Direct Sampling, TEM Analysis and Optical Measurement of Soot Particles at Different Axial Locations in a Transient Spray Flame

In order for better understanding of soot formation and oxidation processes in diesel spray flame, the morphology, microstructure and sizes of soot particles directly sampled in a transient spray flame were analyzed via high-resolution transmission electron microscopy (HRTEM). The soot distribution in the spray flame was simultaneously observed by high-speed shadowgraphy. The transient spray combustion was achieved in a constant volume combustion chamber under a high pressure and high temperature condition (940 K, 2.5 MPa). The soot samples were taken at different axial locations in the spray flame, 40 - 90 mm from the injector nozzle, using an intrusive soot sampler. Pressure histories, heat release rates and laser shadowgraphs of spray combustion were compared between the cases with and without the soot sampler in order to check the intrusion effect of soot sampler on combustion. Density of soot particles directly sampled onto TEM grids in the spray flame increased from 40 to 70 mm, and then decreased from 70 to 90 mm from the injector nozzle tip, which correspond to formation and oxidation regions in the spray flame observed by laser shadowgraphs. Diameter of primary particles, radius of gyration of soot aggregates and fractal dimension of soot particles were also analyzed.