A new technique for capturing the complicated behavior of turbulent flames produced during combustion has been developed by scientists.
A new high-speed 3D imaging method can capture the complex behavior of the turbulent flames produced during combustion. Shown are two cross sections of the 3D density measurement at Z = 16 mm and X= 0 mm, respectively(a) and the 3D iso-surface of the largest density gradient between the mixture and burned product (b). Image Credit: Qingchun Lei, Northwestern Polytechnic University
The knowledge offered by this high-speed 3D imaging method could be utilized to develop highly efficient and cleaner combustion systems for airplanes, cars, factories, and power plants.
The high-speed imaging approach we developed provides detailed insights into flame dynamics, ignition processes, and combustion behavior.
Qingchun Lei, Associate Professor, Northwestern Polytechnic University, China
Lei added, “This can provide insights into combustion efficiency, pollutant emissions, and the optimization of energy production processes that could be used to improve the design and operation of power plants, engines, and other combustion devices, leading to reduced environmental impact and enhanced energy efficiency.”
In the Optica Publishing Group journal Optics Letters, the scientists explain their new method that adds 3D information and high-speed image reconstruction to schlieren imaging, a well-established method for imaging and quantifying phenomena in fluids.
The new method could be utilized to quantitatively achieve the 3D density and velocity distribution of turbulent flames.
The detailed understanding of flame behavior and ignition processes facilitated by this technique can also contribute to more effective fire safety measures by providing information on how fires spread, develop, and can be suppressed.
Qingchun Lei, Associate Professor, Northwestern Polytechnic University, China
Lei added, “This can be used to enhance fire prevention strategies, improve building designs and develop more efficient fire suppression systems that could ultimately help save lives, protect property and improve overall fire safety standards.”
Adding Speed and Multiple Perspectives
Since turbulent combustion is known to be highly dynamic and 3D in nature, it is hard to quantitatively capture it adequately utilizing measurement methods like traditional schlieren imaging. For this issue to be resolved, the scientists integrated three imaging methods: Schlieren imaging, fiber imaging, and computed tomography (CT).
The new method makes use of a series of fiber bundles to send light containing flame information from various angles.
Every angle of light rays develops a Toepler’s lens-type Schlieren system that has the potential to image the density changes of the target flames. CT, which is generally utilized in medical imaging, is further employed to rebuild the 3D Schlieren images. Eventually, post-processing of the 3D schlieren images has been utilized to achieve 3D density and velocity information.
Fiber imaging enables high-speed, simultaneous Schlieren imaging from multiple perspectives in a flexible and cost-effective manner while adding CT enables the 3D reconstruction of target flames based on the multi-angular 2D images.
Qingchun Lei, Associate Professor, Northwestern Polytechnic University, China
Lei added, “The resulting high-speed 3D Schlieren imaging technique achieves a frame rate beyond tens of kHz, which allows the capture of rapidly changing flame phenomena with exceptional temporal resolution, providing detailed insights into transient flame events.”
Capturing Complex Flame Dynamics
For the performance and effectiveness of the high-speed 3D Schlieren imaging method to be validated, the scientists performed experiments on turbulent and laminar premixed flames and also transient ignition processes.
The experimental setup consisted of two Xenon lamps, a single high-speed camera, and a series of fiber bundles.
The fiber bundles were placed in a way to capture schlieren images of the flames from seven different orientations concurrently while the camera recorded the images at a high frame rate. The experimental setup is comparatively inexpensive than highly complicated and specialized equipment, like lasers, used in other methods.
The outcomes of the experiments displayed that the high-speed 3D schlieren imaging approach successfully captured and quantified the structure, flame dynamics, and ignition processes.
Currently, scientists are working to improve the practicality of the method and the potential for commercialization.
This includes testing its reliability and robustness throughout a wide range of flame conditions and configurations as well as improving the image processing and reconstruction algorithms. Also, they want to enhance system integration and automation and additionally simplify the setup.
Journal Reference
Li, X., et al. (2023) Fiber-based high-speed 3D schlieren imaging. Optics Letters. doi.org/10.1364/OL.496333.