Selective catalytic reduction failure of low NH_(3)-NO_(x) ratio

An insufficient amount of NH_(3) (ammonia)will reduce the conversion efficiency of NO_(x),which may lead to excess NO_(x) emissions,resulting in NH3SCR failure.In this article,SCR failure caused by a low NH_(3)NO_(x) ratio is studied systematically by experiments.The main reasons for a low NH_(3)NO_(x) ratio in SCR include insufficient urea injection,hydrothermal aging of catalysts and urea crystallization.It was found from an insufficient urea injection experiment that with the increase of NH_(3)NO_(x) ratio,the NO_(x) conversion efficiency of the SCR system increased,but the ammonia leakage also increased.The main influencing factors of NO_(x) conversion efficiency are different under different NH3NOx ratios.A flow reactor system was used in the catalyst hydrothermal aging experiment to investigate the effect of hydrothermal aging on catalyst activity.After a 24 h hydrothermal aging experiment at 800℃,the NO_(x) conversion efficiency of the copperbased zeolite catalysts decreased significantly at the boundary of medium and low temperature regions.And the NO_(2)-NO_(x) ratio in the mixture had a significant effect on the catalytic performance.Thermogravimetry coupled to Fourier transform infrared spectroscopy(TGFTIR)was used to analyze the composition of urea deposits in a urea deposits analysis experiment.It was found that the main components of urea deposits were urea and isocyanic acid(HNCO).Preventing HNCO polymerization,especially the formation of CYA,can decrease the formation of urea deposits.

Effect of catalyst diesel particulate filter aging and catalyst loadings on particulate emission characteristics from a diesel vehicle

In this study,the effect of new and used catalyzed diesel particulate filter(CDPF)with different catalyst loadings on the particulate emissions including the particle mass(PM),particle number(PN),particle size distribution(PSD)and geometric mean diameter(GMD)from a diesel vehicle were investigated based on a heavy chassis dynamometer.Results showed that more than 97.9%of the PN and 95.4%of the PM were reduced by the CDPF,and the reduction efficiency was enhanced by the catalyst loading.After using the CDPF,the PSD transformed from bimodal to trimodal with the peak shifting towards smaller particle size,more nucleation mode particles were reduced compared with accumulation mode ones,but the reduction effect on the accumulation mode particles was more significantly influenced by the catalyst loading.Notably,the CDPF increased the accumulation mode particles proportion,producing a larger GMD.For the used CDPF,its reduction effect on the particulate emissions enhanced,especially for the PM in accumulation mode.The PSD returned to bimodal,but the peak at accumulation mode began to be higher than that at nucleation mode,illustrating that more nucleation mode particles was removed.The aging of the CDPF resulted in greater effect on the PN-based PSD than that of PM-based PSD,but the effect of catalyst loading on the PN and PM emission factors was weakened.The used CDPF further increased the GMD,and the effect of catalyst loading on the GMD was strengthened,a higher catalyst loading led to a reduction in the GMD.

Effect of catalyzed diesel particulate filter and its catalyst loading on emission characteristics of a non-road diesel engine

In this study, the effects of a diesel oxidation catalyst(DOC) coupled with a catalyzed diesel particulate filter(CDPF) with different catalyst loadings on the power, fuel consumption,gaseous and particulate emissions from a non-road diesel engine were investigated. Results showed that the after-treatment had a negligible effect on the power and fuel consumption.The reduction effect of the DOC on the CO and hydrocarbon(HC) increased with the engine load. Further reductions occurred coupling with the CDPF. Increasing the catalyst loading resulted in a more significant reduction in the HC emissions than CO emissions. The DOC could increase the NO_(2)proportion to 37.9%, and more NO_(2)was produced when coupled with the CDPF below 250℃;above 250℃, more NO_(2)was consumed. The after-treatment could reduce more than 99% of the particle number(PN) and 98% of the particle mass(PM).Further reductions in the PN and PM occurred with a higher CDPF catalyst loading. The DOC had a better reduction effect on the nucleation particles than the accumulation ones, but the trend reversed with the CDPF. The DOC shifted the particle size distribution(PSD) to larger particles with an accumulation particle proportion increasing from 13% to 20%, and the geometric mean diameter(GMD) increased from 18.2 to 26.0 nm. The trend reversed with the CDPF and the accumulation particle proportion declined to less than 10%. A lower catalyst loading on the CDPF led to a higher proportion of nucleation particles and a smaller GMD.

Emission reduction characteristics of a catalyzed continuously regenerating trap after-treatment system and its durability performance

The primary purpose of this study was to investigate the effect of a catalyzed continuously regenerating trap(CCRT)system composed of a diesel oxidation catalyst(DOC)and a catalyzed diesel particulate filter(CDPF)on the main gaseous and particulate emissions from an urban diesel bus,as well as the durability performance of the CCRT system.Experiments were conducted based on a heavy chassis dynamometer,and a laboratory activity test as well as X-ray photoelectron spectroscopy(XPS)test were applied to evaluate the changes of the aged CCRT catalyst.Results showed that the CCRT could reduce the CO by 71.5%and the total hydrocarbons(THC)by 88.9%,and meanwhile promote the oxidation of NO.However,the conversion rates for CO and THC dropped to 25.1%and 55.1%,respectively,after the CCRT was used for one year(~60,000 km),and the NO oxidation was also weakened.For particulate emissions,the CCRT could reduce 97.4%of the particle mass(PM)and almost 100%of the particle number(PN).The aging of the CCRT resulted in a reduced PM trapping efficiency but had no observable effect on the PN;however,it increased the proportion of nucleation mode particles.The activity test results indicated that the deterioration of the CCRT was directly relevant to the increase in the light-off temperatures of the catalyst for CO,C3H8 and NO2.In addition,the decreased concentrations of the active components Pt2+ and Pt4+ in the catalyst are also important factors in the CCRT deterioration.

Effect of lubricant sulfur on the morphology and elemental composition of diesel exhaust particles

This work investigates the effects of lubricant sulfur contents on the morphology,nanostructure,size distribution and elemental composition of diesel exhaust particle on a light-duty diesel engine. Three kinds of lubricant（LS-oil,MS-oil and HS-oil,all of which have different sulfur contents：0.182%,0.583% and 1.06%,respectively）were used in this study. The morphologies and nanostructures of exhaust particles were analyzed using high-resolution transmission electron microscopy（TEM）. Size distributions of primary particles were determined through advanced image-processing software. Elemental compositions of exhaust particles were obtained through X-ray energy dispersive spectroscopy（EDS）. Results show that as lubricant sulfur contents increase,the macroscopic structure of diesel exhaust particles turn from chain-like to a more complex agglomerate. The inner cores of the core-shell structure belonging to these primary particles change little; the shell thickness decreases,and the spacing of carbon layer gradually descends,and amorphous materials that attached onto outer carbon layer of primary particles increase. Size distributions of primary particles present a unimodal and normal distribution,and higher sulfur contents lead to larger size primary particles. The sulfur content in lubricants directly affects the chemical composition in the particles. The content of C（carbon）decreases as sulfur increases in the lubricants,while the contents of O（oxygen）,S（sulfur）and trace elements（including S,Si（silicon）,Fe（ferrum）,P（phosphorus）,Ca（calcium）,Zn（zinc）,Mg（magnesium）,Cl（chlorine）and Ni（nickel））all increase in particles.