Comparison of the structures of methane-air and propane-air partially premixed flames

A comparison of flame structures between methane-air and propane-air laminar partially premixed flames has been made through the centerline concentration distributions of selected species measured using gas chromatography. The concentrations of fuel, major species like O₂, CO and CO₂ and those of the intermediate hydrocarbons like C₂H₆, C₂H₄, C₂H₂ and CH₄ (for the propane flame only) have been compared. Distinct double flame structures are observed for the experimental conditions under study. With approximately the same equivalence ratio and jet velocity for the primary mixture, the height of the inner flame for propane is less than that of methane. The peak concentration of C₂H₆ in the propane flame is found to be only a little higher than that in the methane flame, while the peak concentrations of C₂H₄ and C₂H₂ are much greater in the propane flame than in the methane flame. In a methane partially premixed flame, the hydrocarbon concentrations drop from their peak values very rapidly at the inner flame tip, but in the propane flames it is more gradual. In a methane partially premixed flame, CO is formed at the inner flame and burns at the outer flame to CO₂. Similar distributions of CO and CO₂ are found in the propane flame also. However, the peak CO concentration in the propane flame is found to be higher than in methane flame. A radial measurement of species distribution for a particular case in the propane partially premixed flame is also done to ascertain the species distributions across the flame.     

Upper flammability limits of some organosilicon compounds

This paper reports the upper flammability limits of 26 organosilicon compounds commonly used in the silicone industry and investigates the correlation between the upper flammability limit and the net heat of combustion. An empirical equation has been developed to predict the upper flammability limit of organosilicon compounds using the net heat of combustion. Copyright © 2004 John Wiley & Sons, Ltd.     

Influence of organophosphorus inhibitors on the structure of atmospheric lean and rich methane-oxygen flames

The inhibition of atmospheric laminar methane-oxygen flames of various compositions by trimethyl phosphate was studied experimentally and by numerical modeling using mechanisms based on detailed kinetics. The H and OH concentration profiles in flames with and without the addition of trimethyl phosphate were measured and calculated. It was shown that the addition of the inhibitor reduced the maximum (in the reaction zone) concentrations of H and OH in lean and rich flames. The concentration reduction was higher in rich flames than in lean flames. The concentration profiles of the phosphorus-containing products PO, PO₂, HOPO, HOPO₂, and (HO)₃PO in lean and rich flames stabilized on a flat burner were measured and calculated. Tests of the previously developed model of flame inhibition by phosphorus compounds showed that the model provides adequate predictions of many experimental results. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 23–31, March–April, 2007.     

Effect of the equivalence ratio on the effectiveness of inhibition of laminar premixed hydrogen-air and hydrocarbon-air flames by trimethylphosphate

This paper reports results of an experimental study and numerical simulation of the effect of the equivalence ratio (φ = 0.6–1.6) on the burning velocity of laminar, premixed atmospheric methane-air and propane-air flames without additives and with 0.06% trimethylphosphate (TMP). The effect of the equivalence ratio (φ = 0.7–4.5) on the burning velocity of hydrogen-air flames without additives and with 0.1% TMP was studied by simulation. The experimental and simulation results show that, in hydrocarbon flames doped with TMP, the inhibition effectiveness decreases sharply with a growth in φ from 1.2–1.3 to 1.4–1.6 and in hydrogen-air flames, the inhibition effectiveness increases with a rise in φ from 1.5 to 4.5. The reactions determining the dependence of the inhibition effectiveness on the equivalence ratio were found by analyzing the flame velocity sensitivity coefficients to changes in reaction rate constants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 14–22, March–April, 2008.     

Effect of flame retardants on flame propagation and flammability properties of oil palm fibre reinforced polyester composite

Oil palm fibre reinforced polyester composite (OPFC) was modified with aluminium tri‐hydroxide (ATH), ammonium phosphate and gum arabic (APP‐GAP) intumescent compound, and their hybrid (ATH/APP‐GAP) flame retardants (FRs) at 0%, 12%, and 18% proportion using hand lay‐up compression moulding technique. The effect of the FR loadings on impact strength, flammability properties, and flame propagation were examined using an impact tester, cone calorimeter apparatus (CCA), and flame spread apparatus (FSA), respectively. The results shows that the FRs added to OPFC enhanced the impact strength of the composite showing greater absorbed energy for 0%OPFC and 12%APP‐GAP specimens. CCA results reveal that 18%ATH/APP‐GAP hybrid specimen enhanced the flammability properties better at 50 kW m^?2, while at 25 kW m^?2, the performance of the specimens varied in properties with content and type of FR loadings. FSA results reveal that with 18%ATH/APP‐GAP hybrid specimen, weakest flame energy for propagation and less flame travel distance could be achieved and suggests a better FR. This paper concludes that the hybrid FR specimen can be of great benefit to the building and transportation industries.     

Effects of combustor size and filling condition on stability limits of premixed H2‐air flames in planar microcombustors

An experimental study on stability limits of premixed hydrogen‐air flames in planar microcombustors (H = 1 mm and 1.5 mm) partially filled with porous medium is carried out, focusing on the effects of combustor sizes and filling conditions. Critical conditions for blow‐off, flashback, and breaking through the porous medium are experimentally measured. The blow‐off limits are nearly independent of combustor sizes and filling conditions, while the flashback limits are strongly influenced by the combustor size and the filling conditions. Critical values for breaking through are identified with two different methods, and it is shown that standing combustion waves are settled over a range of velocities, instead of a fixed value of filtration velocity, which is considered an important characteristic of microcombustion. Most results can be explained by the classic boundary velocity gradient theory by von Elbe and Lewis, and thus the validity of the theory to the present channel spacings is confirmed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2571–2580, 2015     

A numerical study on structure of premixed methane-air microflames for micropower generation

Structure of premixed methane-air microflames at normal and elevated temperatures and atmospheric pressure generated on a microtube was computationally studied, in order to understand the fundamental behavior of the microflames for micropower generation. Based on an earlier experimental investigation of the stability limits of the premixed microflames, the distributions of temperature, fuel and radicals for single microflames near the stability limits and in the stable region were predicted using a two-dimensional CFD simulation with a reduced kinetic mechanism and a detailed transport modeling. The predicted structure of microflames along the stability limits due to heat losses showed substantial fuel leaks between the microflame base and the microtube rim. This observation provided the burning mechanism that a microflame can be generated and sustained only if the injected mixture contains a certain concentration of fuel beyond a certain distance from the tube exit that can avoid quenching. The experimentally observed extended stability limits due to elevated temperature were readily explained by the predicted structure showing intensified burning and reduced heat losses. Finally, the predicted microflame structure showed that the predicted microflame length based on the maximum mass fraction of OH radical well represents the observed visible microflame length.     

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.     

Flame‐retardant materials: synergistic effect of halloysite nanotubes on the flammability properties of acrylonitrile–butadiene–styrene composites

Novel well‐dispersed nanocomposites of halloysite nanotubes and acrylonitrile–butadiene–styrene were prepared. The fire retardancy and thermal stability of these new nanocomposites were improved. A synergistic effect was observed between the halloysite nanotubes and an intumescent flame‐retardant system consisting of ammonium polyphosphate, melamine polyphosphate and pentaerythritol in the acrylonitrile–butadiene–styrene composites. The incorporation of the intumescent flame‐retardant material into the halloysite–polymer nanocomposite system also improved the thermal stability and reduced the peak heat release rate by up to 56.2%, and it significantly reduced the emission of CO and CO₂ gases. The morphology and dispersion of the halloysite nanotubes were characterized using scanning and transmission electron microscopy. The thermal stability and flammability properties were investigated using thermogravimetric analysis and cone calorimeter tests. © 2013 Society of Chemical Industry     

用锥形量热仪研究无卤阻燃HDPE体系的燃烧性

在35kW／m^2热辐照条件下,利用锥形量热仪研究了膨胀型阻燃剂／Mg(OH)2阻燃高密度聚乙烯(HDPE)体系的燃烧性。结果表明：膨胀型阻燃剂／Mg(OH)2能明显降低HDPE的热释放速率、总热释放量、最大生烟速率及总烟释放量。与膨胀型阻燃剂单独使用相比,Mg(OH)2与膨胀型阻燃剂复合使用的阻燃效果明显,总烟释放量减少了38％,总热释放量减少了10％,达到了低发炯、高效阻燃的目的。     

Effect of halloysite nanotubes on mechanical properties and flammability of soy protein based green composites

To address the growing emphasis on the use and development of sustainable materials, bio‐based polymers and fibers are processed to prepare entirely bio‐based fiber‐reinforced ‘green’ composites. To enable these new materials to perform in lightweight vehicle and infrastructural applications, they must be characterized both structurally and in terms of their various performance characteristics. The results of preparation and characterization of bio‐based composites comprising jute fabric and soy protein concentrate (SPC) modified with glycerol and/or halloysite nanotubes (HNT) are reported herein as a first look at the flammability of these bio‐based nanocomposites. The results reveal that SPC has lower flammability (heat release capacity) than petrochemical‐based resins, such as epoxies and vinyl esters. In addition, incorporating 5% mass fraction of HNT is found to reduce the composite flammability, while having no negative impact on the mechanical properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Impact of hybrid flame retardant on the flammability and thermomechanical properties of wood sawdust polymer composite panel

Wood‐based polymer composites represent a growing interest in the building industry. The fire response of this composite type is a concern to many end users. This study utilizes wood sawdust as reinforcement to develop flame retarded wood sawdust polyester composite (WSPC) panel. Flame retardant (FR) chemicals such as aluminium tri‐hydroxide (ATH), intumescent FR (ammonium polyphosphate [APP] Gum Arabic Powder [GAP]), and the combination of ATH and APP‐GAP (hybrid) at 0%, 12%, and 18% were used to modify the WSPC panel using hand lay‐up compression moulding technique. Tensile and flexural properties, thermal and flammability properties, and macroscopic image observations (MIOs) were examined using universal testing machine, thermogravimetric analysis (TGA/DSC), and the cone calorimeter apparatus (CCA), respectively. The results obtained show that the added nonhybrid FR in the WSPC panel enhanced the tensile and flexural strength while a reduction in the tensile modulus was observed. In the thermal stability, TGA analysis reveals that the added hybrid FR did not exhibit significant change in the thermal stability of the WSPC panel while cone calorimeter results show significant improvement in some fire properties. It can be concluded that the hybrid FR when incorporated in WSPC panel can be of great benefit to the building industry.     

电场对甲烷-空气混合气燃烧特性的影响

利用定容燃烧弹研究了外加电场对甲烷-空气混合气燃烧特性的作用。加载电压为0、-5、-10和-12 kV,混合气的过量空气系数λ分别为0.8、1.0和1.6,代表浓燃、当量比和稀燃三种混合气状态。结果表明,电场方向上的火焰发展半径和火焰传播速度明显增加,原先近似圆球形的火焰形状发生变化。特别是稀燃混合气,电场作用下火焰的传播状况增加最为显著,火焰近似呈圆柱形。在加载电压为-12 kV时,对于λ=0.8、1.0和1.6的混合气,火焰拉伸速度最大值分别增加了42.3%、29.7%和111.7%。同时,混合气燃烧压力的发展明显加快,压力峰值出现的时间明显提前。对于浓燃和当量比浓度的混合气,压力峰值变化不大,而稀燃混合气的压力峰值增加较为明显。在-12 kV电压作用下,浓燃、当量比和稀燃三种状态下混合气的压力峰值时间提前了13.4%、7.5%和24.6%,相应的燃烧压力峰值增大了2.2%、1.0%和8.1%。本文应用外加电场对燃烧火焰产生的离子风效应及其对传播火焰形成的拉伸作用对试验结果进行了说明。     

The significance of thermoanalytical measurements in the assessment of polymer flammability

Thermoanalytical techniques have been widely used for the study of polymer decomposition processes, but they cannot accurately represent the very complex process of polymer combustion. The present work discusses some of the advantages and limitations involved in the use of thermoanalytical measurements to elucidate selected aspects of the constituent processes involved during the combustion of an organic polymer. There is no correlation between the flammability of different organic polymers and their thermal stability, even if the latter property is represented by an improved parameter such as the temperature at which 1% of the polymer has decomposed. An attempt has been made to correlate the inverse of the flammability (as measured by the limiting oxygen index) with the ratio of the heats of combustion and of gasification; but the results are not entirely satisfactory. Thermal analysis can, however, be very useful for the study of the effects of additives on a polymeric substrate. The lower heating rates involved, compared with those associated with a fire, allow determinations to be made not only of the ease of decomposition of an organic polymer but also of the thermochemistry of its reactions, of the effects of different atmospheres and of the extent of volatilization of certain species. In particular, thermoanalytical measurements carried out on a polymer-additive system can aid in the prediction of the effectiveness and mode of action of additives as flame retardants.     

浓度和点火位置对氢气-空气预混气爆燃特性影响

开展了氢气-空气预混气在透明方管内的爆燃实验研究,分析在一端开口一端封闭的狭长空间内,浓度和点火位置对氢气-空气预混气爆燃特性的影响。实验结果表明：氢气浓度和点火位置对火焰锋面结构以及发展有重要影响;各当量比条件下,均在距封闭端100 mm位置点火时反应最为迅速;在极贫燃或极富燃条件下,点火位置对火焰发展影响更大。氢气浓度与点火位置共同作用于压力波形,以距封闭端300 mm点火位置为界,分别在管道前后两段点火时,不同当量比条件下超压波形呈现复杂变化。超压峰值对氢气浓度具有极强依赖性,并且浓度对爆燃超压的影响程度远大于点火位置;在各点火位置下,均在Φ = 1.25时获得最大超压;最大超压对应的点火位置取决于当量比。     

Effect of chemically active additives on the detonation wave velocity and the detonation limits in lean mixtures

On the basis of the formalism of the one-dimensional theory of detonation with heat losses and the theory of branched-chain processes by the example of the oxidation of hydrogen-air mixtures in the presence of a hydrocarbon additive, it is shown that taking into account the reactions of termination of reaction chains on molecules of the additive, trimolecular termination, and also chain oxidation of the hydrocarbon additive allows one to qualitatively describe both the passage of the detonation velocity through a maximum with an increase in the additive content of a lean mixture and the existence of two concentration limits of detonation.     

天然气成分波动对其预混火焰传播特性的影响

利用定容燃烧弹试验平台和CHEMKIN PRO气相化学动力学软件,研究了常温常压和化学计量比下天然气成分变化对其层流燃烧速度和火焰不稳定性的影响规律。结果表明,天然气的层流燃烧速度随乙烷、丙烷和正丁烷含量的增加而上升,且乙烷的影响效果最为显著。天然气-空气火焰的不稳定性随着乙烷、丙烷和正丁烷含量的增加而降低,正丁烷对火焰综合不稳定性的抑制能力与丙烷相近,且都强于乙烷。火焰结构分析表明,天然气成分波动时H基浓度峰值的变化最为显著,天然气的层流燃烧速度与火焰中OH基和H基浓度之和的最大值之间有较强的相关性。层流燃烧速度敏感性分析和净反应速率分析表明,天然气成分变化会影响其燃烧过程中重要基元反应的进行,通过正影响的基元反应和负影响的基元反应之间的竞争,火焰中H基的浓度峰值发生变化,乙烷含量变化对H基浓度的影响最大。     

Mass loss and flammability of insulation materials used in sandwich panels during the pre‐flashover phase of fire

Nowadays, buildings contain more and more synthetic insulation materials in order to meet the increasing energy‐performance demands. These synthetic insulation materials have a different response to fire. In this study, the mass loss and flammability limits of different sandwich panels and their cores (polyurethane (PUR), polyisocyanurate (PIR) and stone wool) are studied separately by using a specially designed furnace. Expanded polystyrene and extruded polystyrene are tested on their cores only. The research has shown that the actual mass loss of synthetic and stone wool‐based cores is comparable up to 300 °C. From 300 °C onwards, the mass loss of PUR panels is significant higher. The mass losses up to 350 °C are 7%, 29% and 83% for stone wool, PIR and PUR respectively, for the influenced area. Furthermore, delamination can be observed at exposure to temperatures above 250 °C for the synthetic and 350 °C for the mineral wool panels. Delamination occurs due to the degradation of the resin between core and metal panels and the gasification of the (PUR) core. The lower flammability limits have been established experimentally at 9.2% m/m (PUR) and 3.1% m/m (PS). For PUR, an upper limit of 74% was found. For PIR and mineral wool, no flammability limits could be established. Copyright © 2017 John Wiley & Sons, Ltd.     

On the Nature of Superadiabatic Temperatures in Premixed Rich Hydrocarbon Flames

The propagation of flat laminar flames is studied numerically. It is shown that in rich homogeneous propane–air and methane–air mixtures, the maximum flame temperature exceeds the flame temperature in thermodynamic equilibrium. The degree of superadiabaticity depends on the concentration of the fuel mixed with air. It is shown that the superadiabaticity of rich flames is due to the diffusion of hydrogen from the reaction zone to the preheating zone and its preferential (compared to hydrocarbon) oxidation. The total enthalpy of the gas varies along the coordinate at the flame front and has a maximum.     

无卤阻燃三元乙丙橡胶燃烧性能的影响因素

使用锥形量热仪（Cone Calorimeter,简称CONE）系统地研究了无机氢氧化物的种类及用量、阻燃协效剂、炭黑和增塑剂等对三元乙丙橡胶燃烧特性的影响,并分析了燃烧产物的形貌,揭示了它们在EPDM燃烧过程中的作用。结果表明,高填充氢氧化物的EPDM胶料适用于制备低烟无卤阻燃橡胶材料;添加红磷和硼酸锌可促进胶料燃烧时的成炭行为,有助于提升阻燃性,但会增大发烟量;加入炭黑有助于提升胶料多项阻燃性能,加入增塑剂不利于胶料的阻燃性。