Research On NO_x Effective Removal From Automobile Exhaust By Non-thermal Plasma

The NO_x of automobile exhaust emissions,have caused serious harm to human health as well as the environment pollution.The existing after-treatment technologies have various problems,which can not effectively reduce the NO_x emission.Non-thermal Plasma is a new technology of treating waste water and waste gas in recent years.It is famous for its high efficiency and no secondary pollution.This paper attempts to take method of combination of experimental research and numerical simulation to regular that how to remove NO_x of automobile exhaust by Non-thermal Plasma.Firstly,we use CHEMKIN PRO to research the influencing factors of NO_x removal by Non-thermal Plasma.Secondly,the experimental device for the non-thermal plasma approach to NO_x abatement was designed,in which,the gas source was based on the simulation diesel engine exhaust gas and the relevant questions was studied.Finally,the removal device of NO_x was installed on a single cylinder diesel engine,and some experiments were carried out to verify research results.Research results are as follows.（1）The simulation result show that the removal efficiency of NO is 34% by plasma discharge in the mixture.When adding C₂H₄/C₃H₆ in the mixture,they can promote NO to NO₂.The C₂H₄ makes the NO removal efficiency up to 50%,and C₃H₆ makes the NO removal efficiency up to 90%.（2）In process of dielectric barrier discharge removing NO_x,only to achieve gas breakdown voltage（≥10 k V）,the mixed gas restructure reaction and remove NO_x.（3）Reaction temperature directly affects the effective removal of NO_x,and it is too high or too low will lead to a decline in the conversion rate of NO,and appropriate temperature range is 150℃～250℃.This temperature range is advantageous to the NO_x conversion.（4）In NO/N₂/O₂,the removal of NO_x decreased with increasing of O₂ in air intake system.When the mixed gas is poor O₂,NO_x can achieve a higher removal rate.The main ways of NO_x removal:（a）NO₂ firstly was reduced to NO by N atom.The speed of conversion rate is up with increase of voltage.（b）When the mixture contains a lot of N atom,NO further was reduced to N₂.The existing of O₂,especially when it is many,will greatly weaken the effective removal of NO_x.（5）CO is beneficial to promote the removal of NO_x by NTP.Under NTP,CO not only can react with O₂,and CO can react with NO.They will generate N₂ and CO₂.CO and NO will be removed at the same time.（6）A moderate amount of water vapor is beneficial to the removal of NO_x.Water vapor mainly through three ways influence NO_x removal.（a）Electronic impact water vaport can produce H and OH atoms,and OH reacts with NO to generate nitrite.Nitrite and OH react to produce NO₂.（b）Water vapor can react with excited state O to produce OH,OH has strong oxidizing ability to convert NO₂ to NO.（c）H from H2 O by high energy electron impact and O₂ generated HO₂,HO₂ will NO oxidation to NO₂.Non-thermal plasma technology can effectively remove NO_x from automobile exhaust.The limitation of technology is how to reduce the oxygen content in the exhaust gas and how to save energy in future.