水平管道中瓦斯爆炸火焰传播速度测量（英文）

在煤炭工业中,瓦斯爆炸事故经常发生,造成了巨大的人员伤亡以及材料性能的破坏。在研究瓦斯爆炸机理过程中,火焰前端传播速度是最重要的因素之一。根据中北大学水平管道实验装置设计了一套火焰速度测量系统,用于研究在密闭管道内圆环障碍物的数量和阻塞比对火焰传播速度的影响。结果表明,障碍物对瓦斯爆炸产生的火焰具有明显的加速作用。随障碍物数量和阻塞比的增加,火焰加速更加明显且持续更剧烈。其中,障碍物数量对火焰加速持续的作用更大,而障碍物阻塞比的作用不明显。     

阻塞比对甲烷火焰传播特性影响的数值模拟研究

分别采用标准k-ε湍流模型和六步反应机制,利用Fluent软件对常温常压下甲烷火焰在具有不同阻塞比的障碍物管道中的传播特性进行数值模拟研究,分析了障碍物阻塞比对火焰传播速度、火焰结构形态、火焰到达位置和时刻等参数的影响。计算结果表明:在起初阶段,火焰传播速度逐渐增加,但火焰在流经障碍物过程中其速度大小呈振荡变化特点;在障碍物附近时,火焰速度增加,在相邻障碍物间时火焰速度下降。障碍物阻塞比越高,火焰传播速度越高,加速能力也越强,加速时间越短,火焰传播距离也越长。火焰加速传播主要是火焰与障碍物、管道壁面以及压缩波相互作用的结果。     

ABC干粉抑爆剂在中尺度管道应用效果研究

本文主要研究中尺度管(200×200mm)的瓦斯爆炸在干粉抑爆剂作用下的抑爆情况,从火焰传播速度和压力大小变化的角度来进行数据分析,认识中尺度管道使用不同抑爆剂情况下的瓦斯爆炸传播现象,初步了解抑制爆炸的效果和程度。ABC干粉抑爆剂的物理化学双重抑制作用对中尺度管道内低浓度瓦斯爆炸火焰传播的抑制效果非常明显,在对火焰速度的影响上,ABC抑爆粉剂对火焰的抑制存在一个区间和时间的过程,爆炸火焰在通过抑爆层后,需传播一定的距离才能被完全扑灭。使用ABC抑爆剂时,较未使用时火焰速度的最大降幅可达40%,可以快速熄灭火焰;压力较未使用时的峰值大幅降低,且变化的幅度趋于稳定。     

障碍物对火焰加速实验研究

针对水平管道式气体--粉尘爆炸装置,设计出了两种不同形状的障碍物:环形和半圆形.确定了其在管道中的最佳放置位置.并在此基础上研究障碍物对火焰传播的加速机理.     

氢气-空气预混火焰传播特性的数值模拟研究

应用Fluent流体计算软件,基于标准湍流κ-ε模型和EDC燃烧模型,采用SIMPLE格式算法对常温常压下对常温常压下氢气／空气预混火焰在光滑管道中的传播特性进行二维数值模拟,获得火焰传播速度、火焰结构、表面积、火焰到达位置和时刻沿管道变化情况。结果表明：火焰传播速度先增加后逐渐减小。在离点火端105mm处到达最大值,之后逐渐降低。在t=9．1ms时,火焰开始逐渐呈现典型的郁金香结构。火焰在初始加速阶段的主要物理机理是前方未燃气体受到前驱压缩波作用而被加热和压缩的正反馈微分加速机制,此后在管右端的反射压缩波影响下火焰传播速度略有降低。     

瓦斯爆炸冲击波传播过程的数值模拟

建立瓦斯爆炸沿巷道传播的分析模型,运用DYTRAN软件进行分析,得到瓦斯爆炸冲击波沿巷道的传播过程的参数变化及障碍物表面的等效应力分布.结果表明,应用DYTRAN可以很好地模拟瓦斯爆炸传播过程及冲击波对障碍物的短暂的瞬态动力学过程,对进行矿难救生系统的设计研究有重要意义.     

气体爆炸对白鼠杀伤作用的实验研究

通过实验测试了管道式气体爆炸冲击波对置于管道内的白鼠的杀伤作用,当甲烷体积分数为10％时,爆炸产生的最大压力为0.264 MPa,白鼠受伤最严重.将一些特制的障碍物置于管道可产生更强的冲击波,这有助于增强甲烷爆炸对白鼠的杀伤作用.当甲烷体积分数为10％时,有障碍物条件下的最大爆炸压力可达到0.298 MPa.由此可知,为减小煤矿中事故冲击力,应尽量避免障碍物的存在;随爆炸次数增加,白鼠致死压力减小.     

甲烷二次燃烧火焰传播速度的数值模拟研究

二次燃烧是常见热力设备和高速推进燃烧室内的重要现象,但目前对二次燃烧的研究较为匮乏。为了研究当量比、甲烷添加量对二次燃烧自点火火焰传播速度的影响情况,论文利用CHEMKIN软件中火焰速度反应器模拟研究了向不同当量比(0.3~0.9)甲烷/空气一次燃烧产物中添加不同量(摩尔分数0.02~0.24)甲烷时的自点火火焰传播速度。研究表明当量比主要是通过影响尾气温度和一次燃烧产物中富余氧气来影响火焰传播速度,而甲烷添加量会影响二次燃烧时局部当量比,局部当量比在1附近时火焰传播速度最大。     

气体爆炸对白鼠杀伤作用的实验研究（英文）

通过实验测试了管道式气体爆炸冲击波对置于管道内的白鼠的杀伤作用,当甲烷体积分数为10%时,爆炸产生的最大压力为0.264 MPa,白鼠受伤最严重。将一些特制的障碍物置于管道可产生更强的冲击波,这有助于增强甲烷爆炸对白鼠的杀伤作用。当甲烷体积分数为10%时,有障碍物条件下的最大爆炸压力可达到0.298 MPa。由此可知,为减小煤矿中事故冲击力,应尽量避免障碍物的存在;随爆炸次数增加,白鼠致死压力减小。     

煤粉云火焰传播特性实验研究

煤矿开采中存在煤粉爆炸的重大安全隐患,本实验主要研究煤粉云的火焰传播,为预防和控制煤粉爆炸事故提供理论依据.实验采用粉尘云点火装置对煤粉在燃烧玻璃管中进行试验,通过改变煤粉云浓度探讨其对煤粉云火焰传播过程的影响,并利用高速摄影记录煤粉火焰传播过程.结果表明,点火电极在点燃煤粉云后,火焰沿着玻璃直管管壁竖直传播,火焰在传播过程中发出明亮的黄光并在玻璃直管上端端口形成蘑菇云状的火焰.当煤粉云的浓度为250 g/m3时,其燃烧时间远远小于浓度为500 g/m3和750 g/m3时的燃烧时间.当浓度分别为250 g/m3、500 g/m3和750 g/m3时,其火焰前锋阵面最大传播速度分别在100 ms、353 ms和310 ms时达到相应的最大值1.51 m/s、2.00 m/s和1.61 m/s.火焰前锋阵面达到最大速度的时间和火焰传播的最大速度随浓度的增加先增大后减小.     

Analysis of combustion and flame propagation characteristics of LPG and Gasoline fuels by laser deflection method

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber. The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a great effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.     

Swirl effect on the flame propagation at idle in a spark ignition engine

The objectives of the study are to investigate the effect of swirl on the flame propagation and to propose a flame propagation model that predicts the behavior of the flame front in the presence of significant swirl flow field by analyzing flame images pictured with a high speed digital video at idle. The velocity distribution of the charge in the cylinder was measured using an LDV measurement system. From the experimental results and analyses, a new flame propagation model is proposed in which flame frontal locations can be traced by superposing the convective flow field and the uniform expansion speed of the burned gas, and the proposed model reveals that the increase of the flame propagation speed in the presence of swirl motion within 1 ms after ignition is mainly due to the flame stretch, and mainly due to increased turbulence intensity later than 1 ms after ignition.     

Large-scale Experimental System for Multiphase Fuel/Air Explosions

A large-scale experimental system for multiphase combustion and explosion study was developed and manufactured.The explosion tank consists of a 2 m diameter,3.5 m long tube and ellipsoidal domes on both ends.The volume of the experimental tank is 10 m3.Pressure histories of the explosion pressure can be measured at different locations in the tank.High pressure glass windows of 200～300 mm were used to have access to the visualization of the explosion process.The explosion process of methane/air mixture and methane/coal dust/air mixture initiated by a 40 J electric spark at the center of the tank was studied in the large-scale experimental system.Five pressure sensors were arranged in the tank with different distances from the ignition point.Ten dust dispersion units were equipped to eject dust into the tank.A high-speed camera system was used to visualize the flame propagation during the explosion process.The characteristics of the pressure wave and flame propagated in methane/air mixtures and methane/coal dust/air mixtures have been studied and analyzed.     

Characteristics of propagating tribrachial flames in counterflow

The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.     

飞秒激光诱导的空气等离子体冲击波探究

一定强度的飞秒激光聚焦于空气能生成空气等离子体并诱导生成冲击波。为了观察该冲击波传播特性，引入了超快时间分辨涡旋滤波成像技术，并对观测到的冲击波动力学过程进行了分析。实验探测到泵浦能量为1.5 mJ的飞秒激光经过透镜聚焦到空气中产生等离子体空气冲击波，分析了在3~15 μs时间段冲击波的动态演化过程。结果表明，飞秒激光等离子体空气冲击波在传输时以不对称的球形形状向外扩散，且沿着激光传播方向的传播速度与背着激光传播方向的传播速度不同，分别为372 m/s和341 m/s。这一观察结果与传统的点爆炸模型的对称情形不同，尝试对该不对称动力学过程进行了合理解释。     

某杀爆战斗部破片与冲击波运动规律研究

通过对某杀爆战斗部爆炸后破片运动及冲击波传播的研究,理论推导了破片与冲击波相遇位置的求解全过程。采用Visual C++开发破片与冲击波运动规律计算系统,并用数值积分方法对冲击波速度与位移进行分段积分。通过该系统计算了某预制破片战斗部破片与冲击波的相遇位置,并运用 ANSYS/LS-DYN数值模拟了该预制破片战斗部爆炸后破片与冲击波的运动,数值模拟结果与计算结果基本相符。     

Propagation behavior of SH waves in layered piezoelectric plates

In this study, the propagation of SH waves in a coupled plate consisting of a piezoelectric layer and an elastic layer is analytically investigated. The piezoelectric material is polarized in the z-axis direction and perfectly bonded to an elastic layer. The mathematical model of the SH wave propagation in this plate is based on the type of surface wave solution. Dispersion relations with respect to phase velocity are obtained for electrically open and mechanically free. Numerical examples are provided to illustrate graphically and compare the variations of the phase and group velocities versus the wave number for the different layers. The thickness ratio and the properties of the two layers have a significant effect on the propagation of SH waves. The conclusions are meaningful both theoretically and practically for the design of high-performance surface acoustic wave (SAW) devices.     

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.