Study On Combustion And Infrared Radiation Characteristics Of Mg/PTFE/Viton Fuel-Rich Pyrolants

The burning of infrared decoy flares generates strong infrared signal in the specific band,which can be employed to protect aircraft from the attack of infrared guided missiles.The interference characteristics of infrared decoy flares mainly depend on the combustion chemical reaction performance of the payload in the actual high-altitude operating environment.A clear understanding of the intrinsic physicochemical mechanism of combustion and infrared radiation process is the prerequisite for accurate evaluation of interference efficiency.In this paper,the combination of theoretical analysis,experimental study and numerical simulation is applied to systematically research the combustion and infrared radiation transmission process of the infrared decoy payload（Mg/PTFE/Viton fuel-rich pyrolants）under ground static,ground low-pressure and high-altitude dynamic conditions.The key technology of modeling infrared interference characteristics based on combustion chemical reactions is tackled,the inherent heat and mass transfer laws of pyrotechnic heterogeneous combustion flow field are revealed,and the influence mechanism of environment conditions on the combustion and infrared radiation behavior of pyroalnts is analyzed.The research results provide an experimental and theoretical reference for the application of MTV pyrotechnic system in the aerospace field,the effectiveness evaluation of infrared decoy flares,the target infrared detection and infrared guidance system simulation in the countermeasure environment.The main research contents and achievements are as follows:（1）The aerobic combustion process of MTV fuel-rich pyrolants in atmospheric environment is experimentally studied by using a self-build optical diagnostic system.Meanwhile,the temperature information of pyrotechnic combustion flow field is obtained by using non-contact optical and contact temperature measurement methods.Based on the experiments,an aerobic combustion model for three-dimensional steady combustion and flow coupling calculation is established.By comparing with the experimental results,it is proved that the aerobic combustion model better approximates the realistic combustion and infrared radiation process of pyrolants than the traditional anaerobic combustion model.Combining the experimental and numerical results,the luminous cone shaped region near the burning surface and its periphery region are defined as anaerobic combustion core zone and aerobic combustion diffusion zone,respectively.（2）A small-scale sealed CO₂ laser ignition and combustion experiment system is designed to reproduce the low-pressure operating environment at different cruising altitudes.The effects of ambient pressure on the flame structure,combustion temperature,burning rate of pyrotechnic compositions with different Mg contents are analyzed experimentally.The component distribution characteristics of the pyrotechnic combustion flow field under different ambient pressures are predicted through numerical simulation,and the accuracy of the numerical model is verified by experimental results.The results show that the flame structure under sub-atmospheric pressure and atmospheric pressure are emanative flame and convergent flame,respectively.The burning rate increases monotonously with the pressure,and follows Vieille’s law in the pressure range of 0.02MPa-0.1MPa.The combustion temperature and high-temperature flame zone decrease with decreasing pressure.The pressure has more profound influence on the oxidation reaction（Mg+O₂=MgO+O）of Mg than fluorination reaction（Mg+CF₂=MgF₂+C）.（3）The dynamic combustion behavior of gaseous flame and discrete particles is observed by using a high-speed camera and an infrared thermal imager.The microscale combustion mechanism of Mg particles is revealed based on the results of thermal analysis experiments.The physicochemical properties of condensed combustion products（CCPs）of pyrolants with different formulations under different pressures are characterized by scanning electron microscope,X-ray energy dispersive spectrometer,X-ray diffractometer and laser particle size analyzer.The component distribution characteristics of CCPs are accurately predicted by the three-dimensional flow combustion coupled calculation model with heterogeneous condensation reactions,and the validity of the numerical model is verified by experimental data.The results show that CCPs mainly include excessive Mg,fluoride product MgF₂ and oxidation product MgO.MgF₂ is the major combustion product,which is distributed in the anaerobic combustion core zone and mostly aggregates into spherical agglomerates with a peak particle size of about 12μm.MgO is located in the peripheral aerobic combustion diffusion zone,and mostly presents fine smoke oxide particle structure with a peak size of about 1μm.The increase of Mg content in the formula is beneficial to the reduction of large aggregates and fine smoke particles.When the pressure drops from 0.1MPa to 0.02MPa,the volume weighted average diameter of CCPs increases significantly due to the reduction of burning rate.（4）The coupling characteristics of heat and mass transfer between dispersed solid burning particles and gas-phase jet flame in the pyrotechnic combustion flow field are solved by using the Euler-Lagrangian method.Based on the simulation results of gas-solid two-phase combustion flow field,a numerical calculation model for the infrared radiation characteristics of pyrolants is established by using the reverse Monte-Carlo method.The simulation software of infrared radiation transmission characteristics considering emission,absorption and scattering of participating media is developed,and the rationality of the calculation results is verified by the experimental results.The results show that the dispersed combustion particles in the flow field introduce a negative feedback effect on the propagation of the gas jet.The radiation output capability of Mg particles undergoing dynamic diffusion combustion in the2.0μm-5.5μm band surpasses that of high-temperature gas molecules,and the reduction of ambient pressure seriously deteriorates the radiation capability of both the gaseous phase and the particulate phase.In the 8.0μm-14.0μm band,the infrared radiance of combustion particles under the pressure of 0.02MPa-0.1MPa is lower than that of gas molecules,whose infrared radiation characteristics are more profoundly affected by the negative pressure environment.（5）The combustion and radiation process of MTV based infrared decoy flares in different altitude environments is tested by ground vacuum static ignition combustion experiment.It is found that the characteristic peak of CO₂ at 4.359μm is divided into red spike and blue spike,and the emission intensity ratio of the two peaks remains constant under different pressures.The infrared radiation of the decoy flares is mainly distributed in 1μm-3μm and 3μm-5μm,the infrared radiation intensity decreases with the decrease of pressure in different combustion stages,while the effective radiation time increases with the decreasing pressure.Based on the experiment,the numerical model for the coupling solution of combustion and flow of the decoy flares under dynamic flight conditions is established.Based on the calculation results of dynamic combustion flow field in different operating environments,the infrared dynamic imaging of the decoy flares is carried out by using the self-developed infrared radiation transfer characteristics simulation software.The results shows that in the high altitude operating environment,the influence of air pressure on the combustion and infrared radiation performance is significant,while the influence of air temperature is negligible.The infrared radiance in 3μm-5μm and 8μm-12μm at different combustion time decreases with the increase of altitude.The combustion temperature,flame diffusion area and radiation brightness decrease with the increase of airflow velocity,and the accuracy of the calculation results of infrared radiation characteristics model under different airflow velocities is better than that of Brune empirical model.