Effect of inhibitors on flammability range of flames produced from LPG/air mixtures

Burning velocities of Liquefied Petroleum Gas/air flames of different fuel/air compositions have been measured by the flat-flame method originally developed by Egerton and Powling, and the effects of inhibitors such as chlorinated hydrocarbons (chloroform, methylene dichloride, carbon tetrachloride) on the burning velocities have been investigated. The flammability limits at different fuel/air compositions have also been measured. The difference between upper and lower limits of flammability was narrowed by the addition of inhibitors in the order carbon tetrachloride chloroform methylene dichloride, i.e. the inhibiting effect increased with increase in the number of chlorine atoms. The relative effectiveness of different inhibitors has been expressed as an inhibition efficiency, and it has been found that an interesting correlation exists between the inhibition efficiency (also the narrowing of limits, and the maximum burning velocity) and the number of (dissociable) chlorine atoms present in the molecule of inhibiting compound. Other factors were the degree of dissociation of the inhibiting molecule in the flame, and the concentration of the inhibitor in the fuel/air mixture; the effect of small concentrations was that of specific chemical inhibition whereas at higher concentrations dilution effects were dominant. At the upper limit the flame has maximum tendency to flash back in an ordinary burner and the combustion wave may develop into a detonation wave inducing an explosion hazard. Hence upper explosion limit may be considered an index of explosion risk. The inhibitors lower this largely by reducing the concentration of free radicals in the flame boundary, increasing the difficulty of ignition, and thus increasing safety. A large difference has been found between the experimental and calculated value of the upper limit for the pure gas, probably owing to the chemical effects of ethylene via production of acetaldehyde which catalyses the combustion.     

An experimental study of biomass ignition

An experimental study has been conducted to determine the ignition temperature of biomass at 21% O₂, both under pulse ignition conditions and under thermogravimetric conditions. In the pulse ignition experiments, samples of about 2 g wheat straw were placed in an isothermal reactor. The ignition temperature was determined from the transient CO and CO₂ profiles to approximately 255 °C at a superficial gas velocity of 14 cm/s (STP). The ignition temperature increased for decreasing superficial gas velocity.Thermogravimetric experiments at 20% O₂ and heating rates of 5 °C/min with finely milled biomass indicated ignition temperatures of approximately 220 °C for wheat straw, 235 °C for poplar wood, and 285 °C for eucalyptus wood. These values are significantly lower than values obtained for coal under similar conditions and confirm the relationship between volatile matter content and ignition temperature previously reported for coal.A mechanistic model for ignition of biomass is proposed. We believe that the ignition process is initiated by oxidation reactions on the straw surface. These reactions raise the surface temperature above that of the surrounding gas and promote ignition of the volatiles. Once ignited, the volatiles may form a homogeneous diffusion flame away from the particle surface. The superficial gas velocity affects the particle heating rate as well as the transport of oxygen to the surface. For this reason the ignition process is not entirely controlled by kinetics at low temperatures.     

Coal combustion in O2/CO2 mixtures compared with air

As part of CO₂ abatement strategies for climate change, we are investigating coal combusion behaviour in various O₂/CO₂ mixtures and in air. The goal is to simulate conditions of coal combustion with flue gas recirculation in order to maximize the CO₂ concentration in the flue gas prior to its recovery. A western Canadian sub‐bituminous coal and a U.S. eastern bituminous coal were investigated. Thermal input was set at 0.21 MW with a flue gas oxygen concentration of 5 vol%. Experiments were done using various O₂/CO₂ mixtures and air. The oxygen concentration ranged from 21% to 42%. Up to 95% CO₂ concentrations were achieved in the flue gas. This paper describes experimental results in terms of flame temperatures and pollutant emissions (NO_x', SO₂ and CO).     

空气压缩机后冷却器传热强化试验研究

以横纹管、光滑管为元件，以压缩空气－水为介质的整机对比试验结果表明，横纹管对于压缩空气的冷却有显著的传热强化效果。在试验的压缩空气质量流量范围内，横纹管冷却器的总传热系数比光滑管冷却器的提高７７％～６６％。在额定的质量流量条件下，横纹管的总传热系数提高７５％，可相应节省换热面积４３％。横纹管冷却器的总压降约比光滑管的高一倍。文内还讨论分析了横纹管的传热强化机理。     

A comparative experimental study of the autoignition characteristics of alternative and conventional jet fuel/oxidizer mixtures

Autoignition characteristics of an alternative (non-petroleum) and two conventional jet fuels are investigated and compared using a heated rapid compression machine. The alternative jet fuel studied is known as “S-8”, which is a hydrocarbon mixture rich in C₇-C₁₈ linear and branched alkanes and is produced by Syntroleum via the Fischer-Tropsch process using synthesis gas derived from natural gas. Specifically, ignition delay times for S-8/oxidizer mixtures are measured at compressed charge pressures corresponding to 7, 15, and 30 bar, in the low-to-intermediate temperature region ranging from 615 to 933 K, and for equivalence ratios varying from 0.43 to 2.29. For the conditions investigated for S-8, two-stage ignition response is observed. The negative temperature coefficient (NTC) behavior of the ignition delay time, typical of higher order hydrocarbons, is also noted. Further, the dependences of both the first-stage and the overall ignition delays on parameters such as pressure, temperature, and mixture composition are reported. A comparison between the autoignition responses obtained using S-8 and two petroleum-derived jet fuels, Jet-A and JP-8, is also conducted to establish an understanding of the relative reactivity of the three jet fuels. It is found that under the same operating conditions, while the three jet fuels share the common features of two-stage ignition characteristics and a NTC trend for ignition delays over a similar temperature range, S-8 has the shortest overall ignition delay times, followed by Jet-A and JP-8. The difference in ignition propensity signifies the effect of fuel composition and structure on autoignition characteristics.     

Effect of trimethylphosphate additives on the flammability concentration limits of premixed methane-air mixtures

The effect of small additives of trimethylphosphate (TMP) on the lean and rich flammability concentration limits of CH₄/air gas mixtures were studied using an opposed-flow burner and numerical modeling based on detailed kinetic mechanisms. TMP was found to narrow the flammability concentration limits of premixed CH₄/air mixtures. Modeling using a previously developed model for flame inhibition by phosphorus compounds showed that the model provides a satisfactory fit to experimental results on the effect of TMP additives on the lean concentration limit. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 12–21, January–February, 2008.     

分子筛对CH_4/空气混合气的变压吸附分离研究

为提高煤层气变压吸附浓缩效果,以一种商品分子筛为对象,研究了该分子筛在小型四塔变压吸附装置上的CH4/空气混合气浓缩分离效果,分析了吸附时间、吸附压力以及原料气浓度对混合气浓缩效果的影响。结果表明,吸附时间过长或吸附压力过高,均不利于获得较好的产品气浓度及回收率。吸附时间180 s,吸附压力300 k Pa时,试验商品分子筛对CH4/N2的浓缩分离效果最佳。其中,10%浓度原料气提浓至30.56%,提高约20%,产品气中CH4回收率达到94.45%,对原料气的处理量达到67.77 m3/(t·h);35%浓度原料气提浓至76.33%,提高约40%,产品气中CH4回收率达到69.68%,对原料气的处理量达到68.99 m3/(t·h);65%原料气提浓至89.18%,提高约25%,产品气中CH4回收率达到87.22%,对原料气的处理量达到83.36 m3/(t·h)。     

Effect of diluents of various chemical nature on the flammability limits of gas mixtures

The effect of diluents of various chemical nature [halogenated hydrocarbons, inhibitors developed at the Institute of Structural Macrokinetics and Problems of Materials Science (ISMAN), superheated water aerosol] on the flammability limits of hydrogen-methane mixtures in air was investigated experimentally. It was found that ISMAN inhibitors, which are aliphatic hydrocarbons, reduce the upper flammability limit of hydrogen even more effectively than the well-known inhibitor 1,2-dibromotetrafluoroethane. Flammability curves for hydrogen and methane in mixtures with the above-mentioned diluents were obtained. The results are interpreted qualitatively by considering various kinetic regimes of nonisothermal chain branching reactions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 96–102, November–December, 2006.     

Optimization of fuel/air mixture formation for stoichiometric diesel combustion using a 2-spray-angle group-hole nozzle

This paper describes a numerical study of fuel/air mixing processes for stoichiometric diesel combustion. In order to overcome the deterioration of combustion efficiency that accompanies stoichiometric diesel combustion due to poor mixing and lack of available oxygen, a new nozzle layout, namely a 2-spray-angle group-hole nozzle, which consists a grouped upper spray plume (squish spray) and a lower spray plume (bowl spray) was investigated. The KIVA code with updated physical and chemistry models, including the KH-RT breakup model, 2-step phenomenological soot model, reduced n-heptane and GRI NOx mechanisms was used for the calculations. An optimized 2-spray-angle group-hole nozzle with 170° squish spray angle and 80° bowl spray angle showed significantly improved fuel consumption (178 g/kW h⁻¹) compared to the baseline nozzle layout (213 g/kW h⁻¹) and the 2-spray-angle nozzle without hole-grouping (193 g/kW h⁻¹).     

Thermal decomposition of pyrotechnic mixtures containing either aluminum or magnesium powder as fuel

Thermal behavior of energetic materials is critical to safe production, storage, handling or even demilitarization. In this work, the thermal behavior of Al, Mg, CuO, KMnO₄ and also three mixtures containing Al + CuO, Mg + CuO and Mg + KMnO₄ were studied experimentally using differential scanning calorimetry and thermogravimetry. These mixtures are sometimes used as pyrotechnic mixtures in military industries. Also, the influence of different heating rates (5, 10, 15 and 20 °C/min) on the DSC behavior of the mixtures was verified. The results showed that as the heating rate was increased, melting points and ignition temperatures of the mixtures were increased. On the other hand, TG-DSC analysis for Mg + KMnO₄ mixture indicates that this mixture melts at 283.0 °C and decomposed at 292.1 °C. By replacing KMnO₄ with CuO as the oxidizer of the magnesium, these temperatures enhanced to 368.7 °C and 408.3 °C, respectively. However, replacing Mg with Al in the Mg/CuO mixture decreases the melting and ignition temperatures of the mixture to 231.4 °C and 271.9 °C, respectively. The activation energy for each pyrotechnic mixture was computed. Also, the values of ΔS^#, ΔH^# and ΔG^# of their reaction were calculated.     

空调冷热源能耗及其环境影响评价分析

通过计算风冷热泵冷热水机组、水冷螺杆式冷水机组+电热锅炉、水冷螺杆式冷水机组+燃油锅炉和燃油(气)直燃吸收式冷热水机组这些常见的空调冷热源方案的一次能耗量、CO2、SO2及烟尘的排放量,分析这些方案的能源利用率、耗能过程中造成的温室效应和大气污染情况。     

Spectroscopic study of anthraquinone dye/amphiphile systems in binary aqueous/organic solvent mixtures

The absorption spectra of novel dye/amphiphile systems, in which the dye is a 1,5-bis-(R-phenylamino)anthraquinone [R = o-methoxy, o-ethoxy, H] and the solvents are either organic or H₂O/organic solvent mixtures, have been investigated. It was found that an abrupt λ_max shift of more than 80 nm occurred for the system containing dye having R = o-methoxy and the amphiphile (poly-bis-(2,2′-dimethyl-5,5′-disulphonate)naphthylmethane disodium salt) in pure solvents with a specific E_T(30) value or in H₂O/DMF (N,N-dimethylformamide) mixtures containing at least 38% water. This type λ_max shift was not observed when solvent mixtures containing the other two dyes were studied. The origin of the pronounced λ_max shift is discussed in detail. It is believed that this shift arises mainly from changes in the solvation state of hydrophobic dye having R = o-methoxy when water is introduced in the presence of a dispersing agent. In this regard, dye is converted from the monomolecular state to dispersed particles.     

牙哈处理站液化气分馏塔的节能减排优化

在对塔里木油田公司牙哈处理站液化气分馏塔的现有工艺及控制分析基础上,提出了采用前馈反馈串级控制方案对分馏塔进行优化,在减少生产装置改动的前提下达到节能减排、增加产品产量、稳定分馏系统操作的目的。优化后的分馏塔具有显著效果,可在原有基础上节能约10％左右,减少CO2排放量约237．11吨／年,每日可增加液化气产量约1．5吨,年增加效益351．75万元。     

Kinetics of oxidation of a LPG blend mixture in a JSR: experimental and modeling study

For the first time, a detailed study of the gas-phase oxidation of a LPG blend mixture (propane/n-butane/iso-butane), a spark ignition engine fuel, is reported. The experiments were performed in a jet-stirred reactor at 1 atm, over the temperature range 950-1450 K and for equivalence ratios of 0.25, 0.5, 1, 1.5, 2 and 4. Mole fraction profiles as a function of temperature were obtained for molecular species (reactants, intermediates and final products) via sonic quartz probe sampling and on-line FTIR analyses and off-line gas chromatography analyses. These measurements were used to validate a detailed kinetic reaction mechanism consisting of 112 species and 827 reactions (most of them reversible). Overall, the modeling is in very good agreement with the experimental measurements. Reaction path analyses were used to interpret the results.     

Particle adhesion and removal in ethanol/water mixtures

Adhesion and removal of particles to and from substrates were investigated in water, ethanol and ethanol/water mixtures. Spherical polyethylene and nylon particles of 4-5 ,um in diameter were used. Plates of polyethylene, polyvinylidene chloride, polyvinylidene fluoride, polyethylene terephthalate, and nylon 6 were used as substrates. A plate was perpendicularly immersed in the suspension, and the number of particles adhering to the plate was counted using a microscope video system. Since polyvinylidene chloride (PVDC) substrate showed the maximum particle adhesion in water for both kinds of particles, the particle removal experiments were carried out using the PVDC plates. The PVDC plate to which particles in water adhered was immersed in an ethanol/water mixture. The number of particles remaining on the plate was counted, and this determined the particle removal efficiency. The number of adhering particles decreased with increasing volume ratio of ethanol in the ethanol/water mixtures, and only a few particles adhered to all the substrates in the ethanol volume ratio above 30%. The particle removal efficiency increased with increasing volume ratio of ethanol and reached 90% in the ethanol volume ratio above 30%. The experimental results obtained are discussed in terms of electrokinetic potentials, Hamaker constants, and surface free energies. The particle adhesion and removal phenomena were essentially explained in terms of the free energy changes which were estimated from the dispersive and nondispersive surface free energies of the particle, substrate and liquid.     

Catalytic combustion of lean methane–air mixtures

Catalytic combustion of lean methane–air mixtures was studied on supported iron oxide and platinum monolith catalysts. Flameless catalytic combustion was investigated in the temperature range 600–900°C, GHSV up to 10 000 h⁻¹, and methane concentration in initial gas mixture 1–9 vol%. It was shown that under certain process conditions complete combustion of methane at 4.5 vol% inlet methane concentration occurs.     

An experimental study of air entrainment at a solid/liquid/gas interface

Some data from an experimental study of air entrainment into a fluid bath by a continuous moving plane tape is presented. The separate effects of surface tension and viscosity are described and the various modes of air entrainment are given in the context of fluid properties. The velocity of air entrainment is found to be a function of surface tension and viscosity for viscosities less than 4.65 poise. For viscosities greater than this value, the air entrainment velocity tended to a constant value of 9.5 cm sec^?1 independent of surface tension. Relationships of the form: We = k Re^a and We = c (Bo + 1)Re^d, are suggested by analogy to describe air entrainment data without and with buoyancy effects. Data from studies on four tapes and nine fluids gave a very high correlation when plotted in the above form. The data is in substantial agreement with that from similar studies, and shows that the condition Ca = We/Re = constant is not a global criteria for air entrainment by a plunging surface. The experimental data shows that air entrainment velocity may be estimated from the relationship V_AF = 67.679 (μ√(g/ρσ))^?0.672 for the normally plunging plane tapes studied.     

A Comparative Study of the Explosion Characteristics of IPN and IPN/JP‐10 Mixtures in Air Aerosols

This article presents a comparison of the explosion characteristics of mixtures of isopropyl nitrate (IPN, (CH₃)₂CHONO₂) and JP‐10 (C₁₀H₁₆, tricycle [5.2.1.0^2,6] decane) in air aerosols. The explosion pressure, flame temperature, maximum rate of pressure rise, maximum rate of temperature rise, and lower flammability limits (LFLs) were measured for two sets of IPN and mixed IPN/JP‐10 in air aerosols at different concentrations and Sauter mean diameters (SMDs) of 19 μm and 34 μm, respectively, and the values were compared with the experimental results of JP‐10/air aerosols with SMDs of 20 μm and 35 μm (from our previous research). Experiments were also performed to study various concentrations at various ignition energies for the IPN/air aerosols and the explosions of binary mixture aerosols with various mass ratios of IPN and JP‐10. The experimental results indicated that for the IPN/air and JP‐10/air aerosols with a mean SMD of ∼34 μm, the maximum peak pressure and maximum peak temperature of the IPN/air aerosols were greater than those of the JP‐10/air aerosols. The maximum rate of pressure rise of the IPN/air aerosols reached a maximum value of 395.3 MPa/s at a mean SMD of ∼34 μm, and the pressure increased more abruptly in the IPN/air aerosols than in the JP‐10/air aerosols. The LFLs of the IPN/air aerosols occurred with a total concentration of 197 g/m³ at a mean SMD of 19 μm and a total concentration of 233 g/m³ at a mean SMD of 34 μm, whereas the LFLs for the JP‐10/air aerosols with SMDs of 20 μm and 35 μm were less than 47 g/m³ and 40 g/m³, respectively. The experimental results presented here also showed that the maximum peak pressure was 1.07 MPa at a binary liquid mass ratio of IPN:JP‐10 (%) of 72 : 28 and a mean SMD of ∼34 μm.     

An experimental study of the flame propagation and combustion characteristics of LPG fuel

This work investigates the flame propagation and combustion characteristics of LPG (Liquefied Petroleum Gas) fuel. To clarify the combustion process of the heavy duty LPG engine, the flame propagation and combustion characteristics were investigated using a CVCC (constant volume combustion chamber) and a port injection type heavy duty LPLi (Liquefied Petroleum Liquid injection) engine system. Both the laser deflection method and the high-speed Schlieren photography method were employed to measure the flame propagation speed of LPG fuel. In addition, the single cylinder heavy duty LPLi engine was manufactured to analyze the combustion characteristics of the LPG.The experimental results indicated that the laser deflection method showed the measuring accuracy of this method to be less than 5% when compared with the result of the high-speed camera. According to the CVCC and heavy duty LPLi engine experimental results, the flame propagation reached a maximum speed at the stoichiometric equivalence ratio, regardless of operating conditions, and the effect of the equivalence ratio on both flame propagation and combustion characteristics was greater than that of ambient conditions. In addition, we found that the coefficient of variation of combustion duration increased when the equivalence ratio decreased. Furthermore, the combustion stability worsened as the equivalence ratio moved into the lean region.     

涡流空气分级机内物料分布的模拟试验研究

为研究涡流空气分级机内物料分布的规律,探索物料在涡流空气分级机内的分散方法,文中设计了撒料盘试验来模拟涡流空气分级机内物料分布,并进行了物料分布的计算与试验研究。以建筑用标准砂做试验,结果表明:撒料盘转速的提高可以改善大颗粒物料的分散性,而对小颗粒物料的分散性影响较小;物料的粒度分布范围对物料分散性影响较大,粒度分布范围越宽,分散性越差,同时还研究了撒料盘结构对物料分散性的影响。结果表明:双层撒料盘的使用能将物料在承料面上的单位面积堆积量从单层撒料盘的0.067 g/cm2降低到0.042 g/cm2,相对减少量为37.31%,从而提高物料在分级机内的分散性。