| Diesel engines possess strong power, high efficiency and high reliability which has been widely applied. However, the emission of particulate matters would bring harms to serious environment and human health. The Catalytic Diesel Particulate Filter(CDPF)could not only reduce the particles, but also convert the CO, HC and NO in exhaust gas,and achieve effective continuous passive regeneration. Then the reliability of the CDPF and reduction of the CO and HC could be improved with the Diesel Oxidation Catalyst(DOC) combined CDPF, and continuous regeneration of DPF could be achieved as well.In order to further investigate the effects of CDPF on trapping characteristic, the gas pollutants and the structure of particles. Characteristics of flow field and particles distribution in trapping process were studied with numerical simulation in this paper.The emission performances of CDPF and DOC combined CDPF were evaluated through diesel bench test. The influence of DOC and CDPF on the particle morphology structure was examined by transmission electron microscopy(TEM) and image technology.The CDPF model was established on the basis of GT-POWER and AVL-FIRE, the pressure drop result was verified well with experimental result by simulation. In addition, the distribution of pressure drop was mainly analyzed as well as the gas flow and particles distribution inside the CDPF, then the structure parameters of CDPF was optimized. The simulation results showed that in CDPF, depth filtration was given priority to early trapping, and cake capture gradually increased in trapping with time increase. In the expansion tube area, there existed obvious eddy area, which led the nonuniformity of flow velocity entering CDPF, and the particles distribution was nonuniform in axial and radial direction under the effects of flow distribution.Meanwhile, flow uniformity was improved with the increase of the loading particles mass and not obviously affected by increasing initial mass flow. And then, the high collection efficiency and low pressure drop variation could be achieved, and the flow distribution and diesel performance were improved in the CDPF when the the diameter ratio, channel density and wall thickness were set at 3.0, 200 and 0.35 mm respectively.The influences of CDPF and DOC combined CDPF on performance and emission in diesel engine were analyzed by diesel bench test. The experiments results showed that conversion rate of CO and HC were 73% and 64%, and NO was converted by 28%at most in different loads of calibration speed via CDPF. The soot emission was rapidly reduced in high load and the specific fuel consumption was slightly increased compared with original engine. CO, HC and NO has good oxidation impacts with a higher conversion rate, and the DOC has little impact on soot emission via DOC combined CDPF.The microstructure features of particles before and after DOC combined CDPF were obtained by characterization in TEM experiment. The average diameter of particles and the particles box counting dimension were analyzed by image method, and the effects of DOC combined CDPF on particles morphology structure and cluster degree were studied. The TEM results showed that in full loading, the particles were in clamps and ball distribution, and the particles accumulated seriously so that the contour of primary carbon particle was difficult to be distinguished. Under the effect of DOC,the particles were changed to chain structure, and the contour was clearer than before.After passing through the DOC combined CDPF, the particle accumulation was decreased, and the particles contour was more obvious. In addition, the average particles size were reduced, and particles structures became loose. |
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