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Increasing concern, about the health risk due to solid aerosols from engine combustion, has provoked more stringent imission limits, for soot particles in the range of pulmonary intrusion, at critical work-places (e.g. tunnel sites, see Table 1). Within the scope of the joint European project VERT, these emissions were characterized and their effective curtailment through exhaust gas after-treatment investigated. Diesel engines, irrespective of design and operating point, emit solid particulates in the range of 100 nm, at concentrations above 10 million particulates per cm3. Engine tests showed that a drastic curtailment of pulmonary intruding particulates seems not feasible by further development of the engine combustion, nor by reformulation of fuels, nor by deployment of oxidation catalytic converters. Particulate traps, however, can curtail the total solid particulate count, in the fine particulate range 15-500 nm, by more than two orders of magnitude.

Particulate traps are mechanical devices for trapping soot, ash and mineral particles, to curtail emissions from Diesel engines. The filtration effectiveness of traps can be defined, independent of the pertinent engine, as a function of the particle size, space velocity and operating temperature. This method of assessment lowers cost of certifying traps for large-scale retrofitting projects [1,2]. VERT [3] is a joint project of several European environmental and occupational health agencies. The project established a trap-verification protocol that adapts industrial filtration standards [4] to include the influence of soot burden and trap regeneration phenomena. Moreover, it verifies possible catalytic effects from coating substrates and deposited catalytic active material from engine wear or fuel/ lubricant additives.

Diesel engines are irreplaceable in tunnel construction. The particulate emissions of present day engines are so high that the imission limits valid since 1991 cannot be attained by ventilation alone. This problem had to be solved preparatory to the large tunnel projects in Switzerland, Austria and Germany. Several retro-fitting measures were investigated both in the laboratory and in field tests, within the scope of the Project VERT. Oxidation catalytic converters, exhaust gas recirculation, and the usage of special fuels cannot be recommended. Particulate trap deployment, in different systems, was mostly successful. Particular attention was focused on the dependable filtration of finest particulates < 200 nm. The VERT proved that exhaust gas after-treatment with particulate traps is feasible, cost effective and controllable in the field. Pertinent directives are in discussion.

There is growing concern about the risk potential of Diesel particulates. This prompted two Swiss R&D projects focused on the capabilities of different soot trap concepts for filtering finest particulates. Eight different filter media, some in numerous variants, were tested on four different Diesel engines. All traps attained their gravimetric target. However, there are noticeable performance differences for finest particulates at or smaller than 50 nm. Fiber deep filters seem to be noticeably better than other filter types. If the carcinogens are mainly the finest particulates, then this criterion may become important in future trap evaluation.

The acceleration response of a supercharged diesel engine passenger car, equipped with a particulate trap, is studied using a simulation program. The superchargers evaluated are the Comprex(R) pressure-wave supercharger as well as turbochargers with fixed and variable-geometry. The particulate trap is placed before the supercharger to promote the trap regeneration and to reduce the pumping gas-exchange work. Particulate traps currently used are such a large thermal sink that the acceleration response is unacceptable. There are promising innovations in progress to develop a particulate trap with less than a quarter of the present mass. The computations demonstrate that the acceleration response should then be acceptable.

Trapping diesel particulates is effective in reducing both the number and the mass of fine particulate emissions from diesel engines, but unless the accumulated soot can be burned out or regenerated periodically, the vehicle to which the trap is fitted will cease to function after a relatively short time. A programme of work with soot traps using a low treat rate iron-strontium organo-metallic fuel additive to assist and secure regeneration has been carried out. As part of this programme, an advanced specification diesel engine passenger car equipped with a diesel particulate filter (DPF), was operated on roads in the UK for approximately 18 months, during which time the vehicle covered over 50,000 km After completion of 50,000 km on roads, the vehicle was operated on a chassis dynamometer to increase the distance covered with a DPF more rapidly to a final total of 80,000 km.

Ceramic fibers, in a knitted structure, offer an elastic deep-filter medium having a very high specific surface. The robustness of this trap, and its invulnerability to thermo-shock, was demonstrated during a further year of development and tests. By using new manufacturing techniques, the filtration efficiency was further improved, pressure losses reduced, and the required volume diminished. New insight was obtained regarding the employment of the fiber medium for catalysis. The filter concept permits regeneration either electrically or by fuel-additives. The layout versatility facilitates deployment on vehicular and stationary engines, in the pre-turbo position, too.

The Comprex(R) is a pressure-wave supercharger (PWS) for passenger car diesel engines. It has many features which ideally suit it for the continually increasing demands on driveability, fuel economy and reduction of exhaust pollutants. To counter the disadvantages of the previously required belt drive, a free-running machine was developed. It is self driven by the kinetic energy of the exhaust gas; made possible by employing a rotor having reduced inertia. In addition to the well known Comprex features, this advanced development offers advantages such as rapid response, high efficiency, compactness and freedom in placement. The paper discusses the design of the free-running PWS, its construction, supercharging characteristics and preliminary experience.

With growing concern over greenhouse gases there is increasing emphasis on reducing CO2 emissions. Despite engine efficiency improvements plus increased dieselisation of the fleet, increasing vehicle numbers results in increasing CO2 emissions. To reverse this trend the fuel source must be changed to renewable fuels which are CO2 neutral. A common route towards this goal is to substitute diesel fuel with esterified seed oils, collectively known as Fatty Acid Methyl Esters. However a fundamental change to the fuel chemistry produces new challenges in ensuring compatibility between fuel and engine performance/durability. This paper discusses the global situation and shows how fuel additives can overcome the challenges presented by the use of biodiesel.

The atomisation characteristics of DI diesel engine fuel injection nozzles have been the subject of intensive study over the last decade. Much of this work has been related to clean, single hole nozzles spraying into quiescent air, at either ambient conditions or elevated pressures and temperatures. Experience shows that fuel injector nozzles may foul very rapidly in field service, and that this might have a significant effect on the performance of the engine particularly with regard to emissions. The build up of material on the injector nozzle can be controlled by the addition of suitable fuel additives. This paper describes test procedures developed to assess deposit build up and to indicate the efficacy of keep clean additives. The paper then goes on to describe high speed photographic techniques for studying the fuel spray characteristics of clean and fouled injectors in a firing engine.

New Diesel exhaust gas aftertreatment systems, with combined DPF*) and deNOx (mostly SCR) systems represent a very important step towards zero emission Diesel fleet. These combined systems are already offered today by several suppliers for retrofitting of HD vehicles. Reliable quality standards for those quite complex systems are urgently needed to enable decisions of several authorities. The present report informs about the international network project VERT *) dePN (de-activation, de-contamination, disposal of particles and NOx), which was started in Nov. 2006 with the objective to introduce the SCR-, or combined DPF+SCR-systems in the VERT verification procedure. Examples of results for some of the investigated systems are given. These investigations included parameters, which are important for the VERT quality testing: besides the regulated gaseous emissions several unregulated components such as NH3, NO2 and N2O were measured.

The fuel injection equipment (FIE) has always been paramount to the performance of the Diesel engine. Increasingly stringent emissions regulations have dictated that the FIE becomes more precise and sophisticated. The latest generation FIE is therefore less tolerant to deposit formation than its less finely engineered predecessors. However, the latest emissions regulations make it increasingly difficult for engine manufacturers to comply without the use of exhaust aftertreatment. This aftertreatment often relies on catalytic processes that can be impaired by non-CHON (carbon, hydrogen, oxygen and nitrogen) components within the fuel. Fuel producers have therefore also been obliged to make major changes to try and ensure that with the latest technology engines and aftertreatment systems the fuel is still fit for purpose. However, there has recently been a significant increase in the incidence of reported problems due to deposit build-up within vehicle fuel systems.

Diesel fuel distilled from crude oil should contain no greater than trace amounts of sodium. However, fuel specifications do not include sodium; there is a limit of five parts per million for the amount of sodium plus potassium in fatty acid methyl esters (FAME) used as biodiesel. Sodium compounds are often used as the catalyst for the esterification process for producing FAME and sodium hydroxide is now commonly used in the refining process to produce ultra-low sulphur diesel (ULSD) fuel from crude oil. Good housekeeping should ensure that sodium is not present in the finished fuel. A finished fuel should not only be free of sodium but should also contain a diesel fuel additive package to ensures the fuel meets the quality standards introduced to provide reliable operation, along with the longevity of the fuel supply infrastructure and the diesel engines that ultimately burn this fuel.

Most particulate traps efficiently retain soot of diesel engine exhaust but the potential hazard to form secondary emissions has to be controlled. The Diesel Particle Filter (DPF) regeneration is mainly supported by metal additives or metallic coatings. Certain noble or transition metals can support the formation of toxic secondary emissions such as Dioxins, Polycyclic Aromatic Hydrocarbons (PAH), Nitro-PAH or other volatile components. Furthermore, particulate trap associated with additive metals can penetrate through the filter system or coating metals can be released from coated systems. The VERT test procedure was especially developed to assess the potential risks of a formation of secondary pollutants in the trap. The present study gives an overview to the VERT test procedure. Aspects of suitability of different fuel additives and coating metals will be discussed and examples of trap and additive induced formation of toxic secondary emissions will be presented.

A diesel particulate filter (DPF) is a crucial weapon in the fight to control the downsides traditionally associated with diesel engined vehicles. The DPF not only produces the benefits required from an environmental standpoint but also has the consumer benefit of eliminating the visible black smoke associated with diesel engines. Thus DPFs have now become a reality, both for series production vehicles and as a retrofit application. Inevitably there are a number of alternative types of DPF and alternative techniques are used for ensuring they continue to function in an acceptable manner. Due to the complexity of the diesel combustion process and the emissions produced it is only to be expected that a device intended primarily to control one parameter would have some effect on other parameters. This paper looks at some different DPF technologies and how they effect emissions, with the emphasis on particulate emissions and the speciation of oxides of nitrogen.

In an attempt to improve ambient air quality, retrofit programmes have been encouraged; targeting reductions in PM emissions by means of diesel particulate filters (DPFs). However depending on the DPF design and operating conditions increased nitrogen dioxide (NO2) emissions have been observed, which is causing concern. Previous work showed that retrofitting a DPF system employing a fuel borne catalyst (FBC) to facilitate regeneration, reduced NO2 emissions. This paper outlines the investigation of a base metal coated DPF to enhance the reduction of NO2. Such a DPF system has been fitted to older technology buses and has demonstrated reliable field performance.

Transport Refrigeration Units (TRU) powered by small diesel engines emit high PM and cause locally high PM levels. The concomitant health risks spurred efforts to devise a cost-effective curtailment of these emissions. Diesel particulate filters (DPF) of ceramic honeycomb construction very efficiently trap PM emissions, even ultrafines in the lung penetrating size range of below 300 nm. A fuel borne catalyst (FBC) can facilitate trap regeneration, by lowering the exhaust temperature requirements, but cannot alone guarantee reliable regeneration under all operating conditions of the TRU. A Swiss development team together with industrial partners therefore developed a fully automatic active regeneration system for the California Air Resources Board.

Metallic substances, usually added to fuel as organic compounds are, as fuel additives proven to curtail particulate emissions from diesel engines and, as fuel borne catalysts (FBC), to promote regeneration of particle traps. During combustion, these substances form catalytic metal oxides and exit the combustion chamber as ultra-fine solid clusters in the mobility diameter range of 5-30 nm. Particles of this size and composition have a health impact and should not enter the respiratory air. FBC should therefore only be used together with particle traps, which can efficiently collect these metal oxide particles at all operating conditions. This and other requirements are stipulated in the VERT suitability tests for particle trap systems. The approval procedure includes a particle size-specific analysis to verify trap penetration in trace quantities.

Diesel particulate filters (DPF), in conjunction with fuel borne catalysts (FBC) to facilitate regeneration, are now an accepted technology for passenger car application. Retrofitting of such systems has demonstrated the possibility of applying this technology to heavy-duty vehicles. To demonstrate the efficacy of DPF/FBC systems and to assess their affect on engine durability and economy, five heavy-duty trucks were fitted with DPF/FBC systems. After the completion of over ¼ million kms four trucks underwent a full engine strip-down and rating. This paper briefly reviews the installation of the systems and their effect on the regulated emissions, present details of the mileage accumulation and of the engine strip-downs. The conclusions drawn are that after a ¼ million km of use with the DPF/FBC systems the trucks had not suffered any abnormal deterioration and in fact there was some indication of reduced wear on the engine.

Four of these Particulate Reduction Systems (PMS) were tested on a passenger car and one of them on a HDV. Expectation of the research team was that they would reach at least a PM-reduction of 30% under all realistic operating conditions. The standard German filter test procedure for PMS was performed but moreover, the response to various operating conditions was tested including worst case situations. Besides the legislated CO, NOx and PM exhaust-gas emissions, also the particle count and NO2 were measured. The best filtration efficiency with one PMS was indeed 63%. However, under critical but realistic conditions filtration of 3 of 4 PMS was measured substantially lower than the expected 30 %, depending on operating conditions and prior history, and could even completely fail. Scatter between repeated cycles was very large and results were not reproducible. Even worse, with all 4 PMS deposited soot, stored in these systems during light load operation was intermittently blown-off.