In a Technology Foundation STW project, Coen van Gulijk has developed a new concept for a robust soot filter for diesel engines. As well as filter stages, the filter has an open canal so as to exclude the danger of blockage and thus fire.
The new soot filter consists of series of perforated ceramic foams. The surface of the ceramic is impregnated with a catalyst on which the incoming soot particles are burnt and released as gases. Ash particles from impurities in the diesel, which enter the filter with the soot, remain in the pores of the ceramic foam plates. The ceramic foam can absorb a large quantity of ash before it risks becoming blocked and can therefore be used for a long time. The filter is highly suitable for removing soot from so-called heavy diesel oil. Heavy diesel oil is a heavy fuel containing many minerals and metals which produce ash. Existing filter systems would become blocked if used with heavy diesel oil.
As the filter is built from separate filter plates instead of a single block, it is almost indestructible. Even if all of the plates were to break, the filter function remains intact. An inbuilt open canal prevents the filter from becoming blocked. However, a disadvantage of the design is that it requires a lot of space. This means it is not suitable for cars but it can be used for ships, which often use heavy diesel oil, as equally fixed motors or trains.
The design of the new filter is partly based on studies concerning the form and size of soot particles. Diesel particles have a structure which consists of branched lumps of soot chains. Research has shown that due to this fractal structure, diesel particles are in fact up to ten times bigger than is indicated with measuring instruments. This was established with the aid of an electron microscope. Accordingly the behaviour of the soot particles relevant to the filtering is different than was thought; they diffuse more slowly but are more likely to stick to the filter.
Michel Philippens | alfa
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