A Planar Mixing Layer (PML) Configuration to Perform Spatially Resolved High-Resolution Differential Mobility Analysis (HR-DMA) in Diffusion Flames

Mahmoud Ashour, FARNAZ KHOSRAVI, Francesco Carbone, University of Connecticut

     Abstract Number: 565
     Working Group: Combustion

Abstract
The unraveling of soot inception in non-premixed flames is an unsolved challenge that may further the understanding of soot formation in real combustion applications. Over several decades, the Axysimentric coFlow (AcoF) and Counterflow (CF) canonical flame configurations have been invaluable for studying many aspects of soot formation in diffusion flames. However, the steep gradients and the small sizes of the flame these canonical configurations can stabilize made them incompatible with the use of dilution probes necessary to implement aerosol diagnostics. To address this problem, we introduced the Planar mixing Layer (PML) by modifying the original Wolfhard-Parker burner design which consists of two adjacent planar nozzles, one yielding the fuel and the other the oxidizer, both surrounded by a nitrogen flow to shield the reactants from surrounding air. The flame is stabilized near the Mixing Layer Interface (MLI) between the reactants within the boundary layer which grows at increasing Height Above the Burner (HAB) until buoyant instabilities disrupt the steadiness of the flow. The PML novelty consists of the flow stabilization achieved by installing a plate downstream of the burner nozzles, which is equipped with an exhaust slit for evacuating the hot flame products. Buoyancy anchors the flame in the middle of the slit and keeps the flow laminar and steady at large HABs so that a flat and approximately 10mm thick flame can be stabilized. The geometry enables the implementation of intrusive sampling of the PML flame products without limitations related to the spatial resolution of the results. This work reports the first spatially resolved measurements of the PML flame products performed using High-Resolution Differential Mobility Analysis (HR-DMA). The results show that soot nucleation occurs in the proximity of the maximum temperature and is followed by growth taking place while the materials are advected towards the MLI at progressively lower temperatures.