3D Printing of Spark-Ignited Flame Kernels, Experimentally Captured by 3D-Computer Tomography and Multi-Directional Schlieren Photography

Non-scanning 3D-CT(Computer Tomography) technique employing a multi-directional quantitative schlieren photographic system with flash light source, has been performed to obtain instantaneous density distributions of spark-ignited laminar / turbulent flame kernels. For simultaneous schlieren photography, the custom-made 20-directional schlieren camera was constructed and used. The concept of the multi-directional shclieren system is shown in top-right figure. Each quantitative schlieren optical system, indicated in top-left figure, is characterized by a rectangular-shaped right source with uniform luminosity. Middle-left picture gives the appearance of the multi-directional schlieren camera. The flame kernels are made by spark ignition for a fuel-rich propane-air premixed gas (flow velocity :1.0 m/s, equivalence ratio :1.4 ). Spark electrodes of 0.4 mm diameter with 1.0 mm gap are used. First, development of laminar flame kernel is indicated in high-speed images of middle-right figure. 3D printed model of the CT reconstruction result (left in bottom-left photograph) shows the spherical shape of flame kernel with a pair of deep wrinkles. The wrinkle is considered to be caused by spark electrodes. Next turbulent flame kernel behind turbulence promoting grid is selected (turbulence intensity 0.26 m/s). The high-speed images of bottom-right figures show corrugated flame shape. 3D model of CT result (right in bottom-left photo.) expresses the instantaneous 3D turbulent flame kernel shapes. These 3D solid models based on 3D-CT reconstructed data of 2 ms, are 3D-printed as 2 times large size for threshold density level of 0.7 kg/m³.