Aluminum Agglomeration on Burning Surface of NEPE Propellants at 3–5 MPa

Aluminum agglomeration and agglomerate sizes of NEPE propellants were studied by cinephotomicrography at pressures of 3 and 5 MPa. Accumulation, aggregation, and agglomeration of aluminum particles similar to that at pressures below 1 MPa were observed. Coalescence of two agglomerates on the burning surface is obtained for the first time. A decrease in the burning rate from 8 to 5 mm s⁻¹ leads to about 20 % increase in the agglomerate diameter. The pressure is found to have no direct influence on the agglomerate diameter when the burning rate is kept constant. The evolution of the agglomerate diameter according to the increase of the virgin aluminum size from 16 to 36 μm is convex in shape and reached its maximum at a particle diameter of 29 μm. Increasing the amount of RDX crystals added in the propellants causes a larger agglomerate diameter. The experimental mass average agglomerate diameters were compared with various agglomeration models. It is found that Hermsen and Salita empirical models have a higher accuracy for NEPE propellants rather than Becksted, Liu, or pocket models.     

沙特SCC2×10000t／d水泥熟料生产线烧成系统技术介绍

当今世界上为数不多、规模最大的沙特SCC2×10000t／d水泥熟料生产线是中国中材国际承担的EPC工程项目,其烧成系统（回转窑、旁路放风和预分解系统等）采用了中国中材国际（南京）自主创新研制的工艺技术及装备,项目如期履约,并实现达标稳产。详细介绍了该生产线烧成系统主要设备的技术特点和运行情况及达到的技术指标。性能考核数据显示,该项目烧成系统技术及装备的各项技术经济指标已达到行业内国际先进水平,竞争优势突出。     

Characteristic Properties of an End Burning Grain with Smoke Reduced Ferrocene Containing Composite Propellant

Design, formulation and properties of an end burning grain are described which works for underwater propulsion operating at the level of 1200 N thrust for 20 s burning time. To avoid cavitational noise the formation of hot particles must be prevented. For this reason a smoke reduced composite propellant based on AP/HTPB with 86% energetic solids including 14% HMX and with 1% ferrocene derivative was adapted to grain size and motor configuration. For inhibition a pyrolytically stabilized polyurethane insulation was applied. The thermal insulation was made from a stiff high temperature resistant phenolic resin. The propellant exhibited a smooth burning behaviour with good processibility and mechanical properties. The desired performance was delivered at 120 bar operating pressure connected to 165 mm grain diameter and 93% thrust efficiency. Looking closer to the system it was found that part of the ferrocene derivative and plasticizer migrated from the propellant block to the inhibition layer. In the course of migration a small change of burning but a larger change of mechanical properties occurred in the boundary of the propellant. Despite these disadvantages burning times of 5 s and 10 s had been successfully realized with a case bonded configuration. For larger grain sizes, however, cracks occurred around the surface of the cylindrical propellant block. Calculation of the mechanical stresses which built up upon thermal shrinkage after curing and cooling showed values higher than the mechanical strength of the propellant could fit. These problems finally were overcome by a free standing grain. It led to a successful function of the motor for burning times of 20 s and more.     

Agglomeration Characteristics of Aluminum Particles in AP/AN Composite Propellants

Most solid rockets are powered by ammonium perchlorate (AP) composite propellant including aluminum particles. As aluminized composite propellant burns, aluminum particles agglomerate as large as above 100 μm diameter on the burning surface, which in turn affects propellant combustion characteristics. The development of composite propellants has a long history. Many studies of aluminum particle combustion have been conducted. Optical observations indicate that aluminum particles form agglomerates on the burning surface of aluminized composite propellant. They ignite on leaving the burning surface. Because the temperature gradient in the reaction zone near a burning surface influences the burning rate of a composite propellant, details of aluminum particle agglomeration, agglomerate ignition, and their effects on the temperature gradient must be investigated. In our previous studies, we measured the aluminum particle agglomerate diameter by optical observation and collecting particles. We observed particles on the burning surface, the reaction zone, and the luminous flame zone of an ammonium perchlorate (AP)/ammonium nitrate (AN) composite propellant. We confirmed that agglomeration occurred in the reaction zone and that the agglomerate diameter decreased with increasing the burning rate. In this study, observing aluminum particles in the reaction zone near the burning surface, we investigated the relation between the agglomerates and the burning rate. A decreased burning rate and increased added amount of aluminum particles caused a larger agglomerate diameter. Defining the extent of the distributed aluminum particles before they agglomerate as an agglomerate range, we found that the agglomerate range was constant irrespective of the added amount of aluminum particles. Furthermore, the agglomerate diameter was ascertained from the density of the added amount of aluminum particles in the agglomerate range. We concluded from the heat balance around the burning surface that the product of the agglomerate range and the burning rate was nearly constant irrespective of the added amount of aluminum particles. Moreover, the reduced burning rate increased the agglomerate range.     

Effects of equivalent diameter on vertical PMMA combustion in natural convection environment

A series of combustion experiments of polymethyl methacrylate (PMMA) plates with two shapes, three thicknesses, and different sizes was performed to investigate the effects of equivalent diameter on combustion characteristics of vertical PMMA in a natural convection environment. Two digital video cameras were used to record the burning process. The temporal variation of mass was recorded by an electronic balance. The influence of equivalent diameter on mass loss rate and flame height was then analyzed theoretically. Convection and radiation heat transfer were calculated and modeled in the theoretical analysis and compared to experiment. The result shows that the theoretical prediction of mass loss rate for each equivalent diameter is in good agreement with the experimental measurements. In addition, the relationship between flame height and heat release rate was analyzed using dimensionless analysis method. It was found that the flame height for vertical PMMA burning in a nature convection environment is dominated by heat release rate and equivalent diameter.     

Modelling of heat release rate in upholstered furniture fire

Many fatal residential fires started from burning upholstered furniture, and so upholstered furniture fire has been studied rather extensively in developed countries. As many upholstered furniture were made in China, the hidden fire risk should be studied more. In this paper, full‐scale experiments on the burning of upholstered furniture manufactured in China were conducted and analyzed. The oxygen consumption method was used to measure the heat release rate in a room calorimeter. An ignition source of a 20‐kW gasoline pool fire of 0.2‐m diameter was used to test square foam cushions and 4‐seater sofas. A model of heat release rate predicting upholstered furniture fire in a room was developed on the basis of earlier Swedish works. Results were then used to justify the application of the Combustion Behaviour of Upholstered Furniture model to predict the heat release rate of furniture manufactured in China. The numerical values of key parameters in the model were determined. It is proposed to build up a database that can be used to model heat release rates upon burning furniture. Detailed procedures are illustrated in this paper.     

Dependence of burning rate on sample size in the Ni + Al system

Burning rates were measured for samples of the starting mixture of Ni + Al and the same mixture subjected to mechanical treatment in argon and then in water. The dependences of the burning rate on the diameter of the samples of the original and mechanically activated mixtures are similar. The burning rate passes through a maximum as the diameter increases from 8 to 12 mm. It is found that the burning rate of 270–360 µm thick films obtained by rolling the starting mixture of Ni + Al and the mixture mechanically activated and then activated in water (dispersed) is 4–20 times the burning rate of cylindrical samples 8–12 mm in diameter, pressed from the same powders. The data obtained in this study were explained using a convective-conductive model of combustion-wave propagation.     

对二甲苯液相氧化过程中燃烧副反应动力学

During the liquid-phase oxidation of p-xylene, over-oxidation of reactant, intermediates and solvent to carbon dioxide and carbon monoxide is generally known as the burning side reaction. Batch and semi-continuous experiments were carried out, and the experimental data of the burning side reaction were analyzed and reported in this paper. The results showed that the rates of burning side reactions were proportional to the rates of the main re-action, but decreased with the increasing concentrations of reactant and intermediates. The inter-stimulative and competitive relationship between the burning side reaction and the main reaction was confirmed, and the rates of the burning side reaction could be described with some key indexes of the main reaction. According to the mecha-nism of the side reactions and the kinetics model of main reaction which were proposed and tested in the previous papers, a kinetic model of the burning side reactions involving some key indexes of the main reaction was devel-oped, and the parameters were determined by data fitting of the COx rate curves. The obtained kinetic model could describe the burning side reactions adequately.     

Low and High Order Detonation in Tetryl

The detonation behaviour of tetryl has been investigated by analysing published charge diameter effect data for two mesh sizes of powders, using slightly divergent flow theory. Evidence found within the published data for the existence of high and low order detonation velocities regimes has been substantiated. The form of the global heat release function during low order detonation was found to be of the hot spot/grain burning type, and during high order detonation, of the thermal explosion type. Particle size effects are discussed both for low and high order detonation. The observed stability of low order detonation at the smaller charge diameters is explained in the model used, which predicts a ‘forbidden zone’ in shock velocity/inverse charge diameter space. The kinetics are discussed in terms of the pressure dependent functional form used in the CPeX detonation model, and models of hot spot formation in powder explosives.     

Prediction of burning rate of coal in fluidized-bed combustion

A theory has been proposed to evaluate the burning rate of a single carbon particle in a continuously operated coal-fired fluidized bed. Experimental verification was carried out in a laboratory scale 200 mm × 200 mm combustor. The burning rate increases with the increase of the fluidization velocity and the size of the bed material. The predicted data on burning rate agree fairly well with the experimental values. The gas concentration in the bed and freeboard has also been measured and it is seen that the consumption of oxygen mostly takes place in the bed.     

Gas combustion in a narrow channel at high pressure

This paper presents experimental results on the effect of pressure on the flame propagation velocity in a tube with diameter close to the critical diameter. An important feature of the investigated combustion regime is heat transfer along the tube wall from the combustion products to the fresh mixture. Methane-air and hydrogen-air mixtures were used. The experiments show that with increasing pressure, the burning velocity of methane-air flames decreases whereas the burning velocity of hydrogen-air flames is almost unchanged. This behavior is explained by the pressure dependence of the laminar burning velocity.     

The persistence of burning of textiles in different oxygen environments and the determination of the extinction oxygen index

The influence that oxygen has on the burning behaviour of cotton single- and multilayered fabries has been determined by recording persistence of burning times as a function of oxygen concentration. For a given fabric subjected to a specified igniter application time, an extinction oxygen index parameter, EOI, may be determined. EOI is defined as the oxygen concentration expressed as a volume fraction in an oxygen-nitrogen mixture, necessary to give a persistence of burning time equal to zero. For a given fabric, EOI is found to decrease as the igniter application time increases and two limiting EOI values may be observed, one corresponding to zero inginter application conditions and one for igniter application times greater than 10 s. At any given ignition time, the extinction oxygen index increases linearly with fabric area density and decreases linearly with the logarithm of the respective air permeability. Similar results are observed for nylon 6.6 and polyester single- and multilayered fabrics. The validity of the extinction oxygen index is discussed with reference to other published works.     

Particle size and density changes during fluidized-bed combustion

Experiments have been performed which demonstrate that petroleum coke particles (initial diameters between 7 and 13 mm) and brown coal char (initial diameter between 3.5 and 6.4 mm) burn in a manner close to that of an ideal shrinking sphere. These observations confirm the previously assumed mode of burning for particles in fluidized-bed combustors. Analysis of the data for petroleum coke indicates that pore diffusion may become increasingly significant for particles less than 5 mm in diameter. The method of data presentation provides a sensitive means of demonstrating the effect of particle attrition.     

我公司#5窑燃无烟煤技改后运行情况简介

福建水泥股份有限公司为充分利用当地产无烟煤生产,以降低生产成本,采用了中材国际南京水泥设计研究院“回转窑燃无烟煤生产新技术”,对其2 000 t/d熟料的#5窑进行了技术改造。改造内容涉及煤粉制备系统、烧成系统、冷却机系统和相关环节的技术优化整改。改造后经1 a多的生产运行,在无烟煤掺量达到70％的情况下,生产正常稳定,熟料产质量及其它技经指标均达到并超过改前水平。     

Critical diameter and transverse waves of powder combustion

A critical review is given of the problem of powder extinction with a decrease in the sample diameter due to heat release. The results of our experimental studies of the critical combustion diameter are presented. A comparison of the experimental data on the critical diameter as a function of burning rate is shown to be the most informative. These functions follow a power law with an exponent of −1.15 to −1.17. The relations between the sizes of the cells (hot spots) formed by the set of transverse waves on the burning surface and the burning rate follow the same law. The sizes of the cells are 2.1–2.3 times smaller than the critical combustion diameter. It is also found that the transverse wave decays if its curvature exceeds a critical value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 72–78, March–April, 2007.     

Combustion and Sensitivity Characteristics of Mg/TF Pyrolants

Burning rate characteristics and sensitivity characteristics of energetic mixtures composed of metal particles and oxidizers, the so called ‘pyrolants’, were studied experimentally. The pyrolants tested were made of various particle sizes of magnesium (Mg) and polytetrafluoroethylene (TF). Mg/TF pyrolant produces high combustion flame temperature, so it is used as heat sources and igniter pyrolants. The maximum flame temperature (Tf) is 3271 K at 0.1 MPa, and 3483 K at 1 MPa. These values are obtained when Mg concentration is 30%. When the Mg concentrations are less than 50% the pyrolants are not able to burn stably at one atmosphere. The burning rate increases with increasing the concentration of Mg and decreases with increasing the mean diameter of Mg particles at constant pressure. Explosive energy evaluated with drop hammer test decreased with increasing burning rate, so there is strong relationship between burning rate and explosive energy.     

Mechanism of Catalytic Effects on AMMO/HMX Composite Propellants Combustion Rates

Thermal decomposition and the burning properties of AMMO/HMX propellants have been investigated. The heat generated by the AMMO decomposition initiated and accelerated the thermal decomposition of HMX, and the reaction between decomposed AMMO and HMX depended upon the heating rate. The rate determining step of the reaction path was different in higher and lower heating rate conditions. 2,2-bis(ethylferrocenyl)propane (CFe) and copper chromite (CuC) significantly altered the mechanisms of the thermal decomposition and the burning properties. CFe showed an increase in burning rate with a slight increase in burning rate exponent. However, CuC yielded high values for the burning rate exponent. The combined additive yielded the highest burning rate with the lowest burning rate exponent. The influence of CuC on the burning rate exponent disappeared by the combination with CFe. Though CFe and the combination additive improved the ignitability of the propellants, the propellant with CuC was difficult to ignite because of the relatively small quantity of heat feedback and/or heat released by the decomposition.     

Burning of liquid fuels: effect of burner diameter on burning rate and measurements of quenching diameter

Laminar pool flames of four straight-chain alcohols were studied in uncooled glass and copper burners and water-cooled glass burners. The mass burning rate $\text{m}\text{?}$ increased with the burner diameter d decreasing as $\text{m}\text{?}$ ∝ d^?n, where n ≈ 1.2 for uncooled glass burners. The values of $\text{m}\text{?}$ in copper burners were lower by a factor of 1.5–2 than those in glass burners of the same diameter. Vigorous boiling of the subsurface layer of liquid occurred in sufficiently narrow uncooled glass burners, and numerous burning droplets were observed to traverse the flame. The quenching diameter d_c was measured. For uncooled copper burners d_c increased with increasing molecular weight M_r of the alcohol, from ≈ 2 mm for propanol to ≈ 20 mm for decanol. For uncooled glass burners d_c was much lower (1–2 mm) and less dependent on molecular weight. The product of d_c and the critical mass burning rate is assumed to have a characteristic value for the stability of diffusion burning, in accordance with the Zel'dovich criterion (Pe) = (Pe)_c = const. for flame stability in gas mixtures. However, the stability of diffusion burning increased with increasing heat losses from the burner wall. Two possible interpretations of this paradoxical effect are suggested.     

Measurement and Modelling of Pyrotechnic Time Delay Burning Rates: Application and Prediction of a Fast Burning Delay Composition

A predictive numerical model was implemented for a time delay based on the Si+Pb₃O₄ system. The reaction kinetic parameters were estimated by comparing predicted surface temperature profiles with experimental data acquired with an infrared camera. Fair agreement between the modelled and measured burning rates was achieved. The burning rate is predicted to increase by 9.4 % for every 50 °C increase in ambient temperature. The core diameter was found to have a slightly larger impact on the burning rate than the wall thickness. The effect of using different wall thickness materials was evaluated and indicated that the burning rate is significantly influenced by the wall material when the thermal conductivity is increased and the volumetric heat capacity is reduced. The shape of the combustion front was found to widen with a long tail for materials with a low thermal conductivity and a narrower combustion front with a short tail for materials with high thermal conductivity. Preheating occurred for pyrolytic graphite‐ and diamond‐based elements but no radial combustion was observed. The external heat transfer parameters (convection and radiation) did not affect the burning rate of the fast delay composition. It is concluded that the ambient temperature, volume fraction solids, molar heat of reaction, core and outer diameter are the factors that most significantly influence the burning rate of the Si+Pb₃O₄ composition in long cylindrical elements.     

喷雾射流中粒度、时间和速度信号的双重自仿射性

采用双模颗粒动态分析仪 (DualPDA)同时测定了气流式喷嘴雾化过程中液滴在不同空间位置的三维速度向量、粒度和滞留时间等物理量 ,研究了液滴速度分量、粒度分布及滞留时间的时间序列 ,通过域重新标度分析法 ,计算出时间序列的赫斯特指数、谱密度指数及其分形维数 ,发现各空间点测得的各物理量的归一化域值对时间具有标度性质 ,相对于均值的累积偏差曲线具有自仿射性 ,各物理量的时间序列彼此也具有自仿射性 ,其Hurst指数和分维数分别近似相等 .所得到的结果和前人用激光诱导荧光 (LIF)技术获取湍流 /非湍流界面图像而得到的结果一致 .