KH2PO4/SiO2复合粉体抑制铝粉爆燃效果及机理分析

为研究KH₂PO₄/SiO₂复合粉体抑爆剂对铝粉爆燃的抑制作用,采用球磨机将KH₂PO₄和SiO₂混合研磨制备出新型的KH₂PO₄/SiO₂复合粉体抑爆剂。在哈特曼管实验装置上,开展爆燃火焰传播抑制实验,结果表明:随着KH₂PO₄/SiO₂复合粉体抑爆剂含量的增加,爆燃火焰传播长度和速度逐渐减小,当添加质量比10∶6的KH₂PO₄/SiO₂复合粉体抑爆剂时,可实现铝粉爆燃火焰传播的抑制。在20 L球形爆炸装置上,开展复合粉体抑爆剂抑制铝粉爆炸压力测试实验,结果表明:随着KH₂PO₄/SiO₂复合粉体抑爆剂含量的增加,铝粉爆炸最大爆炸压力p_max和最大爆炸压力上升速率(dp/dt)_max逐渐减小,当添加质量比10∶9的KH₂PO₄/SiO₂复合粉体抑爆剂时,可实现铝粉爆燃的完全抑制。通过KH₂PO₄粉体、SiO₂粉体与复合粉体抑爆剂对比可知,复合粉体抑爆剂对铝粉火焰传播和爆炸压力的抑制效果都优于单体粉体抑爆剂。通过对铝粉在空气中燃烧的热分析研究,从化学和物理两个方面分析了KH₂PO₄/SiO₂复合粉体抑爆剂对铝粉爆燃的抑制机理。     

CO2-超细水雾对CH4/Air初期爆炸特性的影响

为了研究CO₂和超细水雾对9.5%甲烷/空气初期爆炸特性的影响,采用高速纹影系统和定容燃烧弹对9.5%甲烷/空气初期爆炸特性进行了研究。分别改变CO₂稀释体积分数和超细水雾质量浓度,分析在二者单独和共同作用下球形火焰传播过程、火焰传播速度和爆炸超压的变化规律。结果表明:58.3 g/m3超细水雾增强了火焰不稳定性,促进了火焰加速和爆炸超压增加,表明超细水雾不足能产生促爆作用,只有当超细水雾充足时才会抑制甲烷爆炸;CO₂和超细水雾共同作用时能避免因超细水雾带来的促爆现象,可以明显减弱火焰不稳定性,减小火焰传播速度,降低爆炸超压和平均压升速率,以及明显推迟超压峰值来临时间。     

Heat flux measurements in stagnation point methane/air flames with thermographic phosphors

Light-induced phosphorescence from thermographic phosphors was used to study the wall temperatures and heat fluxes from nearly one-dimensional flat premixed flames. The investigated flames were stoichiometric, lean and rich laminar methane/air flames with equivalence ratios of φ = 1, φ = 0.75 and φ = 1.25 at ambient pressure. The flames were burning in a stagnation point arrangement against a water-cooled plate. The central part of this plate was an alumina ceramic plate coated from both sides with chromium-doped alumina (ruby) and excited with a Nd:YAG laser or a green light-emitting diode (LED) array to measure the wall temperature from both sides and thus the heat flux rate from the flame. The outlet velocity of the gases was varied from 0.1 to 1.2 m/s. The burner to plate distance (H) ranged from 0.5 to 2 times the burner exit diameter (d = 30 mm). The measured heat flux rates indicate the change of the flame stabilization mechanism from a burner stabilized to a stagnation plate stabilized flame. The results were compared to modeling results of a one-dimensional stagnation point flow, with a detailed reaction mechanism. In order to prove the model, gas phase temperatures were measured by OH-LIF for a stoichiometric stagnation point flame. It turns out that the flame stabilization mechanism and with it the heat fluxes change from low to high mass fluxes. This geometry may be well suited for further studies of the elementary flame wall interaction.     

Ar稀释C2H2+2.5O2预混气高频爆轰的端面结构

为了研究预混气爆轰的内部结构,对不同浓度的Ar稀释的C₂H₂+2.5O₂预混气进行爆轰实验和数值计算。首先,在内径63.5 mm的管道内进行爆轰实验,使用烟熏玻璃记录了不同初始压力下C₂H₂+2.5O₂预混气的爆轰端面结构。使用数字化图像处理技术来分析烟熏玻璃记录的三波点轨迹,以减少人为误差。然后,观察实验结果并描绘规则图形,图像识别程序经过验证后,用于分析实验结果。从端面结构中对封闭图形进行圆的拟合,用胞格半径方差来表示胞格大小的均匀程度;用相邻胞格圆心距的方差来表示胞格分布的规则程度。通过对比不同Ar稀释下半径方差和圆心距方差随胞格数量的变化,给出不同浓度Ar稀释下C₂H₂+2.5O₂预混气的端面胞格尺寸及分布规律,随着Ar浓度的升高,预混气端面胞格分布更加规律。     

无氢类金刚石薄膜表面H2O和O2分子共同作用的第一性原理计算

无氢类金刚石碳基薄膜(Diamond-like carbon,DLC)在潮湿大气环境中具有较低的摩擦系数,这主要是由于环境中的H₂O和O₂两种活性分子钝化了无氢DLC薄膜表面的悬键,但迄今两种活性分子对无氢DLC薄膜低摩擦行为的协同影响机制仍不清楚. 本文中通过第一性原理计算方法研究了H₂O和O₂分子共存时在金刚石表面的钝化状态,并推测了无氢DLC薄膜实现低摩擦的可能途径. 结果表明:H₂O和O₂两种活性分子在金刚石表面分解形成OH、H及O基团,其中O原子和H原子的相互吸引能够促使其形成OH基团. 当H₂O分子和O₂分子按比例2:1共存时,金刚石表面全部由OH基团钝化,而非2:1比例时,金刚石表面会形成C-OH、C-H和C-O共存的复杂情况.      

开放空间H2/CH4/空气爆炸实验与数值模拟研究

近年来氢的使用范围逐渐发展到各个领域, 含氢多元混合物气体在工业生产及生活燃料中被普遍使用. 为了保障含氢气体在生产、运输、使用等各个环节的安全性, 构建了开放空间混合气体爆炸测试实验系统, 研究了H₂/CH₄/空气混合气体爆炸压力及火焰传播特性, 给出了不同氢摩尔分数(100%, 75%, 66.67%, 50%, 33.33%)、混合气体当量比(0.8, 1.0, 1.1, 1.2, 1.4)、可燃云团尺寸(1 m3, 4 m3, 8 m3)及障碍物约束等因素对混合气体爆炸压力及火焰的影响规律. 基于经典TNT当量法, 建立了考虑混合气体组分比及可燃云团尺寸的最大爆炸超压预测模型, 修正了爆炸火焰传播半径理论模型. 结合高精度数值模拟技术揭示了加气站内建筑结构对混合气体爆炸的影响. 研究表明, 氢气的加入能够明显增强气体爆炸强度, 最大爆炸超压、火焰传播速度均随氢摩尔分数的增加而增大, 随当量比的增大先增大后减小, 当量比为1.1~1.2时最大; 通过对大尺度混合气体爆炸数值仿真与分析发现, 加气站内不同建构筑物条件下爆炸火焰传播距离、传播速度、最大爆炸超压等关键参数明显不同, 顶部和背部同时约束时, 爆炸伤害范围及事故后果最严重, 因此在划定加气站安全距离时, 应充分考虑不同建筑结构的影响.      

Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters

Lean limit flames in methane/hydrogen/air mixtures propagating in tubes of internal diameters (ID) of 6.0, 8.9, 12.3, 18.4, 25.2, 35.0, and 50.2 mm have been experimentally studied. The flames propagated upward from the open bottom end of the tube to the closed upper end. The content of hydrogen in the fuel gas has been varied in the range 0–40 mol%. Lean flammability limits have been determined; flame shapes recorded and the visible speed of flame propagation measured. Most of the observed limit flames in tubes with diameters in the range of 8.9–18.4 mm had enclosed shape, and could be characterized as distorted or spherical flame balls. The tendency was observed for mixtures with higher hydrogen content to form smaller size, more uniform flame balls in a wider range of tube diameters. At hydrogen content of 20% or more in the fuel gas, limit flames in largest diameters (35.0 mm and 50.2 mm ID) tubes had small, compared to the tube diameter, size and were “lens”-shaped. “Regular” open-front lean limit flames were observed only for the smallest diameters (6.0 mm and 8.9 mm) and largest diameters (35.0 and 50.2 mm ID), and only for methane/air and (90% CH₄ + 10% H₂)/air mixtures, except for 6 mm ID tube in which all limit flames had open front. In all experiments, except for the lean limit flames in methane/air and (90% CH₄ + 10% H₂)/air mixtures in the 8.9 mm ID tube, and all limit flames in 6.0 mm ID tube, visible flame speeds very weakly depended on the hydrogen content in the fuel gas and were close to- or below the theoretical estimate of the speed of a rising hot bubble. This observation suggests that the buoyancy is the major factor which determines the visible flame speed for studied limit flames, except that last mentioned. A decrease of the lean flammability limit value with decreasing the tube diameter was observed for methane/air and (90% CH₄ + 10% H₂)/air mixtures for tubes having internal diameters in the range of 18.4–50.2 mm. This effect has been attributed to the stronger combined effect of the preferential diffusion and flame stretch in narrower tubes for flames which resemble rising bubble.     

掺氢比对甲烷-氧气爆轰特性的影响

含氢多组分燃料由于其优良的燃烧特性逐渐成为研究关注的重点。为了对掺氢燃料的爆轰特性作进一步的研究,设计了长3 000 mm、管径30 mm的圆柱形半封闭燃烧室,对不同初压下的CH₄-2O₂、6CH₄-H₂-12.5O₂、3CH₄-H₂-6.5O₂（掺氢比分别为0%、5.1%、9.5%）3种预混合气的爆轰特性进行了实验研究,并采用烟熏膜、离子探针和压力传感器分别探测胞格结构、火焰位置和内部压力。结果表明,甲烷/氧气掺氢后可以有效提高爆轰波的传播速度,且掺氢浓度越高,传播速度越快;同时,氢气的掺入可减少管道出口处的速度亏损并在初始压力较低时加速火焰和激波的耦合,降低胞格尺寸,提高爆轰敏感性。     

LES Modeling of the Impact of Heat Losses and Differential Diffusion on Turbulent Stratified Flame Propagation: Application to the TU Darmstadt Stratified Flame

Common combustion chambers often exhibit turbulent flames propagating in partially-premixed mixtures. This propagation is generally governed by aerodynamics, unsteady mixing and chemical processes and may also be affected by conductive heat losses when the reactive zone develops close to the burner lips. The Filtered TAbulated Chemistry for Large Eddy Simulation (F-TACLES) model has been recently developed to include tabulated chemistry in Large Eddy Simulation (LES) of adiabatic stratified flames in flamelet regimes. The present article proposes a modeling approach to account for both differential diffusion and non-adiabatic effects on flame consumption speed following the F-TACLES formalism. The adiabatic F-TACLES model is first detailed using a generalized formalism for diffusive fluxes allowing either to account for differential diffusion or not. The F-TACLES model is then extended to non-adiabatic situations. A correction factor based on the non-adiabatic consumption rate is introduced to recover a realistic filtered flame consumption speed. The objective is here to tackle flame stabilization mechanisms when heat losses affect the reaction zone. The proposed approach is validated through the simulation of the unconfined stratified turbulent jet flame TSF-A for which stabilization process is affected by heat losses. Five simulations are performed for both adiabatic and non-adiabatic flow conditions comparing unity Lewis number and complex diffusion assumptions. The adiabatic F-TACLES model predicts a flame anchored at the burner lip disagreeing with experimental data. The non-adiabatic simulation exhibits local extinction due to heat losses near the burner exit. The flame is then lifted improving the comparison with experiments. Results also show a significant impact of molecular diffusion model on both mean flame consumption rate and angle.     

页岩储层纳微米孔隙CO2/CH4吸附及驱替特性研究进展

利用CO₂开采页岩气不仅能够提高页岩气采收率, 还能够节省水资源并且对CO₂进行地质封存, 有助于实现页岩气开采过程的碳中和. 富有机质页岩储层纳微米孔隙中气体运移机制不同于常规储层, CO₂在储层中具有超临界特性, 致使开采机理复杂, 无法得到CO₂开采页岩气微观机理的准确认识, 所以研究CH₄, CO₂及其二元混合物在页岩储层纳微米孔隙中的吸附及驱替特性对准确评估和高效开采页岩气至关重要. 本文从实验、理论以及模拟方面对页岩储层纳微米孔隙中CH₄的吸附特性、CO₂/CH₄二元混合物竞争吸附特性以及驱替特性进行了综合分析, 对气体在纳微米孔隙中吸附及驱替特性的基础研究及关键问题进行讨论分析并提出了展望. 研究表明CH₄在页岩储层中表现为物理吸附, 有机质特征(丰度、成熟度、类型)、孔隙结构、无机矿物组成、温度和压力、含水率对页岩的CH₄吸附能力均有一定程度的影响. 在相同条件下, CO₂比CH₄更易被页岩储层吸附, 在页岩储层中注入CO₂可以促进CH₄的解吸, 并有利于CO₂的地质埋存. 开采方案的部署可采用井网形式的注采方式, 可以通过调整注入井的位置、数量以及CO₂注入速率对开采方案进行优化.      

An Experimental Investigation of the Turbulence Structure of a Lifted H2/N2 Jet Flame in a Vitiated Co-Flow

Measurements of mean velocity components, turbulent intensity, and Reynolds shear stress are presented in a turbulent lifted H₂/N₂ jet flame as well as non-reacting air jet issuing into a vitiated co-flow by laser doppler velocimetry (LDV) technique. The objectives of this paper are to obtain a velocity data base missing in the previous experiment data of the Dibble burner and so provide initial and flow field data for evaluating the validity of various numerical codes describing the turbulent partially premixed flames on this burner. It is found that the potential core is shortened due to the high ratio of jet density to co-flow density in the non-reacting cases. However, the existence of flame suppressed turbulence in the upstream region of the jet dominates the length of potential core in the reacting cases. At the centreline, the normalized axial velocities in the reacting cases are higher than the non-reacting cases, and the relative turbulent intensities of the reacting flow are smaller than in the non-reacting flow, where a self-preserving behaviour for the relative turbulent intensities exists at the downstream region. The profiles of mean axial velocity in the lifted flame distribute between the non-reacting jet and non-premixed flame both in the axial and radial distributions. The radial distributions of turbulent kinetic energy in the lifted flames exhibit a change in distributions indicating the difference of stabilisation mechanisms of the two lifted flame. The experimental results presented will guide the development of an improved modelling for such flames.     

Structures and stabilization of low calorific value gas turbulent partially premixed flames in a conical burner

Experiments are carried out on partially premixed turbulent flames stabilized in a conical burner. The investigated gaseous fuels are methane, methane diluted with nitrogen, and mixtures of CH₄, CO, CO₂, H₂ and N₂, simulating typical products from gasification of biomass, and co-firing of gasification gas with methane. The fuel and air are partially premixed in concentric tubes. Flame stabilization behavior is investigated and significantly different stabilization characteristics are observed in flames with and without the cone. Planar laser induced fluorescence (LIF) imaging of a fuel-tracer species, acetone, and OH radicals is carried out to characterize the flame structures. Large eddy simulations of the conical flames are carried out to gain further understanding of the flame/flow interaction in the cone. The data show that the flames with the cone are more stable than those without the cone. Without the cone (i.e. jet burner) the critical jet velocities for blowoff and liftoff of biomass derived gases are higher than that for methane/nitrogen mixture with the same heating values, indicating the enhanced flame stabilization by hydrogen in the mixture. With the cone the stability of flames is not sensitive to the compositions of the fuels, owing to the different flame stabilization mechanism in the conical flames than that in the jet flames. From the PLIF images it is shown that in the conical burner, the flame is stabilized by the cone at nearly the same position for different fuels. From large eddy simulations, the flames are shown to be controlled by the recirculation flows inside cone, which depends on the cone angle, but less sensitive to the fuel compositions and flow speed. The flames tend to be hold in the recirculation zones even at very high flow speed. Flame blowoff occurs when significant local extinction in the main body of the flame appears at high turbulence intensities.     

二硫化钼/硫化锌纳米粉体的制备及其改性聚酰亚胺复合材料的摩擦学性能研究

采用一步水热法设计制备了二硫化钼/硫化锌(MoS₂/ZnS)纳米杂化体,并利用热压成型技术得到聚酰亚胺/二硫化钼/硫化锌(PI/MoS₂/ZnS)复合材料. 采用扫描电子显微镜、透射电子显微镜、X射线衍射仪以及光电子能谱仪对所制备材料的形貌和化学组成进行表征,结果表明MoS₂纳米薄片均匀致密地包覆在ZnS纳米颗粒表面. 热重分析和差示扫描量热曲线结果表明,MoS₂/ZnS纳米杂化体的引入显著地提升了PI基体的热稳定性能. 摩擦磨损测试结果表明,三种填料(MoS₂,ZnS和MoS₂/ZnS)均能有效改善PI基体的摩擦学性能,其中MoS₂/ZnS纳米杂化体的增强效应最为显著,这主要归因于MoS₂纳米片和ZnS纳米粒子之间的协同增强效应. 当MoS₂/ZnS纳米杂化体的质量分数为1.5%时, PI/MoS₂/ZnS复合材料的摩擦学性能达到最优,相较于纯的PI,复合材料的摩擦系数和磨损率分别下降了15. 9%和34. 3%.      

On the stabilization of flames on multijet industrial burners

Measurements of velocity and temperature characteristics, together with the analysis of the process of flame extinction, are reported for a range of high-intensity flames stabilized on a model of an industrial oxyfuel burner installed in a divergent quarl. The burner consists of a central axisymmetric jet surrounded by 16 circular jets, simulating the injection of oxygen in practical burners. A laser-Doppler velocimeter was used to measure density-weighted velocity characteristics, and bare-wire thermocouples were used to measure near unweighted temperature characteristics. Experiments were carried out to improve knowledge of the flow in the near field of multijet burner heads, which is essential to design further modifications in their geometry and to predict their effects. Isothermal and combusting flows are studied; for the latter, the experiments quantify the effect of quarl geometry, fuel-to-air ratio, swirl number, and central-to-peripheral jet velocity ration on the flame characteristics.

The results show that flame stabilization occurs in the vicinity of the quarl and is affected by its geometry owing to changes in the rate of entrainment of cold air. Increasing the swirl level and decreasing the peripheral airflow improves flame stability by promoting the mixing of fuel and air along the annular stabilization region. Turbulence measurements show common features with and without combustion and suggest the absence of large-scale mixing in the present flames. Although the laminar flamelet concept may represent most of the features of the flames investigated, the local quenching of burning flamelets is shown to preclude the internal ignition of flame gases in a way that influences the process of flame stabilization.     

磁控溅射NbSe2和MoS2薄膜不同湿度下的摩擦学行为

针对MoS₂在潮湿环境易氧化和润滑失效的问题,从增强离子键强度的角度探索改善其抗氧化以及润滑湿度适应性. 选择了离子键更强的NbSe₂进行对比,采用磁控溅射法分别制备了NbSe₂和MoS₂薄膜,研究了两种薄膜在不同湿度下的摩擦学性能,对比其在摩擦稳定阶段的结构和化学组成,探讨了NbSe₂在大气高湿度环境下的优势与作用机理. 结果表明:NbSe₂薄膜在大气环境下的摩擦表现出更佳的湿度适应性,在20% RH、35% RH和55% RH下摩擦系数稳定在0.08左右,直到75% RH下摩擦系数才开始增大,而MoS₂薄膜在35% RH下面临润滑性能快速失效的问题,进一步结合XPS和XRD等表征结果发现:相较于MoS₂,NbSe₂在大气摩擦条件下更难氧化,其层层滑移状态能较好维持,能保持长时间的润滑性能,这为大气高湿度服役润滑材料的改进提供了新的思路.      

Kinetics of ultrafine coating of SiO2 nanoparticles, suspended in non-thermal CH4/C2H6 plasma

Capacitively coupled RF discharges in methane and ethane (1000–3000 Pa, 5–15 W/cm³) were used for the in-flight coating of SiO₂ nanopowders (NP) with an a-C:H layer [A. Kouprine, F. Gitzhofer, M. Boulos, A. Fridman, Polymer-like C:H thin film coating of nanopowders in capacitively coupled RF discharge, Plasma Chemistry and Plasma Processing 24 (2) (2004) 189–215]. In this present work a model of the chemical kinetics of this plasma processing has been developed, based on the GRI-Mech 3.0 mechanism [G.P. Smith, D.M. Golden, M. Frenklach, Gas Research Institute, Detailed chemical reaction mechanism. Available from: ], and calculations are performed, using the Chemkin-II code. The model includes the formation of two solid phases: an amorphous C:H coating, deposited on the suspended NP, and soot, incepted in the gas phase. Non-equilibrium plasma effects are taken into account by the rates of radical species’ production, using the reference data on the “G-value”. The CH₃ and H species appear to have key roles in surface activation and the nanofilm growth. The results demonstrate the competitive character of the formation of the two solid phases: the C:H coating is dominant under T_gas < 1400–1600 K, depending on the conditions, and soot commencing to dominate at higher temperatures. This division corresponds to the passage from non-thermal plasma conditions, with the dominance of single-valent radicals and solid phase growth on the substrate only, to the plasma thermalisation with the formation of two-valent radicals and v. inception of the solid phase. The results are validated experimentally by the observation of soot formation as a function of the gas temperature, by the mass spectrograph data on the gas composition after plasma reforming, and by the reference data on coating growth rates and induction times for soot formation.     

原位合成Ag/Ag2MoO4纳米复合润滑剂对YSZ涂层摩擦学性能的影响

通过大气等离子喷涂工艺制备了氧化钇稳定氧化锆(YSZ)涂层,采用真空浸渍技术和水热合成的方法,将含有反应物离子或分子的前驱体溶液引入YSZ涂层内部固有的微裂纹和孔洞等缺陷中,并在缺陷中原位合成了直径约78~111 nm的Ag/Ag₂MoO₄类球形纳米颗粒,首次制备出了YSZ-Ag/Ag₂MoO₄复合涂层. 摩擦试验结果表明:与YSZ涂层相比,YSZ-Ag/Ag₂MoO₄复合涂层由于在室温和600 ℃下形成了润滑层,抑制了YSZ涂层摩擦表面的脆性断裂和磨粒磨损,从而显著降低了涂层的摩擦系数和磨损率,有效提高了涂层的摩擦学性能.      

CO2 will probably not help to save Venice from the sea

It has been proposed to rise Venice by injecting CO₂ into an aquifer lying 600–800 m below its lagoon. It is shown that because of the prevailing ambient conditions in the aquifer phase change of CO₂ cannot be avoided. The ensuing change of specific volume and compressibility will inhibit a uniform uplift pattern which is needed to avoid cracks in historical buildings. Further, both liquid and gaseous CO₂ produce capillary effects at the contact surface with water in the voids of the reservoir rock and this affects its mechanical response. Hence further non homogeneity in the uplift pattern will be produced. This prevents the use of CO₂ in the proposed conditions.     

Experimental Characterization of Gelled Jet A1 Spray Flames

Gelled propellants provide energetic performance similar to conventional liquid propellants and safety during storage and handling like a solid propellant. Experiments on unconfined gelled Jet A1 spray flames and the comparison with ungelled spray flames are reported for the first time in this paper in terms of the global features, burning regimes, stability limits, visible flame height, emission spectra, natural luminosity, and CH ^? chemiluminescence. Propellants were atomized by an internally impinging two-fluid atomizer, developed specifically for efficient atomization of non-Newtonian gels. Swirling and non-swirling spray flames were successfully stabilized on a burner incorporating bluff body and annular jet of combustion air over a wide range of operating parameters. Structural features of the atomizer impart high momentum to the (central) spray jet, such that the recirculation zone could be penetrated under all conditions. Long-exposure smoke and high-speed visualizations were employed to study cold flow structures and droplet-vortex interactions. Short-exposure direct and backlit imaging were used to observe global features of spray flames. Stability limits and visible flame heights were mapped for different thermal inputs, swirl numbers, and flow rates of atomizing and combustion air jets. Non-swirling stable anchored, partially blown off, and neck-blown off flames were observed. Lifted, and a transition regime, in which the flame could burn in stable and lifted mode repetitively, were observed for the swirling flames. Interactions between central and annular jets are important in these regimes, determining flame shape, symmetry, and flame height. Jet-like propagation zone determines the flame height through its dependence on momentum of spray jet. The length of this zone is affected by variations in thermal input, gas-liquid ratio, and air-fuel ratio. The gelled Jet A1 flames are remarkably shorter despite having a larger average droplet size than ungelled Jet A1. This experimental observation directly supports theoretical predictions reported in literature. These flames are more luminous than ungelled Jet A1, especially at the base and the neck regions. While, majority of the heat is released in the jet-like propagation zone for both the flames, significant heat is released in the neck zone of ungelled Jet A1 spray flame in comparison to ungelled Jet A1 spray flame due to intense turbulence and smaller droplet size.     

Experimental characterization of non-premixed turbulent jet propane flames

This paper reports an experimental study conducted on turbulent jet propane flames aiming at further understanding of turbulent structure in non-premixed slow-chemistry combustion systems. Measurements of mean and fluctuating velocity and temperature fields, mean concentration of major chemical species, correlation between velocity and temperature fluctuations, and dissipation of temperature fluctuations are reported in a turbulent round jet non-premixed propane flame, Re=20 400 and 37 600, issuing vertically in still air. The experimental conditions were designed to provide a complete definition of the upstream boundary conditions in the measurement domain for the purpose of validating computational models. The measured data depicts useful flow field information for describing turbulent non-premixed slow-chemistry flames. Velocity–temperature correlation measurements show turbulent heat fluxes tended to be restricted to the mixing layer where large temperature gradients occurred. Observations of non-gradient diffusion of heat at x/D=10 were verified. Temperature fluctuation dissipation, χ, showed the highest values in the shear layer, where the variance of temperature fluctuations was maximum and combustion occurred. The isotropy between the temperature dissipation in the radial and tangential directions was confirmed. By contrast, the observed anisotropy between axial and radial directions of dissipation suggests the influence of large structures in the entrainment shear layer on the production of temperature fluctuations in the flame region. The value of the normalized scalar dissipation at the stoichiometric mixture fraction surface, χ_st, was calculated, and ranges between 2 and 4 s⁻¹. The measured data were used to estimate the budgets in the balance equations for turbulent kinetic energy, Reynolds shear stresses, turbulent heat flux and temperature variance, quantifying the mechanisms involved in the generation of turbulence as well as in the transport of the temperature.