Detonation Limits of Air Mixtures with Two-Component Gaseous Fuels

The problem of detonation limits for ternary mixtures of air with a two-component gaseous fuel is considered for a detonation region represented using the Le Chatelier rule. Examples are given of incorrect treatment of conditions for detonation suppression in hydrogen–air mixtures by the addition of hydrocarbons ignoring the overall composition of the mixture. It is suggested that the range of explosion hazard of lean hydrogen–air mixtures is extended by the addition of small amounts of hydrocarbon gases. Key words: detonation, detonation limits, multicomponent fuel mixtures, suppression and promotion of detonation.     

Heterogeneous Continuum Model of Aluminum Particle Combustion in Explosions

A heterogeneous continuum model is proposed to describe the dispersion and combustion of an aluminum particle cloud in an explosion. It combines gasdynamic conservation laws for the gas phase with a continuum model for the dispersed phase, as formulated by Nigmatulin. Interphase mass, momentum, and energy exchange are prescribed by the phenomenological model of Khasainov. It incorporates a combustion model based on mass conservation laws for fuel, air, and products. The source/sink terms are treated in the fast-chemistry limit appropriate for such gasdynamic fields, along with a model for mass transfer from the particle phase to the gas. The model takes into account both the afterburning of the detonation products of the booster with air and the combustion of the Al particles with air. The model equations are integrated by high-order Godunov schemes for both the gas and particle phases. Numerical simulations of the explosion fields from 1.5-g shock-dispersed-fuel charges in 3 different chambers are performed. Computed pressure histories are similar to measured waveforms when the ignition temperature model is employed. The predicted product production is 10–14% greater than that measured in the experiments. This fact can be ascribed to unsteady ignition effects not included in the modeling.     

Numerical simulation on the bomb case effects of non-ideal aluminized explosive

The detonation process of non-ideal explosives is influenced by the casing of the bomb. Non-ideal charges in the process of the explosion of live ammunition energy output mechanism and distribution ratio, the impact of the case on the explosion flow field, and other issues cannot be obtained through the existing theoretical analysis and testing techniques to obtain specific values. This paper establishes a “detonation+afterburning” energy output model to characterize the energy release characteristics of non-ideal charges, using step-by-step numerical simulation of the near and middle, and far fields of the explosion, and verify simulation results through experiments, quantitative analysis the case of a type of earth penetrator on the normal particle size (4 μm) and two times the normal particle size (8 μm) of non-ideal charges of aluminum powder explosion process. The results indicate that the presence of the casing enhances the energy output of aluminum powder with 4 μm by ≈5 %. When the particle size of aluminum powder is doubled, the maximum reaction rate and the peak of the shock wave are merely around 35 % and 75 %, respectively, compared to those of normal particle size. The detonation products, case fragments, and air constitute 49 %, 48 %, and 3 % of the overall explosion energy, respectively. The proportional equation of the conversion between the chemical energy of the explosion and the kinetic energy of the case fragments is obtained. These conclusions can provide data support for the design of non-ideal charge warheads, lethality assessment, and establishment of engineering protection standards.     

Numerical study of laminar rich hydrogen–air flames with added ethanol

The propagation of fuel-rich hydrogen–air flames with added ethanol has been studied using numerical methods. It has been shown that the inhibition by ethanol is less effective compared to propane and propylene. The addition of ethanol leads to the effect of superequilibrium temperatures, but it takes place only at ethanol concentrations above a certain value. At the flammability limit of fuel-rich mixtures of hydrogen, ethanol, and air, determined by the Le Chatelier rule, the estimated maximum flame temperature is constant. The exception is mixtures with a small addition of ethanol.     

The KaoIinite-Mullite Reaction Series: I, A Survey of Outstanding Problems

This reaction series has been a subject of extensive investigation since the work of Le Chatelier in 1887. Nevertheless, major problems have remained concerned with the nature of metakaolin, the manner in which it transforms into a spinel-type phase and mullite, and the relation of this spinel-type phase to mullite. The present survey brings these problems into sharp focus and provides the necessary historical background fora new approach to their solution.     

The hydration of calcium sulphate hemihydrate

The isothermal kinetics of calcium sulphate hemihydrate hydration have been determined (i) by thermogravimetry and microcalorimetry for water vapour hydration and (ii) by microcalorimetry for liquid water hydration. The dehydration conditions of gypsum modify the reactivity of the obtained product. Only gypsum dehydrated in a vacuum or in a very low water pressure is likely to rehydrate. The mechanism “Le Chatelier” would not be only one to apply during hydration with liquid water.     

Stress‐Enhanced Swelling of Silica: Effect on Strength

From the work of Le Chatelier [1884], it is well known that chemical reactions that exhibit a change in volume are sensitive to the ambient pressure of the reaction. Increasing the pressure will alter the ratio of reaction products to reactants. If the change in volume is constrained to occur at a surface, then such reactions can result in residual stresses that affect the strength of the solid. These effects are applicable to silica glass, which increases in volume when reacting with water. In this paper, we discuss the possibility of using this effect to strengthen silica glass. Using a modification of Le Chatelier's theory to handle applied stresses, we show that water penetration into the surface of silica glass can yield sufficient residual stress to increase the strength of silica glass into the GPa range. Applying these ideas to recent data published by Lezzi et al., we are able to attribute the strengthening they observe to a water/silica reaction under an applied tensile stress.     

Thermally safe operation of liquid-liquid semibatch reactors Part II: Single diffusion controlled reactions with arbitrary reaction order

The thermally safe operation of an indirectly cooled semibatch reactor in which an exothermic liquid-liquid reaction occurs corresponds to conditions of potentially very high macrokinetic conversion rates compared with the supply rate of the coreactant, which accumulation in the system remains consequently low. This leads to the definition of a target temperature that can be compared with the real temperature-time profile, in order to develop boundary diagrams which summarize all the possible thermal behaviors of the reactor and can be used for safe scale-up purposes. The variable parameters which appear in such diagrams are an exothermicity and a reactivity number derived from the expressions of the conversion rates in the kinetically or diffusion controlled regime, respectively.In this work the influence of the microkinetic rate of reaction on the shape and location of the boundary diagrams for single liquid-liquid diffusion controlled reaction systems is discussed, extending to this regime the results previously obtained for kinetically controlled reactions.Also in the case of diffusion controlled reactions, it is shown that for many practical systems, using boundary diagrams based on (1,1) reaction orders can lead to both unsafe or not necessary low production operating conditions. Consequently, a number of new boundary diagrams for arbitrary reaction orders is presented and some rules-of-thumb useful to their application are discussed.     

凝聚相炸药爆炸火光现象的初步研究

为弄清凝聚相炸药爆炸火光现象的形成机制及影响爆炸发光现象的相关因素,对凝聚相炸药爆炸过程中存在发光现象的各阶段发光机制进行了理论分析,用文献试验结果分析了影响爆炸发光强度的因素。采用高速摄像的试验手段研究了16种凝聚相炸药的爆炸火光现象。结果表明,凝聚相炸药的爆炸发光过程由爆炸和后燃两阶段组成。凝聚相炸药的爆炸发光强度与炸药的爆压、爆温、爆速和氧平衡均有关系。而炸药的氧平衡和质量则影响爆炸火光现象持续的时间。     

Dust/gas mixtures explosion regimes

The explosion features of nicotinic acid dust in atmosphere of methane and air at different concentrations of either dust or gaseous fuel are studied. Experimental measurements of the pressure history, deflagration index and flammability limits are performed by the standard 20 l Siwek bomb though adapted for such hybrid mixtures.Data show non linear effect of explosion severity and the synergistic effects when hybrid mixtures explode. Results allow the definition of five different regimes of the gas/dust/air mixture explosion in the plane dust concentration vs. fuel concentration.     

高钙粉煤灰的粉磨改性研究

研究了粉磨对两种高钙粉煤灰物理化学性能的影响。通过混合水泥雷氏夹膨胀值、强度和自由线膨胀率等的试验测定,对两种高钙粉煤灰经粉磨后进行性能研究。结果表明,通过粉磨可以减缓甚至消除高钙粉煤灰带来的安定性问题,提高混合水泥强度,降低混合水泥自由线膨胀率。     

钢渣砂的安定性及其检测方法的研究

钢渣代砂制备的砂浆具有密度大,强度高,抗渗性好等优点。然而钢渣中的f-CaO等易引起体积安定性不良。研究表明：钢渣的体积安定性并不单纯地随f-CaO的含量增大而降低;雷氏夹法及粉化率法在衡量钢渣体积安定性方面均不可靠;而压蒸法测定强度变化是比较可靠的方法。     

Estimation of the Fireball Size in an Ethyne–Air Cloud Explosion

A gas explosion accident is often followed by a serious fire. In order to effectively prevent fire induced by a gas explosion accident, it is necessary to have some knowledge of the related explosion processes. The subject of the present study is to examine deflagration behaviors beyond the original cloud of the ethyne–air mixture and the fireball size in an ethyne–air explosion by means of numerical simulations. The explosion overpressure, flow velocity, and reaction rate distribution in an ethyne–air explosion are obtained. The peak explosion overpressure is found to reach its maximum beyond the original cloud for ethyne–air mixtures with ethyne concentrations greater than 13% (by volume). The explosion pressures beyond the original cloud may be higher than those within the cloud for these ethyne–air mixtures. The ratio of the combustion range to that of the original cloud is 1.4–2.7 in the radial direction on the ground and 1.5–4.0 along the axis of symmetry perpendicular to the ground.     

Plume model for large particle fluidized-bed combustors

A model is proposed to represent the underfeed, fluidized coal combustor. Its assumptions are described and its mathematical representation developed. This model accounts for the possible rapid release of volatiles near the feed ports, particle reaction and shrinkage in the bed, elutriation of unburned fines and afterburning of volatiles above the bed. Design charts are then presented to predict the carbon efficiency of the combustor as well as the temperature jump above the bed in terms of the type of coal used, the number of feed ports in the bed, percentage excess air, gas velocity and the amount of secondary air needed to introduce the coal. As a special case, this model also represents the fluidized combustor with an overfeed of large coal particles or any combination of overfeed of large particles and underfeed of fines.     

Explosion limits estimation and process optimization of direct propylene epoxidation with H2 and O2

Direct propylene epoxidation with H₂ and O₂, an attractive process to produce propylene oxide (PO), has a potential explosion danger due to the coexistence of flammable gases (i.e., C₃H₆ and H₂) and oxidizer (i.e., O₂). The unknown explosion limits of the multi-component feed gas mixture make it difficult to optimize the reaction process under safe operation conditions. In this work, a distribution method is proposed and verified to be effective by comparing estimated and experimental explosion limits of more than 200 kinds of flammable gas mixture. Then, it is employed to estimate the explosion limits of the feed gas mixture, some results of which are also validated by the classic Le Chatelier's Rule and flammable resistance method. Based on the estimated explosion limits, process optimization is carried out using commercially high and inherently safe reactant concentrations to enhance reaction performance. The promising results are directly obtained through the interface called gOPT in gPROMS only by using a simple, easy-constructed and mature packed-bed reactor, such as the PO yield of 13.3%, PO selectivity of 85.1% and outlet PO fraction of 1.8%. These results can be rationalized by indepth analyses and discussion about the effects of the decision variables on the operation safety and reaction performance. The insights revealed here could shed new light on the process development of the PO production based on the estimation of the explosion limits of the multi-component feed gas mixture containing flammable gases, inert gas and O₂, followed by process optimization.     

Effect of distributed injection of air into the afterburning chamber of a ram-rocket engine on the efficiency of combustion of boron particles

A mathematical model of combustion of boron particles in a ram-rocket engine is developed. The boron combustion efficiency for one-stage and two-stage injection of air into the afterburning chamber is calculated. It is demonstrated that two-stage injection of air sometimes allows the time of complete combustion of boron particles to be significantly reduced (by a factor of 1.5–3); thus, the fuel combustion efficiency in the ram-rocket engine can be increased. The simulated results are consistent with available experimental data.     

粉煤灰-石灰-二水石膏胶凝材料的体积稳定性及水化产物的性能

用雷氏夹法对粉煤灰-石灰-二水石膏胶凝材料(FLD)的体积稳定性进行了研究,用SEM和XRD对FLD的水化产物形貌和数量变化规律进行了研究。FLD中SO3含量为2.33%时体积稳定性良好,而SO3含量大于4.65%时体积稳定性差。在FLD中,随龄期增加,钙矾石数量不断增加,CaSO4.2H2O和Ca(OH)2数量不断减少。配比为粉煤灰:石灰:二水石膏=65:25:10的FLD到420d龄期时仍在进行着粉煤灰的水化反应,还有钙矾石生成。FLD中钙矾石为典型的针状晶体,水化硅酸钙凝胶为无定形物质。FLD体积稳定性差的原因是石膏含量过多,硬化后在很长龄期内针状钙矾石晶体不断产生。     

合成氨生产系统中支链反应爆炸的影响因素

根据合成氨工艺气－空气体系静态爆炸的实验研究,结合对支链反应的理论分析,讨论了合成氨生产系统中影响支链反应爆炸的各种因素,能有助于合成氨厂防止支链反应爆炸事故     

Temperature diagrams for preventing decomposition or side reactions in liquid-liquid semibatch reactors

The operation of an indirectly cooled semibatch reactor in which an exothermic reaction occurs is usually considered safe if the characteristic time of the coreactant dosing is much higher than the characteristic times of all the other phenomena involved (chemical reaction and mass transfer), so that the conversion rate is controlled by the coreactant supply itself. Such operating conditions imply a small accumulation of the coreactant in the system and are characterized by a temperature evolution which quickly approaches a target temperature and remains close to it throughout the dosing period, at the end of which the conversion is almost complete.The so-called boundary diagrams are useful tools for identifying safe operating conditions without solving the mathematical model of the reactor. However, avoiding accumulation phenomena can be not sufficient for classifying a set of operating conditions as thermally safe when the maximum temperature reached by the system under normal operation exceeds a maximum allowable temperature (which can be related either to safety problems, when dangerous decomposition reactions can be triggered, or to productivity problems, when side reactions can significantly lower the product yield above a given threshold temperature).In this work the boundary diagrams for the prevention of excessive accumulation conditions in liquid-liquid semibatch reactors are coupled with new diagrams, called temperature diagrams. These new diagrams, involving the same dimensionless parameters used for the representation of the boundary diagrams, allow determining—for a given set of operating conditions—the maximum temperature increase with respect to the initial reactor temperature which can be expected to occur during normal operation. This information can be compared with the maximum allowable temperature for the reacting mixture. Then the operating conditions can be verified through the boundary diagrams in order to reject conditions of excessive coreactant accumulation.Several temperature diagrams are provided for various kinetically or diffusion controlled reactions with different reaction orders and their use together with a general procedure for calculating them is presented.     

Reaction mechanisms of concrete admixtures

Concrete admixtures influence the kinetic of cement hydration mainly during the dormant period. The dominant influence of admixtures seems to lie in different bound forces between dissociated ions in the pore water solution. Repulsive forces characterize the solvation process while attractive forces dominate during crystallization. These changes of ion bound forces lead twice to volume changes during phase transitions of hydration. Volume changes measured with an immersion weighing setup show clearly the effect of concrete admixtures on cement reaction. Retarder agents produce a volume swelling while accelerators force an immediate shrinkage behaviour. A mechanism as introduced by Le Chatelier involving a solution-crystallization step seems to describe the hydration process most adequately. As long as repulsive forces dominate, a volume swelling occurs and no strength gain can take place. The dormant period is defined by the length of the swelling process. Hardening and strength growth start at the point at which volume shrinkage appears.