Convective heat transfer from a partially premixed impinging flame jet. Part I: Time-averaged results

Axial and radial profiles of time-averaged local heat fluxes of methane-air jet flames impinging normal to a cooled plate are reported, as functions of equivalence ratio, Reynolds number, and nozzle-plate spacing. Time-resolved behavior for these conditions is examined in the companion paper, Part II. Flame structure was studied visually and photographed. Both premixed and diffusion flame behavior was observed. Nozzle-stabilized flames revealed a stable, axisymmetric flame structure at nozzle-plate spacings less than 14 diameters. At greater nozzle-plate spacings, buoyancy-induced instabilities caused the flame to oscillate visibly. Lifted flames exhibited varied flame structures dependent upon the Reynolds number, equivalence ratio, and nozzle-plate spacing, stabilizing in the free jet, at the stagnation zone, or downstream in the wall jet. Local heat flux measurements made in the stagnation zone and along the plate adjacent to the wall jet flame revealed correlation of the local heat flux to the flame structure. Negative heat fluxes resulted from cool gases impinging on the hotter plate. The magnitude of positive heat fluxes depended on the proximity of the flame to the sensor surface, the rate of heat release, and the local molecular and turbulent transport.