3D flame surface measurements in low-turbulence Bunsen flames via scanning and orthogonal cross-planar techniques

Abstract

Quasi-instantaneous 3D flame surfaces were reconstructed in a turbulent Bunsen flame via a laser scanning technique based on an acoustic-optic-deflector (AOD). Instantaneous flame surface areas were reconstructed from a series of flame contours at different vertical planes via droplet Mie scattering with a Nd:YLF high-frequency laser at 527 nm. Mean total flame surface areas 〈A〉 were estimated and compared with estimated area demands based on total mass flow rates of fuel/air mixture divided by density and unstrained laminar flame speed, m˙/(ρusL). Flame surface density (FSD, both 2D and 3D) and flame surface curvatures were also measured and compared with those acquired using 3D cross-planar methods at particular locations. Differences of up to 67% were measured at a given location in the flame brush, with 3D FSD values generally higher than corresponding 2D measurements. The present measurements are the first comparisons of FSD and 3D curvatures comparing scanning and orthogonal cross-planar techniques allowed the measurement of 2D flame contours on two orthogonal planes, leading to improved accuracy in the determination of principal curvatures in 3D flame surfaces. Novelty and significance statementTurbulent Bunsen flame surfaces were reconstructed by a high frequency scanning technique. Values of the 3D flame surface area were for the first time measured and compared to the required area for burning the total incoming mass flow rate. Values of local 3D FSD were measured via the scanning technique and for the first time compared to corresponding measurements using cross-planar technique. True 3D principal curvatures of flame surfaces were measured by combining scanning and cross-planar techniques to provide a sufficient accuracy.