| As an important part of after-treatment system,the heating characteristics of DOC directly affect the timeliness and effectiveness of DPF regeneration,the conversion efficiency of the exhaust component over the DOC is directly related to the emission of harmful substances during the regeneration process.Therefore,this project proposed an experimental investigation on the influence factors of DOC oxidation performance in post injection environment.While using a uniform-coated monolithic DOC as the research object,the simulated gas test bed was applied to analyze the temperature variation of DOC outlet gas and the influence mechanism of DOC to adjust NO2/NO ratio.The main work and conclusions were as follows:?1?Based on the simulated gas test bed,the temperature programming test under C3H6/O2/H2O,C3H6/NO/O2/H2O atmosphere was carried out to investigate the effect of temperature on the oxidation performance over the DOC,and the conversion efficiency of exhaust components under various temperature conditions was evaluated,while analyzing the interactions between the various exhaust components.The results showed that the activity of DOC catalyst was limited in low temperature conditions,and the conversion rate of C3H6 was low in low temperature conditions.At the same time,C3H6 had strong chemisorption in low temperature environment and adhered to the surface active site of the catalyst,which had an inhibitory effect on self oxidation.Under high temperature conditions,as temperature increased,the conversion of C3H6did not decrease with the increase of C3H6 concentration.When the temperature was higher than 400°C,the chemical adsorption effect of C3H6 was weakened,and the inhibition on self oxidation was reduced or eliminated.Under low temperature conditions,the DOC activity was controlled by temperature.As the temperature increased,the amount of NO2 increased.Under high temperature conditions,the oxidation of NO was limited by thermodynamic equilibrium,and the amount of NO2decreased with increasing temperature.Addition of C3H6 was found to inhibit NO oxidation by delaying the ignition temperature of NO and reducing NO2 field.?2?Using the simulated gas test method,selected the temperature point in the range of 100600°C,and carried out the constant temperature oxidation test of C3H6/O2/H2O and C3H6/NO/O2/H2O atmosphere to explore the heating characteristics and the influence mechanism of DOC on the conversion rate of each exhaust component.The results showed that the order of temperature rise of C3H6/O2/H2O at300,400 and 500°C from high to low was:?300?>?400?>?500?.There was a linear relationship between the temperature rise of DOC outlet gas and the concentration of C3H6.With the increase of C3H6 concentration,the temperature rise under various temperature conditions gradually increased.Under low temperature conditions,C3H6had an inhibitory effect on NO oxidation due to the chemisorption of C3H6 and the strong oxidizing ability of NO2.At the same time,1.1%C3H6 reactd with NO,reduced NO to N2,and inhibited NO2 formation.Under high temperature conditions,the inhibitory effect of C3H6 on NO oxidation was due to the strong oxidizing ability of NO2.When 1.1%C3H6 concentration was added,its reaction with O2 released heat,resulting in temperature rise,and NO oxidation was limited by thermodynamic equilibrium,resulting in NO2 formation reduction.?3?Periodic cycle tests were carried out using a simulated gas test bed.The C3H6addition state was periodically changed under NO/O2 and NO/O2/H2 atmospheres to investigate the effect of C3H6 and H2 on DOC oxidation performance.The results showed that the amount of NO2 formation was significantly reduced by the introduction of 1.1%C3H6.When the test time was long,the peak value of NO2production in the NO/O2/H2 atmosphere gradually decreased.H2 reacted with Pt to form H*with strong chemisorption.H*occupied the active site on the surface of the catalyst and hindered NO oxidation. |
PDF Full Text Request