HCHO PLIF investigation of the flame shape in an unsteady swirling jet flow

This paper describes the experimental study of the spatial structure of a chemical reaction zone in a turbulent flow of a jet swirled by means of panoramic laser-induced formaldehyde fluorescence. The burning of an air–methane mixture under atmospheric pressure and at different excess coefficients of fuel $\phi$: the burning of an inverse cone shaped flame $\phi$ = 0.7–1.4 and the burning of an elevated flame $\phi$ = 2.5. Aside from small-scale deformations, the changes in the shape of the chemical reaction zone is coupled with two types of large-scale coherent structures, namely the virtually axisymmetric deformation mode of the flame front, which is probably due to the action of Archimedes forces on the combustion products, and the rotation of the asymmetric mode due to the precession of the swirled flow.