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.

2种保护性耕作措施对农田土壤团聚体稳定性的影响

在2种保护性耕作措施（秸秆还田和免耕）的长期定位试验（湖北省武穴市和荆州市）基础上,通过湿筛法测定不同土层（0 20 cm和20 40 cm）的不同粒径（＞5 mm,2～5 mm,1～2 mm,0.5～1 mm,0.25～0.5 mm和＜0.25 mm）水稳性团聚体的含量,并对土壤团聚体平均重量直径（MWD）、平均几何直径（GMD）和分形维数（PSD）等进行分析,研究2种保护性耕作措施对农田土壤团聚体稳定性的影响.结果表明：秸秆还田和免耕处理均会影响土壤各级团聚体的分布状况,同时其也会增加农田表层（0-20 cm）土壤粒径＞0.25 mm团聚体的百分含量、MWD和GMD值,但是会降低PSD值.其中PSD与粒径＞0.25mm团聚体的含量呈极显著负相关性（武穴处理相关系数为-0.997,荆州处理相关系数为-0.993）,但是MWD和GMD与粒径＞0.25 mm团聚体的含量有显著正相关性.表明秸秆还田和免耕均会增强土壤团聚体的稳定性,有利于改善土壤结构.但秸秆还田处理的土壤粒径＞0.25 mm团聚体百分含量、MWD和GMD值均高于免耕处理,说明秸秆还田改善土壤结构的效果要优于免耕的.秸秆还田和免耕措施相结合,土壤结构改良效果最佳.武穴和荆州两地的保护性耕作措施对于粒径＞0.25 mm团聚体百分含量、MWD、GMD和PSD的影响基本一致.

喷嘴结构对喷雾特性的影响

为了解高压共轨喷嘴结构对喷雾的影响,试验采用三维相位多普勒粒子分析仪（PDPA）,在高喷射压力条件下研究了不同的喷嘴结构的喷雾粒径空间分布情况.结果表明：高压燃油喷雾的粒径分布呈现轴线大、两边小的趋势,并在喷雾边缘稍微增加;同时随着喷射压力的增加,喷雾索特平均直径（SMD）的分布呈现粒径减小的趋势,小粒径区域逐渐向喷嘴顶端靠近,喷雾雾化效果随喷射压力增加而改善.随着喷孔直径的减小,喷雾总体SMD呈减小趋势;当喷孔直径减小到一定程度时,进一步减小喷孔直径对喷雾雾化效果的影响逐渐减弱.孔径为0.18,mm的喷嘴,喷雾SMD随着长径比（L/D为3.89~5.00）的增加而增大;孔径为0.13,mm的喷嘴,喷雾SMD随着长径比（L/D为5.38~7.69）的增加而降低.

基于粒径谱仪的畜禽养殖场空气颗粒污染物测量研究

为了分析采用空气动力学粒径谱仪实时测量畜禽养殖场空气颗粒污染物的可行性及效果,首先使用APS和MOUDI在实验室对玻璃球粉末和植物油滴进行同步测量与对比分析,然后在畜禽养殖场实时地对下风向空气颗粒污染物进行测量。结果表明:在实验室中,APS测得的2种玻璃球粉末和植物油滴的结果较准确;通过线性回归证明这2种仪器测得的玻璃球粉末和植物油滴的累积质量浓度具有一定相关性,R2都大于0.9,表明拟合度较好。在使用APS实时测量畜禽养殖场的空气颗粒污染物时,APS能够较好地反映空气颗粒污染物的变化情况,能基于其实时测量的颗粒物几何平均直径、数量浓度和质量浓度等指标从多个角度对空气颗粒污染物进行分析。

甲醇-柴油双燃料发动机微粒数量排放特性

【目的】为减小甲醇-柴油双燃料发动机排放微粒中核模态粒子的数量(nucleation mode particle number,PNN).【方法】在1台由电控高压共轨柴油机改装的甲醇-柴油双燃料发动机上分别进行了甲醇掺烧比(co-combustion ratio,CCR)、引燃柴油喷射正时与负荷率特性试验.【结果】随着掺烧比的增大,核模态与积聚态微粒数量(accumulation mode particle number,PNA)均明显减小,生成微粒几何平均直径减小;引燃柴油喷射正时提前可减小生成微粒的总数量(total particle number,PNT),但掺烧比较大时提前柴油喷射正时粒径分布出现"双峰"现象,PNN大幅增加;增大发动机负荷率,PNN与PNA均有所增加,粒子几何平均直径增加,小负荷时生成的PNN明显高于中大负荷.【结论】提高掺烧比与提前引燃柴油喷射正时有利于减小PNN的生成,但当掺烧比较大时应注重柴油喷射正时的调节以防止PNN显著增加.

二元粗集料间隙率形成规律与机制研究

为了研究二元粗集料间隙率形成的规律与机制,将A(19~31.5 mm)、B(13.2~19 mm)、C(9.5~13.2 mm)及D(4.75~9.5 mm)4档规格的石灰岩粗集料进行两两组合,获得6种二元粗集料,通过振实试验得到各二元粗集料的间隙率。试验结果表明:二元粗集料的间隙率随着粗集料加入量的增多呈现凹形曲线变化,存在一谷值。但各凹形曲线变化的速率与谷值不同,粗集料与较细粗集料的几何平均粒径比越大,曲线变化速率越大,谷值越低。通过回归分析,建立了各二元粗集料间隙率的有效统计模型。提出了填充效应系数的概念,以反映较细粗集料对较粗粗集料的填充程度,并建立了填充效应系数与粗集料几何平均粒径比的有效统计线性关系式。线性关系式表明:粗细集料粒径差距越大,即粒径比越大,较细粗集料对较粗粗集料的填充效果越好,即二元粗集料的间隙率越小。在此基础上建立了二元粗集料统一回归模型,揭示了二元粗集料间隙率的形成机制。

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.

计径效率试验粒径的分析与对比

采用粒子计数法评定空气过滤器的计径效率时,粒径是试验前首先要确定的主要参数之一。介绍了空气粒子计数器常用的几种粒径的定义,通过试验对比分析了几何等效粒径和几何平均粒径、空气动力学粒径等的关系与区别。结果表明:这些粒径之间相互关联,但是计径效率试验时使用的粒径种类不同,获得的试验结果也不相同。

基于GIS几何计算的杉木树干横断面面积模型构建

【目的】在林业实际调查中,树干横断面面积是林分与单木调查尺度中的重要变量。为了精准统计树干横断面面积大小及形状,分析了几种不同测量与统计方法在处理直径数据、估算断面积时的精度差异,建立圆盘断面积模型,确定最优断面积估算方法。【方法】用GIS几何计算面积和周长功能,测量杉木(Cunninghamia lanceolata)不同高度上的几何圆盘断面积、周长和直径,构建断面积和周长模型,计算树干圆盘横断面圆周率(称为横断面形状圆周率),分析不同统计方法对断面积精度的影响,应用杉木树干横断面形状圆周率及最优统计方法分析树干断面积精度。【结果】通过断面积(G)与周长(C)关系G=0.077 666 3C^2(R^2=0.998 5),求得杉木树干横断面形状圆周率F=3.218 899 32,充分说明杉木树干横断面不是完整圆,而是一个圆周率为3.218 899 32的近似圆。几何平均法在树干横断面积统计中具有明显精度优势,算术平均法略差,根据几何算术平均直径和精准测定的断面积,拟合得到断面积与直径(d)的关系为G=0.817 7d^(1.990 2)(R^2=0.990 5)。结合几何平均直径法和树干横断面形状圆周率F进行横断面积计算,使用F和π分别进行分析发现两者残差有显著正负异号性,前者偏大,后者偏小。基于树干横断面形状圆周率F与π的树干横断面形状圆周率平均数f(3.180 246 0),在预测树干横断面积时,f中和了F偏大和π偏小的缺点,具有较高预测精度和稳定性。【结论】以不同的统计方法计算树干横断面积的精度不同,在林业实际调查中,可结合几何平均直径和f(3.180 246 0)统计解析木圆盘断面积,以实现更精确的估算。