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1 Small off-road 4-stroke SI-engines have extraordinarily high pollutant emissions. These must be curtailed to comply with the new Swiss clean air act LRV 98. The Swiss environmental protection agency (BUWAL) investigated the state of the technology. The aim was a cleaner agricultural walk behind mower with a 10kW 4-stroke SI-engine. Two engine designs were compared: side-valve and OHV. A commercially available 3-way catalytic converter system substantially curtailed emissions: In the ISO 8178 G test-cycle-average, HC was minimized to 8% and CO to 5% of raw emissions. At part load points, the residual emission was < 1%. Simultaneously, fuel consumption improved 10%. Using a special gasoline (Swiss standard SN 181 163), the aromatic hydrocarbons were curtailed, e.g. Benzene < 1%, and fuel consumption further improved. Those results were confirmed in field tests. The engine is approved for retrofitting.

By means of catalysts, either coatings or fuel-borne, the temperature level for triggering the combustion of soot stored in particulate traps can be lowered from 600°C to 300°C, in case of CRT even to 250°C; but even that may fail, if in dense traffic application of a city-bus only 150 - 200°C are attained - similar situations of low load duty cycles exist in most other applications too. Mere passive regeneration may then not be sufficient, active support is needed. This paper presents an “active” method applicable to any Diesel engine to increase the exhaust temperature whenever required: load of Diesel engines is controlled by the fuel flow only; consequently, excess of air above stochiometric requirement is increasing from λ = 1.5 to λ = 8 with decreasing load, which is in fact the principal cause of the low temperature at light loads.

Based on the emission inventory Fig. 1, the Swiss 1998 Ordinance on Air Pollution Control (OAPC) mandates curtailment of carcinogenic diesel particle emissions at type B construction sites [1]. Moreover, particle traps are compulsory at underground workplaces [2]. In compliance, more than 6,000 Diesel engines were retrofitted with various particle trap systems. Many traps surpassed 99% filtration efficiency and secondary emissions were mostly prevented. However, trap failure due to mechanical and thermal damage was initially rather high at about 10%. By the year 2000 the failure rate was halved to about 6%. Thanks to focussed improvements, the year 2003 statistics show yearly failures of “only” about 2%. The Swiss target is to retrofit 15,000 construction machines with traps, fully compliant with environmental directives, having 5,000 operating hours durability and failure rates below 1%. Traps must pass the VERT suitability test before deployment.

Vegetable oils blended to Diesel fuel are becoming popular. Economic, ecological and even political reasons are cited to decrease dependence on mineral oil and improve CO2 balance. The chemical composition of these bio fuels is different from mineral fuel, having less carbon and much more oxygen. Hence, internal combustion of Diesel + RME (Rapeseed Methyl Ester) blends was tested with particular focus on nanoparticle emissions, particle filtration characteristics and PAH-emissions. Fuel economy and emissions of bus engines were investigated in traffic, on a test-rig during standardized cycles, and on the chassis dynamometer. Fuel compositions were varied from standard EN 590 Diesel with <50 ppm sulfur to RME blends of 15, 30, and 50%. Also 100 % RME was tested on the test-rig. Emissions were compared with and without CRT traps. The PAH profiles of PM were determined. Particles were counted and analyzed for size, surface, and composition, using SMPS, PAS, DC and Coulometry.

Ceramic fibers with high specific surface area and adequate high-temperature strength are commercially available for filtration of diesel particulates and in-situ hot regeneration. The manufacturing of a deep bed filtration medium, using such brittle fibers, became possible after a special knitting technique was developed which forms the loops with minimum friction and pretension. Within this structure, the fibers are very little constrained and expose their active surface almost completely. Hence, high filtration efficiencies in the range of 95% could be demonstrated with favorable back-pressure characteristics. Blow-off phenomena were never observed. Endurance testing on engines, with full-flow burner regeneration, proved the high robustness to mechanical and thermo-mechanical loading. This is one of the particular advantages of the new concept.

Microfibers with high specific micro-surface can be knitted into two-dimensional structures with large internal porosity. Catalytically active metals can be deposited on the fibers with high dispersion by wet-impregnation, sol-gel or CVD, respectively. These microfiber knits may be used for exhaust gas treatment systems with a triple function: particle filtration, gas conversion and muffling. The total oxidation of propane on Pd and Pt coated fibers has been studied as a test reaction. Conversion temperature could be remarkably reduced compared to cellular structures. For a bimetallic (Pt-Pd) coating, the activity is independent of humidity or oxygen concentration. Thus a catalytic converter based on micro-fiber knits appears feasible. Its high mass and heat transfer prevent hot spots. And it functions as submicron filter for combustion aerosols. Integrated electric heating can also be provided in case of low gas temperatures. First tests on engines show promising results.

Swiss EPA and European occupational health authorities have sponsored the development of a new sampling and measuring system designed to fulfil future requirements of differentiated particle analysis in field use and for certification purposes. The system suppresses the formation of condensates by applying hot dilution. Solid carbonaceous particles are distinguished from ash particles by means of two different sensors. Particles are size classified by their mobility; their active surface is measured. The measurable size ranges from less than 10 nm to 1 micrometer. The detection limit corresponds to a mass concentration of elemental carbon (EC) of about 0.1 μg/m3. The time resolution of 1 second is suitable for on-line analysis of particulate emission during all types of transient cycles, even no-load acceleration. The system includes a compact diluter with tunable dilution factor from 30 to 3000.

Diesel particle filters (DPFs) efficiently eliminate soot, fuel-, and oil-ash emissions of diesel engines, but little data are available with respect to long term aging or deterioration effects of DPFs under real world operating conditions. Aging of wash coat- and catalyst-materials, catalyst poisoning, ash sintering, adsorption and long lasting storage of semi- or non-volatile substances can take place, which over time may influence filtration and conversion properties of DPFs. Herein we report to what extent DPF aging may affect particle filtration characteristics. We compared particle number concentrations (PN), and particle mass (PM) emissions after a 2000 operating hours endurance test (VFT2). Such a controlled field test is required by VERT verification procedures, which lately were published as a national standard (SNR 277205).

High levels of particulate emissions from Diesel engines, in tunnel construction sites, force the aftertreatment of exhaust gases with particulate traps. Sub-micron particulates are suspected to be carcinogenic. Hence, the size distribution of particulates was compared for different particulate trap systems. The two extreme types are the ceramic monolith surface filter and the typical deep-bed filter of knitted fiber. These two types have distinctly different properties. The gravimetric evaluation of both systems show comparable efficiencies around 90%. If, instead, the particle count is evaluated: the efficiency of the surface filter drops below 70%, whereas that of the deep-bed filter increases. The spectral analysis of distinct solid particulates shows that the efficiency of the surface filter deteriorates for particles smaller than 100 nm. The toxicological consequences are disquieting.

1 Switzerland is enforcing the use of particulate traps for offroad applications like construction as well as for occupational health applications like tunneling. This decision is based on the results of the VERT-project (1994-1999), which included basic aerosol research, bench screening and field testing of promising solutions as well as the development of implementation tools like trap specification, certification scheems and field control measures. On the other hand there is no corresponding regulation for city-buses yet although PM 10 is about 2× above limit in most Swiss cities. Public pressure however is growing and city transport authorities have reacted by retrofitting Diesel city-buses instead of waiting for cleaner engine technology or CNG-conversions. The favored trap system with about 200 retrofits so far is the CRT.

1 Occupational Health Authorities in Germany and Switzerland require the use of particulate traps (PT) on construction machines used in underground and in tunneling since 1994. Swiss EPA has extended this requirement 1998 to all construction sites which are in or close to cities. During the VERT*-project, [1, 2, 3, 4, 5]**, traps systems were evaluated for this purpose and only those providing efficiencies over 95% for ultrafine particles < 200 nm have received official recommendation. 10 trap-systems are very popular now for these application, most of them for retrofitting existing engines. Efficiency data will be given as well as experience during a 2-years authority-controlled field test. LIEBHERR, producing their own Diesel engines in Switzerland and construction machines in Germany is the first company worldwide supplying particulate traps as OEM-feature (Original Equipment Manufacturing) on customers request.

1 The VERT project aimed at curtailing the construction site diesel emissions of ultra-fine particles to 1% of the raw emissions. Thus, compliance with occupational health legislation should be achieved. Particulate traps have attained this target. In contrast, engine tuning, reformulated fuels and oxidation catalytic converters are almost ineffective. This paper reports on the concluding project stage in which 10 traps were field tested during 2 years. Subsequent detailed measurements confirmed the excellent results: > 99% filtration rate was achieved in the nano-particulate range. The PAH, too, were very efficiently eliminated. Trap deployment becomes therefore imperative to fulfill VERT-targets.

Knitted fiber particulate traps facilitate deep-bed structures. These have excellent filtration properties, particularly for ultra-fine particulates. They are also suitable as substrate for catalytic processes. The two characteristics are: high total surface area of the filaments, and good mass transfer. These are prerequisites for intense catalytic activity. The deposited soot is uniformly distributed. Therefore, temperature peaks are avoided during regeneration. The tested coatings lower the regeneration temperature by about 200°C to burn-off temperatures below 350°C. Further improvements seem attainable. Thus, a purely passive regeneration appears feasible for most applications. The system is autonomous and cost effective. However, in extreme low load situations, e.g. city bus services, the necessary exhaust temperatures are not attained. Hence, burners or electrical heating is necessary for trap regeneration.

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.

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.

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.

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.

Fine pored hot gas traps have filtration efficiencies exceeding 99% of the solid particles in the diesel exhaust gas. There is a favorable trend to deploy this technology ex-factory and retrofitting on-road and off-road engines. The trap system however functions as a chemical reactor. The filter has a large effective area and the engine exhaust gas has plenty of reactants, which can promote undesirable chemical reactions that release toxic secondary emissions. These effects may be amplified when traps have catalytic influence, e.g. due to surface coatings or fuel-borne catalysts. The VERT suitability tests for particle trap systems therefore include a detailed test procedure for verifying the presence of over 200 toxic substances. These include PAH, nitro-PAH, chlorinated dioxins, furans as well as metals. The paper describes test procedures, test reporting, sample extraction and analysis.

Transient conditions are typically encountered in passenger car engine operation, and they have a major impact on the control system driver/vehicle, as well as on emissions. While turbocharging generally deteriorates the transient behavior of a vehicle engine, supercharging with the pressure wave machine Comprex retains characteristics which are nearly equal to those of a naturally aspirated engine. The elements involved in the transient process are discussed, and their effect on road performance and emissions is shown on the basis of experimentally obtained data.