Diesel Engine Particulate Emissions: A Comparison of Mobility and Microscopy Size Measurements

Abstract Sub-micron particulates emitted from diesel engines have serious negative effects on human health and environment. Accurate characterizations of such particulate matter based on independent diagnostic techniques are necessary to monitor, regulate, and model atmospheric pollution levels. The relevant sizes, in addition to mass, are of special interest as they determine the transport, toxic, optical, chemical, and deposition properties of particulates. While there is abundant information in the aerosol literature on the apparent size distributions of diesel particulates measured with mobility sizers, it is unclear how well such commercial instruments can characterize aggregated particles due to spherical interpretation and potential alterations of physical properties within extensive sampling and dilution lines. In this study, these experimental concerns were assessed by comparing equivalent size measurements from a differential mobility analyzer to the actual physical dimensions and morphologies obtained from direct TEM observations of particulates sampled from the exhaust of a diesel engine with rapid thermophoretic deposition technique. Because mobility analyzers yield an overall equivalent particulate size, the measured mobility sizes were much larger than the microscopy spherule diameters, which dictate the available surface area for their interactions with the surrounding atmosphere. Mobility size distributions were also narrower with smaller sizes compared to the TEM aggregate measurements. The average mobility diameters were found to be approximately half the average microscopy aggregate gyration diameters for the present diesel engine operating conditions. Some of the differences in fractal dimension of diesel soot aggregates were also discussed in view of the present experimental results.

[1]  Philip D. Whitefield,et al.  Methodology for Particle Characterization in the Exhaust Flows of Gas Turbine Engines , 2004 .

[2]  Constantine M. Megaridis,et al.  Morphology of flame-generated soot as determined by thermophoretic sampling , 1987 .

[3]  P. Mcmurry,et al.  Structural Properties of Diesel Exhaust Particles Measured by Transmission Electron Microscopy (TEM): Relationships to Particle Mass and Mobility , 2004 .

[4]  Bo Yang,et al.  Soot measurements at the axis of an ethylene/air non-premixed turbulent jet flame , 2003 .

[5]  A. Schmidt‐Ott,et al.  In situ measurement of the fractal dimensionality of ultrafine aerosol particles , 1988 .

[6]  Heinz Burtscher,et al.  High fractal-like dimension of diesel soot agglomerates , 1998 .

[7]  Ümit Özgür Köylü,et al.  Effect of operating conditions on the size, morphology, and concentration of submicrometer particulates emitted from a diesel engine , 2006 .

[8]  Jacob A. Moulijn,et al.  Measuring diesel soot with a scanning mobility particle sizer and an electrical low-pressure impactor: Performance assessment with a model for fractal-like agglomerates , 2004 .

[9]  S. Weinbruch,et al.  Transmission electron microscopical and aerosol dynamical characterization of soot aerosols , 2003 .

[10]  Hung V. Nguyen,et al.  The Mobility and Structure of Aerosol Agglomerates , 1993 .

[11]  J. Keskinen,et al.  Effect of engine load on diesel soot particles. , 2004, Environmental science & technology.

[12]  D. Kittelson Engines and nanoparticles: a review , 1998 .

[13]  D Mark,et al.  Characterization of Particles from a Current Technology Heavy-Duty Diesel Engine , 2000 .

[14]  C. Sorensen,et al.  Diffusive mobility of fractal aggregates over the entire Knudsen number range. , 1999, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[15]  Raj Sekar,et al.  Morphological investigation of the microstructure, dimensions, and fractal geometry of diesel particulates , 2002 .

[16]  M. Maricq,et al.  Signature size distributions for diesel and gasoline engine exhaust particulate matter , 2001 .

[17]  M. Choi,et al.  Effects of engine operating conditions on morphology, microstructure, and fractal geometry of light-duty diesel engine particulates , 2005 .