推进剂及其组分的光学性质对点火特性的影响

通过实测的NEPE推进剂在多种热流密度下的点火延迟时间，借助于转化系数，计算获得假设忽略深度吸收的点火延迟时间，其相对误差随着热流密度的增加而显著增大，表明推进剂及其组分的光学性质对点火特性的影响是不能忽略的，且这种影响随着热流的增加而增大，因此，建立推进剂点火模型，在高热流辐射时，必须考虑深度吸收，极限吸收率和建立模型，消除其光学性质的影响提供了依据。     

丁羟复合推进剂的辐射点火

采用CO2激光点火装置,对丁羟复合推进剂的点火过程进行了实验研究,利用描述固体推进剂物化现象的一维传热模型对复合推进剂的辐射点火特性进行了理论分析。通过最小二乘法拟合实验数据得到了丁羟复合推进剂的点火准则。结果表明,丁羟复合推进剂的点火过程主要包括惰性加热及气相点火过程,惰性加热时间和点火延迟时间随热流密度的增大而减小,且随着热流密度的增大,热流密度的影响逐渐降低。固相传热数学模型能够比较准确地描述复合推进剂的辐射点火特性。     

硼颗粒在固冲环境中点火过程影响因素的数值模拟

采用修正的Williams 硼颗粒燃烧模型对固体推进剂燃烧环境条件下的硼颗粒点火进行了数值模拟,计算了环境温度、气相氧化剂种类和分压、颗粒初始半径及氧化层厚度对硼颗粒点火的影响.结果表明,环境温度升高可以缩短硼颗粒点火延迟时间和点火时间;环境中氧分压过大会延长点火延迟时间;水蒸气分压越大,点火时间越短;硼颗粒半径增大会导致氧化层厚度增大进而延长点火时间和点火延迟时间.     

不同气氛对铝粉点火燃烧特性的影响分析

为了研究流化气体对粉末推进剂点火燃烧性能的提高作用,采用CO_2激光点火器和光纤光谱仪相结合的实验方法,研究了不同气氛条件下Al粉的点火燃烧特性。采用光谱信号拟合测温法计算了Al粉在不同气氛环境中的点火温度。结果表明,常压环境下,粒径1μm的Al粉在N_2O和空气氛围下的点火延迟时间分别为10ms和359ms,从点火成功过渡到全面燃烧的时间分别为829ms和1 579ms,说明Al粉在N2O环境中点火阶段的表面异相反应速率与燃烧阶段的反应速率均快于在空气中;粉径1μm的Al粉在N2O和空气环境下的点火温度分别为1 550~1 650K和1 450~1 500K,两者相近,但都明显低于毫米级Al粉的点火温度(2 300K),说明Al粉的点火温度受粒径影响较大。     

GAP/ADN/nano–Al膏体推进剂的能量特性与激光点火特性

采用最小自由能原理方法计算了GAP(聚叠氮缩水甘油醚)/ADN(二硝酰胺铵)/nano–Al推进剂的能量特性,制备了一系列ADN质量分数为8%~38%的GAP/ADN/nano–Al膏体推进剂,采用CO2激光点火的方法研究了4种配方在不同激光功率密度作用下的激光点火特性。结果表明:GAP/ADN/nano–Al膏体推进剂的标准理论比冲(Isp)、特征速度(C*)、燃烧温度(Tc)均随ADN含量增加而依次增大,爆热(Qv)则主要随铝粉含量的增加而增大;GAP/ADN/nano–Al膏体推进剂的点火延迟时间和点火能量总体上随着激光功率密度增加呈现减小的趋势;配方中ADN含量较高时,GAP/ADN/nano–Al膏体推进剂具有较好的激光点火特性。     

炸药激光起爆过程的准三维有限差分数值模拟

根据含锌材料的热起爆机理，建立了在激光作用下炸药点火过程的三维(二维轴对称)有限差分模型，运用此模型对RDX、PETN、HMX和改性B炸药在激光作用下的温度成长过程、温度场分布及点火延迟时间进行了数值模拟。结果表明，三维模型延迟时间计算结果与实验结果较为符合；药柱温度增长主要是在激光照射面上很薄一层药剂内发生；激光的光斑直径、脉宽和炸药的激光吸收系数对点火能量阈值有较大的影响。     

铝镁贫氧推进剂的点火性能

为研究镁铝富燃料固体推进剂组分对点火性能的影响,采用改进的靶线法燃速测试系统对多种含镁铝富燃料固体推进剂在常压和加压下进行了通电金属丝点火性能的对比实验。被测试推进剂的镁铝合金含量为20%～40%,或者同时含镁铝合金及硼,氧化剂含量为30%～53%。实验表明,在固定外界输入热源的情况下,推进剂的点火性能主要与氧化剂含量和粒度有关;金属的含量和种类也有一定的影响;催化剂对点火延迟时间影响很小;压强对此种点火方式几乎无影响。该点火延迟测试方法简单易行,并具有一定的可靠度,适于配方调试。     

CL-20含量及其粒度级配对NEPE推进剂燃烧性能的影响

采用静态与水下声发射法测试了CL-20含量及其粒度级配对NEPE推进剂燃速与压强指数的影响;采用DSC与TG-IR联用研究了CL-20对NEPE推进剂热分解行为的影响。结果表明,随着CL-20质量分数由42%增至50%,推进剂燃速与压强指数上升,燃烧效率提高,表明CL-20氧化能力高于GAP/硝酸酯含能黏合剂体系;随着CL-20/HMX、CL-20/Al质量比增高,推进剂燃速上升,燃烧效率上升;CL-20对推进剂燃速和压强指数的贡献高于HMX;随着CL-20/AP质量比增高,CL-20/AP混合体系分解产物氧化能力降低,燃烧反应速率降低,燃速降低;CL-20粒度级配对NEPE推进剂燃烧行为影响显著,当CL-20的粒径(d50)在5~50μm时,随着细粒度CL-20含量增高,推进剂燃速与燃速压强指数下降;当体系中存在超细粒度CL-20(d50=500nm)时,推进剂燃速与燃速压强指数随着超细粒度CL-20含量的增加而有所增加,4种粒度CL-20对NEPE推进剂燃速的贡献顺序为:粗粒度>中粒度>超细粒度>细粒度。     

硼烷合乙二胺的点火、燃烧及热解特性

为探索高氢含量硼烷合乙二胺储氢材料在空气中的燃烧性能,使用气相合成方法制备了硼烷合乙二胺(EDAB)微米颗粒。通过连续激光点火实验,测试了其点火和燃烧参数;通过在氮气和空气中的热解实验,研究了其燃烧过程机理。结果表明,硼烷合乙二胺的燃烧具有点火延迟时间短、点火能量低的特点,在常温常压静止空气流中,点火功率密度为10~9 W/m~2量级时,微米级硼烷合乙二胺的点火延迟时间为0.000 2~0.000 9s,最小点火能量仅0.000 1J;其连续激光点火燃烧过程分为两个阶段,分别产生亮蓝色与黄色火焰。结合材料在氮气及空气中的热解行为,推测该材料燃烧第1阶段蓝色火焰对应其热解释放氢气的燃烧,第2阶段的黄色火焰对应其骨架高温裂解所生成挥发物的燃烧。     

四种混合不同碳材料的FOX-7粉末激光点火：点火延迟实验与简化计算（英文）

针对1,1-二胺-2,2-二硝基乙烯(FOX-7)因点火相对困难而限制其广泛应用的问题，利用CO₂激光器在一定的功率密度范围对4种混合不同碳材料的FOX-7粉末开展了点火实验，研究点火延迟时间的变化趋势。采用两种简化模型对点火延迟时间进行计算与分析，以探究点火机理和指导FOX-7的点火性能提升。结果表明，几种碳材料的添加会导致FOX-7粉末点火延迟时间发生不同程度的缩短。石墨烯和氧化石墨烯在缩短点火延迟方面表现出相对较强的促进作用，石墨的效果较为轻微。计算结果显示，模型1比模型2更适合预测FOX-7粉末的点火延迟时间。机理分析表明，石墨烯的添加能够有效提升FOX-7粉末对辐照能量的吸收且减小能量损失。研究表明FOX-7粉末样品的主要点火诱导过程受到激光辐照下传热性质的强烈影响。     

Experimental Investigation on Laser Ignition and Combustion Characteristics of NEPE Propellant

The ignition and combustion property of solid propellant is the main content in internal ballistic research, which has a great significance for propulsion application and combustion mechanism. In this study, the detailed gas‐phase reaction mechanism of Nitrate Ester Plasticized Polyether Propellant (NEPE) was developed. It is helpful to understand the intricate processes of solid‐propellant combustion. The factors which may have influences on ignition delay time and temperature distribution of propellant surface was analyzed by laser ignition experiment. Using high‐speed camera and an infrared thermometer, the ignition and combustion process and the surface temperature distribution of NEPE propellant under laser irradiation were measured. Laser heat flux, ambient pressure and initial temperature of NEPE propellant have an influence on the ignition delay time and the surface temperature. Results show that the ignition delay time decreases with the increase of laser heat flux, ambient pressure and initial temperature of NEPE propellant. At the same time, with the increase of laser heat flux, the influences of ambient pressure and initial temperature on the ignition delay time decrease. Besides, laser irradiation, ambient pressure and initial temperature have significant influences on the surface temperature distribution of the propellant.     

带延迟点火部件的发射药点火性能试验研究

为了更好地研究发射药的点火性能,在基于密闭爆发器原理的点火性能测试装置基础上增加了一个延迟点火部件,构建了一个新型点火性能模拟试验装置,根据该装置建立了简单的火药分层点火过程模型,模拟并对比了高能太根-18/1、双芳-3-18/1及NR11-18/1三种发射药的点火性能。结果表明,NR11-18/1发射药较易点火,双芳-3-18/1发射药最难点火,点火时间分别为19和45ms。增加延迟点火部件后,可将点火药的燃烧和发射药的燃烧阶段有效区分,不仅有利于对比点火性能差异较小的发射药之间的区别,还有助于分析发射药低压段的燃烧速度。随着延迟点火部件长度的增加,点火时间也增长。     

Laser Ignition of Various Pyrotechnic Mixtures – an Experimental Study

Ignition of several pyrotechnic mixtures by diode‐laser was studied experimentally using a novel combustion chamber. The ignition delay times dependence on laser intensity could be fit by the expression t_ign=aI⁻ⁿ for all compositions, with I being the laser intensity at target and n=1.4–2.1. This is roughly in accordance with thermal ignition theories assuming a semi‐inert solid. Differences in ignition delay times did not depend on fuel alone or oxidizer alone. The temperature of oxidizer decomposition does not correlate with ignition delay time. Furthermore, the steady state combustion temperature, deduced from emission spectra of the composition products are not correlated with ignition delay time. It is proposed that chemical reactions, taking place in the gas‐phase or in the solid‐phase, play a significant role, but are not solely responsible for ignition delay time. The seemingly uncorrelated ignition delay results between pyrotechnics containing either the same fuel or oxidizer hamper the construction of a “unified theory” for laser ignition of pyrotechnic mixtures.     

Modeling and Simulation of Laser‐Induced Ignition of RDX Using Detailed Chemical Kinetics

A laser‐induced ignition model of RDX is developed, in which a detailed chemical kinetics scheme, containing 45 species and 231 reactions, is employed to describe the reaction in the gas phase. The model is spatially one‐dimensional and includes the transient development of two regions: the condensed phase and the gas phase. The condensed phase is composed of solid RDX, liquid RDX, and some decomposition products. The main physicochemical processes include melting, decomposation, vaporization, and radiation absorption. The gas phase is composed of RDX vapor and reaction products and the main processes include convection, diffusion, heat conduction, chemical reaction, and radiation absorption. With interfacial boundary conditions, the governing parameters for the condensed phase are conservation equations of energy and species concentration, whereas those for the gas phase are the conservation equations of mass, momentum, energy, and species concentration. A finite difference program using FORTRAN is compiled and numerical simulation is carried out. The ignition process of RDX is discussed from the distribution and evolution of temperature and species concentration. The model can provide a reasonable prediction of the phenomenon that the flame moves towards the surface immediately after ignition, and then departed from the surface.     

Decomposition and Ignition of the High‐Nitrogen Compound Triaminoguanidinium Azotetrazolate (TAGzT)

The high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure.     

Comparison of flame propagation properties of petroleum coke and coals of different rank

Ignition and flame propagation characteristics of 18 kinds of coal and a petroleum coke were investigated through a laser ignition experiment. Flame stability was strongly influenced by amount of volatile matter and pyrolysis rate. Lean limit of flame propagation was strongly influenced by amount of volatile matter. Flame propagation was observed when pyrolized volatile matter was mixed with surrounding air or oxygen, until the concentration of pyrolized volatile matter reached a constant value. Flame propagation velocity was strongly influenced by pyrolysis rate. As the pyrolysis rate increased, the flame propagation velocity increased. The flame propagation velocity of petroleum coke was higher than that of coal with the same volatile content. The flame propagation of petroleum coke was superior to what was expected based on the volatile content, primarily because the high pyrolysis rate caused a shorter ignition delay than what would be expected given the volatile content. A database for the lean limit of flame propagation was used to develop a flame stability model to estimate lean flammability of a large-scale burner. The model could predict the effect of the coal rank, the particle diameter distribution for lean flammability limit. The estimated lean flammability limit of petroleum coke (volatile content 11.5%) was equal to that of lv bituminous coal with volatile content of about 15%.     

Ignition of Particles of Wet Woody Biomass under Convective Diffusion of Water Vapor in the Near-Wall Region

This paper presents the results of an experimental and theoretical study of heat and mass transfer during ignition of wet wood particles in a high-temperature gas medium. Experiments were carried out in a setup which provides conditions similar to the combustion spaces of boiler units. The main heat transfer parameters (ambient temperature) and integrated ignition characteristics (ignition delay) were measured. The measurement error of these parameters did not exceed 18%. The convective transfer of water vapor formed during evaporation of pore moisture and pyrolysis products were found to have an insignificant effect on the ignition characteristics and conditions. From the results of the experiments, a mathematical model of the ignition process was developed which describes the simultaneous occurrence of the main processes of thermal preparation under conditions of intense phase (evaporation of water) and thermochemical transformations (thermal decomposition of the organic part of the fuel, thermochemical interaction between water vapor and carbon coke, ignition of volatiles) taking into account the convective diffusion of water vapor and pyrolysis products in the near-wall gas area during the induction period. The theoretical ignition delay is in satisfactory (within the confidence interval) agreement with the experimental value. The numerical model of the diffusion flame adequately (good agreement between experimental and theoretical ignition delays) describes the ignition of a wet wood particle.