Numerical Simulation Of Radial Shearing Interferometric Thermometry For Laminar Ethylene Diffusion Flame

Laser interferometer technique in the measurement of temperature field for laboratory flame shows the virtue of non-contact,real-time and full field measuring as the same as radiometric image processing technique employed in industrial furnace, but their principles are independent. Laser interferometer technique can be effectively used to test radiometric image processing technique.Cyclic radial shearing interferometric thermometry system offers many advantages such as compact layout, online monitoring, anti-disturbance ability and no reference beam needed.Local concentration of main species must be known in the reconstruction of temperature field. This process is especially difficult for flame due to its unknown fierce chemical reaction. The result will bring obvious error by assuming that local composition corresponds to air. Interferometric thermometry for hot air flow was often reported but rarely for flame.With the numerical simulation data including temperature,density and species concentration for laminar axisymmetric ethylene diffusion flame in setting conditions, optical imaging process such as plane wave's distortion after flame region and radial shearing Interference of the distorted wavefront were simulated. Radial shearing Interference fringe patterns with series spatial carrier frequency at setting noise level were also made.Using frequency-domain phase shifting method (also called Fourier Transform Method), the distribution of fringe phase difference could be extracted from the simulative fringe pattern which carried bidirectional high spatial frequency. Important parameters such as frequency-domain identification scope,carrier frequency's intensity and conjugated spectrum bandwidth were quantitatively given during frequency-domain analysis. It shows that frequency-domain phase shifting method for flame can only proceed when carrier frequency's intensity and fringe resolution meet certain conditions.Refractive index distribution was got after finishing iterative reduction and projection inversion process. Its relative error compared with original value is less than 2 percent generally in flame field. Both the concentration data and the "air assuming" condition were respectively applied to solving temperature field. In this simulation condition it shows that the "air assuming" brings about 5 percent to 10 percent relative error in the upper part and middle part of the flame field. The error increases rapidly from the Lower part to root and the measure result becomes meaningless.