基于三维层析技术的光学柴油发动机机内火焰重构

Flame Reconstructions in an Optical Diesel Engine Using Three-dimensiona Computed Tomography Technology

本文搭建了基于一台光学柴油发动机的三维层析测量系统,利用高速相机和光纤束可以同时从8个不同方向获得燃烧室内的火焰投影,同时提出了一种特殊的标定装置,能够从多个不同方向标定光纤束与燃烧室之间的相对位置关系。本文分析了光学发动机中由缸套扭曲引起的重构误差大小,并应用三维层析技术对光学发动机内的火焰发展过程进行了重构,获得了不同发动机转速下的火焰三维结构。通过对火焰二维投影和三维结构的分析发现,随着发动机转速增加,燃烧效率变高,最大火焰面积/体积和火焰强度出现的时刻提前,但是利用二维火焰投影得到的最大火焰面积与利用三维火焰结构得到的最大火焰体积出现的时刻不同,这是由于火焰在燃烧室内除了沿着燃烧室直径方向扩散,还会沿着活塞运动方向扩散。利用火焰三维重构结果,可以获得火焰在沿活塞运动方向上的分布,有助于分析燃烧过程,为提高发动机效率提供依据。

A three-dimensional(3D)tomographic measurement system is set up around an optical diesel engine.In the system,two high-speed cameras and fiber-endoscope bundles(FEB)are used to capture flame projections in the combustion chamber from eight different orientations.Meanwhile,a special calibration plate is designed for calculating locations between the combustion chamber and FEBs.In addition,reconstruction errors induced by refractions are quantified using simulations.Finally,3D flame structures in the combustion chamber under different engine speeds are obtained using the 3D tomography technology.According to the comparison between 2D projections and 3D structures,with the increasing of engine speeds,the moment when the maximum fame area/volume and intensity are advanced.However,the moment calculated by 3D structures are delayed compared with that calculated by 3D projections because in the combustion process in the combustion chamber,flame propagate towards the direction of cylinder diameter as well as towards the direction of piston movement.Using 2D projections can only observe the propagation towards cylinder diameter.If utilizing 3D flame structures,the propagation towards the direction of the piston movement can also be obtained,which is helpful to analyze the combustion process and provide the guidance for improving the efficiency of engines.