Computer study of the effect of the turbulence of an oncoming flow on the V-shaped combustion of a homogeneous methane-air mixture

Numerical simulation of the V-shaped turbulent combustion of a homogeneous methane-air mixture has been performed using the program Fluent from the ANSYS-CFD software package. The combustion process was described by the two-dimensional unsteady Navier-Stokes equations and the one-step kinetic mechanism. The unsteady profiles of the velocity components at the input domain of the calculation area were modeled by means of the artificial turbulence algorithms. These algorithms made it possible to set the pulsation intensity and the integral turbulence scale in the oncoming flow. Comparison of the calculated and experimental data has shown that experimentally observed broadening of the combustion front can be a result of its instability to the perturbations of the velocity in the oncoming flow.     

Mathematical model of the gas combustion rate in a vortex chamber

A mathematical model of the combustion rate of a gaseous fuel in a turbulent flow, which enters into a numerical procedure for calculation of a combustion chamber, is presented. Results of calculations according to the model are compared with experimental results.     

Numerical and experimental studies on nozzle two-phase flow characteristics of nanometer-scale iron powder metal fuel motor

Metal iron powder is a promising new type of energy source that is of enormous practical and research interest for future automotive power systems. To better optimize engine design, this study was devoted to the characteristic investigation of a two-phase flow. Experimental studies involving nanometer iron powder particle combustion and engine thrust measurement were conducted to confirm the results obtained from numerical calculations that were performed using a fourth-order Runge–Kutta–Gill method. Governing equations for nozzle two-phase flow were established to perform a theoretical study to analyze the combustion properties of iron oxide particles and flow in the nozzle. The results indicate that variations in the size and coagulation content of particles play a significant role in the loss of two-phase flow. Significant emphasis was placed on the effect of particle size (0.4–1.0?μm) and condensate content (10–40%) of ultrafine particles on the specific impulse. To further validate the theoretical results, the burning rates of particles of three different sizes were experimentally measured. In addition, the motor thrust and the specific impulse with the particle size of 50?nm were tested through combustion experiment, and the results show excellent agreement.     

Drop Tower Experiments and Numerical Modeling on the Combustion-Induced Secondary Flow in Standing Acoustic Fields

From the microgravity experiments on single fuel droplet combustion and on spark-ignited premixed flame in acoustic field, that have been done in this decade, secondary flow has been confirmed. The flow occurs only when combustion occurs and always in the direction to the neighboring node of velocity oscillation in standing acoustic field. This flow is thought to be driven by a kind of acoustic radiation force that arises from density non-uniformity due to combustion. According to the hypothesis, the driving force is expected to be very similar to buoyancy, being a volumetric force proportional to density difference. Since the mechanism tells that only the density difference due to combustion is the requirements for the occurrence of the secondary flow, a simpler system is employed for the hypothesis validation. A hot wire in a standing acoustic field gives a local temperature rise and the secondary flow is successfully reproduced. To avoid buoyancy that covers the radiation force, microgravity conditions are used. Through direct- and modeled numerical simulations and with drop tower experiments, the validity of the hypothesis is checked out. As a result, the supposed radiation force is found to be able to explain well the characteristics of the secondary flow. It is found that adding an acoustic radiation force term determined from acoustic parameters into conventional CFD calculation, one can sufficiently reproduce and predicts the behavior of the secondary flow numerically.     

Study on scale-up characteristics of oxy-fuel combustion in circulating fluidized bed boiler by 3D CFD simulation

The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MW_th to 330 MW_e). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO₂ in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.     

Modeling of Nonstationary Flow in the Ramjet Channel with a Distributed Pulse-Periodic Energy Supply

A study has been made of the influence of a pulse-periodic supply of energy that is equal to the energy released in combustion of hydrogen in air on the structure of supersonic flow in a channel of variable cross section, which models the ramjet duct. The flow has been modeled based on two-dimensional nonstationary gas-dynamics equations. Different regimes of flow depending on the configuration of the zones of energy supply and the excess-air coefficient have been obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 152–157, July–August, 2005.     

分解炉内煤粉燃烧和CaCO3分解流场的数值模拟

针对国内某大型水泥高性能分解炉，基于Fluent软件，采用有限速率／涡耗散模型模拟了炉内煤粉燃烧和生料分解的湍动多相流场，给出了炉内速度矢量、温度、压力和组分分布，结果显示。炉内流动趋势合理，可为分解炉的研究提供参考。     

Nonstationary flow in the model channel of a ramjet engine in pulse-periodic energy supply

A study has been made of the influence of the pulse-periodic supply of energy that is equal to the energy released in the combustion of hydrogen in air on the structure of supersonic flow in a channel of variable cross section, modeling the duct of a ramjet engine. The flow has been modeled on the basis of two-dimensional nonstationary gas-dynamic equations. Different flow regimes have been obtained depending on the configuration of the zones of energy supply and the excess-air coefficients. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 464–469, May–June, 2008.     

Evaporation of single droplets and dispersed liquid flow in motion through high-temperature combustion products

Experimental study of the evaporation of single droplets and droplets in a flow of dispersed liquid in their motion through high-temperature combustion products of a typical fuel is performed. The evaporation rates of droplets of different sizes are compared; the characteristics of vaporization in a flow of dispersed liquid are analyzed. The conditions under which the drops moving first in the flow significantly slow the evaporation of the following drops are found.     

Premixed combustion study: Turbulence in the nozzle behind grids and spheres

The experimental investigation of turbulence in the nozzle behind grids and spheres as the instrumentation for turbulent combustion of premixed flows by means of PIV and thermoanemometry was carried out. These methods were compared and applied in turbulent flows behind grids and spheres. Flows with relatively low turbulence intensities of the mean flow velocity (~1%), corresponding to the laminar flow in the case of absence of obstacles at low flow rates were investigated. Numerical simulation of the flow in a channel with changing geometry was carried out. A good agreement between laboratory experiments and numerical simulations was obtained. The developed experimental device is recommended for use in turbulent combustion of premixed flows.     

Fuel ignition and flame front stabilization in supersonic flow using electric discharge

Recent achievements in the field of stabilization of the front of high speed combustion using electric discharge are presented. Near-surface discharge at the plane wall between electrodes installed in the plane of the wall is applied in this study. Hydrogen and ethylene directly injected from the wall to the flow with a Mach number M = 2 and an air total temperature T ₀ = 300–760 K are used as fuel. The excess fuel coefficient calculated by the total air flow rate in the channel does not exceed ER = 0.1. The value of electric power input into the discharge is W _pl/H _tot < 2% of the total flow enthalpy, while the thermal power due to combustion exceeds W _com/H _tot > 100% at a low initial gas temperature. Electric discharge is first applied to stabilize combustion under conditions of a fixed separated zone and on the plane wall of the combustion chamber. A two-stage combustion regime is demonstrated. It is shown that the application of electric discharge makes it possible to achieve complete fuel combustion η > 0.9 in a wide range of experimental parameters.     

Numerical analysis of aerodynamics and hydraulic loss in the GTÉ-150 combustion chamber of gas-turbine power plant with the use of the fluent suite

The aerodynamic structure of the flow in the combustion chamber of the GTé-150 gas-turbine power plant has been simulated numerically by means of the FLUENT suite CFD. The influence of the processes of turbulent heat and mass transfer (and combustion) on the hydraulic loss in the combustion chamber has been investigated. Detailed comparison of the calculated and experimental data on the total pressure loss both n the combustion chamber proper and in its individual units has been carried out. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 45–49, July–August, 2006.     

Influence of the rates of gas flows through the smoke-removal and input-ventilation systems on the height of the smoke-free zone in a fire within a building

Integral, zonal, and empirical methods of calculating the mass rate of the gas flow through the smoke-removal system in the case of fire in a building were considered. Numerical experiments on investigation of the influence of the flow rates of the smoke removed and the cold air supplied by the input-ventilation system on the height of the smoke-free zone in a model fire within a building have been carried out. It is shown that, in the case where cold air is blown into the near-ceiling layer zone, to prevent the propagation of smoke to the adjacent rooms it is necessary to substantially increase the rate of gas flow through the smoke-removal system. It has been established that the simulation of a combustion region in the form of a point heat source positioned lower relative to the combustion surface gives incorrect results. It is shown that, in the integral and zonal models, account must be taken of the fact that air is entrained from the cold-air zone through the lower boundary of the near-ceiling layer by the smoke-removal system.     

基于金属熔流的未爆弹药销毁技术研究进展

结合未爆弹销毁作业的特点,分析常用销毁方法的适用范围,将烟火切割技术应用于弹药销毁作业,介绍了一种引燃非引爆的销毁方法。概述了金属熔流销毁技术的原理,梳理了燃烧剂配方和燃烧炬结构的研究现状,分析了燃烧剂体系配比,添加剂成分和燃烧炬结构对金属熔流的作业时间、熔穿金属效率、效果的影响。对比文献资料,采用火箭发动机型燃烧炬和利用高热剂、合金剂、稀释剂和造气剂优化燃烧剂,更有利于未爆弹药的销毁。并为下一步深入研究基于金属熔流的弹药销毁技术提供参考。     

Observation of sooting behavior in single droplets combustion in direct current electric fields under microgravity

Because of ions and electrons in flame, flow is induced around flame in electric filed. It affects combustion phenomena, and the effect has seemed to be significant for droplet combustion in previous study. This study is focused on movement of soot particle in single droplets combustion in direct current electric fields under microgravity in order to obtain some information about flow field around droplet. The large soot particles were observed by high-speed CCD camera, and the soot velocities are measured by PTV method. The single droplets were burned in the center of electrodes, which are two parallel rectangular wire nettings. Distance between electrodes is 50mm and applied voltages between electrodes are from 0kV to 6kV. Fuels tested are n-octane and toluene and the initial droplet diameters are around 0.8mm. All experiments were performed in microgravity in order to eliminate the natural convection. The results shows the velocities of soot particle are mainly in the direction of electric field, and most soot particles move to the cathode but some move to the anode. This indicates some soot particles have some negative charges. The velocities of soot particle increase with increasing in the distance from the droplet in both directions, and the velocity to cathode is larger than that to anode. From these results, the change of electric field and flow field around droplet are discussed.     

Initiation of combustion of supersonic propane-air flow by magnetoplasma compressor discharge

Results are given of investigations of the initiation of ignition and combustion of an air-propane flow in a supersonic wind channel with preheating by a pulsed discharge of a low-power magnetoplasma compressor of the erosion type. The mode of explosive ignition of mixture with formation of a combustion wave propagating towards the flow is revealed. The effect of initial conditions (fuel excess coefficient, preheating of air) on the spatial position and intensity of ignition is investigated.     

单屏式多点气流温度传感器现场校准工况参数影响分析

采用数值仿真的手段对燃烧室试验环境下单屏式多点气流温度传感器进行仿真计算,改变温场、流场环境,分析研究了来流总温、来流总压以及马赫数等工况参数对单屏式多点气流温度传感器的测量结果的影响规律,并用试验进行验证.数值模拟结果表明:在燃烧室试验环境下,单屏式多点气流温度传感器的测温偏差随着来流总温的增大而增大,每增加1000...     

Investigation of formation of a spatial position of longitudinal discharge in a supersonic flow by fitting the configuration of an anode under conditions of injection of propane and kerosene into the discharge zone

Results of gas-dynamic and spectroscopic studies of the possibility of a longitudinal discharge formation in a supersonic flow using an artificial zone of low pressure behind an anode under conditions of hydrocarbon fuel injection in the discharge region are presented. An absence of the connection of the combustion zone to the walls of combustion chamber is a feature of the investigated configuration of module. An advantage of this module is the creation of the stabilization effect of the combustion zone with simultaneous intensification of fuel mixing and plasma-chemical reactions due to the use of an incipient gas-dynamic peculiarity of the flow and a nonequilibrium electric discharge. Experiments are carried out at the Mach number M = 2 and static pressure in the flow ∼3.47 × 10⁴ Pa (260 Torr) in a wind tunnel with a closed test section with a cross section of 120 × 120 mm². The discharge current is kept at a level of 1 A; the consumption of propane, used as a hydrocarbon fuel, is 1.2 g/s; and the consumption of kerosene is 1.3 g/s. A comparison between the intensity distributions of the radiation of incipient products of chemical reactions given different variants of fuel injection in the discharge zone is carried out.     

Enlargement of the diamond deposition area in combustion flame method by traversing substrate

In this study, diamond deposition on traversing substrate was carried out in order to get useful information for utilizing combustion flame method. In the case of stationary substrate, diamond particles were obtained on the condition that C₂H₂/O₂ flow ratio was from 1.00 to 1.15, while no particles could be obtained in oxygen rich environment. However, in the case of traversing substrate, dense diamond belt was deposited without oxidizing of the diamond particles due to oxidative flame. From these results, it was proved that large area deposition by substrate traversing was available even in the case of combustion flame CVD.