Burning rate and other characteristics of strontium titanate （SrTiO3） supplemented AP/HTPB/Al composite propellants

In a quest of search for a new burning rate modifier for composite propellant, strontium titanate (SrTiO3), a perovskite oxide has been chosen for evaluation in a composite propellant formulation based on its other catalytic applications. Initially, SrTiO3 was characterized for particle size, morphology and material/ phase identification (using XRD). By varying SrTiO3 content in a standard composite propellant, different compositions were prepared and their performance and processing parameters like the end of mix (EOM) viscosity, mechanical properties, density, burning rate, pressure exponent (n-value), etc. were measured. The results reveal that 2% SrTiO3 causes more than 12% enhancement in propellant burning rate (at 70 ksc pressure) in comparison to the standard propellant composition. The pressure exponent also increases to 0.46, whereas the standard composition was having its value as 0.35.

Research on the influences of confining pressure and strain rate on NEPE propellant:Experimental assessment and constitutive model

In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade confining pressure system and material testing machine.The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed.The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant.As confining pressure increases(from 0 to 5.4 MPa),the maximum tensile stress and ultimate strain increase gradually.With the coupled effects of confining pressure and strain rate,the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s^(-1)is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s^(-1),respectively.Afterwards,the influence mechanism of confining pressure on the NEPE propellant was analyzed.Finally,based on the viscoelastic theory and continuous damage theory,a nonlinear constitutive model considering confining pressure and strain rate was developed.The damage was considered to be rate-dependent and pressuredependent.The constitutive model was validated by comparing experimental data with predictions of the constitutive model.The whole maximum stress errors of the model predictions are lower than 4%and the corresponding strain errors are lower than 7%.The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates.This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.

Cu–Co–O nano-catalysts as a burn rate modifier for composite solid propellants

Nano-catalysts containing copper–cobalt oxides(Cu–Co–O) have been synthesized by the citric acid(CA) complexing method. Copper(II) nitrate and Cobalt(II) nitrate were employed in different molar ratios as the starting reactants to prepare three types of nano-catalysts. Well crystalline nano-catalysts were produced after a period of 3 hours by the calcination of CA–Cu–Co–O precursors at 550 °C. The phase morphologies and crystal composition of synthesized nano-catalysts were examined using Scanning Electron Microscope(SEM), Energy Dispersive Spectroscopy(EDS) and Fourier Transform Infrared Spectroscopy(FTIR) methods. The particle size of nano-catalysts was observed in the range of 90 nm–200 nm. The prepared nano-catalysts were used to formulate propellant samples of various compositions which showed high reactivity toward the combustion of HTPB/AP-based composite solid propellants. The catalytic effects on the decomposition of propellant samples were found to be significant at higher temperatures. The combustion characteristics of composite solid propellants were significantly improved by the incorporation of nano-catalysts. Out of the three catalysts studied in the present work, Cu Co-I was found to be the better catalyst in regard to thermal decomposition and burning nature of composite solid propellants. The improved performance of composite solid propellant can be attributed to the high crystallinity, low agglomeration and lowering the decomposition temperature of oxidizer by the addition of Cu Co-I nano-catalyst.

Studies on composite solid propellant with tri-modal ammonium perchlorate containing an ultrafine fraction

Composite solid propellant is prepared using tri-modal Ammonium perchlorate(AP)containing coarse,fine and ultrafine fractions of AP with average particle size(APS)340,40 and 5 mm respectively,in various compositions and their rheological,mechanical and burn rate characteristics are evaluated.The optimum combination of AP coarse to fine to ultrafine weight fraction was obtained by testing of series of propellant samples by varying the AP fractions at fixed solid loading.The concentration of aluminium was maintained constant throughout the experiments for ballistics requirement.The propellant formulation prepared using AP with coarse to fine to ultrafine ratio of 67:24:9 has lowest viscosity for the propellant paste and highest tensile strength due to dense packing as supported by the literature.A minimum modulus value was also observed at 9 wt.%of ultrafine AP concentration indicates the maximum solids packing density at this ratio of AP fractions.The burn rate is evaluated at different pressures to obtain pressure exponent.Incorporation of ultrafine fraction of AP in propellant increased burn rate without adversely affecting the pressure exponent.Higher solid loading propellants are prepared by increased AP concentration from 67 to 71 wt.%using AP with coarse to fine to ultrafine ratio of67:24:9.Higher solid content up to 89 wt.%was achieved and hence increased solid motor performance.The unloading viscosity showed a trend with increased AP content and the propellant couldn't able to cast beyond 71 wt.%of AP.Mechanical properties were also studied and from the experiments noticed that%elongation decreased with increased AP content from 67 to 71 wt.%,whereas tensile strength and modulus increased.Burn rate increased with increased AP content and observed that pressure exponent also increased and it is high for the propellant containing with 71 wt.%of AP due to increased oxidiser to fuel ratio.Catalysed composite solid propellant is prepared by using burn rate modifiers Copper chromite and Iron oxide.Addition of Copper chromite and Iron oxide has enhanced the burn rate of tri-modal AP based composite solid propellant.The catalytic propensity of copper chromite is higher than that of iron oxide.The pressure exponent increased with the catalyst concentration and the values obtained are compatible for solid rocket motor applications.

Application of transient burning rate model of solid propellant in electrothermal-chemical launch simulation

A 30 mm electrothermal-chemical(ETC) gun experimental system is employed to research the burning rate characteristics of 4/7 high-nitrogen solid propellant. Enhanced gas generation rates(EGGR) of propellants during and after electrical discharges are verified in the experiments. A modified 0D internal ballistic model is established to simulate the ETC launch. According to the measured pressure and electrical parameters, a transient burning rate law including the influence of EGGR coefficient by electric power and pressure gradient(dp/dt) is added into the model. The EGGR coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005 MW-1. Both simulated breech pressure and projectile muzzle velocity accord with the experimental results well. Compared with Woodley's modified burning rate law, the breech pressure curves acquired by the transient burning rate law are more consistent with test results. Based on the parameters calculated in the model, the relationship among propellant burning rate, pressure gradient(dp/dt) and electric power is analyzed. Depending on the transient burning rate law and experimental data, the burning of solid propellant under the condition of plasma is described more accurately.

Effects of Plasticizers,Antioxidants and Burning Rate Modifiers on Aging Performance of the HTPB/HMDI Composite Solid Propellant

The effects of plasticizers,antioxidants and burning rate modifiers on the aging performance of the composite solid propellant based on hydroxyl-terminated polybutadiene(HTPB)/hexamethylene diisocyanate(HMDI)were explored by apply-ing an accelerated aging program for 90 day at 70 ℃. The HTPB propellant matrix with the diisooctyl sebacate(DOS)as plasti-cizers and diisooctyl azelate(DOZ), antioxidants as N,N ′-Diphenyl-p-phenylenediamine(AO) and 2,2′-methylenebis(4-methyl-6-tert-butylphenol)(cyanox 2246)and burning rate modifiers as barium ferrite(BF),copper chromites(CC)and fer-ric oxide(FO)were varied. Results show that sample(S1)which based on DOS decreases the stress value and increases the strain value which considered to be an excellent start for aging program. Sample(S3)containing AO presents the higher resis-tance to oxidation showing the better performance that reflects on increasing the shelf life of the composite solid propellant mo-tor. Sample(S5)which based on BF enhances the ballistic performance among over the other tested two samples. The accelerat-ed aging program allowed us to estimate the motor in-service lifetime.

CALCULATION OF BURNING RATE CHARACTERISTICS IN ACCELERATED FIELD FOR SOME ALUMINIZED SOLID PROPELLANTS

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电动自走式玉米-花生带状复合种植模式施药机设计与试验

针对玉米-花生带状复合种植模式施药农艺要求,设计了一款基于STM32单片机控制系统的电动自走式玉米-花生带状复合种植模式施药机。对施药机的驱动电机、转向机构、喷杆及防飘装置、施药管路等关键部件进行了选型与设计;采用流量传感器和速度传感器实时采集管路药液流量和底盘行驶速度,通过增量式PID算法实时调节比例控制阀开度,实现了变量施药控制;开发了基于Android手机的APP控制软件,实现了对施药机的远程控制。流量控制精度试验表明,调控后单个喷头目标流量与实际流量的相对误差η≤4.0%;变量施药试验表明,施药系统平均超调量为2.7%,施药量与理论值相差2.1%;雾滴沉积试验表明,雾滴沉积个数极差为4个/cm^(2),单位面积最低沉积量为35个/cm^(2),符合国家标准。

三基发射药热烧蚀特性及变化规律

为了研究三基发射药热烧蚀特性及变化规律,制备了组分含量不同的多种三基发射药,采用半密闭爆发器模拟烧蚀试验方法测定发射药样品的烧蚀性,分析了发射药高能组分含量、增塑剂含量对发射药爆温的影响规律,以及发射药爆温对烧蚀特性的影响规律。结果表明,环三亚甲基三硝胺(RDX)、硝基胍(NQ)、邻苯二甲酸二辛酯(DOP)含量改变会引起发射药爆温的变化,进而影响烧蚀性能。RDX含量增加1%,爆温增加0.59%,发射药烧蚀率增加1.23%;与未加入RDX相比,加入2%RDX的发射药烧蚀率增加23.38%;NQ含量增加1%,爆温降低0.23%,发射药烧蚀率降低0.56%;DOP含量增加1%,爆温降低2.99%,发射药烧蚀率降低7.01%。针对爆温在2600~3100 K的范围内的三基发射药,建立了质量烧蚀率与爆温的指数关系式,并分别给出了RDX、NQ、DOP体系的特征系数,为0.106、0.101、0.163。

应变率对高固含量HTPB推进剂力学特性与破坏机制的影响

通过不同拉伸速率下的单轴拉伸力学性能试验,研究了应变率与90%固含量(固体颗粒的质量分数)HTPB推进剂力学性能之间的相关性,并采用扫描电镜对拉伸断面进行了观察,分析了应变率对推进剂力学性能和破坏机制的影响。结果表明,在低应变率条件下,推进剂的应力—应变曲线出现了弧段现象;随着应变率增加,推进剂应力—应变曲线逐渐由5段式变为4段式;推进剂的初始模量、最大抗拉强度随应变率的增大呈现出上升趋势;推进剂的最大延伸率随应变率增大呈现出降低趋势,在应变率为1190.48×10^(-4)s^(-1)时最大延伸率仅为33.9%;随着应变率增大,高固含量HTPB推进剂的破坏机制逐渐由颗粒“脱湿”转变为基体撕裂,无颗粒破碎产生。

发射药燃气对身管材料的烧蚀速率的计算模型

为构建贴合实际需求的发射药烧蚀性能评价体系,设计半密闭爆发器烧蚀管实验,根据烧蚀管的几何尺寸及实验测量p-t曲线,建立了二维非稳态流动与传热模型,通过烧蚀管壁温的时空分布建立了烧蚀速率模型参数与烧蚀总量的关系。将半密闭爆发器烧蚀管实验的烧蚀量作为基准,采用粒子群算法对烧蚀速率模型参数进行了优化计算。结果表明:随着发射药燃气对烧蚀管冲刷时间增加,燃气与烧蚀管间的流固耦合界面温度有所降低,烧蚀管截面熔融深度的增速减缓;烧蚀管材料为45#钢,发射药为典型双基药(双芳-3)时,优化得到烧蚀速率的指前因子和表观活化能分别为0.3403 s^(-1)和134.6 kJ·mol^(-1),此时损失函数值仅为3.0×10^(-6),可推广应用于身管武器平台的烧蚀状态计算。

超级铝热剂在固体推进剂中的应用研究进展

超级铝热剂具有高放热和高活性的特点,其反应速率和能量释放效率均显著高于传统铝热剂,应用于固体推进剂有望改善释能速率、效率、感度等指标,已成为固体推进剂的发展方向。总结了超级铝热剂的制备工艺、特点及其工业化应用潜力;论述了超级铝热剂在固体推进剂中的适用性;综述了超级铝热剂的微结构(燃料/氧化剂界面控制、核壳结构、多层膜结构)和组分(金属氧化物、氟材料、碳纳米材料)对固体推进剂燃烧性能和能量释放的影响。超级铝热剂的添加显著提高了热反应活性和放热量,增强了推进剂的点火及燃烧性能,同时存在工业生产成本高、工艺控制要求复杂、燃烧过程精密控制难度大等问题,展望了未来超级铝热剂在固体推进剂中应用的研究重点和发展方向。

降速剂及其作用位点对丁羟四组元推进剂燃烧性能的影响规律

为研究降速剂对丁羟四组元推进剂燃烧性能的影响规律,将典型季铵盐和金刚烷衍生物两种高效降速剂引入核壳结构铝基复合颗粒Al@HMX和AP@Al,使其分别作用于HMX颗粒内部和AP颗粒表面,制备了4种含降速剂的铝基复合颗粒(Al/A@HMX,Al/B@HMX,AP@Al/A和AP@Al/B);采用扫描电子显微镜对样品形貌进行了表征;采用高速红外相机拍摄推进剂燃烧过程的火焰红外照片,并对推进剂的爆热、密度、点火延迟时间和燃速进行了测试。结果表明,加入惰性降速剂会导致推进剂爆热降低,而Al@HMX复合颗粒能部分抵消这一现象,使推进剂爆热值增加了338 J/g;降速剂能够抑制AP和HMX的热分解过程,使达到AlO辐射峰值前维持低强度的“平台段”;而引入Al@HMX后,推进剂的点火延迟时间比基础配方减小49.4%;在10~20 MPa范围内两种降速剂均能有效降低推进剂燃速,在此基础上采用Al@HMX可使含季铵盐丁羟四组元推进剂20 MPa下的燃速降低7.1 mm/s(38.4%),压强指数降至0.25;当降速剂作用于AP表面时,含质量分数1%季铵盐的推进剂在20 MPa下燃速可降低5.0 mm/s(27.3%)。

降速剂及其作用位点对三组元推进剂燃烧性能的影响规律研究

针对两种典型季铵盐和金刚烷衍生物降速剂,研究了其作用位点对推进剂点火燃烧性能的影响。基于两种不同结构的Al@AP和AP@Al复合颗粒,将降速剂分布在不同作用位置:即AP颗粒内部和表面。利用扫描电子显微镜(SEM-EDS)和计算机断层扫描(CT)等技术对所制备复合颗粒微观形貌和结构进行表征,研究了降速剂对推进剂爆热、点火延迟和燃烧性能的影响。惰性降速剂的加入会使得推进剂爆热值降低,但Al@AP复合颗粒的高反应活性能部分抵消这一现象。与机械混合方式相比,当降速剂作用于AP表面时能明显延缓推进剂点火过程,其中金刚烷衍生物能使推进剂点火延迟时间增加至420 ms,比基础配方增加了192%。在基体中直接加入降速剂可以有效降低推进剂燃速,但其降压强指数效果有限。铝基复合颗粒和降速剂的共同作用能显著降低推进剂的高压燃速和压强指数:当作用位置在AP内时,两种降速剂使推进剂1~20 MPa内压强指数从基础配方的0.45分别降低至0.20和0.33,同时可使10~20 MPa压强指数分别减小了48%和49%。

A Model of Steady-State Convective Combustion of Micropore Propellants

Aim To develop a physical and mathematical model related to micropore para- meters of steady-state convective combustion of micropore propellants(MPP). Methods The micropore parameters were measured by WXT-88 mage analysis apparatus and the convective combustion characteristic of MPP was measured by a large volume closed bomb, respectively. Rasults Statistical physical model of burning in the micropore and granular burning were developed. The burning rate equation of steady-state convective combustion of MPP was obtained. Conclusions This model correlates the convective burning rate with micropores para- meters for the first time,and the calculating values of convective burning rate are in agreement with test results.The model also can be used to estimate the effects of microporous parame- ters, basic mass burning rate, MPP density and pressure in combustion chamber on the convective combustion characteristics of MPP.

基于近红外光谱技术的固体推进剂燃速模型化快速预估方法

利用近红外光谱技术建立了基于近红外光谱的固体推进剂燃速快速预估模型,通过波谱范围筛选和光谱预处理对模型进行优化,并采用内部验证和外部验证对该模型进行评价,验证模型的精密度及准确度。结果表明,基于近红外光谱技术的固体推进剂燃速快速预估模型测试时间约为2 min,燃速偏差范围为-0.122~0.067 mm/s,精密度测试相对标准偏差≤0.4%,准确度测试偏差-0.029~0.057 mm/s。该方法能够在药浆混合阶段快速预测固体推进剂的燃速,提供了一种简单快捷和稳定可靠的燃速测定新方法。

一种面向丁羟推进剂燃速预测的机器学习融合模型

建立了以端羟基聚丁二烯(HTPB)推进剂原材料参数和组分含量为输入变量、燃速值为输出的机器学习预测模型。首先,通过经验性单因素规律对包括随机森林回归、支持向量回归、高斯过程回归、核岭回归和径向基函数模型等进行了初筛;然后,以最大绝对误差(AE_(max))、最大相对误差(RE_(max))、均方根误差(RMSE)及平均绝对误差(MAE)作为模型的性能评价指标,对不同模型的预测性能进行对比,筛选出最大相对误差RE_(max)<5%的模型,对通过筛选的模型进行融合获得最终的燃速预测模型,并将融合模型与单一模型的预测性能进行对比;最后,利用样本集外的10组数据对融合模型的预测精度进行了验证。结果表明,融合模型的RE_(max)和RMSE小于任何单一模型,其中AE_(max)=0.68、RE_(max)=3.97%、RMSE=0.3214、MAE=0.253,可实现对此类HTPB推进剂燃速的高精度、高效率预测。

宽温域宽应变率下丁羟四组元HTPB推进剂单轴压缩力学行为

为研究丁羟四组元端羟基聚丁二烯(HTPB)推进剂在宽温域宽应变率下的单轴压缩力学行为,基于万能材料试验机、高速液压伺服试验机、分离式霍普金森压杆,结合可程式恒温恒湿试验机等温控手段,开展了宽温域宽应变率下的推进剂单轴压缩力学性能实验,获取了-40,-25,-10,20,50℃5个温度下10-4~103 s-1应变率的丁羟四组元HTPB推进剂的应力应变曲线,并建立了HTPB推进剂的分段式单轴压缩率温本构关系。结果表明,HTPB推进剂的力学响应存在显著的率温相关性,在任意应变率下其力学响应都呈阶段性变化,即线弹性阶段⁃非线性屈服阶段⁃应变软化阶段或应变硬化阶段;且在高应变率下,非线性屈服行为后的应变软化现象明显弱于低、中应变率。此外,高应变率时,随着温度的降低,应力应变曲线的变化速率逐渐减缓;而低、中应变率却恰恰相反,随着温度的降低,应力应变曲线的变化速率逐渐加快。HTPB推进剂的力学强度随着温度的降低显著增大,温度从50℃降低至-40℃时,HTPB推进剂试件在宽应变率作用下的最大应力从2.2~8.8 MPa增长至约11~22 MPa。同时基于实验数据构建了分段式率温本构关系,发现其在温度较高时拟合效果更好,能够较好地预测HTPB推进剂的力学行为。

Recent advances in catalytic combustion of AP-based composite solid propellants

Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides(MOs),complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.

Study on the analysis method on ballistic performance of deterred propellant with large web size in large caliber artillery

As for the characteristics of combustibility of deterrent propellant with large web size which is used in large-caliber gun and interior ballistic performance, the combustion characteristics of deterrent propellant are obtained by using closed-bomb experiments. The combustion law of deterrent propellant and the classic interior ballistic model of composite charge are given. By simulation and analysis the results of the artillery firing test, the burning rate variation law and the interior ballistics simulation parameters of propellant A are determined, and the burning rate relationship between propellant A and propellant B obtained from closed-bomb, then the ballistic performance of propellant B is predicted. The results show that the predicted results are in good agreement with the experimental results. The study shows that the burning rate law of deterrent propellant with large web size can be obtained by closed-bomb experiment. Using the method provided in this paper can accurately predict the interior ballistic performance and provide an important basis for improving the accuracy of interior ballistic calculation.