The effect of diesel engine conditions on the size and morphology of soot particles

Soot agglomerates emitted by diesel engines are variable in size and morphology, both characteristics having important environmental implications. The main geometrical characteristics of soot emissions can be quantified by means of the size distribution and the fractal dimension, the latter being a measure of the particle irregularity. In this work, size distributions were obtained with a scanning mobility particle sizer connected to a partial-flow dilution mini-tunnel, while fractal dimensions were obtained from high resolution transmission electron microscope images of agglomerates collected by thermophoretic sampling. Both the mini-tunnel and the thermophoretic probe sampled from the same point in the exhaust line, where smoke opacity and gas temperature were also measured. The engine was tested under different engine speeds, air/fuel ratios and exhaust gas recirculation rates, to evaluate their independent effects on the morphology of the emitted particles. Finally, the obtained trends were combined to estimate the effect of real driving conditions in a modern automotive engine on the main morphological characteristics of the soot particles.