High repetition rate two-dimensional laser induced incandescence studies in a C_2H_4/H_2/N_2 non-premixed flame

摘要

This paper presents an investigation of high-repetition-rate excitation for two-dimensional laser-induced incandescence (LII) imaging of soot evolution and distribution in ethylene/hydrogenitrogen (C_2H_4/H_2/N_2) jet flames. This work focuses primarily on characterizing the intrusive effects of repetitive pulsing on the LII signal and investigating the feasibility of utilizing high-power burst-mode lasers for LII studies of turbulent sooting flames. Prior work has indicated that at the laser fluences that are typically used for LII, the first pulse may sublimate the soot in the measurement volume, leading to a decrease in the signals obtained from subsequent pulses when operating at kHz rates. However, this effect appears to be absent when inspecting images obtained in a turbulent jet flame. Indeed, data from a steady flame indicates that the LII signal reaches a steady state after an initial transient, suggesting that it may be possible to perform soot studies at high repetition rate. This study quantifies the changes in signal level occurring at different laser fluences and pulse separation times and presents LII data in jet diffusion flames at different Reynolds numbers to evaluate this effect under turbulent conditions.