The effect of exit strain rate on soot volume fraction in turbulent non-premixed jet flames

Abstract

Laser-Induced Incandescence (LII) measurements from soot were used to determine the soot volume fraction (SVF) in three attached turbulent non-premixed jet flames, of a similar C2H4H2N2 fuel mixture, with different exit strain rate. For all three cases, the jet exit Reynolds number was maintained at 15,000 while varying both the jet diameter and the fuel exit velocity. Measurements are reported of the mean, instantaneous, and radially integrated SVF, together with soot intermittency, for all three flames. They reveal an inverse relationship between the exit strain rate and all of the aforementioned quantities. This observation is consistent with previous trends reported both in laminar flames and turbulent flames, although this is the first systematic assessment for flames that are also well-suited to model validation. The probability density functions of maximum instantaneous SVF exhibit similar trends with regards to exit strain rate, although the most probable SVF increases with decreasing exit strain. The volume integrated SVF reveals an inverse relationship with the exit strain rate, which can be characterized by an exponential fit. A linear correlation was also found between the exit strain rate and the maximum instantaneous SVF, the maximum mean SVF, and the total soot volume per flow rate of fuel.