Soot-turbulence interaction in turbulent jet flames based on 10-kHz laser-induced incandescence measurements

A novel 10-kHz laser-induced incandescence (LII) measurement system was developed to address the scarcity of high-frequency soot diagnostics in turbulent flames. The LII measurement was integrated with particle image velocimetry to investigate soot-turbulence interactions in turbulent non-premixed methane jet flames. Simultaneous time-resolved measurements of soot volume fraction ( f v ) and velocity fields were conducted in the soot formation region of flames at Reynolds numbers of 5000 and 10 000. The high-frequency LII system demonstrated excellent capability in tracking the dynamic evolution of soot structures while maintaining an adequate signal-to-noise ratio. The results of the soot dynamic evolution show that the soot evolution is driven by the vortex structure and affected by turbulent shearing and stretching effects. The joint probability density functions based on high-frequency measurement statistics show that the spatial location of the soot structure with high f v is correlated with the axial velocities of about 6-8 m/s, the relative velocities of 0-3 m/s, the shear rate around zero, the strain rate of near 300 s⁻¹, and the vorticity below 500 s⁻¹. The correlation patterns between the high f v soot and the turbulence properties are similar for the two flames, despite the significant difference in jet velocity. The time-resolved statistics of the fluctuation velocities demonstrate the correlation between soot formation and turbulent fluctuations. The findings emphasize that local flow field conditions governing residence time are crucial for soot formation in turbulent flames.