柴油机排气颗粒物吸湿特性与机理研究

Hygroscopic properties of atmospheric particles are the bridge of micro-particle physics and chemical parameters, and play a key role in the formation of fog haze. Diesel exhaust particulates, one of main sources of atmospheric fine particles, have their unique hygroscopicity. The hygroscopic properties and mechanisms of diesel exhaust particulate matters are investigated to verify the inner impulse causing the atmospheric environment problem. The effects of the atmospheric temperature and humidity and aging on the hygroscopic growth factor and mass change of the particles are researched. The relevance between the hygroscopicity of diesel exhaust particles and fuel type, sulfur content of fuel, and engine operation are established. The adsorption kinetics and thermodynamics of water vapor onto the particle surface are studied. A suitable kinetics model is determined including saturated absorption capacity and absorption rate. The enthalpy, entropy and Gibbs free energy are calculated. The surface activity absorption parameters of the particles are measured including morphology, size distribution, pore structure, specific surface area, radical group and functional group. By measuring the contact angle among three-phase boundaries, the particle surface free energy is calculated, and the absorption performance of the particles is evaluated. The results have important theoretical significance value to clarify the hygroscopic behavior between the particles and water vapor and its effect on fog haze formation.

颗粒物的吸湿性是联系颗粒物微物理、化学参数的重要纽带之一，在雾霾的形成过程中起着关键性作用。柴油机排气颗粒物作为大气细颗粒物的主要来源之一，有其独特的吸湿性。本项目对柴油机排气颗粒物的吸湿性质和机理进行研究，以探明颗粒物引起大气环境问题的内在驱动力。研究大气温湿度与老化对颗粒物吸湿增长因子和质量变化的影响，建立柴油机颗粒物吸湿性与燃油类型、硫含量及工况之间的关联性；研究水蒸汽在颗粒物表面的吸附动力学和热力学特征，确定合适的动力学模型及饱和吸附量、吸附速率常数等动力学参数，计算焓变、熵变和吉布斯自由能等热力学参数。测量颗粒物的形貌、粒度分布、孔隙结构、比表面积、化学基团、官能团等表面活性吸附结构参数；通过测量气/液/固三相界面体系的接触角，计算颗粒物的表面自由能，对颗粒物的吸附性能进行评价。研究结果对于阐明颗粒物与水蒸汽之间的吸湿行为在雾霾形成中的作用机理具有重要的理论意义。

颗粒物的吸湿性是联系颗粒物微物理、化学参数的重要纽带之一，在雾霾的形成过程中起着关键性作用。柴油机排气颗粒物作为大气细颗粒物的主要来源之一，有其独特的吸湿性。本项目对柴油机排气颗粒物的微观结构进行研究，以探明颗粒物引起大气环境问题的内在驱动力。. 研究了发动机工况、喷油参数及喷孔参数、燃烧室参数对碳烟尺寸和碳烟数密度的影响规律，研究了生物柴油和含硫量较多的DLF燃油的燃烧特性和颗粒物微观结构。研究高、低负荷工况下不同粒径级柴油机颗粒物形貌的盒维数及其碳组分特性以及大气条件下机动车源的颗粒物粒径分布及碳组分特征，建立颗粒物吸湿的评价方法和装置。. 大气环境下燃烧试验得到生物柴油的碳烟粒径比柴油的碳烟粒径小，且碳烟粒子排列较为紧密，而柴油的碳烟粒子排列较为疏松。从粘结程度上看，生物柴油的碳烟粒子粘结较强，多呈大片粘结，而柴油碳烟粒子的粘结较弱。残炭试验条件下（520℃）得到的生物柴油的残炭呈较大的片状，粘结性较强。由于氧化环境的不同，生成的颗粒物形貌不同，而且生物柴油的吸收水蒸气的能力更强。. 颗粒物粒径级越小，其吸附的可溶性有机物(SOF)越多，由分形理论计算得到的盒维数数值增大。低负荷工况下的颗粒物聚集现象严重，从而导致其分形盒维数比高负荷的高；在较小粒径级或低负荷工况时，因细颗粒物的吸附效应，最易挥发的OC1 组分增多。随着粒径级增大，发动机原排颗粒物质量浓度逐渐降低。实验室排空大气颗粒物在0.32-0.56μm粒径级浓度较高；地下停车场大气颗粒物在1.0-1.8μm粒径级浓度较高。在扩散区域有较多的二次颗粒物生成。. 通过柴油机缸内外颗粒物特性的系统研究，阐明颗粒物时空变化规律及影响因素，为柴油机排气颗粒物的吸湿性能评价提供参考依据。