Relationship between soot and scalar dissipation rate in the soot-inception region of turbulent non-premixed jet flames

Abstract

Abstract In previous work we employed the Krypton Planar Laser-Induced Fluorescence technique combined with simultaneous Laser Induced Incandescence to obtain measurements of mixture fraction, temperature and soot volume fraction in the soot inception region of turbulent non-premixed ethylene-air flames (Park et al., 2017). This paper extends that work and reports the first simultaneous measurements in turbulent flames of the scalar dissipation rate and soot-volume fraction. The specific jet composition was 50% C2H4, 46% N2 and 4% Kr and the jet Reynolds number was 8300. The measurements were made 10 cm downstream of the jet exit where the soot first begins to form. The present study uses the same data set to derive the scalar dissipation rate fields and relate the dissipation to mixture fraction, soot volume fraction and temperature. The peak mean soot volume fraction was found to be well inside of the stoichiometric surface near values of mixture fraction from 0.3 to 0.4, which roughly corresponded to the regions of peak mean scalar dissipation. The polycyclic aromatic hydrocarbon field was also imaged, but not simultaneously with the other quantities. Although, the mean soot location is correlated to the mean dissipation, this result is misleading as shown by joint probability density function (PDF) between soot volume fraction and scalar dissipation. The joint PDF shows that soot is in fact no typically spatially coincident with regions of high scalar dissipation; in fact, higher dissipation is correlated with lower values of soot. These latter observations are consistent with results from recent numerical simulations that soot was preferentially found in the areas of low scalar dissipation rate and soot is locally inhibited by high scalar dissipation rates.