Right now the manufacturers are having a hard time fulfilling the Euro-6 regulation. Those who don't change their engines between now and next year, have to fulfil the requirements right now. It is noticeable, that the Diesel engine has not only drawn even with the petrol engine as far as the NO_X is concerned, the emission is even lower. Motorcycles by the way, are to be bound to the same values as motor cars, indeed, only after 2020. Truck Diesels are tested using different values, in the meantime however, they must all have a closed in particle filter system or even better, SRC-systems.

As far as motor cars are concerned, the limits seem to lie e.g., between the VW-Golf and the Passat, or the BMW with- or without all-wheel drive. If the values are made even more strict, the limits will become lower. There are also however, hybrid forms with both SRC-systems and storage catalysers. By the way, the videos below show clearly the difficulties in the truck sector.

A storage catalyser swings between two states: either, and this is mostly the case, through its upstream oxidation catalyser and it's precious metal, converts NO into NO₂ and stores it in an alkaline earth metal, e.g., Barium (lean combustion), or the alkaline earth metal is induced, through the presence of gases like HC, CO and H₂, to release the NO₂ again (rich combustion). In this case, catalytically, the NO₂ once again becomes N₂.

A particularly difficult phase during the warming up period is not present in the reduction of NO_X, because it is found more when the engine is particularly warm. However, the temperature, e.g., in truck engines during the partial load range, may not rise too much, because then the catalytic effect of the precious metals decreases and the thus developing NO can no longer be treated according to the above plan. Thus, high combustion temperatures are actually an advantage, a greater distance from the engine and an additional cooling e.g., through the airstream, can be useful for the particle filter.

Sulphur has long since been considered troublesome for the intake of NO_X and also for the regeneration. For the latter, high temperatures are required. If over a longer period, these are not reached, then the storage catalyser is clogged with sulphur and no longer suitable for the intake of NO_X. The problem must now be solved somewhere between changing the sulphur content in the fuel and/or special regeneration.