Research On The Temperature And Particle Characteristic In Diffusion Flames Using Hyperspectral Imaging Technique

Inhalable particle is the major pollutant in urban atmosphere in China,long period of heavy air pollution makes solving this problem extremely urgent.Soot particle emitted from combustion process is one of the primary source of this kind of pollution,research,control,and management of soot particle all rely on accurate,reliable soot measurement techniques.Due to the non-intrusion,low cost,and non-requirement of a high-quality radiation source,emission-based spectroscopy is very suitable for in-site measurement.In hyperspectral imaging device,each pixel measures radiation intensity at a large number of continuous wavelengths,providing radiation images at these wavelengths,which contain both spatial and spectral information.Combined with spatial reconstruction of emission spectrum,these images can be used to conduct simultaneous measurement of distributions of parameters.The detailed description of this paper is as follows.A multi-wavelength thermometry using Newton-type iterative algorithm to determine the temperature and the polynomial relationship between the radiation parameter and wavelength is proposed,with which distributions of radiation temperature and emissivity of ethylene laminar diffusion flame with 194 mL/min C₂H₄and 284 L/min air are experimentally studied using a hyperspectral imaging device.The emissivity of the ethylene/air laminar diffusion flame decreases as wavelength increases,in measurement wavelength region,the highest emissivity is slightly larger than 0.22,appearing under wavelength 400 nm.Four ethylene laminar diffusion flames in air atmosphere are experimentally studied using a hyperspectral imaging device.Considering the self-absorption,distributions of temperature,absorption coefficient,and soot volume fraction are iteratively calculated.For ethylene laminar diffusion flames in air atmosphere,the highest temperature occurs near the flame root and the flame edge.For each flame,there is another local peak of the soot volume fraction in the upper center part.With fixed air flow,reduction in the ethylene flow will not have significant effect on the temperature peak,but will make lower soot volume fraction peak.Ethylene laminar diffusion flames in oxygen-enriched air and oxygen/carbon dioxide atmospheres are experimentally studied.For these two kinds of flame,with fixed ethylene and oxidant flows,higher oxygen content makes shorter flames,and higher temperature peaks.In oxygen-enriched air atmospheres,with fixed ethylene and oxidant flows,reduction in oxygen content makes higher soot volume fraction peak,demonstrating that reduction in oxygen content of the oxidant will promote the formation of soot particles,while in oxygen-enriched oxygen/carbon dioxide atmosphere,with fixed ethylene and oxidant flows,reduction in oxygen content makes lower soot volume fraction peak.Scattering coefficients under wavelength 632.8 nm of ethylene laminar diffusion flame with 194 mL/min C₂H₄ and 284 L/min air are experimentally measured.Combined with measured distributions of absorption coefficient,soot particle sizes and number densities at several heights are calculated.Results show that,particle diameters are in the range of 20 to 60 nm.What’s more,at 60 mm height,the strongest scattering effect appears in the center part,validating the existence of the second local peak of soot volume fraction in air atmosphere.