Volumetric flame reconstructions in an optical engine cylinder involving refraction and blockage

Abstract

Practical applications of computed tomography (CT) in optical engines require an advanced algorithm that can correct the light refraction via optical windows and reconstruct the 3D signal field partially blocked by structural obstacles. In this work, an advanced CT algorithm is designed for optical engines to simultaneously eliminate the imaging distortion by refraction and diminish the reconstruction errors using partial signal blocking. By combining the pinhole model and Snell’s law, the ray tracings from discretized 3D voxels in the measurement domain to 2D pixels in the imaging planes are accurately calculated, thus restoring the distortion in recorded projections. Besides, by deciding the locations and numbers of voxels that actually participate in iterative CT calculation, the iterative update process of voxel intensity becomes independent of the blocked rays, reducing the reconstruction errors. The algorithm is then numerically validated by reconstructing a simulated signal phantom inside an optical cylinder with a lightproof obstacle between the phantom and a recording camera, which imitates the refraction and blocking conditions in practical optical engines. Moreover, experimental demonstration is performed by reconstructing practical premixed flames inside optical engines. Both the simulation and the experiment present significantly enhanced flame chemiluminescence reconstruction by applying the optimized CT algorithm compared to the original algorithm utilized in open space applications.