Hydrocarbon combustion has been the primary source of energy which enabled technological leaps. Soot is a product of incomplete combustion which causes negative impacts on the environment and health. To combat these negative effects, it is important to understand the factors which promote soot formation and oxidation. Adding diluents to fuel streams assists in inhibiting soot formation via temperature effects, chemical effects and diluent transport properties effects. Increasing the oxygen content of the oxidizer increases pyrolysis (soot forming reactions) and rates of oxidation. The rates of change of these two processes dictate the rate of change in soot production as oxygen content changes. Generally, increasing the flux of the oxidizer promotes the fuel combustion efficiency which lowers soot production. In this thesis, oxidizer oxygen contents were varied in 10% increments from 30% to 70% in ethylene inverse diffusion flames (IDFs) with four different diluents: CO2, N2, He and Ar. Particle size distribution functions (PSDFs) of the exhaust of these flames were collected using a scanning mobility particle sizer (SMSP) system. The SMPS system detected flame exhaust particles in the diameter range 14.3 nm to 673 nm. With the first three diluents, the total particle concentration of flame PSDFs initially rise as the oxygen concentration is raised then fall at oxygen concentrations beyond. In most cases, the peak total particle concentrations were observed at 40% or 50% oxygen concentrations. Moreover, the diluted flames’ total concentrations were compared at a fixed oxidizer to fuel-diluent velocity ratio (VR) at oxygen concentrations 30%, 50% and 70%. At 70% the maximum total particle concentration was in the He diluted flame and the minimum was in the CO2 diluted flame. At 30% and 50%, the maximum total particle concentrations were in the N2 diluted flames. Furthermore, increasing the flux of the oxidizer decreased the total particle concentration of the PSDFs. This is expected as the flames become leaner with higher oxidizer flux. Lastly, thermocouple temperature measurements of flames were taken at twice above the flame height. The highest temperatures were in the Ar diluted flames and the coolest flames were the CO2 diluted ones.
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