Investigation and optimization of sampling characteristics of light field camera for flame temperature measurement

Abstract

It is essential to investigate the light field camera parameters for the accurate flame temperature measurement because the sampling characteristics of the flame radiation can be varied with them. In this study, novel indices of the light field camera were proposed to investigate the directional and spatial sampling characteristics of the flame radiation. Effects of light field camera parameters such as focal length and magnification of the main lens, focal length and magnification of the microlens were investigated. It was observed that the sampling characteristics of the flame are varied with the different parameters of the light field camera. The optimized parameters of the light field camera were then proposed for the flame radiation sampling. The larger sampling angle (23 times larger) is achieved by the optimized parameters compared to the commercial light field camera parameters. A non-negative least square (NNLS) algorithm was used to reconstruct the flame temperature. The reconstruction accuracy was also evaluated by the optimized parameters. The results suggested that the optimized parameters can provide higher reconstruction accuracy for axisymmetric and non-symmetric flame conditions in comparison to the commercial light field camera.

Spatial resolution of light field sectioning pyrometry for flame temperature measurement

“…It can be seen that the depth resolution (𝐷𝑅) varies significantly with the LFCs. The depth resolution of the Raytrix R29 [18] is 2027.04 mm, which is worsened than the other LFCs. The maximum 𝜎 of PSF for the Raytrix R29 is solved as 𝜎 𝑓 = 32.17 and 𝜎 +∞ = 3.58 .…”

“…where 𝐼 𝜆,0 is the spectral radiation intensity when the radiation is emitted, 𝐿 is the length of the path that the beam of radiation propagating through the flame medium, which can be solved by ray-tracing technique [18]. The attenuation coefficient 𝛽 𝜆 is given by 𝛽 𝜆 = 𝜅 𝑎,𝜆 + 𝜎 𝑠,𝜆 , where 𝜅 𝑎,𝜆 and 𝜎 𝑠,𝜆 are the absorption coefficient and the scattering coefficient, respectively.…”

“…To solve the value of 𝜎, a calibration was carried out based on the edge method [43]. Since the PSF is rotationally symmetric [18], the PSF model of Eq. ( 3) can be integrated along a line to obtain the line spread function (LSF).…”

“…Consequently, the modified reconstruction algorithm may not be ideal for improving the spatial information and, in some cases, it may increase the computational cost. Therefore, it is necessary to optimize the LFC parameters to obtain adequate spatial information of flame radiation [18]. So that the correlation between the adjacent sections can be reduced, and the depth resolution of LFSP can be improved.…”

Perspective on the development and application of light-field cameras in flow diagnostics

“…[www.raytrix.de accessed May 2021]. (C) Relayed MLA to support rapid prototyping [27]. © [2017] IEEE.…”