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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.

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.

Fuel additives are emitted in the particulate phase, either incorporated in soot particles or forming new ultrafine particles. Formation of new particles occurs as soon as the amount of additive exceeds a certain limit, depending on the soot emission factor. This has been shown by measuring particle size distributions as function of additive concentration and engine power using SMPS analysis. In addition a gravimetric and coulometric analysis has been performed. Finally, filter samples were analyzed by ion coupled plasma mass spectroscopy to investigate residua of the additive in the exhaust. If the additive concentration is increased beyond the onset of particle formation, no further decrease in soot emissions is observed. From this point of view, an additive dosage just at the limit of particle formation seems to be optimal.

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.

NanoMet is a new technique for on-line characterization of nanoparticle size and composition and their diffusion behavior. NanoMet consists of a pocket size diluter with tunable dilution ratio, a sampling interface for high concentration measurements and two on-line sensors. Simultaneous operation of the two sensors yields both the active surface (corona discharge diffusion charging sensor, DC) and the active surface times material coefficient (photoelectric aerosol sensor, PAS). Division of the readings provides the material coefficient which turns out to be characteristic of the particle source. Thus, information on source and toxicity of the aerosol is obtained. Thanks to the diluter and the sensitivity of the sensors the measurable concentration range stretches from (vehicle) raw emissions to ambient air / occupational exposure measurements. A particle sizing unit with a diffusion battery and a centrifuge is under development. NanoMet measures particles in-situ, i.e. as aerosol.

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.

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.

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.