Probability density functions of product concentration in a turbulent reacting coflow jet of NH3 and HCl

Abstract

The distribution of product in a turbulent reacting coflow jet was investigated in which dilute HCl issued into a coflowing stream of dilute NH3. Mass concentrations of the product, NH4Cl aerosol, were inferred from Mie scattering measurements. Probability density functions (PDFs) of the product exhibited a preferred concentration, or mode, that remained constant across the jet while the flow was in an early stage of reaction, indicating that production occurred in large scale structures that extended across the jet. In contrast, in regions where the reaction had progressed to a significant degree, the mode marched to lower concentrations with radial distance from the centerline, such that the PDF resembled that of a passive scalar. In these regions, radial distributions of the mean and rms fluctuations of product concentration were similar to those of mixture fraction, measured using laser induced fluorescence of acetone. In regions where reaction was still in the early stages, product distributions differed markedly from mixture fraction distributions. The PDFs suggested that product was formed at the edges of large structures of rather uniform reactant concentration. A two-dimensional image of Mie-scattered laser light from the aerosol product supports this interpretation by revealing long, narrow regions of product.