Combustion kinetics of laser irradiated porous graphite from imaging Fourier transform spectroscopy

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• 作者：Roberto I. Acosta ^{racosta755@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Kevin C. Gross ^{kevin.gross@afit.edu" class="auth_mail" title="E-mail the corresponding author} ; Glen P. Perram ; ^{glen.perram@afit.edu" class="auth_mail" title="E-mail the corresponding author} ; ^{perramg@earthlink.net" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Graphite ; Laser heating ; Combustion plume kinetics ; Hyperspectral imaging ; Laser lethality
• 刊名：Combustion and Flame
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：163
• 期：Complete
• 页码：90-99
• 全文大小：2981 K

文摘

The combustion plumes arising from laser-irradiated graphite targets were investigated experimentally using hyperspectral, imaging Fourier transform spectroscopy (IFTS). Porous graphite targets were irradiated with a 1.07 µm, 20-kW ytterbium fiber laser at irradiances of 0.25–4 kW/cm². Emissive plumes from the oxidation of graphite in air were monitored using a mid-wave infrared imaging Fourier-transform spectrometer with spatial resolution of 0.52 mm per pixel. Strong spectral emission of CO and CO₂ were observed in the infrared between 1900 and 2400 cm⁻¹ with an instrument spectral resolution of 2 cm⁻¹. A homogeneous single-layer plume, line-by-line radiative transfer model (LBLRTM) and two band models (EM2C and RADCAL) were applied to estimate spatial maps of temperature and column densities of CO and CO₂ with a temporal resolution of 0.47 s per hyperspectral image. Steady surface temperatures of 1800–2900 K are achieved after ∼1 min for irradiances of 0.25–1.0 kW/cm². A stable, gas phase combustion layer extends from 4 to 12 mm from the surface, with buoyancy driving a gas flow of ∼8 m/s. Plume extent and intensity is greater for the larger porosity (6 mm particle size) samples. Steady-state gas temperatures exceed surface temperature by up to 400 K. Column densities for CO and CO₂ of up to 10¹⁸ molec/cm² were observed. The CO/CO₂ concentration ratio peaks at 2500 K. The initial rise with temperature is consistent with effective activation energies of 149–111 kJ/mol at distances between 0.72 mm and 3 mm, respectively.