Experimental Research On Measurement Of Aluminum Combustion In Solid Propellant By Using Digital Holography

Aluminum powder is a widely used metal additive in modern composite propellants.Addition of aluminum powder can improve engine specific impulse,filling ratio and inhibit the high-frequency combustion instability.Carrying out the research on measurement of propellant aluminum particle combustion,revealing the mechanism and rule of aluminum particle combustion have important scientific significance and engineering value for the optimization of solid rocket motor performance and improvement of combustion instability.In order to solve the problem that the depth of field is too small and can't measure online in real time of the traditional optical photography and the particle collection for the solid propellant aluminum combustion,it is urgent to develop finer combustion diagnostic techniques.Based on this,digital holography(DH)which is a three-dimensional measurement technology is applied to measure the aluminum combustion of solid propellant.The main research work carried out in this paper is as follows:(1)Based on the scalar diffraction theory and mathematical description of holographic technology,the digital holographic reconstruction algorithm is compiled,including Fresnel transform method,convolution method and angular spectrum method.Three kinds of reconstruction algorithms are respectively used to carry out holographic reconstruction,the results show that all these reconstruction methods can carry out the reconstruction of digital holography.Because of the different spatial sampling,the three algorithms have their own scope of application,and the reconstruction speed is not the same.After verification,convolution and angle spectrum method is more suitable for the reconstruction of particle holography.(2)Combining with the combustion features of aluminum particles in solid propellant,a set of digital holographic measuring system is designed and constructed independently,which includes laser,spatial filtering system,acquisition and imaging system.And the optical component parameters of digital holography measurement system are designed in detail.To ensure the accuracy of the measurement,the accuracy of the measurement system is calibrated with standard particle size particle board.A measurement experiment of Al2O3 particle field in cold state is carried out,which can clearly obtain focused images of particles in different positions of space.(3)Using the designed digital holography measuring system to carry out the test experiment of propellant aluminum particle combustion under the conditions of 0.1MPa and 1Mpa,the satisfying experimental results are obtained.From the aluminum particles captured during the experiment,we can clearly distinguish the condensed particle zone and the gas flame zone.Based on the digital holographic measurement system,the whole dynamic combustion process of propellant aluminum combustion is obtained,including the dynamic agglomeration process of aluminum particles,the dynamic fusion process of agglomerates,the filigrees formation process,the rupture process of agglomerates and the dynamics between agglomerates collision fusion process.(4)Using the numerical reconstruction algorithm to measure the spatial distribution of the aluminum particles,the spatial distribution of the aluminum particles in the combustion field can be accurately obtained.The particle size of the aluminum particles in the near surface of the propellant is obtained by counting the burning of aluminum particles in the holographic images at different time.(5)Experiments using digital holography are carrying out to measure the propellant aluminum combustion at 3MPa,5MPa.Problems existing in the measurement of aluminum combustion at high pressure are analyzed.The research in this paper shows that digital holography can not only obtain the dynamic process of propellant aluminum particle combustion,but also accurately measure the particle size,particle size distribution and spatial distribution of the combustion particles,which can provide important data for the aluminum combustion mechanism and combustion model establishment.