Three-dimensional tomographic reconstruction for gaseous fuel jets based on background oriented schlieren technique

Abstract

The optical diagnostics of transparent gaseous flows are of great significance to the fields of aerodynamic experimental research, gas fuel development and utilization, and fuel emission characteristics research, which has attracted the attention of the field. Since the transparent gaseous flow is difficult to measure directly and common two-dimensional test methods could not completely recover the structures of the complex flow field, three-dimensional test methods with the function of visualizing transparent flow field are the research need of gaseous fuel combustion system designs. This paper proposes a three-dimensional reconstruction method of Ray Tracing 3D Background Oriented Schlieren (RT-3D-BOS) and uses the Runge-Kutta iteration to calculate the path of light in the non-uniform flow field by ray tracing. This technique is also combined with a 3D tomographic reconstruction method to acquire the 3D density of the transparent gas flow field quantitatively. In this paper, the RT-3D-BOS method is used to reconstruct the 3D density field of helium jet gas which is the surrogate fuel gas for the hydrogen fuel from single-hole and multi-hole fuel injectors, and different regularization methods are introduced and tested in the reconstruction process. The results show that the proposed RT-3D-BOS method can effectively implement the measurement of the complex three-dimensional transparent gas density field. The total variation and Tikhonov regularization strategies commonly used in tomographic reconstruction for reducing the effect of noises can further improve the measurement fidelity.