Simultaneous Particle Size And Velocity Measurement In Spray With IPI Technique

In flash boiling spray,the droplet size and velocity distribution have an important influence on the formation of the mixed gas in the direct injection gasoline engine.Interferometric particle imaging(IPI)technique,based on Mie scattering theory,is a popular method for instantaneously measuring the size of the spherical particle,utilizing the interference fringes or glare-point pairs on a defocused or focused image plane.Combined with particle tracking velocimetry(PTV)technique,the particle size,velocity and spatial distribution can be simultaneously derived from focused or defocused IPI images,and this technique has been widely applied to sprays,bubbles,flow fields,and other situations.In this paper,the size and velocity measurement of particles in spray with IPI technique are investigated from three aspects: theory,algorithm and experiment.The main work is as follows: 1.Based on the principle of particle size measurement with IPI,the equation offringe size is given,and the uncertainty in the size measurement is analyzed.Thecenter discrepancy between the focused and defocused image,and the centerdeviation between the particle center and geometrical center of focused ordefocused image,with respect to the particle position and size,are analyzed.Based on the IPI simulator,it is determined that the extracted center isgeometrical center of focused or defocused image,and then the particle center isacquired.2.The improved correlation-based image processing method for particleidentification is proposed with extended glare-point imaging technique.Thealgorithm is capable of identifying particle position and size as well as trackingand matching droplet displacement vectors.The employed template matchingalgorithm using the serial particle mask and centroid method provide higheraccuracy for estimating droplet displacement,and the cross-correlation matchingalgorithm and the two-frame particle tracking algorithm further ensure highermatching rate for droplet pairs.The performance of the algorithm has been wellvalidated by simulations.3.An experimental system of IPI with opposition of two laser-sheets illumination atscattering angle ?=90o is built.Combined with PTV technique,the droplet sizeand velocity are measured simultaneously.Furthermore,the droplet size and velocity distribution of n-heptane flash boiling spray are obtained under different experimental conditions and measurement positions.The results reveal the formation mechanism of flash boiling spray.The flash boiling phenomenon has a critical effect on the spatial distribution of droplet size,but little effect on the droplet velocity.The air entrainment,droplet collision and polymerization have an important influence on the size distribution.In the intense flash boiling spray,the particle size distribution is uniform because the micro-explosion of bubbles promotes the atomization of the fuel.The results show that the proposed algorithm has high measurement accuracy,matching rate and robustness.