| In recent years,the problem of ambient air quality in Guanzhong region had become prominent,manifested as frequent haze in autumn and winter,and increased frequency of ozone in summer.Vehicle exhaust emissions were one of the major sources of urban haze.More than 90%of PM2.5 emissions from motor vehicles were contributed by diesel vehicles,and NOx and VOCs with higher emissions from diesel vehicles were also one of the precursors formed by O3.In Guanzhong area of Shaanxi Province,the number of diesel vehicles in use was relatively small,but emissions were relatively high.Diesel vehicle emissions below the national III emission standard were not up to the standard.The retrofitting of the post-treatment system to reduce the PM and NOx emissions in the diesel vehicle exhaust was a common vehicle emission reduction method.In this paper,a large passenger vehicle was selected and the performance test of the selected retrofit system was performed through a bench test,which included detailed tests on PM mass,PM quantity,and particle size distribution before and after the vehicle exhaust gas passes through the after-treatment system;GT-Suite conducts numerical simulation of wall-flow particle filter?WF-DPF?and urea-selective catalytic reduction?Urea-SCR?to study the filtration efficiency and Urea-SCR performance of the selected aftertreatment device WF-DPF.The factors that simulated the best emission reduction effect,proposed parameters that were not taken into account in the optimization experiment,and reached the main conclusions:?1?Through a bench test,an electronic low-pressure impingement instrument?ELPI+?was used to study the particle concentration,mass concentration,and particle size distribution of a heavy-duty diesel passenger car.The degree of decontamination efficiency is about 64%,and there was a significant difference between the PM concentration and the concentration distribution of the mass concentration of heavy-duty diesel vehicle exhaust.The particle number concentration was mainly concentrated in the ultrafine particle size?DP<100nm?,while the mass concentration of 98.61%particles was concentrated in the coarse mode particles?DP>1?m?;the nuclear mode?5nm<DP<20nm?and the root The removal efficiency of the nuclear membrane?20 nm<DP<100 nm?particles was 89.8%and 73.9%,respectively;the nuclear modality,the root-loving modal particle,the accumulating modality?100 nm<DP<1?m?and the coarse mode?DP>1?m?particle concentration purification efficiency was91.1%,62%,87.4%,74.5%,respectively.The total mass concentration of PM2.5.5 and PM100 in the tail gas of passenger cars before the installation of the post-treatment device was 10.3mg/m3 and 780 mg/m3,respectively;the PM2.5.5 and PM100 in the exhaust after installation of the post-treatment device were 4.7 mg/m3 and 361 mg/m3,purification efficiency were 54.1%and53.7%,respectively.In the later period,it was found that the NOx removal effect of the vehicle during road running was stable.In addition to abnormal conditions such as starting and stopping of the vehicle and failure to reach the SCR inlet reaction temperature,the NOx concentration before installation of SCR was 1000 mg/m3,and the NOx concentration after installation was500mg/m3,the NOx removal rate is between 50%,the applicable temperature range is between 230500?,suitable for medium and heavy diesel vehicles.?2?Evaluation of the performance of wall-flow particle filter?WF-DPF?filtration performance was the initial filtration efficiency and pressure drop.The structural parameters positively related to the initial filtration efficiency were:filter diameter?D?,length?L?and channel density?CPSI?;structural parameters positively related to pressure drop were:channel density;structural parameters negatively related to pressure drop There was:filter diameter.The length and diameter of the filter had little effect on the purification efficiency.The filter length,diameter,and number of channels had a linear relationship with the time corresponding to a peak pressure drop of 25 kPa.The contribution of carbon deposits in the DPF filter was small,mainly determined by the surface active carbon content of the catalyst.The influence of filter length,diameter,and number of channels on the pressure drop was linear,and they were multivariately fitted to obtain the general formula:t=6.6×10-4?L-126.6??D-193.8??CPSI+460.9?.?3?The index for evaluating the Urea-SCR performance was the NOx reduction efficiency and the inlet NH3 concentration.The design parameters to consider when optimizing the conversion rate of NOx were:length,diameter,and number of channels of the catalytic reducer. |
PDF Full Text Request