Since most industrial flows are turbulent, it is necessary to have physical understanding of the flow and mixing process in three dimensions. In general, experiments are limited to two-dimensional planar imaging of the flow characteristics. This project developed a dual-plane imaging method to obtain quantitative information of the additional out-of-plane dimension of the mixing process, in addition to the planar information. Planar Laser-Induced fluorescence (PLIF) from acetone tracer molecule is utilized to mark the mixing of a central jet fuel stream with surrounding coaxial swirl coflow of air. The length and time scales of air/fuel mixing are characterized by the scalar dissipation rate (SDR). The quantification of the SDR requires the instantaneous measurement of the spatial gradients of fuel concentration in all three directions. This information is obtained using a dual-plane acetone-PLIF technique. In addition to the optical set-up, new data processing approaches are proposed to de-noise the PLIF image and to obtain thickness (length scale) of dissipation layers in the flow. Finally, the effect of flow swirl intensity on the mixing process is quantified. The dissemination of this work is in progress. There are three manuscripts in preparation, which focus on a) Development of the new experimental technique and corresponding image processing strategy, b) Fluid mechanics of turbulent mixing, and c) Effect of flow swirl number on turbulent mixing.