| As an important technology for current and future energy storage,lithium-ion batteries are being used more and more widely,and air transportation has become one of the optional ways to transport lithium-ion batteries.However,due to the high risk of lithium-ion battery itself,it will largely affect the safe transportation of civil aviation,especially its important component,electrolyte.As a flammable liquid with low stability,electrolyte is a key factor contributing to the high fire hazard when transporting lithium-ion batteries by air.When the lithium-ion battery is short-circuited,the sparks generated will ignite the flammable electrolyte inside the lithium-ion battery in a short time,and the shell of the lithium-ion battery will be ignited by the burning electrolyte,which will lead to the burning of the whole battery,and the burning battery will ignite other flammable objects around,thus forming a fire or even an explosion accident.At the same time,the aircraft cargo hold environment is complex,low pressure and many sources of interference,resulting in the aircraft cargo hold fire detection system false alarm rate has been at a high level,not only easy to cause significant losses,but also a threat to the flight safety.Currently,the main smoke detectors used in aircraft cargo holds are photoelectric smoke detectors,which work on the principle of scattering of incident light by fire smoke,and the morphological characteristics of fire smoke,particle size distribution and light scattering characteristics are the key parameters affecting the performance of the detectors,therefore,there is a need to investigate the fire detection of electrolytes in aircraft cargo compartments.The results of previous studies show that fire smoke and interference sources can be distinguished by using dual-wavelength and dual-scattering angle fire detection techniques,but the applicability of this method to the low-pressure environment of the aircraft cargo hold and electrolyte still needs further study.Therefore,in this paper,we studied the distinction between electrolyte fire smoke and interference aerosol based on the morphological characteristics and particle size distribution of electrolyte fire smoke at different combustion stages,combined with the atmospheric pressure and low pressure environment of aircraft cargo hold,using simulation and experimental methods,and the main research contents and conclusions are as follows:(1)Research on the physical properties of electrolyte fire smoke at different combustion stages was carried out,and the differences between the physical properties of different fire smoke at different combustion stages were clarified,which provided parameter guidance for the numerical simulation of electrolyte fire smoke light scattering.We designed and built our own fire smoke collection device to collect fire smoke particles from three electrolytes,n-heptane and kerosene at different combustion stages,and obtained the morphological characteristics and particle size distribution of different fire smoke particles by scanning electron microscopy and particle size statistics software.The results show that the morphology of smoke particles produced by the combustion of three different types of electrolytes is characterized by spherical droplets,and the mean particle size shows a trend of increasing and then decreasing with the development of combustion;The particle size extremes of EC-DMC,EC-DEC and EC-DEC-DMC electrolyte smoke particles were 205.48 nm,245.82 nm and 275.82 nm,respectively,and all appeared in the early and middle stages;The relationship between the particle size of the three electrolyte fumes is EC-DMC<EC-DEC<ECDEC-DMC.Compared with n-heptane/kerosene fire smoke particles,electrolyte fire smoke particles have different morphological characteristics and differ significantly in size:110-140 nm in the early stage,50-90 nm in the early and middle stage,60-120 nm in the middle stage,and 150-210 nm in the end stage.(2)The characteristic parameters of light scattering from electrolyte fire smoke were studied by using MiePlot numerical simulation software,and the variation patterns of extinction,scattering and absorption efficiency factors,scattered light intensity and scattering asymmetry factor were obtained.Based on the experimentally obtained particle size parameters.a numerical simulation software based on Mie scattering theory was selected to simulate the optical scattering characteristics of electrolyte fire smoke according to the morphological characteristics,and the simulation results show that the scattering effect of electrolyte fire smoke particles on light is stronger and the absorption effect is very weak;The scattering characteristic parameters all increase and then decrease with the change of particle size,which corresponds to the change of particle size;The larger the particle size of electrolyte fire smoke particles,the more the scattering asymmetry factor tends to be close to 1.and the greater the difference between front and back scattering.(3)The optical scattering characteristics of electrolyte fire smoke under different ambient pressures are investigated,and a method based on the asymmetric ratio is proposed to distinguish electrolyte fire smoke from interference aerosols.Based on the numerical simulation results,a detector model with suitable wavelength and scattering angle is selected,and the optical scattering characteristics of electrolyte fire smoke under different ambient pressure are measured using a variable pressure and oxygen concentration test chamber and an aerosol scattering experimental device,and the results show that the asymmetry ratio of electrolyte fire smoke always remains between 9 and 12 at 405 nm.The results of previous studies showed that the asymmetry ratio of interfering aerosols at 405 nm remained between 3 and 6,so a method was proposed to distinguish electrolyte fire smoke from interfering aerosols:at 405 nm,an asymmetry ratio greater than 7 is electrolyte fire smoke and less than 7 is interfering aerosols. |
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