| The formation and evolution of sub-micron soot particulates within turbulent non-premixed flames were investigated by conducting laser-based experiments, which were properly interpreted to characterize time-averaged soot volume fractions, spherule diameters, and aggregate sizes. For accurate descriptions of turbulent soot dynamics, various soot processes such as nucleation, carbonization, surface growth, oxidation, and aggregation were separately explored. The measurements at a wide range of axial and radial locations within three different flames burning gaseous ethylene, acetylene, and propane in atmospheric-pressure air yielded the regions of prevailing soot mechanisms. In addition to the effect of fuel type, different Reynolds numbers in the acetylene flame were also considered to identify the effect of turbulent flow condition on the complete soot field. The lightly-sooting propane and ethylene flames offered broader spatial regions of early particulate formation while the heavily-sooting acetylene flames produced the optically-thick conditions that are encountered in practical combustors operating at high pressures. Some of the results were compared to the independent thermophoretic sampling measurements to reveal the diagnostic limitations for soot precursor particles and relatively high soot concentrations. The present experimental findings are crucial to assess computational soot predictions that can be utilized to control fine particulate matter in many power systems such as diesel engines and gas turbines. This will ultimately lead to the combustion technology that can satisfy stringent emission regulations for undesirable pollutants, which significantly contribute to human health problems, global warming, and air pollution levels. |
