Application of diffuse background illumination to lean direct injection combustion undergoing oscillations

Diffuse background illumination (DBI) diagnostics is applied to study spray instabilities in lean direct injection combustion systems for gas turbines. Experiments were performed in a reacting kerosene spray at atmospheric pressure using DBI, Mie Scattering, and OH* chemiluminescence (OH*-CL) imaging to delineate instability dynamics. Comparison of DBI and Mie scattering results shows that the Mie scattering is effective in illustrating the planar structure of the dispersed spray, but the line-of-sight DBI provided an improved visualization of the off-axis features of the spray to aid in understanding the spray dynamics. Measurements were postprocessed into phase-reconstructed data to illustrate the dynamic relationship between spray and OH*-CL oscillations and to demonstrate the effectiveness of DBI imaging for illustrating the influence of spray structure on the flame topology. Results show that DBI provides a clear illustration of how spray oscillations govern the switching between premixed (lean or rich) and diffusion modes of combustion over the course of the oscillation cycle.