These sealed-systems, used for upgrading, should actually, not be available, since these systems have no regeneration control-circuit. Nevertheless, there are individual manufacturers who offer such systems for vehicles with constant operating cycles. Typical, in this case, are, eg., the garbage trucks, which make only small demands on the engine while gathering the garbage, however, on the trip tö the disposal company, the demands on the engine are higher. Apparently, the risk in these cases, is calculable.
The above shown particle filter, is used in a double articulated bus, and is relatively easy to exchange. It is a sealed system without a direct connection to the engine-electronics. Apparently the bus engines, which are somewhat weaker than truck engines, are suitable, particularly in urban traffic, to deliver enough heat for the exhaust system. Because busses have a clearly higher ratio of net weight to gross weight, the weaker engine must always have sufficient thrust. In addition, there is an oxidisation catalyser in the front part of the casing, which also raises the exhaust gas temperature. One thing however, is clear, that at the moment (2005), even new vehicles delivered with this system, can only achieve the Euro-3-norm. Obviously the busses are still surviving on the by-products of the utility vehicle technology. Their manufacturing is also much more individual, which makes the finding of fundamental solutions that much more difficult. At least nowadays, for about 25% of the average inventory, an effective upgrade is possible. Why then, is the particle filter so easy to be removed and exchanged? Not so much because of the soot development, but more because of the engine-oil deposits. They can't be removed by free burning (regenerating). Actually, because of the whole problem of soot filtering, the engine-oil additives have become more and more important. Through the choice of low-ash engine-oils, the replacement intervals of the particle filters can be doubled.