odense were interviewed about their attitude to the project. The interview revealed that the project has received considerable attention. The citizens were satisfied with the municipality's commitment and they knew a lot about the problem. However, the citizens have in general not noticed that the air quality has improved owing to the use of particulate filters, which also agrees with the measurements carried out in the street canyon. Some citizens have registered the smell of swimming pool, which can be traced back to the increased emission of NO2 from certain filters.
The questionnaire completed by people employed in the Municipality and involved in the project showed that an improved air quality has been obtained, which is also confirmed, as the garages have become cleaner. Evaluation of the general working environmental impacts has mainly been positive with the exception of filter handling and maintenance.
All in all, the large-scale project in Odense has shown that it is possible to retrofit particulate filters on a considerable share of the heavy-duty diesel vehicles. However, the project has also demon-strated that not all vehicles have a driving profile or state of maintenance that permits efficient operation of retrofitted filters.
About this report
In chapter 2 the background of the project is described; the existing knowledge of the impacts of particulate pollution, EU legislation within the field and filter technology. In chapter 3 the results of the various measurements carried out as part of the project are discussed and in chapter 4 the
experience gained in the course of the 2 years of operation are described. In chapter 5 conclusions are drawn. Enclosure 1 gives a more detailed description of the course of the project starting with the plan of action which the Danish Road Safety and Transport Agency prepared in 1998 for planning, invitation to tender and collection of experience.
2 The background of the project
This chapter describes the background of the project including the existing and planned EU regulation of air pollution and emissions from vehicles. In addition, some of the most important terms connected with emissions into air and their measurement are defined and explained. A brief evaluation of the health related conditions and particulate filter impacts as well as a brief description of the course of the project is given. Chapters 2.1 to 2.6 are partly a summary of chapter 2, 3 and 4 in the inter-ministerial report2 "Particulate filters on heavy-duty diesel vehicles". There are no deliberate differences in the contents. In the following, the report is called "Report from the inter-ministerial working group".
2.1 Regulation of air pollution in general
Since 1980, the EU has - through the adoption of several directives - fixed limits for the air quality. The limits have been transferred to Danish legislation in the form of executive orders issued accor-ding to legislation on environmental protection. The limits have been fixed on the basis of estimates on health effects combined with an assessment of technical, financial and political considerations. Ongoing revision is carried out and new limits will be in force from year 2005 or 2010 depending on which substances are in question.
The ongoing revision of the limits has its starting point in a decision from 1996 concerning a new EU framework directive for air quality3. The directive will be completed with sub-directives for the individual substances and for particulates. In addition to the limits, which in most cases are sharp-ened the sub-directives will include requirements to the measurement methods, publication of results etc. In 1999, a sub-directive was adopted for sulphur dioxide, nitrogen dioxide, particulates and lead4.
As part of the implementation of the directives, Denmark has carried out preliminary evaluations of the air quality with regard to planning a measurement programme. The objective is to identify the areas where the limits might be exceeded and afterwards to establish air observation posts and to carry out a more detailed evaluation of the air quality in the specific areas.
2 Particulate filters on heavy-duty diesel vehicles – Report from the working group to illustrate how the use of
particulate filters for trucks and buses in Denmark can be encouraged. Danish Ministry of Transport, Danish Road Safety and Transport Agency, 2001.
3 Council Directive 1996/62/EC of 27 September 1996 on ambient air quality assessment and management. 4 Council Directive 1999/30/EC of 22 April 1999 relating to limit values for sulphur dioxide, nitrogen dioxide and
2.2 Particulate pollution
ParticulatesThe designation particulates comprises a complex combination of solid components that vary with regard to physical properties (size, surface etc.) and chemical composition. The original source can be natural as well as man-made. Particulates can be emitted directly to the air (primary particulates) or they can be created in the air from other types of pollution (secondary particulates).
The primary particulates originate from both man-made and natural sources. The man-made sources are traffic, coal-fired power plants, industrial plants etc. The natural sources are trees (pollen), wind-swept soil etc.
The secondary particulates primarily consist of sulphate, nitrate and different organic compounds that are created slowly when the air is carried over long distances. The original source could be SO2 and NOx produced through the combustion of fossil fuels.
The particulate content in air typically appears in three clearly separated sizes: Ultra-fine particu-lates (0.01-0.1 micrometer or 10-100 nanometer), fine particuparticu-lates (0.1-2.5 micrometer) and coarse particulates (> 2.5 micrometer), cf. figure 1.
Figure 1. Typical size distribution of particulates in air
F e C a S i C… P A H m etal + + N O3 -S O4 --0 .1 1 0 0 .01 1 2 .5 1 00 U ltra-fine F in e C o arse P articulates fro m cars
W in d-sw ept d u st W h irled u p ro ad du st P articulates carried o v er lo n g distan ces 0 .00 1 D iam eter (M icrom eter) P M2 .5 P M1 0
The shape of the curve depends on the chosen unit on the vertical axis. If the unit is weight (mass) of particulates, the ultra-fine part of the distribution will disappear. The same is the case for the coarse part of the distribution if the unit is number of particulates.
The ultra-fine particulates typically originate from car engines. They have either been formed at high temperatures in the engine, through exhaust pipe condensation or immediately after emission to the atmosphere. The fine particulates are typically formed from the ultra-fine particulates through coagulation and adsorption of gaseous material from the atmosphere on existing particulates.
The secondary particulates also belong to this group. The coarse particulates are typically created mechanically (wind-swept dust, whirled up road dust and wear products from tires and brakes)5. Measurements of the particulate content in air
During the period from 1988-1998, the measurements at the Danish air observation posts have shown a general decline in the measured particulate concentrations of between 30 and 50%. The decline comprises both coarse and fine particulates. In connection with coarse particulates the reason is believed to be improved "housekeeping" near construction sites and green fields during winter. In connection with fine particulates the reason is believed to be improved cleaning of power plant smoke, the introduction of unleaded petrol and reduced particulate emissions from diesel vehicles.
The ultra-fine particulates emitted from petrol and diesel vehicles only contribute a little to these measurements, which are based on weight. In connection with ultra-fine particulates methods have to be used that make it possible to measure the number of particulates.
The Danish National Environmental Research Institute (DMU) has by means of special measuring equipment carried out measurements at heavily trafficked streets in Copenhagen (Jagtvej) and in Odense (Albanigade)6. By means of special calculation methods it has been possible to estimate the amount of ultra-fine particulates emitted from petrol and diesel vehicles, respectively. On the basis of these calculations, DMU has concluded that a diesel car emits app. 25 times more ultra-fine parti-culates than a petrol car.
Only a few diesel cars drive on Jagtvej and therefore the result is that the two types of cars almost contribute equally to pollution with ultra-fine particulates. In Albanigade the contribution from diesel cars is considerably higher than the contribution from petrol cars.
From the measurements on Jagtvej, DMU has concluded that close to 90% of the ultra-fine particulates in the street canyon in Denmark originate from the traffic. In connection with the measurements carried out on Jagtvej it has also been ascertained that the amount of ultra-fine particulates from diesel vehicles was diminished by one half from 1999-2000. The reason is believed to be that the sulphur content in diesel fuel during the same period was reduced from 500 ppm to 50 ppm7.
5
With regard to measuring technique different particulate definitions are used. Until a few years ago the measurements solely comprised the content of suspended particulates (TSP, ”total suspended particulates”) and soot in air. TSP typically includes all particulates with a diameter of up to app. 25 micrometer. The amount is determined by means of weighing after collection on a filter. Soot comprises coloured (black) particulates that mainly are created through combustion of fossil fuels. The soot content is determined empirically from the blackening of a white filter. In recent years, attention has concentrated on the smaller particulates and the measurement of the PM10 content in air (particulates
with a diameter of less than 10 micrometer). In addition some measurements of PM2.5 (particulates with a diameter of
less than 2.5 micrometer) are being carried out. As it appears from figure 1, PM10 is not the most appropriate method of
measurement for the smallest particulates as the dividing line is in the middle of the fraction that is called coarse particulates. PM2.5 is a better measurement, as it precisely comprises the total of fine and ultra-fine particulates. As the
smallest particulates only contribute insignificantly to the weight of the total particulate mass, more accurate future health related evaluations will presuppose that information about the number of the smallest particulates is available.
6 Measurements in Albanigade in Odense have been carried out as part of this project. 7 ppm = parts per million, i.e. 1 ppm is 0.0001%.
According to evaluations carried out by Danish Technological Institute an average 13% reduction in particulate emissions, measured on weight basis (TSP)8, can be expected for the mentioned
reduction in sulphur content.
Some analyses have indicated that modern engines with reduced particulate emission (weight) could emit more ultra-fine particulates than older engines. However, the most recently published analyses do not support that conclusion. Analyses exist on passenger cars that show that new engines emit less particulate mass as well as less particulate number. For heavy-duty engines recent analyses conclude that Euro 2 heavy-duty engines (1996) emit more nanoparticles (10-70 nm) than Euro 1 engines (1993). The new Euro 3 heavy-duty engines (2001) have a reduction in both mass and number.
Particulate emission distribution on sources
No official figures exist of the total Danish emission of particulates and its distribution on sources. However, the European Commission has carried out calculations that comprise all sources (traffic, power stations, boilers, industry, agriculture etc.). The calculations show that in 1995, diesel vehicles9 contributed with app. 11% of the total emission10 of primary particulates.
The contribution from petrol cars and from tires and wear and tear are estimated to amount to 3% and 2%, respectively, of total emissions, so the contribution from traffic – when secondary parti-culates are not taken into account – amount to app. 16% of total particulate emissions. It should be stressed that these figures are based on weight and therefore they do not take the special impacts from the ultra-fine particulates into account.
In connection with the annual reporting to EU on air pollution in Denmark, DMU prepares state-ments of particulate emissions in Denmark from diesel vehicles. The development of the emissions from 1990 – 1999 appear from table 1.
Table 1: Particulate emissions from Danish road traffic 1990-1999 (
tons
)
1990 1995 1999
Passenger cars 600 400 400
Vans 2,500 2,400 1,700
Trucks/buses 1,700 1,600 1,400
Total 4,800 4,400 3,500
In the 90s, the total emission of particulates was reduced by app. 25%.
8 Possibilities for environmental improvements of diesel vehicles, Danish Technological Institute (for the Danish
Environmental Protection Agency), May 1998.
9 The statement only comprises emissions from the exhaust, cf. later.
10 The calculation is based on the measurement of weight and therefore nothing is indicated about the amount of
Diesel car emissions
DMU has grouped the emissions11 of diesel vehicles according to vehicle category and driving conditions. The fragmentation appears from table 2.
Table 2: Diesel car emissions in Denmark 1999,
grouped according to vehicle category and driving conditions
Particulate emission (tons) No. of
vehicles Town Highway Motorway Total
Passenger cars 104,600 190 100 60 350 Vans 206,300 870 660 210 1,740 Trucks 3.5-7.5 t 5,800 20 10 10 40 Trucks 7.5-16 t 10,600 70 70 20 160 Trucks 16-32 t 17,000 130 200 130 460 Trucks exceeding 32 t 15,500 120 200 130 450 Buses 4,500 110 60 10 180 Tourist buses 5,300 70 70 20 160 Total 1,580 1,370 590 3,540
It appears from table 2 that diesel vans emit the most substantial amount of emissions in cities and they represent 55% of emissions while trucks and buses constitute app. 33% and passenger cars 10%.
2.3 Regulation of motor vehicle emissions, EU legislation
In December 1987, the EU adopted a directive on measures to reduce the emission of pollutants from diesel engines12. The basis of the directive was various recommendations concerning the emission of harmful gases as well as particulates.
An amendment of the directive in 199113 meant that the Council of the European Union made the emission limits binding and sharpened them in two stages as of 1993 and 1996 (Euro 1 and 2). At the same time, the directive introduced maximum limits for the emission of particulates from trucks that gradually had become a serious problem in city traffic. As of 1 October 1993, there has been a binding maximum limit in the EU for the emission of NOx, HC, CO and particulates from trucks and buses. The most recent amendment of the directive took place in 199914 and concerns new requirements in three stages of which the first (Euro 3) was implemented on 1 October 2001.
11 The statements of the emissions do not comprise petrol vehicles. Other vehicle related emissions (tire wear and tear,
material from brake lining, whirled up road dust etc.) are not included either. Calculations show that the contribution from petrol cars and from wear and tear cannot be ignored as the contributions are estimated to amount to app. 20% and 10%, respectively, of total emissions. In total, the contribution from diesel cars is estimated to amount to app. 70% of the road traffic's total particulate pollution.
12 Council directive 88/77/EEC of 3 December 1987 on the approximation of the laws of the Member States relating to
the measures to be taken against the emission of gaseous pollutants from diesel engines for use in vehicles.
13 91/542/EEC of 1 October 1991 amending directive 88/77/EEC on the approximation of the laws of the Member
States relating to the measures to be taken against the emission of gaseous pollutants from diesel engines for use in vehicles.
14 Directive 1999/96/EC of the European Parliament and the Council of 13 December 1999 on the approximation of the
laws of the Member States relating to measures to be taken against the emission of gaseous and particulate pollutants from compression ignition engines for use in vehicles, and the emission of gaseous pollutants from positive ignition engines fuelled with natural gas or liquefied petroleum gas for use in vehicles and amending Council Directive 88/77/EEC.
An overview of the development in emission standards for heavy-duty diesel vehicles is given in table 3.15
Table 3: Emission standards for diesel trucks and buses (g/kWh)
Commencement NOx Hydrocarbons (HC) monoxide Carbon (CO) Particulates (PM) EC directive 88/77 Euro 0 1/10 1990 14.4 2.4 11.2 (1.0) EC directive 91/542 Euro 1 Euro 2 1/10 1993 1/10 1996 8.0 7.0 1.1 1.1 4.5 4.0 0.36 0.15 EU directive 99/96 Euro 3 Euro 4 Euro 5 1/10 2001 1/10 2006 1/10 2009 5.0 3.5 2.0 0.66 0.46 0.46 2.1 1.5 1.5 0.10 0.02 0.02 It is the general assumption that the requirements in Euro 4 in practice will imply that heavy-duty diesel vehicles will have to be delivered with particulate filters. Already today, trucks, buses and passenger cars can be delivered with factory-mounted particulate filters.
In 2001, the European Commission submitted a proposal for an additional reduction of the sulphur content in petrol and diesel from the 50 ppm16 that will become compulsory in 2005. The proposal implies that as of year 2005 sulphur-free fuels shall be marketed (sulphur content less than 10 ppm) and a complete transition to sulphur-free fuels will take place at the end of 2010.
EU calculations have shown that the sharpened standards (incl. the sharpened requirements to stationary sources) will result in a decline in total particulate emissions of app. 30% from 1995-2020. The reduction is calculated to be app. 80% for diesel vehicles. For this reason, the total emission of particulates from diesel cars is expected to be reduced to app. 3% of total particulate emissions against the current 11%. In its white paper17 on transport, the European Commission has concluded that the air quality in the cities has improved due to the technical requirements that were introduced through the 90s.
2.4 Health conditions
The health hazards attached to particulate pollution (probably especially fine and ultra-fine parti-culates) give rise to concern. Through investigations in USA and Europe it has been documented that air pollution with particulates or dust in cities involves serious health hazards. However, the implemented investigations have mainly concerned the impact of particulates from the total particulate mass.
15 It should be noted that the method of measurement that forms the basis of the below emissions varies from the
method that is used to carry out measurements in the street canyon – which means that there is a difference between what is measured as particulates – e.g. condense etc.
16 ppm = parts per million, i.e. 1 ppm is 0.0001%. In Denmark, the sulphur content in "low sulphur diesel" is <50ppm. 17 The European transport policy up to 2010 – the difficult choices. White paper from the European Commission
A comprehensive survey in the USA that indicates a considerable impact on the number of cases of lung cancer implies that especially the fine and ultra-fine particulates are carcinogenic.
However, it is still unclear which properties make particulates unhealthy. Particulates above 10 micrometer will mainly be deposited in the upper respiratory passages (nose/throat), while parti-culates with a diameter below 10 micrometer will be deposited further down in the bronchial tubes. Particulates smaller than 5 micrometer can reach down into the pulmonary (alveoli). Particulates that are deposited in the bronchial tubes are removed rather quickly due to the movement of the cilia while the particulates that reach the alveoli are exposed to an encapsulation that means that the retention time can be long.
Which damages are caused to a high degree depends on the particulate size itself and on the che-mical composition, i.e. which substances might be adsorbed on the surface of the particulates. The particulates partly influence the lung tissue and partly the viscosity of the blood and the cardiac function.
The importance of the calculated values for increased mortality can be illustrated via calculations carried out by WHO in the light of the investigations carried out among Americans. WHO has calculated that the increased mortality that can be expected when the PM2.5 level increases 10 microgrammes/m³ will shorten the average life expectancy by app. 1 year.
Danish evaluations contain preliminary and uncertain estimates showing that a reduction in the particulate level of app. 30% would mean that from among 200.000 children, 1.700 fewer children would suffer from bronchitis symptoms.
In the evaluation of the extent of the health hazards it is emphasised that all calculations – also concerning increased mortality – are related to the general occurrence of particulates and do not include any special evaluation of the contribution from traffic. In 1999, calculations were carried out in the municipality of Copenhagen and they showed that between 100 and 280 premature deaths are due to the exposure to PM10. The figures are based on a conservative evaluation and might be much higher. The calculations from Copenhagen also show that the exposure to PM10 leads to 190-540 additional hospitalisations especially among people with pulmonary diseases and older people.
2.5 Effects of particulate filters
18The specification of health related impacts from particulate pollution are connected with consider-able uncertainty. Therefore, the health related specification of what is gained by using particulate filters on heavy-duty diesel vehicles in Denmark is also connected with considerable uncertainty. An expert group has evaluated the health-related impacts through a hypothetical situation where all trucks and buses in Denmark are equipped with particulate filters. In such a situation the health related impacts (expressed as avoided, annual premature deaths) have been estimated to 22. The modest impact is related to the fact that the calculations were based on urban background PM10, which primarily consists of fine and coarse particulates that only are reduced a little when
18 The expert group that is referred to carried out a project to illustrate the effect on air quality and health by mounting
filters on all heavy-duty diesel vehicles (more than 3.5 tons) in Denmark. The expert group consisted of representatives from DMU, the University of Copenhagen and the Danish Cancer Society.
particulate filters are used because the traffic's share of total emissions of fine and coarse parti-culates is limited.
New investigations suggest greater health related impacts from ultra-fine particulates. The traffic's share of ultra-fine particulates is high. Therefore, particulate filters can reduce the total emission of ultra-fine particulates considerably. The expert group could not evaluate the effect quantitatively but stated a presumed upper limit of the positive effects of particulate filters on heavy-duty vehicles on the basis of ultra-fine particulates. The estimated upper limit that is connected with a much greater uncertainty corresponds to 1.000 avoided premature deaths. At the same time it is believed that the use of particulate filters can reduce the number of hospitalisations connected with
circulatory diseases and respiratory diseases and can reduce the number of bronchitis cases and asthma attacks. The assessment of these effects is also connected with great uncertainty.
2.6 Filter technology and filter types
Basically, a particulate filter works by collecting soot particulates from the engine exhaust gas. The particulate filter is constructed of many small channels made of ceramics. The neighbouring chan-nels are closed at the opposite ends so the exhaust gas is forced to pass through the channel wall where the particulates are caught. Even though the particulates are small the filter will quickly be-come clogged with soot, if the filtration is not combined with a method to remove the soot. Re-moval takes place through ongoing burning of the collected soot. The process is called regeneration of the filter. Some filter systems have passive regeneration (i.e. it is spontaneous), others have active regeneration (i.e. it requires help to burn off the particulates – e.g. by supplying electricity).
Figure 2: Particulate filter design
Normally, a temperature of app. 600oC is required to carry out soot combustion. That is higher than the temperatures that are obtained in the exhaust system which can vary from 150-400oC. However, ignition of the soot particulates collected in the filter can take place at much lower temperatures (250 – 300oC). That can i.a. be obtained by combining the filter with a catalyst that produces large amounts of NO2, by using an additive in the fuel or by adding additional energy (from the car's electric system). Which system is best to a high degree depends on the vehicle in question and how the vehicle is used.
Filter types
There are many different filter products in the market. Common to them all is that the efficiency on the particulate emission is declared to be 95-99% under laboratory conditions and more than 80% under practical conditions. Some of the filters are combined with an oxidation catalyst and therefore they can also reduce the emissions of HC and CO. The greatest difference between the particulate filters is how the collected particulates are removed (burned) – i.e. how the filter is regenerated. In addition, technologies exist that can reduce NOx and they are often used together with particulate filters. Below, different types of filters are briefly described.
Filter types that formed part of the Odense project Johnson Matthey, CRT 19
Johnson Matthey is one of the largest catalyst and filter producers in the world. The CRT filter (Continuous Regenerated Trap) was originally developed by Emissionsteknik in Sweden, which now is part of Johnson Matthey. CRT is the most well-known particulate filter and with a sale of app. 12,000 units it is also the most widespread in the European market. In Europe, the CRT filters are made under license by Eminox in England and they are sold as Eminox CRT. The filter is also sold by Volvo as Volvo CRT for original or retrofitting on buses and trucks.
Johnson Matthey, CRT filter
CRT is a passive filter that is regenerated by means of NO2, which is produced in a pre-catalyst. Johnson Matthey requires fuel with less than 75 ppm sulphur.
Engelhard DPX
Engelhard is also a large producer of catalysts and particulate filters. At the beginning of the project, Engelhard DPX filters were made under license by Ferrita in Sweden, but subsequently they are made under license by Dinex in Denmark.
DPX is a passive filter that is regenerated by means of NO2, which is produced in the catalytically covered filter itself. Contrary to CRT, the filter has no pre-catalyst. Engelhard also recommends fuel with less than 75 ppm sulphur.
Engelhard DPX filter
Silentor
On an international scale, Silentor is a small Danish company and mufflers are their speciality. Silentor makes particulate filters with monoliths from NoTox.
Silentor is a passive filter that is regenerated by means of an additive, which is added to the fuel. Today, Silentor uses the additive Octel Optimax 4804, which contains 4% Iron and 1% Strontium. Normally, the additive is dosed with 200 ppm during summer and 400 ppm during winter. Silentor is available with or without an oxidation catalyst.
Energietechnik Bremen, ELR
ETB makes particulate filters with electric regeneration and they are called ELR. This type of filter makes it possible to use filters at low exhaust temperatures as the collected soot particulates are burned continuously by means of power from the vehicle's generator.
DeNOx systems that formed part of the additional tests
Svensk Turbo Teknik EGR
The company Svensk Turbo Teknik (STT) has developed an EGR (Exhaust Gas Recirculation) system for retrofitting and it is used in combination with a Johnson Matthey CRT filter. The EGR system recirculates part of the exhaust gas to the engine's inlet air and in that way reduces the NOx emission. The recirculated exhaust gas is cooled in a heat exchanger.
The STT system uses an electronically controlled EGR valve and its operation has to be programmed to the engine in question and therefore the system is adapted to a limited number of engines.
Volvo sells Johnson Matthey CRT filters and STT EGR systems as original Volvo auxiliary equipment under the name VEC.
When deNOx systems are used in connection with particulate filters that are regenerated by means of NO2 there is a natural limit to the efficiency of the deNOx system as NOx can only be reduced so much so there is enough NO2 to regenerate the filter. In practice that means that the NOx efficiency should not exceed 40-45%. Otherwise, there is a risk of damaging the filter.
Ferrita EGR
Another Swedish company, Ferrita, has also developed an EGR system for retrofitting - at first together with Engelhard DPX filters. Ferrita's system is purely mechanical and an orifice that is adapted to the individual engine type limits the EGR amount. Ferrita's EGR system also has a heat exchanger for cooling of the recirculated exhaust gas.
The same considerations as above apply to efficiency. Ceryx, QuadCat
Ceryx was a small American company (now closed down) that produced an active filter called QuadCat. It was regenerated through secondary fuel injection, i.e. a small amount of fuel is injected into the exhaust before the filter. A patented heat exchanger is incorporated in the system, which reduces the energy consumption to some degree. QuadCat also has an oxidation catalyst that
removes HC and CO and a deNOx-catalyst that reduces NOx. The catalyst should have an efficiency of 25-40% depending on how much fuel is used in secondary injection. Typically, additional
consumption is 2-6%. Other filter types
The above-mentioned products are the most important in the market, but there are also other pro-ducts in the market or they are on their way into the market. In that connection we would like to mention:
Unikat
Swedish UNIKAT AB supplies a filter system where the burning of particulates takes place by means of electricity from the grid. This system requires the vehicle to be connected to the grid (400 volt) for 8 hours every time it has driven 8-10 hours and the use of the system limits the use of the vehicle.
2.7 The large-scale project in Odense
In connection with the negotiation of the EU directive 99/96, the Danish Road Safety and Transport Agency carried out various considerations about expediting the use of particulate filters. The
considerations resulted in a proposal for the implementation of a large-scale project concerning retrofitting of particulate filters.
Figure 3: General timetable of the project
Project planning Tender for filter purchase Filter fitting Measurement of filter effects Monitoring Street canyon measurement Reporting etc. April Quarter 1999 July Quarter 1999 October Quarter 1999 January Quarter 2000 April Quarter 2000 July Quarter 2000 October Quarter 2000 January Quarter 2001 April Quarter 2001 July Quarter 2001 October Quarter 2001 January Quarter 2002 The project was to cover operation with one or several different types of particulate filters on a large group of heavy-duty diesel vehicles. Odense Municipality was chosen as co-operation partner and it was agreed that particulate filters were to be retrofitted on the main part of the Municipality's heavy-duty diesel vehicles. Through political initiatives and agreements with private transport companies, Odense Municipality was to ensure that using filters became more widespread among carrier and distribution services, taxis and private buses.
The objective of the project has been to illustrate the environmental impacts as well as the oper-ational and financial conditions that arise when filter technology is used.
Odense Municipality and the Danish Road Safety and Transport Agency have jointly been respon-sible for the project. A steering group that also had the main financial responsibility has handled the superior management of the project. A working group has been in charge of the project's daily management and for involving external parties with specialised knowledge (Danish Technological Institute, the Danish National Environmental Research Institute (DMU) etc.). The composition of the steering group and the working group appears from enclosure 2.
The project has comprised the main activities described in the general timetable, figure 3. Below, the purchase of filters is described. A more detailed description of the course of the project appears in enclosure 1.
EU tender concerning filter purchase
The purchase of filters took place in the form of a public EU tender. As far as possible, the tender comprised the purchase of different types of filters. In addition to the filters, the delivery also included guiding and instructing the garage staff in connection with fitting and servicing of the filters.
The tender comprised filters adapted to specific vehicles. The filter suppliers had to guarantee that the filters would work for at least 2 years/200,000 km. Table 4 includes an overview of the
purchased and tested filters. Enclosure 3 gives a detailed overview of vehicles and filters.
Table 4: Overview of purchase of filters
In connection with tender
Filter type Make No. Odense Public Bus
Transportation
Parks and Roads Management Odense Waste Management Ltd. Eminox CRT 28 24 4 Johnson Matthey, CRT Volvo CRT 11 11 Engelhard, DPX Ferrita 35 32 3 Silentor Silentor 36 8 28
Additional testing of electrically regenerated filters
Filter type Make No. Odense Public Bus Transportation Parks and Roads Management Management Ltd. Odense Waste Energietechnik
Bremen, ELR
Energietechnik
Bremen, ELR 3 2 1
All filtertypes 113 75 9 29
Additional purchase for other transport companies Filter type Make No. Odense Technical College
"Odense Fragtcentral" (carrier service) Post Denmark Silentor Silentor 3 3 Engelhard, DPX Ferrita 3 3 Johnson Matthey, CRT Volvo CRT 2 2
In total, 121 filters were purchased for the project. In addition, deNOx systems were tested on 9 vehicles, cf. table 5.
Table 5: Additional testing of deNO
xsystems
Type Filter No. Odense Public Bus
Transportation
Ferrita EGR Ferrita 3 3
STT EGR Eminox CRT 3 3
3 Measurements of the effects of the project
In this chapter, the results of the measurements that were carried out as part of the project are described. The measurements partly concern the cleaning efficiency of the filters in a test stand, air quality measurements in the street canyon and the interview/questionnaires among citizens in Odense who regularly frequent the city centre as well as among local municipal employees who participated in the project.
3.1 Cleaning efficiency of the particulate filters
Emission measurements have been carried out on the tested filter types at Danish Technological Institute, Centre for Engine Technique, in Aarhus. The main objective of the emission measure-ments has been to follow the development of the filters in the course of time.
Some filters have been tested three times: when the project started in January 2000, after app. 1 year (December 2000) and after app. 2 years (December 2001). Other filters that were fitted subse-quently were tested once or twice. Besides, a measurement without filter has also been carried out on one bus in order to be able to evaluate the efficiency of the filter.
Method of measurement
The official method of measurement used to determine emissions from heavy-duty diesel vehicles is called 88/77/EEC with subsequent amendments. The engine is fitted in a test bench and measured in 13 stationary modes (13-mode test). The emission (g/s) and power (kW) measured at each mode is given a predetermined weight and summarised to produce a single value. (g/kWh).
Centre for Engine Technique has previously shown that a similar result can be obtained by mea-suring the vehicle on a chassis dynamometer in 5 different modes selected from the 13-mode test, but with different weight factors. This "5-mode test" has been used when measuring the emissions. The weight factors and loads are shown in table 6.
Table 6: 5-mode test
Mode no. Rpm Load % Weight %
1 Idling 0 25
3 max. torque 25 16
4 max. torque 50 16
6 max. torque 100 25
8 max. power 100 18
5-mode load and weight factors.
The following parameters were measured: NOx, NO2, HC, CO and particulates as well as exhaust gas temperature, back-pressure, engine power and a number of other parameters for conversion and control of emissions.
In the following, the results of the emission measurements carried out on the individual filter types are summed up and experience and conclusions from the measurements are emphasized. The tech-nically interested reader is referred to the four measurement reports.20
Johnson Matthey CRT
Emissions from two types of CRT filters (Volvo CRT and Eminox CRT) have been measured. In principle, the filters are identical and therefore they are treated collectively. A total of 6 measure-ments have been carried out on a chassis dynamometer with CRT filters.
As it appears from table 7, the CRT filters have given fluctuating and at times very high particulate results during emission measurements. (On one bus (no. 16) the filter was replaced and therefore two measurements are marked "1st time"). In addition, the results of the measurements are shown graphically in figure 4.
20The following measurement reports are in question:
1. Measurements of Emissions at project start, Danish Technological Institute, Centre for Engine Technique, May 2000.
2. Follow-up on the Danish Road Safety and Transport Agency's Large Scale Particulate Filter Demonstration Project in Odense, Danish Technological Institute, Centre for Engine Technique, January 2001.
3. Measurement of the "true" efficiency of a CRT filter, Danish Technological Institute, Centre for Engine Technique, May 2001.
4. Follow-up on the Danish Road Safety and Transport Agency's Large Scale Particulate Filter Demonstration Project in Odense – Emission measurements after 2 years of operation, Danish Technological Institute, Centre for Engine Technique, January 2002.
Table 7: Emission measurements CRT filters
FILTER Vehicle Vehicle info Measurement Particulateemission (g/kWh)
Filter "age" (Km in operation)
Volvo CRT - I Bus 16 Volvo B10 BLE 1999 (Euro 2) 1st Measurement 0.18 32,862
Volvo CRT - II Bus 16 Volvo B10 BLE 1999 (Euro 2) 1st Measurement 0.29 52,294
2nd Measurement 0.07 136,134 Eminox CRT Bus 139 Volvo B 10 M 1987 (Before requirements) 1st Measurement 0.13 6,471 2nd Measurement 0.09 75,097 3rd Measurement 0.26 141,012
After the first series of measurements in January 2000 the fluctuating measurement results and at times very high emission values were discussed in detail with the manufacturer Johnson Matthey, who gave an explanation of the phenomenon. In short, the explanation is that sulphate (formed of sulphur from fuel and lubricating oil) is stored in the washcoat21 in the pre-catalyst of the CRT filter at temperatures below app. 375ºC and it is emitted at higher temperatures. If a vehicle with a CRT filter is used in a driving profile with low exhaust temperatures, e.g. urban driving, then sulphur will be stored in the system. When the vehicle subsequently is tested on a chassis dynamometer under a heavy load, sulphate will be released which is measured as particulates.
Figure 4: Results of measurements on buses with CRT filters
Bus 16, 2nd time Bus 16, 1st time Bus 16, 1st time Bus 139, 3rd time Bus 139, 2nd time Bus139, 1st time 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000
Filter age [km in operation]
Particulates [g/kWh]
21 A ”washcoat” is a material that is applied to the catalyst substrate, partly to increase the active surface and partly to
Therefore, the Danish Road Safety and Transport Agency asked Danish Technological Institute to carry out a series of measurements on a CRT filter on an engine in a test bench to determine the "true" efficiency of a used CRT filter and to clarify how long it takes before the emission from the filter becomes stable. Finally, the measurement series was (if possible) to dis- or confirm the sulphur storage theory.
Through repeated measurements on a used CRT filter in a test bench, Danish Technological Institute has proved that the minimum particulate emission is in the order of 0.06 – 0.07 g/kWh. In addition, the measurements have shown that repeated measurements are required (in this specific case 3 measurements) to reach this low and stable value. Analyses of the composition of the
particulates have shown that they by and large consisted of sulphur compounds and water bound to the sulphur compounds.
Therefore, it is rendered probable that Johnson Matthey's explanation is true. The particulate emission is due to sulphur from the fuel and two separated processes are in question:
•
When the exhaust temperature is below app. 375°C, the washcoat stores sulphur in the pre-catalyst of the CRT filter. The sulphur is released when the exhaust temperature is above app. 375°C – and on its way through the exhaust system it is transformed to sulphate or other sulphur compounds. This results in high particulate emissions when the CRT filter is measured with high loads as in the 13-mode test. If the sulphur content in the fuel is reduced sulphur storage will still take place as there also is sulphur in the lubricating oil, but the process will take place slower. In connection with the 13-mode test where the filter is fully pre-conditioned (i.e. no sulphur is stored) the use of fuel with a low sulphur content will give lower particulate measurements.•
When the filter is in a state of equilibrium the sulphur from the fuel will to a certain degree be transformed to sulphate which is measured as particulates. That phenomenon, which moreover can be expected to appear on many types of catalytic particulate filters (including Engelhard's DPX), can be redressed by reducing the sulphur content in the fuel.The two above processes – of which the first very well could be the dominating – in total result in a particulate emission of 0.06-0.07 g/kWh for a used CRT filter. That is app. twice as much as what was stated by the manufacturer Johnson Matthey, who anticipates 0.03 g/kWh at 50 ppm sulphur in
the fuel.
More particulate mass has been deposited on the white measurement filters (at the bottom) used during testing of a CRT filter than on the dark measurement filters used during testing without a particulate filter – although it is not visible!
However, Danish Technological Institute estimates that the information from Johnson Matthey only takes into consideration the emission in a state of equilibrium and not sulphur storage/release, which is the reason for the deviation.
Figure 5: Particulate emission from a CRT filter
Johnson Matthey’s own information about the emission of particu-lates from a CRT filter as function of the sulphur content in the fuel (SAE 200-01-1875).
As can be seen, it is difficult to conclude anything in general about the CRT filter efficiency on particulates as the efficiency for the vehicle in question depends on whether (and how often) the exhaust temperature rises above app. 375°C – and on the frequency of high exhaust temperatures. In addition, the measurement of particulate emissions depends on which test cycle is used during measurements. However, it must be ascertained that the lowest particulate emission measured during the project – on a chassis dynamometer or on a test bench – is app. 0.06 – 0.07 g/kWh22.
The measurement of particulate size distribution in the range of 10 - 1,000 nm (the so-called ultra-fine particulates) shows that at high load it is sometimes possible to measure extremely large amounts of particulates in the range of 10-50 nm (nanoparticles), which presumably are condensed sulphate compounds23.
It should be noted that the CRT filters increase the NO2 share of NOx from around 5% to app. 15-20%. That is an unfortunate side-effect, as NO2 constitutes a health risk. Before the project started, the Danish Environmental Protection Agency evaluated that the increase in NO2 emission was undesirable but acceptable in consideration of the serious environmental problem the particulate filters solve. By the way, NO2 smells almost like chlorine and at the beginning of the Odense project there were a number of complaints of buses that "smelled like swimmingpool". On the other hand, CRT filters reduce the emission of CO and HC, which do not constitute serious environmen-tal problems for heavy-duty diesel vehicles, but HC (hydrocarbons) are the reason for what some people call the "smell of diesel".
22 In the European stationary test cycle.
Engelhard DPX
Emissions were measured on two Engelhard DPX filters that both were fitted on a bus (bus 5). Measurements were carried out three times. All three times, the particulate emission was between 0.03 - 0.08 g/kWh. The measurement results appear from table 8. In addition, the results are shown graphically in figure 6.
Table 8: Emission measurements on Engelhard DPX filter (Ferrita)
FILTER Vehicle Vehicle info Measurement Particulateemission (g/kWh)
Filter "age" (Km in operation)
Engelhard DPX - I Bus 5 1996 (Euro 2) Volvo B 10 L 1st Measurement 0.03 12,633
Engelhard DPX - I Bus 5 1996 (Euro 2) Volvo B 10 L 2nd Measurement 0.08 71,165 Engelhard DPX - II Bus 5 Volvo B 10 L
1996 (Euro 2) 1st Measurement 0.06 25,607 The DPX filter does not use any washcoat and therefore it does not have the sulphur storage and release problem, which the CRT filter has. As the filter is catalytically coated it will, however, continuously transform sulphur to sulphate which is measured as particulates as shown for the CRT filter in figure 5.
The DPX filter also converts a larger amount of NOx to NO2 – again from around 5% to app. 15-20%. The DPX filter also reduces the emission of CO and HC considerably.
Figure 6: Results from measurements on the bus with a DPX filter
1st time 1st time 2nd time 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000
Filter age [km in operation]
Particulate
s [g/k
Wh]
Silentor
Emissions were measured on a Silentor filter fitted on a bus (bus 8) on a chassis dynamometer. The filter was measured three times. The results of the measurements are shown in table 9.
Table 9: Emission measurements on Silentor filter
FILTER Vehicle Vehicle info Measurement Particulateemission (g/kWh)
Filter "age" (Km in operation)
Silentor Bus 8 Volvo B 10 L
1996 (Euro 2) 1st Measurement 0.04 0 Silentor Bus 8 Volvo B 10 L
1996 (Euro 2) 2nd Measurement 0.06 59,878 Silentor Bus 8 1996 (Euro 2) Volvo B 10 L 3rd Measurement 0.03 140,164
The results are also shown graphically in figure 7.
Figure 7: Results from measurements on the bus with a Silentor filter
3rd time No filter 1st time 2nd time 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0 20000 40000 60000 80000 100000 120000 140000 160000
Filter age [km in operation]
Particulate
s [g/k
Wh]
The filter was dismounted and repaired but not replaced. The bus was also measured without a filter immediately before fitting.
All three times, particulate emissions amounted to 0.03 - 0.06 g/kWh. The highest result was mea-sured in December 2000. Subsequently, a small hole was found in the particulate filter caused by the metal ring that keeps the filter in position (see photo). Since then, Silentor has changed the design and positioning of the metal ring on all filters in Odense in order to avoid the phenomenon.
On bus no. 8 the small hole was mended between second and third measurement and emissions again declined to the original level.
The outlet side of the Silentor filter on bus no. 8 with soot deposits that show the hole caused by the metal ring.
(Photo: Silentor).
The bus on which this Silentor filter was fitted was measured at the beginning of the project without particulate filter. At that time, particulate emissions amounted to 0.33 g/kWh.
The Silentor filter, in the version used in Odense, has no catalyst. On the one hand, that means that there are no problems with sulphur or NO2. On the other hand, the filter cannot reduce the CO and HC emissions that constitute minor problems in proportion to NO2 and particulates.
Energietechnik Bremen ELR
This filter was fitted on two smaller road-sweepers that are not suited for emission testing. Just before the project ended an additional filter was fitted on a larger refuse collection truck and it was tested on a chassis dynamometer immediately after fitting. Particulate emissions amounted to 0.05 g/kWh.
Table 10: Emission measurements on ELR filter
FILTER Vehicle Vehicle info Measurement Particulateemission (g/kWh)
Filter "age" (Km in operation)
ELR Truck 26 Mercedes Atego 2001 (Euro 3)
1st
Measurement 0.05 29
The ELR filter does not have a catalyst. As mentioned, that means that on the one hand there are no problems with sulphur and NO2. On the other hand, the filter cannot reduce the CO and HC
emissions that constitute minor problems in proportion to NO2 and particulates.
Particulate size distribution in the exhaust gas
As the fine and ultra-fine particulates do not contribute much to the measurements of weight a special measurement of particulate size distribution in the exhaust gas has been carried out24.
24 Measurement of particulate size distribution in the exhaust gas from public buses from Odense, Danish National
During the second measuring round in 2001 particulate size and number distributions were measured for all seven technologies. The objective of the test was to disclose the efficiency of the filters with regard to fine and ultra-fine particulates.
In figure 8 particulate size distribution is shown at mode 3 (app. 25% load) of the engine.
Figure 8: Particulate size distribution for all particulate filters (mode 3)
1E+00 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 1E+08 1E+09 1 10 Particle size [nm] 100 1000 Part ic le concent rat ion [ #/ cm³] No filter CRT Volvo CRT Volvo CRT+EGR DPX, jan DPX DPX+EGR Silentor, jan Silentor QuadCat
The X-axis shows the particulate size in nanometer. A nanometer (abbreviated nm) corresponds to a millionth millimetre (10 –9 metre). The Y-axis shows the number of particulates per cubic centimetre for each measured size
fraction of particulates. Please note that the X- and Y-axis are logarithmic.
Please note that the figure primarily can be used to show the particulate size distribution. Due to the difference in the vehicles on which the filters are fitted and the difference in emissions from the vehicles it is not possible to compare the efficiency of the filters. However, it is possible to see that the shape of the curve by and large is the same for all filters and that indicates that all filters reduce equally in connection with all particulate sizes. That means that the particulate filters also are efficient with regard to fine and ultra-fine particulates.
Figure 9: Particulate size distribution for all particulate filters (mode 6)
1E+00 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 1E+08 1E+09 1 10 Particle size [nm] 100 1000 Particle concentration [#/cm³ ] No filter CRT Volvo CRT Volvo CRT+EGR DPX, jan DPX DPX+EGR Silentor, jan Silentor QuadCatThe X-axis shows the particulate size distribution in nanometer. A nanometer (abbreviated nm) corresponds to a
millionth millimetre (10 –9 metre). The Y-axis shows the number of particulates per cubic centimetre for each
measured size fraction of particulates. Please note that the X- and Y-axis are logarithmic.
Figure 9 shows the result of the same measurement at app. 100% load25. It appears that one of the CRT filters during this load has considerably greater emission of particulates in the smallest size groups, which presumably is due to the creation of sulphur particulates, cf. previous description. In general, the measurements show that the filters have an effect with regard to particulates in all sizes. However, the measurements also show that under very heavy loads (and thus high tempera-tures) the CRT filters can emit a considerable amount of particulates in sizes between 10 and 100 nm.
Summary of measurement results concerning particulate filters in the project
In the light of the measurements it can be concluded that when they have been used for some time all filters have particulate emissions of 0.03 - 0.08 g/kWh.
Measurements of particulate size distribution show that the filters have an effect on particulates in all sizes. At the same time, the measurements also show that under very heavy loads (and thus high temperatures) the CRT filters emit a considerable amount of particulates in sizes between 10 and 100 nm (nanoparticles) – that presumably consist of condensed sulphate compounds.
In general, the filters have proved capable of functioning during the entire two-year project period. In connection with the CRT filters the measurements give scattered results that vary according to the stored amount of sulphur. Therefore, it is difficult to arrive at a conclusion about the
development of the filter in the course of time. The Silentor filter had low emissions during all three measurements and there seemed to be no changes in emissions over time. The measurements
connected with the Ferrita filter point to the filter becoming less efficient in the course of time. As only one measurement has been carried out on the ELR filter it is not possible to evaluate if the operation of the filter is reduced over time.
Testing of deNOx systems
As part of the project, three different deNOx systems were tested, all in combination with particulate filters:
• Ferrita EGR (with Engelhard DPX)
• Svensk Turbo Teknik EGR (with Johnson Matthey CRT) • Ceryx QuadCat (combined filter and deNOx).
Ferrita EGR
The Ferrita EGR system was tested once with a good result as the NOx emission was as low as 4.1 g/kWh, which corresponds to a NOx efficiency of app. 50%.
When NOx is reduced so much, the rise in NO2 caused by the DPX filter is eliminated by the EGR system and in total the NO2 emission is reduced compared with a bus without filter and EGR. Paradoxically, the efficiency of the Ferrita system is presumably too high as the DPX filter needs NO2 to burn the collected particulates and if there is not enough NO2 the filters are destroyed. After a number of filter damages, the Ferrita EGR systems have been abandoned in Odense; see the chapter on operational experience.
Svensk Turbo Teknik (STT) EGR
During the first test, STT's EGR system gave an NOx emission of 6.9 g/kWh, which corresponds to an efficiency of app. 25%.
STT subsequently explained that the system was calibrated for Volvo’s DH10A-210kW engine and therefore it did not have the optimum effect on the bus in Odense, which has a DH10A-180kW engine. Therefore, STT made a calibration for the 180kW engine and replaced the software in the three buses in Odense.
During the final test, the NOx emission was measured to 4.4 g/kWh, which corresponds to an efficiency of app. 50%, as STT had expected. STT states that they are aware of the problem with too high NO2 reduction and that the next version of the software will be calibrated to a somewhat lower efficiency in order to avoid filter damages.
STT’s EGR system has a filter on the inlet side of the EGR valve to protect the valve against impurities. Experience from Odense shows that this filter, which unfortunately had been fitted rather inaccessibly on the buses, has to be kept clean - otherwise the EGR system will not function.
STT states that on their present system the design and positioning of the filter have been changed in order to ease replacement.
Ceryx QuadCat
Ceryx QuadCat has been tested once but gave no reduction in the NOx emission, which was
measured to 9.4 g/kWh. No actual explanation has ever been given, but presumably the catalyst was damaged. Subsequently, the systems were dismounted due to operational problems.
Summary
In the light of the experience from Odense it can be concluded that there is a need for further development and testing before the deNOx systems for retrofitting which today are in the market can be said to work efficiently and reliably together with the current particulate filters. Develop-ments are ongoing and soon 2nd generation systems and new products can be expected to appear in the market.
3.2 Measurements in the street canyon
As part of the project, the Danish National Environmental Research Institute carried out pre- and post-measurements of the particulate content26 in the air in two streets in Odense. The objective was to evaluate if the use of particulate filters in the project could give a measured improvement of the air quality in the streets of the city.
One measuring point was Albanigade, which is one of the most trafficked streets in Odense with a considerable amount of heavy-duty diesel vehicles. The other point was Vestergade, which has less traffic, but a larger share of vehicles with a particulate filter drive in that street.
From the beginning it was obvious that in the short-term it could be difficult to obtain a measurable improvement as a limited number of vehicles have a filter fitted compared to the total number of vehicles.
Unfortunately, pre-measurements in Albanigade showed that the street could not be used as mea-suring point because the share of vehicles with a retrofitted particulate filter was too small to give a measurable result. It is true that a pronounced change in particulate emissions was ascertained during the period between pre-measurements in May 1999 and post-measurements in March/April 2000. However, that must be assigned to another reason, namely the reduced sulphur content in diesel fuel that was accomplished all over Denmark in July 1999.
Vestergade was chosen instead as alternative measuring point because the public buses (which all have particulate filters) dominate the motorised traffic in that street. Pre-measurements were carried out in November 1999 and post-measurements in March 2001. Measurements were carried out over a period of app. one month. As the pre- and post-measurements took place after 1 July 1999 the reduced sulphur content in diesel has had no influence on the results in Vestergade.
26 Particulate concentrations (number of particles per cubic centimetre) have been measured in the size interval of 6-700
nm. In addition, routine measurements have been carried out of NOx(NO+NO2) and CO, which the traffic also emits.
The measured particulate concentrations in the street were in average higher during post-measure-ments than during pre-measurepost-measure-ments. That is because the wind velocities were lower and resulted in less dilution. When corrections for wind velocity were made a comparison showed a small but not significant decline in the particulate concentration from the first measuring round in 1999 till the second measuring round in 2001.
A comparison between the concentration of the gases - carbon monoxide and nitrogen oxides - emitted from the traffic in Vestergade and at an air observation point on the roof of the town hall (city background) shows that the pollution level in Vestergade only has increased slightly compared to the city background and therefore the air quality in the street is dominated by emissions from other streets in the area. That explains why it has been difficult to show a considerable decline in the concentration of particulates in the street.
3.3 Interview with citizens who frequent the city centre
An interview was conducted among citizens who regularly frequent the city centre. The objective
