| The Emission limit and Measurement method for Light vehicle Pollutant emissions?China Phase VI?was promulgated in December 2016.The emission limit for particulate matter of diesel engines has been reduced from 4.5 mg/km to 3 mg/kg,which is one of the most stringent emission standards at present.Diesel Particulate Filter has become an indispensable device for tail gas treatment.The key technology lies in the efficient and economical oxidation of soot deposition,and the non-thermal plasma is rich in a large number of active free radicals.Soot oxidation can be realized at lower temperature,which has the potential to be applied to DPF regeneration.In this paper,based on the double-layer dielectric barrier discharge?DBD?non-thermal plasma generator,the kinds and concentrations of active free radicals in O2non-thermal plasma were diagnosed by emission spectrum,and the generation and reaction path of key active free radicals were discussed.In order to obtain the controllable preparation of non-thermal plasma active radicals and realize the high efficiency and economy of DPF.Through the review of the research on the O2 non-thermal plasma and the formation of O3,it is found that in the O2 non-thermal plasma,the excited oxygen atoms in the O2non-thermal plasma are 1D°,1F,1S,3S°,3P°,1D,3P,3D,3D°,3F,5S°,5P and 5D°.in the transition process,which is the key intermediate free radical.O?5P,10.74 ev?5S°,9.15ev?and O?3P,10.99 ev?3S°,9.52 ev?play an important role in the O3 formation pathway.Under the experimental conditions,the corresponding oxygen atom transition lines can be detected at 715.6 nm,747.8 nm,777.4 nm and 844.7 nm,respectively.With the increase of the discharge voltage,the spectral intensity of O?3D,15.78 ev?3P°,14.12ev?at 747.8 nm,O?5P,10.74 ev?5S°,9.15 ev?at 777.4 nm and O?3D°,12.76 ev?3P,10.99 ev?at 700.1 nm increase,O?5S°,13.02 ev?5P,10.74 ev?at 543.6nm and O?3P,10.99 ev?3S°,9.52 ev?at 844.7nm have no obvious change.When the discharge gap increased to 2 mm,the concentration of active free radicals decreased,and the change of oxygen flow rate had little effect on the intermediate active free radicals,but too much was not conducive to the formation of ozone.Further analysis shows that active radicals generate ozone through four main pathways.1)O2?O?1D,14.46 ev??O?1D°,12.73 ev??O?3P,0 ev?;2)O2?O?5P,10.74 ev??O?5S°,9.15ev??O?3P,0 ev?;3)O2?O?3D°,12.76 ev??O?3P,10.99 ev?+hv,O?3P,10.99 ev??O?3S°,9.52 ev??O?3P,0 ev?;4)O2?O?3D,15.78 ev??O?3P°,14.12 ev??O?3P,0 ev?Path 2)is the most important and stable.On the basis of experiments,the reaction mechanism of O2 plasma at low temperature was established,and the experimental conditions were simulated by using the zero-dimensional plasma model.The results show that the formation concentration of O3is in good agreement with the experimental results,and the concentration increases with the increase of the reduced field strength.When the reduced field strength is 49.25 Td,that is,the gap is 1 mm,and the voltage is 2.5 KV,the concentration of most active free radicals is between 1010 and 1012 cm-3,and the ground state oxygen atom?O?3P,0ev??has the fastest formation rate.The concentration of O?3S°,9.52 ev?is the lowest(4.26×107cm-3),The concentration of O?5S°,9.15 ev?was second only to the oxygen atom. |
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