The morphology and crystallography of diesel particulate emissions

The morphology and crystallography of particulate emissions from indirect injection diesel engines has been studied using transmission electron microscopy. Samples were collected in a diluted exhaust stream directly onto amorphous carbon films supported on electron microscope grids. Diesel particles closely resemble carbon blacks and consist of chains or clusters of quasispherical subunits. Diffraction patterns were quantified using a microdensitometer and a graphical background correction. Peak intensity was then normalized to background to eliminate exposure variations. Small clusters were found to be less crystalline than large clusters and the centers of two chain-like particulates were more crystalline than the ends. By analogy with the crystallinity studies of heat treated carbon blacks, these differences were interpreted as differences in the time/temperature histories of the particles.