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Department of Mechanical Engineering, Ferdowsi University of Mashad,

Mashad, Iran, Postcode 91775.

ABSTRACT

The present study is concerned with measuring and simulating soot formation and combustion in turbulent liquid fuel spray flames. A full-scale horizontal laboratory combustor with a circular cross-section made of AISI 316 stainless steel is constructed to confine the flame and prevent gas composition fluctuations from the ambient air. The full-scale combustor is 360 mm in diameter and 1000 mm in length, which ensures that the essential physics of full-scale combustor are simulated. An oil burner atomizes the pressurized fuel oil inside the combustor. Soot concentrations inside the combustor are measured by the filter paper technique. The simulation is based on solution of the fully-coupled conservation equations for turbulent flow, chemical species kinetic modeling, fuel droplet evaporation and combustion and soot formation/oxidation. The soot formation is modeled by using the soot particle number density and the mass density based on acetylene concentrations. Two oxidation models simulate the rate of soot combustion: the O₂-oxidation model, which assumes soot combustion is caused by oxygen molecules and, the O₂-OH oxidation model which assumes soot combustion occurrs by both hydroxide radicals and oxygen molecules. The experimental and numerical investigations are conducted for different fuel spray cone angles. The comparison of calculated results against experimental measurements shows good agreement. Both the numerical and experimental results show that both the peak value of soot and its location in the furnace depend on fuel spray cone angle. An increase in spray angle enhances the evaporating rate and increases peak temperature near the nozzle. The results also show that the OH radical has major influence on soot combustion especially while O₂ oxidation is minimal.

Keywords: Soot combustion; soot formation; spray angle; turbulent flames.