Mechanism of Solid Propellant Combustion Submitted to a High Plasma Flux

A simplified mechanism of the plasma effect on the combustion on different types of propellants is presented. The model provides a semi‐quantitative prediction of the burning rate enhancement that should be expected for a given propellant composition and structure. Depending on the propellant structure and composition, one expects a burning rate enhancement either to disappear or to survive a certain time after the plasma injection has been turned off. In order to estimate the internal front propagation rate, we have built a simplified model of the RDX ignition inside the matrix. A cubic lattice topology has been assumed and the ignition front extends from one layer to its nearest neighbor. The propagation rate was found to be dependent on the lattice constant, the particle size, the thermo‐chemical properties of the RDX particles and the matrix background.     

LOVA发射药点火燃烧性能

制备了含有两种不同黏结剂的低易损性发射药(即LOVA发射药),并应用点火燃烧模拟装置与密闭爆发器对其点火燃烧性能进行了研究。结果表明,LOVA发射药难点火,但在点火药中添加高氯酸铵后可有效改善LOVA发射药的点火性能。LOVA发射药燃烧具有燃速系数低、燃速压力指数高等特点。     

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。     

等离子体增强固体火药燃烧性能的实验研究

利用300mL电热化学密闭爆发器研究了在不同输入电能、装填密度和初始温度下等离子体点火对某混合酯高能19孔花边形固体火药颗粒燃烧性能的影响;分析了上述不同条件下等离子体对该固体火药燃烧速率影响的变化规律。结果表明,输入等离子体电能从15.4kJ增大到61.6kJ后,固体火药燃速在100MPa时提高106%,200MPa时提高30%,300MPa以上燃速无明显变化;等离子体点火对低温火药燃烧初期和中期的燃速均有显著的增强作用,对高温火药点火燃烧初始燃速的增强作用较为明显。     

Response of TEGDN Propellants to Plasma Ignition with the Same Magnitude of Ignition Energy as Conventional Igniters in an Interrupted Burning Simulator

In order to consider the potential influence of ignition energy factors on the response of double base propellants plasticized with triethyleneglycol dinitrate (TEGDN propellants), the influence of different ignition methods at the same magnitude of ignition energy level on the response of TEGDN propellants was investigated in an interrupted burning simulator. Compared to conventional ignition methods, plasma ignition exhibits a significantly shorter ignition delay and lower ignition energy. There are stronger ablation and impact interactions of plasma flow with the surface of propellants. For TEGDN propellants coated with titanium dioxide, a greater amount of melted white layer is deposited on the surface of propellants. The content of copper on the surface of recovered plasma‐ignited samples observed by X‐ray Fluorescence (XRF) spectroscopy is much larger than that on the surface of recovered conventionally ignited samples, indicating more deposition of copper wire discharge on the surface of the samples. The test results will benefit the design of plasma generator and electrical parameters of pulse power to satisfy certain propellant compositions.     

Research on the Combustion Properties of Propellants with Low Content of Nano Metal Powders

A comparison of various experimental results for combustionrelated properties evaluation, including burning rates, deflagration heat, flame structures and thermal decomposition properties, of AP/RDX/Al/HTPB composite propellants containing nano metal powders is presented. The thermal behavior of n‐Al (nano grain size aluminum) and g‐Al (general grain size aluminum i.e., 10 μm) heated in air was also investigated by thermogravimetry. The burning rates results indicate that the usage of bimodal aluminum distribution with the ratio around 4 : 1 of n‐Al to g‐Al or the addition of 2% nano nickel powders (n‐Ni) will improve the burning behavior of the propellant, while the usage of grading aluminum powders with the ratio 1 : 1 of n‐Al to g‐Al will impair the combustion of the propellant. Results show that n‐Al and n‐Ni both have a lower heating capacity, lower ignition threshold and shorter combustion time than g‐Al. In addition n‐Al is inclined to burn in single particle form. And the thermal analysis results show that n‐Ni can catalyze the thermal decomposition of AP in the propellant. The results also confirm the high reactivity of n‐Al, which will lead to a lower reaction temperature and rather higher degree of reaction ratio as compared with g‐Al in air. All these factors will influence the combustion of propellants.     

Burning Phenomena of the Gun Propellant JA2

The combustion phenomena of the standard gun propellant JA2 are investigated in experiments and analyzed by a simplified theoretical model. Hereby energy transfer from the gas phase governs ignition and combustion of solid rocket and gun propellants. In addition to the heat conduction and convection, the radiation of the flame contributes to the heat feedback which controls the burning rate in dependence on pressure. The dependence on the initial temperature is given by physical parameters of the conversion from the solid to the gaseous state. Burning rates are measured in dependence on pressure and initial temperature confirming a simplified law for the burning rate. The evaluation yields that the pressure exponent can be directly assigned to the heat feedback and that the temperature of the conversion from the condensed to the gas phase lies at about 675 K. The experiments also comprise spectroscopic measurements at low pressures in the wavelength ranges from 300 nm to 14000 nm which are resolved spatially along the vertical flame profile. The analysis of the spectra delivers the profiles of species in the flames including di‐atomic radicals and tri‐atomic molecules of the final combustion products. In addition, gas phase temperatures are derived by application of the Single‐Line‐Group model which gives approximately 2800 K closely below the adiabatic flame temperature of 2900 K at low pressures. They are compared to temperatures assigned to soot particle emission. In summary, these data enable an estimation of the heat feedback from the flame to the burning surface.     

Burning Characteristics of Consolidated Gun Propellants

To improve the combustion behaviors of conventional consolidated propellants, consolidated propellants were prepared using porous propellant grains as fast‐burning filler. The porous propellant grains were prepared by supercritical fluid foaming process and exhibited the high burning rate. The multi‐perforated structure of the consolidated propellants was designed and adopted to obtain high burning progressivity. To investigate the burning characteristics of the consolidated propellants, closed vessel and quenched combustion experiments were carried out. The results show that deconsolidation of the consolidated propellants does not occur, and that the consolidated propellants exhibit high burning rates and high burning progressivities. Besides, the results show that the consolidated propellants burn steadily even at low (−40 °C) and high temperatures (50 °C).     

含FOX-7发射药的燃烧性能

采用常规密闭爆发器研究了含FOX-7硝胺发射药的燃速、压强指数和压强变化率。结果表明,随着样品中FOX-7含量的增加,发射药的点火延滞时间增加,燃速系数减小,燃速降低;其压强变化率的最大值及增长速率均降低。当燃烧压强小于150MPa时,FOX-7含量对发射药的压强指数没有影响,FOX-7改善发射药压强指数的能力不明显;随着燃烧压强的增加,含FOX-7发射药的压强指数降低,尤其当燃烧压强大于200MPa时,发射药的燃速压强指数显著降低。随着发射药中FOX-7含量的增加,其压强指数及燃速系数均降低,有利于发射药的稳定燃烧。     

Ballistic Modification of Nitramine Propellants with Special Reference to NG‐PE‐PCP‐Based High Energy Propellants

The burning rate pressure relationship is one of the important criteria in the selection of the propellant for particular applications. The pressure exponent (η) plays a significant role in the internal ballistics of rocket motors. Nitramines are known to produce lower burning rates and higher pressure exponent (η) values. Studies on the burning rate and combustion behavior of advanced high‐energy NG/PE‐PCP/AP/Al‐ and NG/PE‐PCP/HMX/AP/Al‐based solid rocket propellants processed by a conventional slurry cast route were carried out. The objective of present study was to understand the effectiveness of various ballistic modifiers viz. iron oxide, copper chromite, lead/copper oxides, and lead salts in combination with carbon black as a catalyst on the burning rate and pressure exponent of these high‐energy propellants. A 7–9 % increase in the burning rates and almost no effect in pressure exponent values of propellant compositions without nitramine were observed. However, in case of nitramine‐based propellants as compared to propellant compositions without nitramines, slight increases of the burning rates were observed. By incorporation of ballistic modifiers, the pressure exponents can be lowered. The changes in the calorimetric values of the formulations by addition of the catalysts were also studied.     

发射药的等离子体点火燃烧中止试验研究

用等离子体点火中止燃烧装置,研究了等离子体点火太根药、双基药、硝胺药及单基药的燃烧中止现象,借助所得回收样品的显微照片和中止压力-时间曲线分析了等离子体与发射药的相互作用规律.结果表明,由于等离子体的侵蚀和辐射作用,发射药的燃烧表面不规则;不同配方发射药的点火延迟时间不同,太根发射药等离子体点火的延迟时间最短,容易实现等离子体点火.发射药的理化性质,包括配方和添加剂成分、表面状况、热传导系数和光学吸收系数等对等离子体点火有着显著影响.     

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.     

一种随行装药定容燃烧性能研究

为了在静态环境下模拟某新型随行装药的内弹道燃烧性能,采用将小粒发射药进行钢筒中压制成型,端面封堵延时处理的方法得到了一种新型随行装药试样。并将制得的随行药与单樟6/7混合进行密闭爆发器实验,测试了其燃烧性能。实验结果表明:与单樟6/7单独装药相比,其燃烧过程分为2个阶段,且第二阶段燃烧速率远大于第一阶段,通过延迟装置质量和装药密度的调节可以实现对随行药点火延迟时间的控制。随行药具有很高的燃速和较强的燃烧渐增性,在内弹道过程中可有效改善膛内压力分布。     

Influence of Particle Size on the Combustion of CL‐20/HTPB Propellants

The effect of nitramine particle size on the combustion behavior of inert binder based propellants has been extensively studied for RDX and HMX, but not CL‐20. Although materials such as RDX and HMX are useful for particular combustion applications, CL‐20 has a greater potential to improve the oxygen balance and energy density of a propellant. The current work investigates the effect of CL‐20 particle size on the combustion of CL‐20/HTPB propellants down to submicrometer sizes. An influence of particle size on the burning rate and combustion mechanism is reported. The 30 micrometer formulation burning rate data showed evidence of convective burning specifically at higher pressures, but the pressure dependence was comparable to neat CL‐20 at pressures below 8 MPa. A change in the combustion mechanism of the submicrometer formulation as a function of pressure was determined to be a result of the interaction of the propellant flame and the combustion residue. Data suggested that at low pressures diffusion in terms of active cooling was dominant for the submicrometer formulation. Higher pressure data for both the submicrometer and 3 micrometer formulations suggest the degree of active cooling is decreased as the burning rate pressure exponent is near 0.5 for both propellants. The indirect evidence for the presence of a melt layer for CL‐20 propellants is discussed.     

Effects of an Organic‐inorganic Nanocomposite Additive on the Combustion and Erosion Performance of High Energy Propellants Containing RDX

A nanocomposite microsphere consisting of solid paraffin, nano‐TiO₂, nano‐BN, zeolitic imidazolate framework‐67 particles and polymethyl methacrylate was prepared and applied as a functional additive for high energy propellants (with about 23 wt % RDX) to reduce the barrel erosion and improve its combustion performance as well. High energy propellants modified with the nanocomposite were manufactured by a solvent extrusion technique. According to the scanning electron microscope and differential scanning calorimetry results, there exists a good compatibility between the nanocomposite and propellant matrix. The energy and combustion performance as well as erosion of the modified propellants were studied by a closed bomb test and an erosion tube device, respectively. Results showed that compared with the unmodified propellant, both the erosion and energy performance of modified high energy propellant gradually decreased with the increase of nanocomposites contents. When the content of nanocomposites was 5.1 %, the erosion mass of the modified propellant reduced to 37.0 % while the propellant force only decreased 5.7 %, indicating that the nanocomposite has enormous ability to improve gun erosion resistance while barely affect energy performance of propellant. Furthermore, the closed bomb burning curves of the samples showed that addition of nanocomposites to propellant matrix could prolong the combustion time, efficiently inhibit the initial generation rate of combustion gas, and further achieve the progressive burning of the propellants.     

Interrupted‐Burning Tests of Plasma‐Ignited JA2 and M30 Grains in a Closed Chamber

Enhanced burning of plasma‐ignited propellants has been deduced in recent years from closed bomb pressure traces. The question remains, however, whether the enhanced burning is inherent or possibly the result of propellant grain fracture. To find out, interrupted and non‐interrupted burning tests were conducted with cylindrical perforated grains of JA2 and M30 in a closed bomb with a loading density of approximately 0.2 g/cm³. Both, conventional black powder and plasma igniters were used, and a few tests were carried out with the propellants cooled to −20 °C. The plasma igniter was an ablating capillary, and the electrical energy density was about 0.7 kJ/g of propellant. The diameters of the collected grains yielded the actual burn distance at the time of the interrupted burning. The experimental pressure traces and the conventional burn rate coefficients of the propellants were used to calculate the theoretical depth burned assuming no plasma‐induced burn rate modifications. From overlapping pressure traces at several interrupted pressures, and from comparison to the calculated versus measured burn distances, it was found that there is burn rate enhancement during the plasma pulse–but not much once the pulse has ended. In contrast to the JA2 burn rates, both ambient and cold M30 burn rates, deduced from the non‐interrupted tests using the BRLCB code, were enhanced even after the plasma turn‐off, thus contradicting the interrupted‐tests results. However, vivacity analysis of the non‐interrupted tests indicated that the M30 grains exhibited increased surface area (possible fragmentation) because of the plasma interaction–an effect that would cause erroneous results from the BRLCB. Indeed, simulation of the non‐interrupted M30 tests using the XNOVAKTC code, and assuming partial fragmentation of the propellant charge, yielded vivacities that mimicked the experimental ones.     

Investigation of the Burning Behavior of Cryogenic Solid Propellants

Cryogenic Solid Propellant (CSP)‐technology is a new approach to develop more powerful rocket motors. CSPs include the advantages of classical solid propellants to save weight as well as those of a high energy content and safety of modern liquid propellants. The charges consist of liquid and/or gaseous fuels and oxidizers, both frozen. Two main versions of CSP‐technology can be realised: 1. Mono‐CSPs show the burning behavior of solid propellants. Experiments with mono‐CSPs have been carried out under inert pressure conditions in a window bomb. Mono‐CSPs have a stable burning behavior with a constant regression rate which follows the Vieille's law under varying pressure conditions. 2. The advantage of high safety is obtained by assembling oxidizer and fuel in sandwich configurations. The grain geometry governs the burning behavior. Such systems can be externally controlled, e.g. by the heat from a gas generator or they can work self‐sustained. A Rod‐in‐Matrix burner shows self‐sustained combustion in an inert pressure atmosphere with overall burning rates in a similar range as solid rocket propellants which obey also a Vieille‐like pressure law. Disc stack burners have also been investigated, the combustion of which is strongly dependent on the disc thickness. For a short time Mach's nodes have been observed in the exhaust plume of a disc stack burner. Currently, the temperature ranges are limited to the boiling temperature of liquid nitrogen. Therefore, liquid oxidizers like H₂O₂ have been used. However, for the first time a propellant strand of polymer rods embedded in solid oxygen was prepared and burnt. The experiments with CSPs end in the combustion of a small rocket motor showing no serious technical obstacles. Simplified models based on the heat flow equation can simulate the burning characteristics of the frozen energetic materials including phase transitions.     

Combustion Characteristics of a Novel Grain‐Binding High Burning Rate Propellant

The novel grain‐binding high burning rate propellant (NGHP) is prepared via a solventless extrusion process of binder and spherical propellant grains. Compared with the traditional grain‐binding porous propellants, NGHP is compact and has no interior micropores. During the combustion of NGHP, there appear honeycomb‐like burning layers, which increase the burning surface and the burning rate of the propellant. The combustion of NGHP is a limited convective combustion process and apt to achieve stable state. The larger the difference between the burning rate of the binder and that of the spherical granular propellants exists, the higher burning rate NGHP has. The smaller the mass ratio of the binder to the spherical granular propellants is, the higher the burning rate of NGHP is. It shows that the addition of 3 wt.‐% composite catalyst (the mixture of lead/copper complex and copper/chrome oxides at a mass ratio of 1 : 1) into NGHP can enhance the burning rate from 48.78 mm⋅s⁻¹ in the absence of catalyst to 56.66 mm⋅s⁻¹ at P=9.81 MPa and decrease the pressure exponent from 0.686 to 0.576 in the pressure range from 9.81 to 19.62 MPa.     

Theoretical Analysis of Plasma Enhancement of Propellant Burning Rate

A theoretical model of the combustion of a nitramine solid propellant in the presence of a plasma jet is proposed. Unlike standard double‐base compositions, nitramine propellants exhibit experimental evidence that plasma induces a burning rate enhancement. The model is based on heat transfer considerations and proposes a closed‐form solution of the enhancement of the propellant burning rate as a function of the thermophysical parameters of the system. The model provides a good qualitative agreement with experimental results.     

多层管状发射药燃烧性能的数值计算

为了模拟和改善层状发射药的内弹道性能和燃烧性能,建立了一种多层管状发射药的燃烧模型.在服从几何燃烧定律条件下,通过多层管状发射药的形状函数推导出其Γ-Ψ表达式.用Γ-Ψ曲线研究了多层管状发射药的缓燃层厚度与药片初始总厚度比、内外层的燃速比以及药柱厚度与药柱长度之比对其燃烧性能的影响.结果表明,(1)多层管状发射药缓燃层...