障碍物管道中湍流火焰发展的数值模拟

应用湍流马赫数修正的非稳态可压缩性K-ε-f-gr四方程湍流模型，模拟了半开口狭长管道中重复布置的障碍物引起的湍流火焰加速现象。结果表明，障碍物产生的扰动对加强燃烧和湍流输运的影响很大。随着火焰向前传播，火焰穿过障碍物时发生变形，反应区越来越长，且火焰速度逐渐上升。同时，火焰速度和管内压力的计算结果与实验测量值吻合良好，修正后的湍流模型能较真实地模拟障碍物管内预混火焰的发展过程。

Visualization of dust explosion under microgravity conditions

The objective of this work was to apply visualization methods to the experimental study of cornstarch dust-air mixture combustion in a closed vessel volume under microgravity conditions. A dispersion system with a small scale of turbulence was used in the experiments. A gas igniter initiated combustion of the dust-air mixture in the central or top part of the vessel. Flame propagation through the quiescent mixture was recorded by a high-speed video camera. Experiments showed a very irregular flame front and irregular distribution of the regions with local reactions of re-burning behind the flame front. at a later stage of combustion. Heat transfer from the hot combustion products to the walls is shown to have an important role in the combustion development. The maximum pressure and maximum rate of pressure rise were higher for flame propagation from the vessel center than for flame developed from the top pan of the vessel. The reason for smaller increase of the rate of pressure rise, for the flame developed from the top of the vessel. in comparison with that developed from the vessel center, was much faster increase of the contact surface of the combustion gases with the vessel walls. It was found that in dust flames only small part of hear was released at the flame front, the remaining part being released far behind it.

Study of Gas Combustion in a Vented Cylindrical Vessel

Complicated interaction of a flame front with a turbulent flow induced by venting is studied during combustion of the stoichiometric propane/air mixture in a relatively large vented cylindrical vessel. Flame position, its shape, and combustion pressure were measured as a function of time and vent parameters. The experimental data were used to verify numerical simulation of the combustion process. The proposed numerical model satisfactorily simulates the main features of combustion in a closed and vented vessel such as flame configuration, flow and temperature fields, and pressure variation pattern. Simulated velocity and temperature distribution are very useful pieces of information because they are not available from experiments.

玉米粉火焰在开口垂直管道中的传播

以对粉尘云状态参数的定量测定为基础，对玉米粉尘火焰在开口垂直管道中向上传播的过程进行了实验研究．在情形A中，火焰从管道的封闭端向开口端传播，在情形B中，从开口端向封闭端传播．实验中，观察到两种粉尘火焰，即湍流火焰和层流火焰，火焰形态转变对应的点火延迟时间约等于1．1s，即粉尘云湍流运动强度为10cm／s．情形A中，层流火焰的传播出现周期性振荡现象，湍流火焰在传播过程中不断加速；情形B中，两种火焰都匀速传播，湍流火焰传播速度明显大于层流火焰．在所考察的实验条件下，粉尘浓度对于玉米粉尘火焰传播速度的影响不大。

Turbulence in laminar premixed V-flames

Strong velocity fluctuations had been found in the laminar premixed V-flames. These velocity fluctuations are closely related to the chemical reaction. But the effects of the upstream combustible mixture velocity on the velocity fluctuations inside the flame are quite weak. The probability distribution function (PDF) of the velocity in the centre region of the flame appears "flat top" shaped. By analyzing the experiment results the flame-flow interactions are found to affect the flame not only at large scale in the flow field but also at small scale inside the flame. These effects will give rise to flame generated small scale turbulences.

Investigation of High-Speed Combustible Gas Ignited by a Hot Gas Jet Produced in the Shock Tube

The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “lineflame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90 m/s and the delay time of ignition is estimated in the range of 0.12–0.29 ms.

障碍物结构对预混火焰压力发展的影响

本文针对不同的可燃气混合物，研究了由于障碍物引起的火焰加速而导致的管内压力上升现象。在实验中，使用了三种不同形状的障碍物，同时改变障碍物的间距W和阻塞比BR。结果表明，障碍物的存在对管内压力的影响是十分巨大的，即使是较小的阻塞面积，也能导致压力大幅度上升。在障碍物阻塞比BR＝0.5、障碍物间距约等于管道内径(W/D≈1)阶管内的峰值压力达到最大值。本实验所用的三种障碍物产生的管内峰值压力并不相同，以园环型的障碍物产生的压力最高，这说明，存在某一种最优化的障碍物，在相同的阻塞比条件下，该障碍物能最大地提高管内的峰值压力。

Influence of Obstacle-Produced Turbulence on Development of Premixed Flames

An investigation into influence of obstructions on premixed flame propagation has been carried out in a semi-open tube. It is found that there exists flame acceleration and rising overpressure along the path of flame due to obstacles. According to the magnitude of flame speeds, the propagation of flame in the tube can be classified into three regimes: the quenching, the choking and the detonation regimes. In premixed flames near the flammability limits, the flame is observed first to accelerate and then to quench itself after propagating past a certain number of obstacles. In the choking regime, the maximum flame speeds are somewhat below the combustion product sound speeds, and insensitive to the blockage ratio. In the more sensitive mixtures, the transition to detonation (DDT) occurs when the equivalence ratio increases. The transition is not observed for the less sensitive mixtures. The dependence of overpressure on blockage ratio is not monotonous. Furthermore, a numerical study of flame acceleration and overpressure with the unsteady compressible flow model is performed, and the agreement between the simulation and measurements is good.

Multiplex CARS measurements in supersonic H-2/air combustion

H-2 and O-2 multiplex coherent anti-stokes Raman spectroscopy (CARS) employing a single dye laser has been explored to simultaneously determine the temperature and concentrations of H-2 and O-2 in a hydrogen-fueled supersonic combustor. Systematic calibrations were performed through a well-characterized H-2/air premixed flat-flame burner. In particular, temperature measurement was accomplished using the intensity ratio of the H-2 S(5) and S(6) rotational lines, whereas extraction of the H-2 and O-2 concentrations was obtained from the H-2 S(6) and O-2 Q-branch, respectively. Details of the calibration procedure and data reduction are discussed. Quantification of the supersonic mixing and combustion characteristics applying the present technique has been demonstrated to be feasible. The associated detection limits as well as possible improvements are also identified.

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at similar to 590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products. (C) 2007 Elsevier B.V. All rights reserved.

Numerical modeling of 3-D turbulent two-phase flow and coal combustion in a pulverized-coal combustor

In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase hows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.

不同重力下窄通道内薄材料表面的火焰传播

在常重力下模拟微重力燃烧对载人航天器的火灾安全具有重要意义。窄通道就是这样一种可以有效限制自然对流的模拟设施。但是，不同重力下火焰传播的相似性仍然是有待研究的问题。本文用实验和数值模拟的方法，比较了不同重力下有限空间内热薄材料表面的逆风传播火焰。不同重力下火焰形状和火焰传播速度的比较表明，1cm高的水平窄通道可以有效地限制自然对流，在常重力下用这种通道能够模拟微重力下相同几何尺寸的通道中的火焰传播。因此，在地面上首先利用水平窄通道，模拟相同环境中的微重力火焰传播，然后考虑通道尺寸变化对火焰传播的影响，有可能成为地面模拟其他尺寸的空间中的微重力燃烧的方法。

采用偏置射流预燃室稳定燃烧水煤浆的原理及应用研究

水煤浆作为经济型清洁燃料引起人们的长期关注。水煤浆偏置射流预燃室具有对浆种适应性强，稳燃性能好等特点。本文对偏置射流预燃室稳定燃烧水煤浆的原理进行了探讨，并对该燃烧技术用于处理造纸黑液的研究情况作了介绍。结果表明，采用低压多级雾化喷嘴对水煤浆进行雾化，形成的雾炬和偏置射流预燃室的流场有良好的匹配，在预燃室内形成大尺度的回流区，有利于煤浆的点火、稳燃和消除灰渣。