Spatially resolved measurements of velocity fields in the reactive zone of a laminar non-premixed flame

Abstract

An experimental and numerical study of flow velocity fields in a flaming environment, particularly in the high-temperature sooting zone, was conducted in a laminar non-premixed flame. A Yale type burner was employed under flame B conditions. Velocity measurements were performed using Particle Image Velocimetry (PIV), and the OpenPIV software for data treatment. The sooting zone was experimentally characterized using extinction and emission measurements, and were treated to obtain spatially-resolved soot volume fraction and temperature fields. The experimental results were compared with numerical simulations of soot volume fraction, gas temperature, velocity fields using the CoFlame code. A synthetic PIV framework based on the simulations was performed to validate the PIV processing. Experimental results exhibit continuous velocity fields, even in the high-temperature sooting zone, where visibility and the density of the tracer particles are low due to the high temperature gradient, driving particles out of the reaction zone. This was achieved by carefully adjusting the optical arrangement and laser characteristics, to enhance the signal-to-noise ratio and ensure the completeness of the velocity field measurements. The experimental results were in close agreement with numerical predictions for both the inert and reactive flow cases. However, some discrepancies were observed, which were more prominent in the inert case due to the lower gas velocity that exerts less drag on the tracer particles. These discrepancies were reduced by applying a correction to the experimental velocity field along the central streamline, based on Lagrangian modeling of the tracer particles, which considers their mass and diameter.