High-Resolution Transmission Electron Microscopy of Soot Directly Sampled at Different Axial Locations in Diesel Spray Flame

For better understanding of soot formation and oxidation processes in a diesel spray flame, morphology, microstructure and size of soot particles directly sampled at different locations in the spray flame (40mm to 90mm from injector nozzle tip) were investigated using a high-resolution transmission electron microscope (HRTEM). The diesel spray flame was achieved in a constant volume combustion chamber under diesel-like conditions (2.5MPa and 940K). The concentration, diameter of primary particles and the radius of gyration of soot aggregates increased in the upstream region (40 to 50mm), exhibited a peak around the mid-stream region (60 to 70mm), and then decreased in the downstream region (80 to 90mm) from the injector nozzle tip, which corresponds to formation, peak concentration and oxidation of soot particles in the spray flame, respectively. The fractal dimension of soot aggregates was also analyzed and is almost constant, with a value of approximately 1.73 over different axial locations in the spray flame.