Experimental characterization of turbulent methane inverse diffusion flames with multiple fuel jets

This paper presents high speed images of OH-PLIF simultaneously with 2-D PIV measurements collected at 10 KHz along the entire length of an inverse diffusion flame with circumferentially arranged methane fuel jets. For a fixed fueling rate, starting from Re = 2500, a double flame structure is observed; a lower fuel entrainment region and an upper mixing and intense combustion region. The entrainment region is confined by an early OH layer, merged through a very thin OH neck to an annular OH layer located at the shear layer of the air jet. Three types of events are observed common to all the flames: breaks; closures; and growing kernels. At low Re, the breaks are counterbalanced by flame closures in the upstream region. As the Re increases, the flame kernels become the main mechanism for flame re-ignition further downstream. These breaks in OH signal were found to occur at locations where locally high velocity flows were imping on the flame. Over the entire length of the flame, the direction of the two dimensional principle compressive strain rate axis exhibits a preferred orientation of approximate 45° with respect to the flow direction. The regions of high OH are associated with high vorticity.