Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Foam Filter for Diesel Emission Reduction

The final STYFF-DEXA project Diesel particulate filter prototype has been manufactured to assess the simulation capability of the software tool and to demonstrate the potential of ceramic foams based filters. The prototype has been designed to minimize the pressure drop without jeopardizing the filtration efficiency performance using a novel design approach: the slits concept and the drilled foams concept. Using the slits concept design the outlet filtering area is increased, not affecting the overall filter volume: by means of lateral slits along the foam stacks a considerable pressure drop decrease is achieved. The other innovative design concept tested at the moment only at laboratory scale, is the drilled foams concept; the filtering area is thus maximised with no increase of the filter volume by inserting a variable number of drilled foams at the inlet side of the filter; this results in a pressure drop reduction without compromising the filtration efficiency. Lab-scale test have been carried out to assess the filtration efficiency of a single foams stack with four drilled foams at the inlet and the preliminary results show an impressive pressure drop decrease as well as an improved or at least equal filtration efficiency capability especially at low flow rates.

The final prototype manufacturing has been meant to account the flexibility requirements for a Diesel particulate filter using seven modular foam stacks. Every stack can hold up to 15 ceramic foams with an external diameter of 48 mm and a thickness of 15 mm; the geometry of the developed device implies the possibility of particulate uneven distribution in the different foam stacks: in particular it appears possible to have a preferential flow path in the central foam stack directly exposed to the inlet gas flow. To discern this issue, fluid-dynamic simulation has been performed and experimental verified: the results show a very good flow distribution in the different foam stacks as designed.

In terms of filtration efficiency, soot accumulation and regeneration capabilities, the STYFF-DEXA project prototype has been tested on a 1.9 l, 16 valves, common rail Diesel, EuroIV compliant engine. The filtration efficiency results are quite encouraging both in particulate mass and particulate number/size; the pressure drop in real conditions is still slightly high compared to a standard wall-flow filter, especially at high engine speed and torque, anyhow the possibility to introduce the drilled foams concept even in the full scale prototype could reduce significantly the pressure drop level. The most impressive results achieved are indeed from the point of view of filter regeneration behaviour; the performed soot accumulation up to 8 g/l and regeneration tests show a very good regeneration rate although the used foams were bare foams. In conclusion, for future real application a performances improvement of the foams based filter will be required, anyway, further filter design enhancement and the introduction-catalysed foams could improve significantly the achieved overall foams filter performances.

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