The particle filter is used primarily in the upgrading of diesel vehicles. Whereby, an additional mounting place must be found for it because it doesn't replace any other part of the exhaust system. In Germany, a certain tax relief is planned for it's installation. This tax relief is rightly, lower than for new vehicles standardly equipped with filters, because when upgrading, one can only assume a regeneration of 30- to 50%. For the country family doctor, who drives roughly 5 kilometers every half an hour and never uses the car for going on holiday, the tax relief could be about zero.
First of all, it must be mentioned, that with an open system, as opposed to a sealed system, the exhaust gas must not pass through a filter. It has channels which are open on both sides, which through certain cavities or deflecting metal points, the particles contained (particularly the small ones!) in the exhaust gas are guided to the fleece above and below the channels, where they should be trapped. At least, the particle filter cannot become clogged. There is however, no guarantee, that no particles have escaped, along with the exhaust gases, into the environment. This is even more valid, as the question of regeneration is left completely to chance, or, as the case may be, the driving conditions. As a rule, the particles deposited in the fleece should be burnt out every 500 - 1000 km. This is however, only possible under certain driving conditions, eg., during motorway driving with a heavy load. If a vehicle is used almost exlusively in urban traffic with exhaust gas temperatures of under 200°C, not only are there more particles, also no regeneration takes place. It is said that, in a vehicle with a sealed filter system, the exhaust gases are cleaner than the air that was taken in. This is certainly not the case with the open filter system. However, with an annual diesel vehicle market-share of 44% in Germany, and 48% in Europe, this solution is a lot better than nothing at all.