Several diesel powered passenger car manufacturers in the European Union announced recently the future use of catalysed diesel particulate filter systems on their vehicles.
The filtration of the exhaust gas is being worked on since several years. Different filter materials and filter designs proved their ability to achieve high filtration efficiencies over the lifetime of the vehicle. The major technological challenge is the periodic regeneration of the filters loaded with the retained diesel particulates.
In order to promote filter regeneration, catalytic activation of the accumulated soot is advantageous. Therefore, the first serial application of diesel particulate filter system (diesel oxidation catalyst combined with an uncoated filter substrate) uses catalytically active fuel additives. These systems have been introduced about four years ago and proved to be a viable technology to clean the exhaust gas of passenger car diesel engines.
Since that time, other systems that use a dedicated catalytically activated diesel particulate filter combined with a dedicated upstream diesel oxidation catalyst, have been introduced as well. They allow filter regeneration without extra fuel additives.
In the past, adding catalytic coating to a filter substrate often resulted in increasing the pressure drop over the filter to an unacceptable value. Using a newly developed microwashcoating technology, one is able to apply a catalyst to the filter substrate without causing a noticeable increase of the backpressure. The technology's suitability for application to passenger cars is proven by intensive engine bench tests. These studies are reported.
Finally, with regard to catalytic activity and ageing resistance, the excellent performance of the microwashcoated catalyst could even be improved by applying a so called macrowashcoat catalytic function to the filter, using another newly developed, dedicated processing technology. This technology allows the application of outstanding catalytic functions even on standard filter substrates without a severe backpressure increase. Studies on the performance and durability of this type of catalysed filter system are reported as well.