不同燃料当量比条件下烟炱(soot)形态及光吸收增强效应

The morphology of soot and light absorption enhancement under different condition of fuel equivalence ratio

借助烟炱(soot)燃烧炉、扫描电迁移率粒径谱仪(SMPS)、气溶胶质量分析仪(APM)、三波段光声黑碳仪(PASS-3)探究不同燃料当量比(φ)条件下soot形态及光吸收增强效应.结果显示,随着燃料当量比(φ)从1.98升高至2.43,产生的soot颗粒物中非黑碳物质(nonrefractory particulate matter,NR-PM)的质量占比(RBC)从0.07升高至1.03,soot颗粒物和BC核的形状因子越低,表明soot结构更紧凑,同时BC核的形变更为显著,并且少量非黑碳物质(NR-PM)包裹即可导致BC核的明显形变.受透镜效应的影响,黑碳的光吸收增强与R BC呈正相关,当R BC从0.07增加至1.03时,相应光吸收增强从1.05增加至1.52(781 nm下);此外,棕色碳(BrC)对405 nm和532 nm下的吸光增强也有贡献,其贡献率随着R BC的增加而增大.同时,soot自身的形态对黑碳光吸收增强也存在影响,结构越紧实的soot,其黑碳光吸收增强越明显,并且越接近核-壳模型下的理论计算值.本研究表明,黑碳的形变对于其光吸收增强的影响不容忽视.

Laboratory experiments were conducted to investigate the morphology of soot particles and the light absorption enhancement under different fuel equivalence ratios with a soot burner,scanning mobility particle sizer(SMPS),aerosol particle mass analyzer(APM),and three-wavelength photoacoustic soot spectrometer(PASS-3).As the fuel equivalent ratio increased from 1.98 to 2.43,RBC correspondingly increased from 0.07 to 1.03,while the shape factor of soot particles and BC core decreased,which indicated that the particles and the BC core were changed from a highly fractal to a more compact form.A small amount of non-BC coatings could result in evident reconstruction of BC core.The light absorption enhancement of BC was positively correlated with R BC,when the R BC increased from 0.07 to 1.03,the corresponding light absorption enhancement increased from 1.05 to 1.52(at 781 nm).In addition to the lensing effect,brown carbon(BrC)also contributed to the light absorption enhancement at 405 nm and 532 nm,and the percentage of contribution increased with increasing R BC.In addition,the morphology of soot contributed to the light absorption enhancement of BC.For more compact soot structure,the light absorption enhancement was more obvious,and closer to the theoretically calculated value using the core-shell model.This study showed that the effect of black carbon reconstruction on the light absorption enhancement cannot be ignored.