10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

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Two-dimensional Diagnostic of Nanoparticle Formation and Transport in Complex Flames Using Phase-selective Laser-induced Breakdown Spectroscopy

YIYANG ZHANG, Yihua Ren, Shuiqing Li, Stephen Tse, Tsinghua University

     Abstract Number: 272
     Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable

Abstract
Recently, a diagnostic technique named phase-selective laser-induced breakdown spectroscopy (PS-LIBS) has been developed, especially aiming at tracing nanoparticle formation and transport in reactive flows. PS-LIBS uses the gap between the breakdown thresholds of gas phase and nanoparticles. By creating nano-sized plasmas around particles without ionization of gas molecules, the technique is able to reveal information from particles while the gas phase is not disturbed. In this study we present our recent work on extending PS-LIBS to two-dimensional imaging and related applications for investigating nanoparticle formation and transport in complex flames. Benefited from the non-spark feature, PS-LIBS can be extended to two-dimensional imaging with bandpass filters, which can not be realized in conventional LIBS measurement. We visualize the quick formation of nanoparticles across the flame sheet, as well as particle transport after the flame. Parametric study shows that the intensity of atomic spectra scales linearly with particle volume fraction. Here we will show two particular examples of two-dimensional PS-LIBS imaging. First, a close-up imaging is used to study particle transport near the stagnation plane of a counter-flow flame. The spatial resolution reaches 10 μm. The measured profile of particle concentration remarkably agrees with the numerical solution of particle transport equation. Another example is single-shot two-dimensional imaging in a turbulent co-flow diffusion flame. The snapshots successfully capture particle concentrate near diffusion flame sheet and diffusion/entrainment to the precursor-free side. The single-shot two-dimensional PS-LIBS imaging can be a powerful tool to study turbulent flame synthesis.