Relationships between Soot and the Local Instantaneous Strain Rate in Turbulent Non-Premixed Bluff-Body Flames

In this paper, the simultaneous measurements of the local velocity using polarized particle image velocimetry (P-PIV) and soot volume fraction, SVF, using planar laser-induced incandescence (LII) are reported for turbulent non-premixed ethylene-nitrogen bluff-body flames. The measured data were used to assess the correlation between soot volume fraction and the shear-strain rate (S), both mean and instantaneous, in different regions of the bluff-body flames. In the recirculation zone, an exponential function was found to reasonably describe the relationship between total SV_RZand S. It was also observed that the strain rate associated with the maximum SVF in the recirculation zone and the jet region are ≲1000 s^-1consistent with the soot inception region of simple jet flames. The joint PDFs show that the SVF is not well correlated with the local instantaneous strain rate in either the recirculation zone or the jet region of these flames. Qualitatively, the correlation of coefficient, R², between the local instantaneous SVF and inverse of the strain rate (1/S) reveals a low to weak correlation, 0.3 < R²< 0.6, in the recirculation zone and the jet region, which is consistent with the joint PDFs. This suggests that the timescales for SVF are significantly greater than those driving local fluctuations. In addition, a high-fidelity experimental dataset has been provided for model development and validations.