Sintered metal filter - SMF®

The centrepiece of all HJS exhaust treatment systems is the sintered metal filter (SMF®), for which HJS was awarded the 2003 German Environment Prize. The SMF® is used to filter the exhaust gases emitted by a diesel engine – specifically to remove the ultra-fine respirable soot particles. The SMF® is adapted to the specific requirements of the particular application. The filter system can take two forms: an 'open system' with particulate reduction rates of up to 70 per cent and a 'closed system' with reduction rates of over 99 per cent.

The specific properties of steel as a material mean the filters are robust, extremely heat-resistant and offer a long service life. These characteristics provide the ideal basis for use in different diesel engines. The range of potential applications covers diesel-engined passenger cars, light to heavy goods vehicles, buses, construction machinery, agricultural machinery and industrial trucks, but also stationary equipment such as power generators. Thanks to the inherent characteristics of its concept, the innovative filter can be installed as original equipment (OE) in new vehicles and machines or retrofitted to vehicles and machines already in service.

Without a shadow of doubt, this environmental protection technology is making an outstanding contribution to cleaning up diesel engine emissions all around the globe. And it's still gaining ground. In view of the increasingly stringent pollution control and emissions regulations being passed and enforced, the future belongs to SMF® technology.

Operating principle

The hot exhaust gases containing the soot particles are fed into the filter housing where they then flow through the porous metal foil. The gaseous components flow through the microscopic pores of the filter material; the soot particles, including the ultra-fine particles, are trapped on the surface and deposited on the individual filter pockets.

The pores of this filter medium trap as good as all particulates present in the exhaust gases, right down to the detectability threshold. The filtered exhaust gases flow out from the rear side of the approximately 0.40 mm-thin filter medium. In this way, the soot particles in exhaust emissions are removed effectively and efficiently by the SMF®.

Technical features

The SMF® consists of a combination of rust-proof metal powder and an equally heat-resistant expanded metal. The thin and porous metal foil made by sintering is stamped, folded and welded to form a three-dimensional filter concept that exploits the geometrical freedoms to the full. The key component comprises dozens, indeed hundreds, of filter pockets connected in parallel, in order to obtain a filter surface area large enough to perform the job in hand. Its good thermal conductivity and metallic flexibility protect the SMF® against damage that could occur during thermal regeneration and enable it to store large amounts of soot without any noticeable increase in exhaust backpressure.

One particular result of HJS's development work worth highlighting is the degree of flexibility offered by the filter design. Both the structure and the size of the filter can very easily be adapted to the circumstances and the requirements (e.g. available installation space) of the respective application. The clogging phenomenon known from conventional ceramic filters with their honeycomb structure is made impossible by the pocket-type construction.

The capacity of the SMF® for holding non-regenerable particles, such as ash from engine-oil, is three to four times higher than that of conventional ceramic filter systems. This significantly increases the mileage before an HJS filter requires cleaning, including in the case of older vehicles and machines that suffer from particular high oil consumption. For whereas a ceramic filter requires cleaning after just a short period of operation, an SMF® is capable of several years of operation before maintenance is needed. Another advantage of the SMF®, which results from its special design and its use of sintered metal, is that it is far easier to clean. Whereas ceramic filter designs require complex cleaning equipment, the SMF® can be cleared of residues using a standard high-pressure cleaner.

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