Several diesel passenger car manufacturers in the European Union recently announced the future use of catalyzed diesel particulate filter systems on their vehicles.
The major technical challenge is the periodical 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 systems uses catalytically active fuel additives. These systems were introduced about four years ago.
Since that time, other systems, using a dedicated catalytically activated diesel particulate filter combined with an upstream diesel oxidation catalyst, have been introduced as well. This allows filter regeneration without extra fuel additives.
In the past, adding catalytic coating to a filter substrate has often resulted in increasing the pressure drop over the filter to an unacceptable level. Using a newly developed, dedicated processing technology, coatings with outstanding catalytic functions even on standard filter substrates can be applied without a severe backpressure increase. This so-called “macrowashcoating” technology enables the possibility to integrate the diesel oxidation catalyst's functions directly in the filter substrate.
The HC and CO oxidation performance of a filter with integrated oxidation catalyst functionality is compared to a conventional flow-through monolith by computer simulation and experiment. Simulation and experiment both show a systematic advantage of the catalyst filter over the conventional monolith configuration. Computer simulation provides some explanation for this observation.
Finally, the technology's suitability for application to passenger cars is proven by intensive engine bench and vehicle tests.