The exhaust gas aftertreatment of spark injection engines has been incorrectly described as having reached the end of its development since existing technologies had already made it possible to build cars that cleaned the environment. Since modern standard catalysts are already able to achieve the required level of efficiency, the aim of “turbulent” substrates is to reduce catalyst and system costs. This must primarily include the functions relating to lambda control and catalyst diagnostics.

A modern standard catalyst system usually consists of two substrates that are arranged behind each other inside a jacket. In order to improve cold starts the first substrate has a smaller diameter than the second; this is known as a cascade system. The gap between the two substrates is generally used to accommodate a second lambda sensor. The gap also causes flow mixing and flow equalisation.

In these widely used, very efficient systems both the LS design and the PE design produce significant functional and cost advantages. The two structures have a lower thermal mass, which makes it possible to dispense with the first, smaller substrate in the cascade.

By adding another innovation to this structure, that is, the lambda sensor catalyst, the gap between the substrate becomes superfluous, because this type of substrate allows one or more lambda sensors to be positioned directly inside the substrate. The radial “permeability” inside the substrate now also allows diffusion equalisation of the pollutant concentration, which has a positive effect on the control accuracy of the fuel mixture generation.