Experimental Study On Aluminum Agglomeration On The Burning Surface Of NEPE High Performance Propellant Based On Optical Measurement

Aluminized Nitrate Ester Plasticized Polyether(NEPE)is high-energy composite solid propellant,which possesses both good energy characteristics of double-base propellant and excellent mechanical properties of composite propellant.It is a kind of solid propellant with the highest specific impulse at present and has a nice application prospect.However,the agglomeration commonly exists in the combustion process of aluminized NEPE,which causes negative effects such as two-phase flow loss and specific impact decline,and there are still some deficiencies in the knowledge of agglomeration particle size distribution law and agglomeration combustion mechanism under high pressure.Therefore,carrying out experimental study on agglomeration of aluminized NEPE is of great significance for further understanding and grasping the particle size distribution law and agglomeration mechanism of Al aggregates,providing a certain reference for the formulation optimization of aluminized NEPE,and providing a certain experimental data to support for the model study of aluminized NEPE.In this paper,a high-pressure combustion chamber with windows was designed with presssure more than 10 MPa,independently and adopting rotating aluminum alloy base instead of flange structure significantly improves the experimental efficiency.The digital inline holography(DIH)experimental system,high pressure direct photography experimental system and multi-wavelength radiation temperature measurement experimental system were built with the windowing high pressure combustion chamber as the core.The agglomeration particle size distribution,burning rate parameters,agglomeration combustion process and agglomeration combustion temperature in NEPE combustion process were studied.For the DIH experimental system,the standard particle board is used to calibrate the error of the experimental system,which verifies the accuracy of the measurement of the experimental system.According to the principle of DIH and the gray gradient adaptive threshold algorithm,the particle size of Al aggregates was measured.Mathematical statistical method was used to analyze the particle size distribution of Al aggregates,and the influence law of pressure,Al,HMX,AP initial particle size on the particle size distribution of Al aggregates was obtained by quantitative analysis.Based on the high pressure direct photography experimental system,the burning rate of NEPE was measured under 1-8 MPa using image processing technology.The burning rate coefficient and pressure index were obtained by fitting Vieille’s empirical burning rate formula.The influence law of formula composition on burning rate coefficient and pressure index was analyzed.The influence mechanism of pressure on burning rate is obtained.Meanwhile,the experiment found the inflection point of burning rate of3#NEPE at about 5 MPa.The agglomeration and combustion process of aluminized NEPE at 1,4 and 7 MPa were studied.The results show that there are three kinds of agglomeration combustion modes for Al particles under different pressure.The effects of pressure on agglomeration time,agglomeration size and agglomeration combustion process were analyzed qualitatively.In addition,it is found that secondary agglomeration phenomenon is common in NEPE combustion process,and the analysis shows that low pressure and high pressure will lead to two different secondary agglomeration modes.According to Planck’s law,this paper uses the four wavelength radiation temperature measurement method to measure the agglomeration combustion temperature of NEPE at1 MPa.The results show that the agglomeration combustion temperature is 2531.8,2516.6 and 2540 K respectively at three groups characteristic wavelengths.The experimental results prove the feasibility of multi-wavelength radiation temperature measurement.Meanwhile the colorimetric temperature measurement is highly dependent on the characteristic wavelength.