Local Fluctuations of Physicochemical Parameters in Condensed System Combustion

Using the 3Zr + 2WO₃ system as an example, it is shown that fluctuations of physicochemical parameters in the combustion wave of a condensed system in both loose and pressed forms can be recorded by means of two parallel wires placed in the burning system. It is established that changes in the initial density of the system and its burning rate results in corresponding changes in the fluctuation frequency. The relationship between these three parameters can be expressed, as a first approximation, by a fairly simple analytical relation.     

Three-Dimensional Unsteady Solid Flame Combustion under Nonadiabatic Conditions

The effect of heat losses on solid flame combustion characteristics is considered. New steady-state three-dimensional periodic regimes are found that do not occur under adiabatic combustion conditions. The essence of these regimes is explained using as an example the regime with six spots moving on helical lines in the near-surface layers of a cylinder. The spots are localized in the near-surface layers of a cylinder and do not intersect the central (located along the axis) zone of the sample. The interior of the cylinder (core) burns in a steady-state regime; i.e., along the cylinder axis, the front propagates at a constant velocity. An explanation is given for the existence of such regimes.     

端部初始燃面可变的星孔火箭装药燃烧特性

采用上、下端面均无包覆星孔装药的小型自由装填式固体火箭发动机,其药柱端面与垫片间的间隙会受温度等因素影响而发生变化.端部初始燃面变化规律较为复杂,无法使用经典的燃面计算理论.通过引入端面燃烧参与度和端面等效燃烧厚度的方法,结合试验条件导出了燃面面积经验计算公式,解决了端部初始燃面可变的星孔火箭装药燃面计算问题.研究了不...     

Analysis of unsteady solid-propellant combustion models (review)

Recent studies of solid-propellant combustion models are briefly analyzed. The models are divided into purely one-dimensional (classical and phenomenological models with various generalizations of the Zel’dovich approach) and non-one-dimensional. The latter include models with local non-one-dimensionality, which is always accompanied by local unsteadiness. This all can be eliminated by averaging. The main disadvantage of unsteady solid-propellant combustion models, which is no fault of their authors, is the same as in the case of steady-state models: the lack of detailed information on chemical and physical processes in the condensed phase. Impropriety of extending the purely one-dimensional approach to the instability region is noted. Possible directions for further development of unsteady (and quasi-steady-state) solid-propellant combustion models for homogeneous compositions may involve accounting for local non-one-dimensionality and the unsteadiness due to instability of the subsurface reactions zone and verification of the possibility of the existence of chemical instability capable of causing similar non-one-dimensionality and unsteadiness. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 35–48, January–February, 2008.     

Numerical Simulation of Quenched Combustion Model for AP/HTPB Propellant under Transient Depressurization

In order to study the out‐of‐phase blowing effect of ammonium perchlorate/hydroxyl terminated polybutadiene (AP/HTPB) under transient depressurization, a two‐dimensional periodic sandwich model of AP/HTPB sandwich unsteady combustion was established. The gas‐solid two‐step total reaction was used to couple the gas‐solid boundary layer, and the AP/HTPB step‐down temperature criterion was applied. The numerical simulation comparative analysis under the initial combustion pressure 3.5 MPa∼10 MPa and the initial depressurization rate of 1000 MPa/s∼2000 MPa/s was experimented. The results show that under the condition of initial combustion pressure of 3.5 MPa and pressure reduction rate of 1000 MPa/s, the formation of narrow diffusion chemical reaction zone appears in the initial stage of depressurization; when the combustion pressure drops to about 1.7 MPa, the flame appears dual characteristics: diffusion and premixed combustion; when the pressure dropped to 0.1 MPa, the flame is premixed combustion. AP(g) is the main factor causing the out‐of‐phase blowing effect. During the initial stage of combustion, AP(g) decomposes rapidly and its decomposition product is close to the combustion surface; with the rapid decrease of pressure, the gas‐phase heat feedback decreases, leading to the decrease of AP(g) decomposition rate and AP(g) diffusion to the gas phase, which is the initial phase of out‐of‐phase blowing effect; when the gas phase heat feedback reduced and the temperature is below 750 K, the decomposition of AP(g) is stopped and the undecomposed AP(g) is further diffused to the gas phase region, which exacerbates the out‐of‐phase blowing effect, leading to the extinguishment of AP/HTPB. The unsteady combustion flame extinction time increases with the initial combustion pressure, and decreases with the initial depressurization rate.     

含硼固体推进剂燃烧残渣中三氧化二硼和碳含量测定及燃烧机理研究

为了研究含硼富燃料固体推进剂燃烧机理,对3种配方的不同批次含硼富燃料固体推进剂在不同压强的燃速进行了测试,利用化学分析法对其燃烧残渣中B2O3和C含量也进行了测定。结果表明,硼粒子表面的B2O3延缓了硼粒子的进一步燃烧,因此残渣中B2O3含量较低;随着氮气压强增高,残渣中B2O3含量降低,而C含量、B2O3与C总含量升高;随着推进剂配方中镁含量增高,残渣中B2O3含量降低,C含量先升后降,B2O3和C总含量则降低。     

片状变燃速发射药燃烧性能的数值计算

为研究包覆方式对片状发射药燃烧性能的影响,建立了不同包覆方式下多层片状发射药的物理模型,并推导了形状函数和燃气生成猛度表达式,利用Matlab软件对不同的宽厚比、长厚比及多层结构的片状发射药进行了数值计算;制备了不同长厚比的片状变燃速发射药,并进行了密闭爆发器实验。结果表明,四面包覆和全包覆可以很好地消除临界宽厚比对片状发射药燃烧性能的影响;与两面包覆的片状发射药相比,四面包覆和全包覆的片状发射药能够延缓内层药减面燃烧的时间,其燃气生成猛度的阶跃程度分别提高了1.17%和1.23%,呈现出良好的燃烧渐增性。     

低燃速低燃温双基推进剂的催化燃烧

研究了含普通铅、铜盐催化剂的低燃速、低燃温双基推进剂的燃烧性能、热分解性能及熄火表面形貌特征和元素分布。观察到如下试验现象：(1)熄火试样表面元素分布不均匀,C元素和催化剂在熄火表面均有不同程度的积累;(2)含催化剂的试样燃烧熄火表面有大小不等的球体出现,催化剂不同,形成的球体直径分布不同,球体成分以Pb为主,兼有少量其它元素,各球体相互连接形成链状、短枝状;(3)含和不含催化剂的配方未燃表面无球体出现。结果表明,适用于普通双基推进剂的铅、铜盐催化剂在低燃速低燃温双基推进剂中同样具有催化作用,对热分解性能也有重要影响。     

Combustion of Volatile Condensed Systems behind the Stability Limit of the Stationary Regime

The nonstationary combustion of gasifying condensed systems behind the stability limit of stationary combustion is studied numerically using the Belyaev–Zel'dovich model with firstorder chemical reactions in the condensed and gas phases. The stability limit of constantpressure stationary combustion is found. A pressure change results in a sequence of perioddoubling bifurcations for burningrate oscillations. A chaotic combustion regime occurs after the fourth bifurcation.     

Reduction of agglomeration effect by aluminum trihydride in solid propellant combustion

Aluminum trihydride (AlH₃) has gained considerable attention as a substitute fuel for aluminum in solid propellants. In this study, we conducted a systematic investigation to evaluate the effects of AlH₃ content, ranging from 0 % to 18 %, on propellant ignition, combustion, and agglomeration. Experimental methods such as thermogravimetry−differential scanning calorimetry (TG-DSC), laser ignition, high-speed photography, and collecting condensed combustion products (CCPs) were employed. The results indicate that AlH₃ significantly promotes the high-temperature decomposition of ammonium perchlorate (AP). Meanwhile, the addition of cyclotetramethylene tetranitramine (HMX) in propellant does not affect the hydrogen release reaction of AlH₃. As the AlH₃ content increases from 0 % to 18 %, the spectral emission intensity of the propellants decreases, and the ignition delay time initially increases from 253 ms to 321 ms, and then decreases to 258 ms. Furthermore, the burning rate increases with increasing the AlH₃ content, while the pressure exponent is reduced from 0.551 to 0.460. The inclusion of AlH₃ in propellants significantly inhibits aluminum agglomeration near the burning surface. Additionally, as the AlH₃ content increases, the mean particle size D₄₃ of the CCPs decreases from 50.95 μm to 8.28 μm at 1 MPa. The agglomeration degree of aluminum is very weak at 7 MPa, especially when the AlH₃ content exceeds 9 %. The conclusions drawn from this study can serve as valuable guidance for optimizing propellant formulations.     

Impact of Structural Factors on Unsteady Combustion Modes of Gasless Systems

Based on the twotemperature, twovelocity timedependent model of gasless combustion, taking into account structural transformations related to the force action of the gas filtering in the pores and vitrification and volume variation of the condensed phase during the chemical transformation, selfoscillatory combustion modes are studied. Structural transformations are shown to have a pronounced effect on the propagation pattern of combustion waves and can either stabilize or destabilize combustion. The major structural parameters appreciably affecting combustionwave stability are the initial porosity, particle size, and pressure.     

Condensed combustion products of aluminized propellants. IV. Effect of the nature of nitramines on aluminum agglomeration and combustion efficiency

The condensed combustion products of two model propellants consisting of ammonium perchlorate, aluminum, nitramine, and an energetic binder were studied by a sampling method. One of the propellants contained HMX with a particle size D ₁₀ ≈ 490 μm, and the other RDX with a particle size _{D 10} ≈ 380 μm. The particle-size distribution and the content of metallic aluminum in particles of condensed combustion products with a particle size of 1.2 μm to the maximum particle size in the pressure range of 0.1–6.5 MPa were determined with variation in the particle quenching distance from the burning surface to 100 mm. For agglomerates, dependences of the incompleteness of aluminum combustion on the residence time in the propellant flame were obtained. The RDX-based propellant is characterized by more severe agglomeration than the HMX-based propellant — the agglomerate size and mass are larger and the aluminum burnout proceeds more slowly. The ratio of the mass of the oxide accumulated on the agglomerates to the total mass of the oxide formed is determined. The agglomerate size is shown to be the main physical factor that governs the accumulation of the oxide on the burning agglomerate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 78–92, July–August, 2006.     

Ignition,combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. II. Experimental studies of agglomeration

The combustion characteristics of propellants containing AP, HMX, an energetic binder, and aluminum particles with various polymer coatings are studied at pressures of 0.15 and 4.6 MPa. It is found that the coatings influence the burning rate, the particle size distribution of condensed combustion products, and the completeness of aluminum combustion. It is shown that the agglomeration can be reduced by using aluminum with fluorine-containing coatings. The application of some coatings results in a reduction in the mass of the agglomerates with an insignificant increase in their size. The greatest effect was achieved when using aluminum coated with (CH₂=CH-CH₂-O)₂Si[OCH₂(CF₂-CF₂)₂H]₂ [bis(allyloxy)-bis(2,2,3,3,4,4,5,5-octafluoropentyloxy)silane]. For this coating, a size reduction is also observed for micron-size oxide particles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 83–97, May–June, 2007.     

Hot-spot combustion of heterogeneous condensed mixtures. Thermal percolation

A model of combustion of heterogeneous condensed mixtures composed of reactive particles separated by an inert heat-conducting substance is considered. Propagation of the reaction in a one-dimensional periodic system of point reaction cells connected by inert thermal bridges is examined. The burning rate is determined as a function of the basic parameters of the system, and stability of the steady combustion mode is studied. It is shown that there exists a range of parameters in which the reaction propagates in an unstable manner. Combustion of the system in the instability domain is examined. It is shown that the reaction propagation loses its stability many times as the adiabatic temperature of the system decreases; in this case, the existing unsteady mode is replaced by another, more complicated mode, and the alteration of the regimes in the examined systems always proceeds as a period-doubling bifurcation. Beginning from a certain value of adiabatic temperature, the reaction-propagation process becomes stochastic. In the systems examined, there exists an ultimate adiabatic temperature, below which self-sustained propagation of the reaction in the system becomes impossible.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 41–54, January–February, 2005.     

内弹道稳定剂对中高燃速RDX-CMDB推进剂燃烧性能的影响

以一种中高燃速改性双基推进剂配方为基础配方,添加不同粒度的Al_2O_3及不同品种的内弹道稳定剂,研究了6~20MPa下推进剂燃速和燃速压强指数的变化规律,并对其燃烧机理进行了分析。结果表明,添加Al_2O_3后推进剂的燃速降低,且随着压强的升高,燃速降低的幅度减小;不同品种的内弹道稳定剂对燃速及燃速压强指数降低和提高的幅度不同,TiO2提高了推进剂高压段的燃速,MgO几乎不影响推进剂燃速,而Al_2O_3、ZrO_2均降低了推进剂的燃速。添加不同粒度的Al_2O_3后,均使燃烧表面的催化剂含量(浓度)降低,改变了催化剂的催化效率,从而导致添加芳香铅A催化剂的推进剂中Al_2O_3粒径分别为10μm和2.5μm时,燃速相应降低0.25mm/s和1.25mm/s。不同品种的内弹道稳定剂对燃烧表面催化剂含量、分散均匀性、催化活性的影响不同,TiO_2、MgO的活性高于Al_2O_3和ZrO_2,从而表现出添加TiO_2、MgO的推进剂燃速高于添加Al_2O_3、ZrO_2的推进剂。