Continuously regeneration trap filter system

The emissions of PM can be reduced using filter technology, where the continuously regenerating trap (CRT) system appears promising [1]. The emission levels of NOx are however only affected by the CRT technology to some extent [1]. 

The continuously regenerating trap (CRT) system (by Johnson Matthey) con-skts of a DPF filter located downstream of a Pt-containing DOC catalyst. CO and HC are oxidized in the DOC, which ako oxidizes NO to NO2. NO2 k much more active in its oxidizing reactions than NO and O2 and reacts rapidly with the soot and initiates its ignition. 

In order to simulate decreasing emission levels a truck engine of Euro III emission level (6 cylinder Volvo, displacement 7 liters) has been equipped with a continuously regeneration trap (CRT) filter system and an additional bypass to this filter by the Swiss EMPA institute. By a variation of the flow ratio of filtered/unfiltered exhaust gas, an emission level of about 60% of Euro IV has been adjusted (Mohr and Lehmann, 2003). The temporal courses of EC mass concentration and EC-specific surface area are depicted in Figure 34. In this graph, the mass and surface emissions of the 13 operation points within this test yield a different behavior. Most pronounced is the small specific surface area for idle operation which is caused by relatively large particles and in agreement to the results of previous studies. 

Incorporating an oxidation catalyst upstream of the filter that, as well as operating as a conventional oxidation catalyst, also increases the ratio of nitrogen dioxide (NO2) to nitric oxide (NO) in the exhaust. Particulate then bums off at normal exhaust temperatures using the powerful oxidative properties of NO2. This continuously regenerates the trap. This system requires diesel fuel containing less than 50 PPM sulphur such as the City Diesel used in Sweden. 

The function of the helium purification system is to continuously remove, from the primary helium, dusts and particles, gaseous impurities including fission products. There is one purification train, which mainly consists of a filter, a molecular sieve trap, a copper oxide fixed bed, a cold charcoal trap and a compressor. The purification train must be regenerated after about 2,000 operation hours. 

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