Plasma Hydrogen Rich Gas Production And The Application In Four-way Catalytic Technology

Vehicular emissions have become the major source of air pollution in many cities with the rapid growth of vehicle population. Compared with gasoline vehicles, diesel vehicles have advantages such as high durability, lower cost of maintenance and less greenhouse gas emissions. Today, the promotion of diesel vehicles is considered an effective way to mitigate the energy crisis. The major pollutants in diesel emissions are nitrogen oxides (NOx) and particulate matters (PM). The aftertreatment technologies for NOx control mainly include selective catalytic reduction (SCR) and NOx storage-reduction (NSR), while PM is usually reduced by particulate filter.At present, four-way catalytic technology is considered an advanced diesel aftertreatment technology which can reduce HC, CO, NOx and PM at the same time. The development of four-way catalytic technology was reviewed in this thesis, and a new kind of regeneration method was proposed based on the analysis of shortages of combined and integrated four-way catalytic technologies in practice. The method uses hydrogen-rich gas produced with diesel fuel to regenerate the NOx storage-reduction catalyst and particulate filter, further improving the four-way catalytic technology of diesel exhaust aftertreatment.Firstly, the storage capability of NOx storage-reduction catalyst was investigated by simulating exhaust gases and the optimal conditions for NSR catalyst regeneration was analyzed in this thesis. Results show that 300℃is the optimal temperature for NOx storage and the presence of O2 significantly promotes the progress of NOx storage reaction, while at 600℃the NOx adsorbed by the catalyst will be completely released. The NSR catalyst can be regenerated in about two minutes whenφ(H2)=5% and it will not be affected by the temperature.According to the optimal conditions for NSR catalyst regeneration found in the simulation experiment, a system that can produce hydrogen with plasma technology was developed. In the system the plasma reactor can ionize air by arc discharge with high voltage and low current to arouse the partial oxidation reaction of diesel fuel to produce hydrogen-rich gas (φ(H2)=5.3%). When the air was replaced by engine exhaust, the hydrogen-rich gas (φ(H2)=3.3%) was also produced successfully.Finally, the use of hydrogen-rich gas for the regeneration of NOx storage-reduction catalyst and particulate filter was studied on a diesel engine. Results show that hydrogen-rich gas (φ(H2)=5%) can completely regenerate the devices mentioned above in a short time (about 240 and 165 seconds, respectively). Thus, the hydrogen-rich gas produced by plasma technology can meet the requirements of regeneration.