Effects of Temperature and Hydroxyl Radical Concentration Distributions on Emissions of Partially Premixed Flames From Elliptical Burners

Abstract

Non-circular burner geometries have shown some promise of reducing pollutant emissions form combustion systems. The use of non-axisymmetric geometries has the potential to alter the behavior of a flame through modification of the flow field. To investigate these flow field effects on combustion performance, a study of the partially premixed flames emitted from a circular burner and a 3:1 aspect ratio (major axis / minor axis) elliptical burner of equal exit area was performed. For laminar conditions, the elliptical and circular burner produced similar global emissions of carbon monoxide and nitric oxide. In turbulent flames, the elliptical burner produced a larger amount of carbon monoxide, but reduced nitric oxide production. In turbulent flames, the enhanced mixing facilitated by elliptical burners froze the CO oxidation reaction and thus increased its emission. In laminar flames, the elasticity did not significantly affect mixing rates, and thus resulted in similar CO emissions between the burners. The hypothesis on CO reaction freezing was confirmed with inflame structure measurements of CO, OH, and temperature. The decreased NO production in turbulent flame was attributed to a reduction of the flame length of the 3:1 aspect ratio elliptical burner and thus a decrease of residence time compared to the circular burner.