IGNITION OF AMMONIUM PERCHLORATE

A simplified theory for the ignition of ammonium perchlorate is proposed, which is derived from a unified theory that also explains the low-pressure deflagration limit as well as the steady deflagration. The theory provides an approximate method of calculating the ignition delay and the minimum external he»t flux for a successful ignition, as functions of pressure and initial solid temperature. The ignition calculations show that there exists a pressure limit due to the weakness of the igniter strength, in addition to the low-pressure deflagration limit which is an inherent property of the solid independent of the igniter strength. The theory can be extended to other monopropellants for which exothermic reaction occurs only in the gas phase.     

Three‐Dimensional Simulation of Pressure Fluctuation in a Granular Solid Propellant Chamber within an Ignition Stage

The effects of the conditions of the ignition system in the propellant chamber of a gun system using a granular solid propellant are numerically investigated with respect to ignition performance criteria such as the differential pressure generation between the breech and the projectile base. Simulations, in which the length of the primer and the igniter mass are varied, are performed using a solid/gas two‐phase fluid dynamics code for three‐dimensional calculation of gas flow and discrete solid propellant particles. This code simulates the igniter combustion in the primer, the movement of burning solid propellant grains, and the formation of pressure gradients inside the chamber in the ignition process. The differential pressures between the breech and the projectile base measured in experiments are well predicted by the simulations for various igniter conditions. In the process of igniting the solid propellant, the propellant grains are accelerated toward the projectile base by the igniter gas flows from the primer vents. Fixed‐particle simulation is also carried out in order to examine the effects of the movement of the solid propellant grains on the chamber pressure profile. The simulated results reveal that the movement of solid propellant grains causes differential pressure fluctuations, which depend on the discharge from the primer vents and the locations of these vents.     

小型固体火箭发动机尾部点火设计与实验

根据固体火箭发动机点火器设计经验,选用赛璐珞为点火器盒体材料、黑火药为点火药,并以点火压强作为发动机装药可靠点燃的判据。采用头部点火设计经验公式对端面一侧面燃烧、尾部点火的小型固体火箭发动机点火药量进行了初步估算。为获得点火器的点火压强、点火延迟时间等性能参数,设计、加工了模拟发动机尾部点火空间的试验容器,研究了电点火头、电点火管点火方案在不同条件下的试验情况。结果表明,虽然点火药量相同,但两种点火方案的点火压强、点火延迟时间、喷管堵片的打开方式却存在较大差异,基于发动机可靠性、维修性考虑,将电发火管点火方案作为优选方案,并通过发动机点火试验的成功考核。     

减小高装填密度发射装药膛内压力波的实验研究

研究了两种能降低某大口径火炮高装填密度发射装药的膛内压力波的点传方案。第一种点传火方案是在制式点传火结构基础上增加横向传火具,增加点火药包;第二种点传火方案是改变制式传火结构为低爆速传火结构,同时增加横向传火具。高装填密度发射装药射击试验表明,这两种点传火方案均能满足点传火要求。第一种点传火方案较制式可燃中心传火管能实现迅速全面的点火,但出现了压力波增大的现象。而第二种点传火方案较第一种点传火方案的传火速度快,能迅速建立点火压力,发射药床的着火延迟时间小,最重要的是能抑制膛内有害压力波。压力波的频谱分析表明在高装填密度装药中,采用第二种点传火方案能削弱和抑制压力波的高频振荡成分,改善其振动特性。     

火炮同步点火管的燃烧实验和数值模拟

为增加火炮点火的同步性，对一种爆轰波传火的火炮同步点火管进行了燃烧实验，测量了点火管不同位置的压力一时间曲线。在考虑火药燃烧过程中同步点火特征、气体湍流和新增燃气质量流流入的基础上，建立了点火管内的燃烧计算模型，用CFD软件对点火管的燃烧过程进行了三维数值模拟计算，并将计算得到的压力一时间曲线与实验曲线进行对比分析。结果表明，点火管具有很高的点火同步性，模拟计算的压力一时间曲线与实验结果基本吻合。     

Shock Tube Effect Inside a Pyrotechnic Igniter

An output closure is a critical component of a pyrotechnic igniter. It controls the heat transfer duration of initiation train, stress loading on the propellant grain, and the pressure drop during closure deployment. Normally the pressure profiles calculated by a quasi‐static interior ballistics code are adequate for igniter design evaluation. But following a case of premature closure deployment in which the propellant failed to ignite, the authors discovered that the design geometry mimicked that of a shock tube. The shock tube effect occurred whenever the high‐temperature gases of the initiator were rapidly discharged into a long conduit. The shock resultant from the initiator opened the closure prior to ignition of the ignition aid. In this paper, we report results from both quasi‐static computations for static pressure and time‐dependent simulations for dynamic pressure. Designers need to consider both static and dynamic pressure when devices have a sudden high‐pressure gas released into a conduit.     

Investigation of Liquid Gun Propellants: Electrical ignition of LGP 1846

Progress achieved in the study of the electrical ignition of the hydroxylammonium nitrate(HAN)-based liquid gun propellant LGP 1846 is described. The goal of the work is to develop an igniter system suitable for regenerative liquid propellant guns. Several igniter configurations of the one- as well as the two-stage types designed by the Ballistic Research Laboratory and the Fraunhofer-Institut EMI-AFB, have been tested. Voltage and current as well as the pressure histories were recorded. Calculations of electrostatic field distributions discussed here were obtained by a finite element code implemented at Dynamit Nobel. The theoretical analysis yielded alternative electrode designs for future testing. In addition, a specially designed igniter chamber equipped with sapphire windows was used at EMJ-AFB to study the fundamentals of the electrical discharge by means of high-speed photography.     

Development of MTV Compositions as Igniter for HTPB/AP Based Composite Propellants

MTV compositions were prepared by keeping the magnesium/Teflon ratio constant and increasing the Viton content of the mixture up to 14% by an increment of 2% to investigate the effect of binder content on the heat of explosion, which is found to increase with the increasing Viton percentage as the magnesium content concomitantly goes down toward the stoichiometric value. In the second part of the study, fuel-rich MTV compositions were prepared by changing the magnesium content and keeping the Viton fraction constant at a specific value to investigate the effect of magnesium content on the heat of explosion and combustion characteristics. The observed general trend is that the heat of explosion of MTV compositions decreases as the magnesium content increases. All the MTV compositions were tested in a closed vessel to measure the maximum pressure achieved and the rate of reaching this pressure. The ignition performance of three selected MTV compositions was examined in 2.75 inch rocket motor by using the same charge of igniter and the same HTPB/AP composite propellant of the equal amount in each test. Two of them have excellent ignition performance and, therefore, can be used as igniter for the HTPB/AP based composite rocket propellants.     

Studies into Laser Ignition of Unconfined Propellants

Prior to laser ignition tests, spectral absorption properties of three different solid motor propellants were analysed. The extruded double base (EDB) propellant exhibited >95 % absorption over the 250–550 nm wavelength band whereas, the cast double base (CDB) showed similar absorption over a wider band extending between 375–800 nm. The composite sample (CP) showed a uniform spectral absorption at about 90 % over 250–800 nm band. Ignition tests using an average of 500 nm output from an Ar‐ion laser showed that the double base propellants undergo deflagration prior to ignition due to the presence of carbon black material. Within the laser power density range of 24–125 Wċcm⁻², the threshold laser energy densities for deflagration and ignition in the double base propellant were found to␣be between 2–2.5 Jċcm⁻², and 40–215 Jċcm⁻², respectively. No deflagration was observed for the composite propellant, and the threshold ignition energy was found to be within the range, 11–18 Jċcm⁻² for the same range of laser power densities. From the ignition map for this propellant, the threshold energy for ignition at this wavelength was found to be approximately 18 Jċcm⁻² and was practically independent of laser power density. In the near infrared wavelength (780 nm) the EDB propellant was not readily ignitable due to its comparatively much higher reflectance at this wavelength. The ignition threshold values were found to be between 19–23 Jċcm⁻² for a similar power density level. The results indicate that the ignitability of propellants is enhanced through the promotion of deflagration.     

点火方式对受限空间油气爆燃规律的影响

通过可视化和数据分析方法,针对电火花、突遇高温热壁、直接加热热源和持续加热热壁4种常见的点火方式,对油气在受限空间的整个爆燃过程进行了对比分析。不同点火方式下油气爆燃的起燃条件、起燃速度、火焰结构、火焰颜色存在很大的区别,并进行了细节分析。尽管油气在受限空间的爆燃过程都呈现出4个阶段,但火焰颜色、持续时间对不同的点火方式是不同的。通过对最大爆炸超压和超压典型曲线的分析,最大爆炸超压由大到小的点火方式依次是突遇高温热壁、电火花、直接加热热源和持续加热热壁,并分析了受限空间中超压曲线的典型特征。     

障碍物对可燃气云爆燃冲量的加强机制

在面积为2000 m的实验基地;针对半球条栅型障碍物对半球形气云爆燃冲量场的影响进行了实验研究。可燃介质是13.3%(体积)的乙炔-空气混合气体;气云由0.02 mm的聚乙烯薄膜约束;利用数据采集系统记录爆燃压力-时间曲线;通过编制程序计算观测点的冲量。对正、负冲量与障碍物的半径、空隙率的关系以及爆燃场的冲量分布进行了分析。结果表明：障碍物的存在极大地提高了爆燃冲量;在该工况下的气云爆炸正负冲量场近似余弦分布;障碍物半径越大、空隙率越低;爆燃正负冲量越大。     

Burning Characteristics of Ammonium Nitrate‐based Composite Propellants Supplemented with Ammonium Dichromate

Ammonium nitrate (AN)‐based composite propellants have attracted much attention, primarily because of the clean burning nature of AN as an oxidizer. However, such propellants have some disadvantages such as poor ignition and low burning rate. Ammonium dichromate (ADC) is used as a burning catalyst for AN‐based propellants; however, the effect of ADC on the burning characteristics has yet to be sufficiently delineated. The burning characteristics of AN/ADC propellants prepared with various contents of AN and ADC have been investigated in this study. The theoretical performance of an AN‐based propellant is improved by the addition of ADC. The increase in the burning rate is enhanced and the pressure deflagration limit (PDL) becomes lower with increasing amount of ADC added. The increasing ratio of the burning rate with respect to the amount of ADC is independent of the AN content and the combustion pressure. The optimal amount of ADC for improving the burning characteristics has been determined.     

加氢裂化循环气支链爆炸形态的区划与应用

对加氢裂化循环气与相关可燃性气体支链爆炸的特性及其应用进行了系统的研究.探索了浓度爆炸极限、爆炸形态与波形及其影响因素;根据爆炸形态与波形的不同,提出了对加氢裂化循环气爆炸形态科学区划的新理念;在爆炸极限内,可以进一步区划4种爆炸形态(冷焰、爆燃、爆轰、爆燃向爆轰转化),与7个爆炸区域（上、下冷焰区,上、下爆燃区,上、下爆燃向爆轰转化区,爆轰区）,并探讨了不同爆炸形态压力波的发展机制.对进一步研究相关的多元支链爆炸体系,促进多元支链爆炸理论的发展,具有一定的理论价值.实验测得了爆炸危险度、火焰蔓延极限、最小点火能等特性参数;引进了“关键组分”的概念,指出加氢裂化循环气的多元体系,引发爆炸的物质是关键组分H₂和氧化剂O₂;探讨了制订防爆安全指标的依据与方法.对于预防混合气体支链爆炸事故的发生、指导防爆电气设备与阻火器的设计、指导支链燃烧与支链爆炸的实践,具有参考价值.     

浓度和点火位置对氢气-空气预混气爆燃特性影响

开展了氢气-空气预混气在透明方管内的爆燃实验研究,分析在一端开口一端封闭的狭长空间内,浓度和点火位置对氢气-空气预混气爆燃特性的影响。实验结果表明：氢气浓度和点火位置对火焰锋面结构以及发展有重要影响;各当量比条件下,均在距封闭端100 mm位置点火时反应最为迅速;在极贫燃或极富燃条件下,点火位置对火焰发展影响更大。氢气浓度与点火位置共同作用于压力波形,以距封闭端300 mm点火位置为界,分别在管道前后两段点火时,不同当量比条件下超压波形呈现复杂变化。超压峰值对氢气浓度具有极强依赖性,并且浓度对爆燃超压的影响程度远大于点火位置;在各点火位置下,均在Φ = 1.25时获得最大超压;最大超压对应的点火位置取决于当量比。     

点火源位置对甲烷-空气爆燃超压特征的影响

开展了化学恰当比φ = 1甲烷-空气预混气在透明方形管道内的爆燃实验研究,改变点火源位置,分析在管道一端闭口一端开口条件下,点火源位置对甲烷-空气预混气爆燃超压特征的影响。实验结果表明:当点火源与闭口端之间距离较小时,时间-超压曲线不发生振荡,随着点火源相对于闭口端距离的增加,超压分别呈微弱等幅振荡、振幅指数增长的振荡,且最大超压峰值随之增加;超压波形与火焰瞬态结构存在密切关联,振荡波形超压峰值的极值点总是位于火焰位置的极值点;当超压发生振荡时,振幅指数增长阶段的振荡周期随时间线性减小,振荡周期与未燃气气柱长度呈现较好相关性;超压振荡的原因在于,泄爆口侧的火焰前沿触发了超压振荡,闭口侧火焰前沿与声波(压力波)在未燃气气柱中相互作用放大了超压振荡。     

The effects of gas explosions in free and partially confined fuel/air mixtures

To obtain a further insight into the complex flame acceleration process of deflagrating fuel/air mixtures experimental investigations were carried out in free and partially confined homogeneous clouds with hydrogen as a fuel. The results of the experiments in an unconfined hemispherical configuration show a distinct dependence of the flame velocity on the cloud size which does not exceed, however, an upper limiting value. The experiments under partially confined conditions without additional turbulence indicate that the flame velocity and consequently the pressure field is governed by the hemispherical flame front initially formed; i.e. the flame velocity is not affected by the partial confinement. To increase the turbulence effects further experiments were carried out with a fan and with jet ignition. In the case of fan induced turbulence the flame velocity was strongly influenced by the fan speed. At a certain fan capacity the transition of a deflagration into a detonation was observed. With jet ignition produced by venting an explosion chamber into the partially confined cloud the transition occured even with hydrogen concentrations in air as low as 22 vol%. The results which are discussed on the basis of turbulence models show that high damaging overpressures or the transition from a deflagration into a detonation are only generated by strong turbulences as a consequence of flow and/or obstacles.     

Chemical heating of the working gas in a short-duration high-enthalpy facility

Operation of a short-duration high-enthalpy facility with products of reactions of propane, hydrogen, and nitrous oxide with air and oxygen is studied. The mixtures are ignited either by an electric arc or by an igniter with a “chamber-plume” principle of operation, which involves local ignition of the mixture from one spot located at the center of the settling chamber. It is confirmed that the use of a combined (electrical and chemical) heating of the working gas completely resolves the problem of reproduction of real values of stagnation pressure and enthalpy for flight conditions of a vehicle with Mach numbers of 4 to 7. The lean flammability limits of ignition by an electric arc turn out to be lower than the data reported in the literature for standard conditions. Combustion of three-species (fuel + oxygen + air) mixtures with hydrogen (mole fraction of hydrogen ) and mixtures with propane is completed in 5–8 msec with combustion efficiency close to unity. The time needed for chemical reactions initiated by an igniter to be completed is significantly greater than that with ignition by an electric arc. The time of combustion with the use of an igniter can be substantially reduced by increasing the number of ignition spots, by using mixtures with a greater fraction of the fuel than that required for reproduction of natural enthalpy, or by replacing a certain part of the fuel in the original mixture by nitrous oxide. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 31–43, September–October, 2007.     

Evaluation of a new organic azide: Hexakis(azidomethyl)benzene (HAB)

HAB is a thermally- and hydrolytically-stable solid, easily prepared from available raw materials. It is not highly sensitive to shock, friction, or electrostatic charge, but is sensitive to some types of impact, although not to others. It shows preliminary promise for possible use as a substitute for normal lead styphnate in less-sensitive bridgewire detonators, and as a substitute for tetracene in percussion detonators, e.g. the M-42 primer. Easy ignition, and a high burning rate without detonation, suggest application as an igniter. HAB is not sufficiently powerful to dent an aluminum witness block; therefore, it would not be suitable as a replacement for lead azide as an intermediate detonator charge.     

加压硝酸旋转点火装置的设计及应用

针对引进加压硝酸装置氨氧化炉原采用的固定式电子点火器存在的问题,云南解化清洁能源开发有限公司解化化工分公司自行设计了氨氧化炉旋转点火装置。与国外氨氧化炉旋转点火装置相比,该点火装置结构简单,操作方便,使用效果好,制造成本低。     

Modification of Thermal Theories to Solid Propellant Ignitibility

The conventional thermal theories are inventively modified for analyzing the ignition behaviors of solid propellants. Based on the modification of the thermal theory with the boundary condition of constant heat flux, the effects of heat flux, pressure, threshold of heat flux and absorbability on the radiant ignition of solid propellant are elaborated. The innovations of theoretical analyses are consistent with most of experimental results depicted in literatures. That the increase of hot gas velocity increases the ignition time of solid propellant is verified to be attributable to the decrease of hot gas temperature, ascertaining insight of the thermal theory with the boundary condition of flowing hot gas. In addition, a tentative estimation of pressurization rate effect on ignition time of solid propellant is proposed.