Determination of the parameters of self-ignition of gaseous mixtures in adiabatic compression

A study has been made of the distinctive features of self-ignition and combustion of fuel-air mixtures containing methane, hydrogen, and ethylene in adiabatic compression.     

Influence of aerodynamics on the critical parameters of thermal ignition

A numerical analysis of the critical conditions of thermal ignition for a two-dimensional cylindrical reactor with flow field occurrence was carried out. The critical conditions of thermal ignition were defined as bifurcation points of the limit type. The dependence of the bifurcation points on aerodynamics was analysed by a sequential variation of the Peclet number. The flow field in the reactor was generated previously by a numerical solution of the Navier-Stokes equations. The nonlinear parabolic equation of heat balance and linear eigenvalue boundary problems occurring in the proposed non-stationary method for calculating the bifurcation points was solved numerically using the finite difference technique. It was shown that the critical points of thermal ignition form a surface bounded by the line of ‘limit of criticality’ in the parameter space. For large values of the Peclet number, the dependence of the critical parameter of ignition on Peclet number becomes linear.     

A method of obtaining steady state flows of gaseous mixtures with a given concentration

A method of obtaining a flow of a gaseous mixture with a given concentration through a supersonic nozzle is examined within the framework of nonviscous equilibrium flow; this method is based on measurements of pressures in a mixing chamber with separate outflow of the components.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 3, pp. 539–542, March, 1971.     

Thermodiffusion in liquid and gaseous multicomponent isotope mixtures

The thermodiffusion process in isotopic mixtures of titanium, tin, and carbon tetrachloride has been studied experimentally. The results are analyzed here.     

Speed-of-sound measurements in liquid and gaseous air

The speed of sound in air has been measured along isotherms for a standard air mixture (0.7811 N₂+0.2097 O₂+0.0092 Ar) in the gas and liquid phases at pressures to 14 MPa. A cylindrical resonator was used in the vapor and supercritical gas phases, and a time-of-flight system was used for measurements of the liquid phase. Data were obtained for the liquid phase at 90, 100, 110, 120, and 130 K. Data were taken at 110, 120, 130, 135, 140, 150, 200, and 300 K in the vapor and supercritical gas phases. These experimental results were compared to a predictive computer model, namely, AIRPROPS.     

Compression ignition of hydrogen-containing mixtures in shock tubes

The state of the art of the problem of discrepancy between the values measured in shock tubes and calculated for the delay of ignition of hydrogen-containing systems has been analyzed. It is shown that in the low-temperature region the off-design appearance of reaction sites leads to the propagation of a flame in a mixture heated by a reflected shock wave. The parameter of the time of mixture combustion in a deflagration regime has been introduced and the use of it together with the calculated delay in self-ignition for delimitation and classification of thermal and gas-dynamic phenomena on compression ignition of hydrogen-containing mixtures in shock tubes has been suggested.     

Acoustical parameters of polyethylene glycol/water mixtures

Ultrasonic velocity (v) and density (d) have been measured for polyethylene glycol/water mixtures at 30°C. The adiabatic compressibility (β _ad), molar compressibility (β), specific acoustic impendance (Z), Rao number (R) and van der Waals constant (b) have been computed. The variations ofv, d, β _ad,β, Z, R andb with mole ratio of water/ether group oxygen have been studied. The association between the components and the formation of tetrahydrate have been reported.     

不同浓度下点火延长时间对煤粉点火能的影响

为评价煤粉爆炸的潜在危险性,掌握使其燃烧所需的最小点火能及其受浓度和点火延长时间的影响,采用垂直哈特曼管研究不同浓度下点火延长时间对煤粉最小点火能的影响。结果表明:对于粒径为54μm的煤粉,随着质量浓度的增加,煤粉最小点火能先减小后增大,最佳点火质量浓度为750 g/m~3;随着时间的延长,煤粉最小点火能先减小后增大继而趋于平缓,最佳点火延长时间为90 ms。     

Influence of superplasticizer type and mix design parameters on the performance of them in concrete mixtures

The use of superplasticizers in concrete manufacture was a milestone in the history of concrete, and this played a central role in the development of high strength and performance concrete. Superplasticizers are admixtures, which are added to concrete mixture in very small dosages. Their addition results in significant increase of the workability of the mixture, in reduction of water/cement ratio or even of cement quantity. Their performance depends on the type of the superplasticizer, the composition of the concrete mixture, the time of addition and the temperature conditions during mixing and concreting.Measurements of workability, slump loss, air content, as well as of strength development have been made to reach a conclusion about superplasticizers performance with the use of two kinds of aggregate: one natural (river) and one crushed limestone. Apart from this, it seems that the quantity of fines in a mixture influences the performance of superplasticizers.     

Influence of ozone concentration and temperature on ultra-fine particle and gaseous volatile organic compound formations generated during the ozone-initiated reactions with emitted terpenes from a car air freshener

Experiments were conducted to identify the emissions from the car air freshener and to identify the formation of ultra-fine particles and secondary gaseous compounds during the ozone-initiated oxidations with emitted volatile organic compounds (VOCs). The identified primary constituents emitted from the car air freshener in this study were alpha-pinene, beta-pinene, p-cymene, and limonene. Formation of ultra-fine particles (4.4-160nm) was observed when ozone was injected into the chamber containing emitted monoterpenes from the air freshener. Particle number concentrations, particle mass concentrations, and surface concentrations were measured in time dependent experiments to describe the particle formation and growth within the chamber. The irritating secondary gaseous products formed during the ozone-initiated reactions include formaldehyde, acetaldehyde, acrolein, acetone, and propionaldehyde. Ozone concentration (50 and 100ppb) and temperature (30 and 40 degrees C) significantly affect the formation of particles and gaseous products during the ozone-initiated reactions. The results obtained in this study provided an insight on the potential exposure of particles and irritating secondary products formed during the ozone-initiated reaction to passengers in confined spaces.     

内压缩流程空分设备中氮气获取方式对能耗的影响

内压缩流程空分设备中,获得高压氮气有三种方式:液氮泵内压缩、上塔抽取低压氮气外压缩和下塔抽取压力氮气外压缩。利用UNISIM软件建立模型,模拟空分精馏过程,比较上塔抽取低压氮气外压缩和下塔抽取压力氮气外压缩两种获得方式对能耗的影响。在不同的下塔氮气流量与氧气流量比下选出合适的氮气获取方式,以实现能耗最低的目标。     

The effect of nonequilibrium excitation on the ignition of hydrogen-oxygen mixtures

The part played by various radicals and excited particles in reducing the induction period is discussed when analyzing the ignition of combustible mixtures under highly nonequilibrium conditions. A review is made of experimental and theoretical investigations of the effect made by atoms of hydrogen and oxygen, electron-excited molecules of O₂(a ¹Δ_g), and vibrationally excited molecules of H₂ and O₂ on the times of induction and on the shift of the limits of ignition of hydrogen-oxygen mixtures.The addition of atoms of oxygen and hydrogen to a combustible mixture may cause a significant reduction of the times of induction and the lowering of the temperature limit of ignition of combustible mixtures. However, the latter effect is observed only in the vicinity of the limit of ignition. In the zone of relatively low initial temperatures, the shift of the ignition limit is largely associated with the self-heating of mixture owing to recombination of atomic particles being added. In so doing, the nonequilibrium pattern of the impact hardly shows up. Molecules of singlet oxygen (SO) may be involved in both chain initiation reactions and chain branching reactions. The rates of these processes increase significantly with the temperature of the mixture. However, the temperature increase further causes an increase in the rate of reaction of hydrogen quenching of singlet oxygen O₂(a ¹Δ_g). The acceleration of deactivation of O₂(a ¹Δ_g) with increasing temperature, which was previously ignored by researchers, causes an abrupt reduction of the effectiveness of the impact of SO on the times of induction. In the low-temperature region, where the quenching is relatively weak, the effect of O₂(a ¹Δ_g) on the ignition of H₂ : O₂ mixtures may be significant in the case of a sufficiently high (in excess of 10^?2) level of relative concentrations of SO.Vibrationally excited molecules of H₂(v) may likewise be involved in chain initiation and branching reactions. The available results lead one to assume the possibility of lowering the temperature limit of ignition of hydrogen-oxygen mixtures in the case of intensive excitation of vibrational degrees of freedom of H₂(v) molecules. However, in the case of electric-discharge excitation (even in H₂ : O₂ mixtures, in which a significant fraction of discharge energy may be delivered to the vibrational subsystem of H₂(v)), it is quite difficult to attain high levels of vibrational excitation (T _v ^H2 ≥ 2000 K). In a stoichiometric mixture of H₂:air, where the bulk of discharge energy is spent for vibrational excitation of nitrogen molecules, this problem becomes even more complicated.     

Flammability limits and explosion characteristics of toluene-nitrous oxide mixtures

Flammability limits and explosion characteristics of toluene–nitrous oxide mixtures are experimentally determined in an 8 l spherical vessel, and are compared with corresponding values of toluene–air mixtures. The experiments, performed at atmospheric pressure and at an initial temperature of 70 °C, show that the flammable range of toluene in nitrous oxide (0.25–22.5 mol%) is about three times as wide as the corresponding range of toluene in air (1.3–7.1 mol%). Maximum values of the explosion pressure ratio and the deflagration index, K_G, are clearly higher when nitrous oxide is applied as an oxidizer. This can be attributed to the increased flame temperature and burning velocity of toluene–nitrous oxide flames. Moreover, extremely high values of K_G for near-stoichiometric mixtures in combination with strong acoustic oscillations in the pressure signals of these mixtures indicate the existence of a flame accelerating mechanism. These phenomena are enhanced when an initial pressure of 6 bara is applied. Finally, when evaluating the lower flammability limit, it was found that pure nitrous oxide decomposes at pressures above 4.5 bara when applying an ignition energy of about 10 J.     

Influence of certain operating and geometrical parameters on the flow structure in an air vortex

The results of measuring the tangential and axial velocity components in a laboratory model of an atmospheric vortex are presented for different values of the geometrical parameters and degrees of swirling of the stream.     

Influence of confinement pressure and air voids on the repeated creep and recovery of asphalt concrete mixtures

A laboratory investigation was conducted to capture the influence of confinement pressure and specimen air voids on the creep and recovery response of asphalt concrete (AC) mixtures. AC specimens were fabricated at 2% and 7% air voids and tested at three temperatures (20, 40 and 55°C) and at unconfined and confined conditions (100 and 200 kPa). A total of 20,000 repetitions of a repeated trapezoidal loading and recovery cycle were applied. The resulting creep curves showed four distinct patterns of the three-stage creep curve depending on the loading condition and specimen density. To quantify the mechanical response during the secondary stage where the response was found to be linear, linear viscoelastic modelling was carried out. Using creep time, energy stored and energy dissipated, which were determined from model parameters; the influence of air voids and confinement pressure was quantified.     

自由空气中爆炸冲击波的数值分析

为准确模拟自由空气中的爆炸荷载及其特性,采用软件ANSYS/LS-DYNA建立了多组不同药量TNT的爆炸模型,并将结果与TM5-1300、Henrych公式以及Baker公式计算结果进行比较分析。通过多次试算分析,给出了自由空气中建立TNT爆炸模型时由比例距离选用网格尺寸的依据,分析了爆炸相似律立方根表达式的适用性及适用条件,并得到了比例距离为0.1≤z≤3时自由空气中TNT炸药超压峰值的简便计算公式。结果可为自由空气中爆炸荷载的准确数值模拟以及简便计算提供依据。     

自由空气中爆炸冲击波的数值分析

为准确模拟自由空气中的爆炸荷载及其特性,采用软件ANSYS/LS-DYNA建立了多组不同药量TNT的爆炸模型,并将结果与TM5-1300、Henrych公式以及Baker公式计算结果进行比较分析。通过多次试算分析,给出了自由空气中建立TNT爆炸模型时由比例距离选用网格尺寸的依据,分析了爆炸相似律立方根表达式的适用性及适用条件,并得到了比例距离为0.1≤z≤3时自由空气中TNT炸药超压峰值的简便计算公式。结果可为自由空气中爆炸荷载的准确数值模拟以及简便计算提供依据。     

Analysis of fire and explosion hazards of some hydrocarbon-air mixtures

Hazards caused by leakage of hydrocarbons have long been a problem. In this paper, the critical initiation energy and explosion limits of some hydrocarbon-air mixtures have been measured in confined (rectangle shock tube) and unconfined (plastic bag) condition tests. Two dimensionless parameters are suggested to compare the fire and explosion hazards of different hydrocarbons. Additionally, a series of experiments was performed to determine the influence of chemical additives on the fire and explosion hazards of some hydrocarbon-air mixtures in confined (rectangle shock tube) tests. These results relate directly to flammability and reactivity of hydrocarbon air mixtures. Such measurements are very important for hydrocarbon safety.