In order to improve the reputation of diesel engines in terms of environmental friendliness and to reach the legislation limits Diesel Particulate Filters have penetrated the passenger car market in Europe. A fuller understanding of filter characteristics is essential for further system optimization, especially for substrate optimization and improvement of regeneration strategy.
The process of filter loading at different engine points and transient conditions has been investigated in depth Studies have also been conducted in regards to filter regeneration with oxygen. Both topics of which are now widely understood.
In contrast to that is the NO2 based regeneration. Even though the chemical base reactions have been known and understood for a considerable time, detailed information concerning its application to the automotive industry is missing regarding the NO2 based reaction, which is very slow and temperature sensitive. Therefore causing local effects within the system.
This paper reports the test results of an investigation into the NO2 effects on the soot distribution during loading, as well as during a regeneration. It was accomplished by testing three different systems, a pure CRT® system, a CSF system and a CCRT system. The soot distribution of which were determined by measuring the gas flow distribution at the rear face of the filters.
As known from other publication the tests show that the CCRT has the strongest NO2 regeneration while the pure CRT system is the poorest. The most important result is, however, that the NO2 reaction leads to a local regeneration and therefore to a very heterogeneous soot distribution.