Coated sintered metal trap

Result: to establish the feasibility of coating SMFs (sintered metal filters). To establish that it is possible to apply a coating to a sintered metal filter that is stable with respect to the chemical properties of the coating. There is potential for use in all heavy-duty vehicles should future legislation require this in Europe and in the US. DPFs (Diesel Particulate Filters) have already been fitted to Diesel passenger cars and there is also thus potential for this technology to be applied in light-duty applications. The number of applications to vehicles is well in excess of 1 million. The result is innovative, as the substrate used has not been applied previously. This result has been achieved, meeting the deliverable "Basis coating material" and contributing toward the milestone "report for a basis method to coat sintered metal filter" due in month 18.

According to DC-pre-investigations with small samples PUREM set-up a cleaning test device for liquid cleaning of the filters. Three full-size systems were cleaned with an efficiency of about 80% (based on gravimetrical measurements). Liquid ash cleaning has shown only minor impacts on backpressure performance and catalytic coating. This result is precondition for a successful product.

The uncoated filter was ash loaded by 25g/l by a rapid ash procedure. Diesel fuel, doped by 5% engine oil, was used for generating ash. During the ash loading procedure the filter was periodically thermal regenerated. The ash loaded in the filter showed an effect on the differential pressure. It was found as a very mobile fine-grained powder. The ash can be easily removed from the filter surface. The ratio of the ash blocked filter surface was visually analysed. About 30% of the surface was clogged by ash deposits. The mobile structure is obviously affected by the temperatures during the thermal regeneration process during the ash loading cycles.

This project consists in a basic research of the reactivity of Diesel soot deposited on a metallic filter. Main results lie in the scientific field. They consist in the understanding of the reaction mechanism of Diesel soot with exhaust gases, in particular nitrogen dioxide and oxygen. The promoting effect of water vapour is also considered. The effect of the presence of an oxidizing catalyst is also studied in terms of reaction mechanism and in terms of kinetics of soot combustion. A detailed kinetic model, which encompasses the effect of these exhaust gas components, has been set-up and could be validated for real Diesel soot deposit on metallic filter. The developed kinetical model applies for thin layer of Diesel soot deposited on a metallic filter. The outputs of this project may be used for prediction and validation of the regeneration strategy of soot traps. In particular, the effect of catalytically active coating of the filter may be assessed for a higher efficiency of the CRT process. The kinetical data provided by this study are required for a complete modelisation of the soot trap regeneration. The effect of a Pt-based catalyst on the soot oxidation rate was also investigated in the temperature 300-400°C. A substantial increase of the oxidation rate is obtained for Pt supported on ferrierite. Also, Ru-based catalysts were investigated. They are looking quite promising as a substitute for Pt. Moreover, the activity of Ru catalysts in the NO2-O2-NO system for carbon oxidation shows some interesting features, which would need further investigation.

The filtration efficiency was evaluated in ESC cycle and 'worst-case' filtration conditions. All filters provided a filtration efficiency of 90% or better. The uncoated filter was ash loaded by 25g/l ash and the filtration efficiency test was repeated. The ash load did not affect the filtration efficiency; the values were about 95% in ESC cycle and under worst-case conditions.

An easy procedure was defined for rapid ash accumulation with the main objective to save expensive time on engine test-benches for investigations on ashes for R&D based on a dosage of additive in fuel and motor oil. A time-lapse factor of about 5 can be reached by adding ash-forming substances to fuel and oil compared to normal operation. The procedure is usable for small filters but not for large filters because it would need weeks to fill a filter with ashes. To have a more effective ash accumulation method PUREM has purchased an ash generator outside the COMET-project. This ash generator is located between engine and filter and reaches a time-lapse factor of 30 - 100.

PUREM has provided different standard and new material variants to the project for investigation of material- and filtration properties and aspects of processing and catalytic coating. In a first phase of the project on material was selected, what met at best the requirements of mechanical properties, weight, size, coatability and thermal resistance to soot combustion. Plate thickness was optimised and held constant during the course of the project. In a next phase PUREM has produced new material variants to increase porosity/pore diameter/permeability to the requirements of catalytic coating. PUREM has investigated the interaction filter material/coating basically in terms of permeability decrease by coating for relevant combinations filter material/coating (without soot) and influence of washcoat loading on pressure drop behaviour with soot loading. The result is shown as pressure drop increase vs. soot loading with increased washcoat loading applied (for specific test conditions on filter sheets). Some materials show slight advantages for higher washcoat loading even if there is a higher pressure-drop without soot. The interaction filter material/coating in respect of oxidation resistance is shown as the effect of washcoat type and washcoat loading on mass increase after 10 h at 1000°C under corrosive atmosphere. The oxidation resistance increases when the metal filter is coated with a proper ceramic washcoat. In combination with a favourable permeability characteristic ferrierite coatings with higher washcoat loading levels look very promising. In terms of design PUREM has developed a new filter design that will particularly be suited for catalytic coated filter units. Further on this design has advantages in size resp. requirements of construction volume. Several filter systems with this design were delivered to AVL and Uni Kaiserslautern for bench tests and used for ash cleaning investigations. PUREM plans to bring such filter systems to the market for series applications starting with EPA 2010 Heavy Duty to meet future emission levels. The market volume amounts about 300000 vehicles.

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