Study On Laser Ignition And Combustion Radiation Characteristics Of Mg/PTFE Based Pyrolant

The burning of pyrotechnic is one kind of coupled combustion with multicomponent heterogeneous reaction.The ignition and combustion course includes endothermic,exothermic chemical processes and physical process of heat and mass transfer.Its output characteristics are affected by combustion characteristics,and then the lack of theoretical research on pyrotechnic combustion may significantly restrict the development of pyrotechnic technology.Therefore,this paper focuses on the complex combustion research of the metal-fluorocarbon pyrotechnic.Taking Mg/PTFE based pyrolant as object,the method of combining experimental research,theoretical analysis and numerical simulation is adopted to systematically study the ignition mechanism and combustion radiation characteristics of Mg/PTFE based pyrolant.The mechanism of solid phase reaction and laws of ignition are revealed.Based on the combustion numerical simulation,the radiation mechanisms are verified.The results can provide some experimental and theoretical basis for the operational safety and reliability of Mg/PTFE based pyrolant,and has guiding meaning for the research and development of metal-fluorocarbon pyrotechnics.The main works and results are as follows:(1)The thermal analysis method is used to design the experimental study on thermal decomposition of Mg/PTFE based pyrolant,the solid phase reaction mechanism and the effect in different environmental atmosphere are revealed,and the results of the intermediate reaction theory are verified.By calculating the kinetic parameters,the activation energy of the solid phase reaction of pyrotechnic is 194kJ/mol in air,the experimental results and parameters are applied to the numerical calculation of the following sections.(2)The ignition process of Mg/PTFE based pyrolant is tested by CO2 laser,and the surface temperature of the pellets is collected by infrared thermometer.The temperature variation of ignition and the influence of ignition delay are studied.According to the temperature measurement of the pellets,the combustion process can be divided into three parts:ignition stage,transition stage and stable combustion stage.The ignition temperature is about 688?.In the ignition transition stage,the influence of laser power density on the surface temperature is related to the particle size of the material and the ignition delay shows different influence relations with the laser power density.In addition,the ignition delay indicates a process of up and down as a whole with the increase mass ratio of the material.The optimum Mg/PTFE ratio is 55/45,which makes the ignition delay reach the minimum value.(3)Based on thermal ignition theory,the 1-D and 2-D solid-phase ignition model are developed for the simulation of laser ignition of Mg/PTFE based pyrolant.The models are programmed and calculated with experimental parameters.By comparative analysis of calculation and test results,the reliability of the model is proved.The influence of physical parameters on ignition delay is analyzed,and the temperature characteristics of ignition process are predicted,which laid the experimental and theoretical foundation for further understanding of ignition mechanism.(4)The combustion process of Mg/PTFE based pyrolant is tested by spectroscopic methods,and then the combustion flame temperature and infrared radiation intensity are calculated.The combustion and radiation mechanism of pyrotechnics and its influencing factors are discussed.According to the experiments,the addition of fine particles and fluorine rubber is beneficial to the burning rate and the flame temperature,which could lead to the increase of the radiation intensity 13-5?m.The maximum radiation intensity appears at the mass ratio of 60/40.(5)The gas combustion process of Mg/PTFE pyrotechnics is simulated by using the method of reaction kinetic analysis and CFD model.The effects of mass ratio and inlet airflow rate on the combustion temperature field,velocity and composition distribution are discussed.Then the combustion characteristics and radiation mechanism are summarized.According to the calculation results,in the anaerobic area,the consumption of Mg is mainly caused by fluorination with CF2,while the product C is quickly converted to C2,which leads to the actually limited content of C in the core area.Later with the diffusion of O2 into the core surface and participate in the oxidation reaction of C,a large amount of C2 is reversely converted into C,so the content of C increases rapidly.In the calculation surface,the total molar fraction of C is relatively less and decreasing with mass ratio,while MgO sharply increases.Therefore,when the radiation component is considered in the fuel rich composition,the main one is MgO.(6)Based on the simulation results of gas phase combustion and related theoretical models,a method for calculating the radiation intensity of pyrotechnics,which considering the factor of the radiation area,the flame temperature and the emissivity,is established.The results verify the change law of spectral experiments,and the influence factors of radiation are analyzed.