Soot Properties in Steady and Unsteady Non-Premixed Counterflow Flames

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ABSTRACT - Koylu This is a study of soot formation in laminar flames that are forced by a controlled time-varying flow field. A counterflow burner is used with a loudspeaker on each side to impose unsteady strain rates on the flames. Measurements are made on steady and unsteady flames including volume fraction of translucent and mature soot particles, particle/aggregate sizes, soot morphology, particle velocity, flame temperature, molecular fluorescence, and radiative losses. Experimental techniques include laser scattering and extinction, thermophoretic sampling with examination by transmission electron microscopy, visible absorption spectroscopy, laser Doppler velocimetry, two-wavelength pyrometry, thermocouple measurements, laser-induced fluorescence, and total radiation heat flux. Fuels used include methane, propane, propylene, and acetylene; strain rates are varied in the range of 20-200 sec -1. Computational predictions of soot and flame properties are made and compared to the experimental observations. This is an attempt to bridge the gap between laminar (which is easily studied) and turbulent (reflecting practical systems) nonpremixed combustion of hydrocarbon fuels. The long-term goal is perfection of methods to control soot formation in a range of applications including internal combustion engines, gas turbines, and industrial furnaces.