| Metal droplets are widely used in manufacturing and defense industries,such as metal 3D printing,microelectronics manufacturing,and propellant combustion.In the case of propellant combustion in the chamber of a solid rocket engine,the dynamic combustion processes of the particles determine the combustion efficiency,combustion rate,and combustion stability.The dynamic combustion process is affected by the three-dimensional distribution of burning particles,particle size and morphology,and the state of motion,so the high-precision measurement of these key parameters is of great significance.However,for metal droplet identification,accurate 3D localization and particle size and shape measurement in the combustion field,and optical methods have been difficult in phase differentiation and 3D measurement of burning particles.As an optical measurement technique,dual-beam interferometric particle imaging(DIPI)enables the measurement of opaque spherical droplet size.Facing a wide range of metal droplet measurement needs also prompts the development of measurement technology toward three-dimensional measurement.To address the above issues,this thesis mainly proposes an astigmatic dual-beam interferometric particle imaging(ADIPI)method for opaque droplet measurement,which realizes the simultaneous measurement of the three-dimensional position,particle size morphology,and velocity of opaque droplets,and applies it to propellant combustion.Firstly,the single-point DIPI is extended to the measurement of two-dimensional planar droplets,and particle size measurement and two-dimensional spatial localization of opaque spherical droplets are realized using two beams of sheet light as the incident light source.Based on the Lorenz-Mie theories,geometric optics theory,simulation,and experimental validation,the two-dimensional configuration of planar dual-beam interferometric particle imaging is comprehensively investigated.Compared with digital holography(DIH),the average deviations of the results obtained from DIPI in particle size measurement and 2D localization are 2.4% and1.9%,which proves the feasibility of DIPI in 2D localization and particle size measurement of metal droplets.Secondly,an astigmatic dual-beam interferometric particle imaging method is proposed to realize the simultaneous measurement of the three-dimensional position and the particle size of spherical opaque droplets.A theoretical model of backscattering region is established based on the Lorenz-Mie theories and geometric optics theory.The quantitative relationship between the depth position and particle size of the droplets and the angle and spacing of the interference fringes of the ADIPI is obtained.The simulation program of the ADIPI is developed,and the influences of each parameter of the system on the factors of the measurement distance,the change of the fringes,and the interference pattern are analyzed,to guide the construction of the experimental system.Based on the ellipse detection algorithm and two-dimensional Fourier transform algorithm,the ADIPI signal processing algorithm is developed for the rapid analysis of the center position of the interference pattern,the spatial frequency and inclination angle of the interference fringes,and to realize the measurement of the two-dimensional position,the droplet size,as well as the depth position.The ADIPI system is built to measure gallium metal droplets and compare them with the results of DIH experiments.The results of ADIPI,in both the depth position and size measuring,exhibit a high degree of consistency with DIH’s,given the average relative deviations of 5% in size measuring and 1% in-depth position,respectively,which proves the accuracy of ADIPI in 3D localization and particle size measurement of metal droplets.On the basis of the theoretical model established above,a generalized model applicable to the forward scattering region,the sideward scattering region,and the backward scattering region is derived.An experimental system for 360° ADIPI signal detection is designed and constructed.The accuracy of depth localization and particle size measurement is verified by measuring the same droplet in three scattering regions for comparison,and the three-dimensional localization and size measurement of the same spherical metal droplet at any detection angle except for the two laser beams’ optical axes are realized.In addition,the droplet depth displacement can be directly calculated from the interference fringe rotation angle.On the basis of the theoretical model of ADIPI,the quantitative relationship between the changes of the interference fringes rotation angles and depth displacements is deduced.The displacement in the depth direction can be improved to an accuracy of tens of microns.A 5 k Hz time-resolved ADIPI system is built,and proof-of-concept experiments are conducted by using micron-scale gallium droplets.In addition,data processing methods based on the angular cross-correlation and the angular cross-power spectral density are developed for calculating droplet depth displacements.Finally,the propagation process of reflected light from irregular particles under dual-beam laser irradiation in an ADIPI optical system is theoretically described to realize the threedimensional localization of irregular particles and the measurement of particle size and shape.A13 k Hz experimental system with the simultaneous coupling of ADIPI and DIH is designed and constructed to measure the solid propellant combustion process.By analyzing typical interference patterns in the propellant combustion field,the phase discrimination of materials such as metal droplets,gas flames,and pyrolysis residues is achieved,and the 3D spatial localization of burning particles,3D trajectory tracking,and the measurement of irregular particle sizes and morphologies are realized under high time resolution.In terms of measurement distance,the depth localization deviation of burning particles is within 1%,which verifies the feasibility of ADIPI for propellant combustion field measurement. |
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