Dual magnetic effects on soot production in partially premixed flames

Abstract

The present paper further explores the potential of the gradient of the square of the magnetic flux density (∇(B2)) to control the soot production in flames. Experimental investigations assess for the first time the influence of ∇(B2) on the soot production in laminar axisymmetric partially premixed flames. The steady rich ethylene/oxygen flames are established in different coflowing mixtures, composed of oxygen and nitrogen, over a Santoro type burner, which is located in an electromagnet. The flame experiences different magnitudes of upward ∇(B2), ranging from 0 to 18.2 T2/m, as well as different oxygen contents of the coflow, ranging from 21% to 50% in volume, and different levels of the equivalence ratio, ranging from 5 to ∞. Soot temperature and volume fraction are mapped in the flame by a Modulated Absorption/Emission technique. Increasing the magnitude of ∇(B2) allows for the modification of soot production in the flame. A reversal of the magnetic effect compared to the non-premixed case is observed. For non-premixed flames, the upward ∇(B2) systematically leads to an increase in soot production, while this magnetic gradient can induce an overall reduction in soot production in some partially premixed flames. This original reversal is attributed to a switch of the magnetic force direction. As a result, this supplementary force can induce an increase or a decrease of the residence time in the rich region of a partially premixed flame, depending mainly on the fields of oxygen mole fraction and temperature in this region. In conjunction with more elaborated magnetic fields, these opposite trends may contribute to strategies for the control of soot production.