Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

Abstract

“Venturi-cascading” technique is a means to control pollutant emissions of diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33% in NO emission index along with a 24% decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, Laser Induced Fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18%, 24% and 12% in the concentrations of OH, CH and CN radical, respectively, from their baseline values. However, in the mid-flame region, a 40% average increase in OH, from its baseline value, was observed. In this region, CH or CN radicals were not detected. The OH radical, in the downstream locations, was mostly affected by soot rather than by temperature. In addition, prompt-NO mechanism appeared to play a significant role besides the conventional thermal-NO mechanism.