3-D Animation Shows Complex Geometry of Diesel Particulates

Diesel particulate matter has a very complex geometry Most studies have observed these three-dimensional structures in two-dimensional images. Argonne researchers were the first to use a unique combination of thermophoretic sampling techniques and high-resolution transmission electron microscopy (TEM) to observe the detailed three-dimensional geometry of diesel particulates.

These studies captured detailed information on particulate morphology and fractal geometry well beyond commercially available particulate size measurements. These studies enhanced the fundamental understanding of the formation and destruction mechanisms of diesel particulates.

This three-dimensional animation shows a single diesel particulate produced by a light-duty engine. As this particulate rotated along a horizontal axis, pictures were taken at every ten-degree viewing angle. This animation revealed that diesel particulates were complex three-dimensional objects, and their shapes were not spherical at all. Most primary particles within this particulate were loosely aggregated together. The darker particles represent the overlaid primary particles on the line-of-sight direction.

A common misconception about diesel particulates is that they all have spherical shapes. In TEM images of particulates, however, particulates appear to consist of an agglomeration of numerous spherical primary particles. These aggregate particles showed a stretched chain-like shape independent of engine speed and load conditions. These particulates, in which tens to hundreds of primary particles cluster around each other, were distributed in a wide range of sizes from tens of nanometers to a few microns.

The discovery of agglomeration shows that the spherical particle shape measured in commercial particulate measurement instruments (such as scanning mobility particle sizers and low-pressure impacters) do not reflect the true nature of particulate spatial geometry.

Argonne is working with Caterpillar, Inc. and Corning Inc. (through a cooperative research and development agreement) to exploit previously unavailable technology and research results on diesel PM filtration and regeneration processes. Researchers aim to make breakthroughs that will enable the technology transfer of advanced PM emission control to industrial applications. Research is also conducted in response to unique requests.

Funding

This work is supported by the U.S. Department of Energy’s Vehicle Technologies Program under Gurpreet Singh and Ken Howden.

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• Emissions Control

February 2010