Mathematical Model of Combustion in Blunt Annular Ceramic Burner

The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.

Diffusion Flame of a CH4/H2 Jet in a Hot Coflow： Effects of Coflow Oxygen and Temperature

This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.

Combustion modeling in a model combustor

The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model.

Combustion Synthesis of MgSiN₂Powder at Different Nitrogen Pressures

MgSiN2 powders have been synthesized by combustion synthesis (CS) using Mg and Si3N4 as starting materials at different nitrogen pressures. The CSed powders were then sintered by spark plasma sintering (SPS) to obtain dense bulk MgSiN2 product. Analysis of the CSed powder using X-ray diffraction (XRD) revealed single-phase MgSiN2 was obtained by CS method. However, the CSed product can be divided into three distinct parts according to its color. Scanning electron microscopy (SEM) observation revealed the grain size and crystallinity decrease gradually from the center to the outer layer. Some small grains clustered together to form larger particles, and there were a large number of pores among the clusters. The grain size seemed increasing with the increase of nitrogen pressure. The bulk density of CS-SPSed MgSiN2 was 3.11 g/cm3, Vickers hardness was 1673.1 kgf/mm2, and thermal diffusivity was 8.718E−2 cm2/s.

Response of Stretched Cylindrical Diffusion Flame to Sinusoidal Oscillation of Air Flow Velocity

An experimental study investigated the characteristics of a stretched cylindrical diffusion flame, with a convex curvature with respect to the air stream, in response to periodic air flow velocity oscillation. The fuel was methane diluted with nitrogen, and the oxidizer air. The oscillation frequency was varied from 5 to 250 Hz. The results are summarized as follows. Though the fluctuation amplitude of the air stream velocity gradient was constant with respect to the frequency, the amplitude of the fuel stream increased. The fluctuation amplitude of the flame radius changed quasi-steadily from 5 to 25 Hz, and decreased with increasing frequency in the frequency range greater than 50 Hz. The flame luminosity did not respond quasi-steadily at 5 Hz, and the oscillation amplitude of flame luminosity was less than that of a steady flame, over the same velocity fluctuation range. The oscillation amplitude of luminosity peaked at 50 Hz, and was greater than that of a steady flame. It is considered that this complex change in flame luminosity with respect to frequency was closely related to the phase difference in the respective time variations in the ratio of flame thickness to radius, the velocity gradients of the air and fuel streams, and the magnitude of these values, with the ratio of flame thickness to radius related to the flame curvature effect, the velocity gradient of the air stream correlated to the flame stretch effect, and the velocity gradient of the fuel stream impacting the fuel transportation.

基于激光诱导击穿光谱的燃烧学实验教学探索

基于激光诱导击穿光谱技术开展了燃烧学实验教学探索,构建“激光诱导击穿光谱-层流反扩散火焰”实验教学系统,设计了具体实验操作方法与步骤,并针对激光诱导等离子体的基本参数和层流反扩散火焰的原子比分布开展了实验测量和分析。通过实验教学探索,促进了学生对燃烧学理论知识的更全面理解,提升了学生在跨学科环境中融会贯通的能力。

旋流对氢气微混扩散燃烧特性的影响

在当量比0.3~0.5的条件下,针对旋流数为0.62与无旋流2种微混扩散燃烧器开展了试验研究,考察了旋流作用对微混扩散燃烧流场、火焰结构、NO_(x)排放以及燃烧不稳定性的影响。实验运用OH*化学发光法与粒子图像测速(PIV)技术捕获了火焰与流动结构。结果表明:加入旋流能够通过改变流场结构,使火焰高度降低44%,进而缩短停留时间,最终实现NO_(x)排放体积分数减少63.4%;无旋流微混扩散火焰脉动的主要驱动因素是高当量比下火焰径向膨胀区的生成,而旋流的加入可以抑制径向膨胀区的生成,从而在宽负荷范围内实现抑制燃烧振荡的效果。

RP-3航空煤油/O_(2)预混火焰不稳定性研究

为获得RP-3航空煤油不稳定燃烧特性,采用定容燃烧实验装置开展初始压力0.1 MPa、0.2 MPa、0.3 MPa,初始温度420 K、450 K、480 K,当量比1.0~1.7工况下RP 3航空煤油/O_(2)预混火焰层流燃烧特性的实验研究。结果表明:随着初始压力和当量比增加,火焰锋面明显由光滑变为褶皱,内部出现胞状结构,火焰趋于不稳定。通过分析过渡加速起始半径发现,随着初始温度、初始压力和当量比增加,过渡加速起始半径减小,预混火焰的不稳定现象提前。另外,计算扰动增长率并分析其对火焰稳定性的影响发现,质热扩散作用对火焰稳定性的影响占据主导地位,流体动力学作用其次。进一步研究发现,质热扩散作用主要取决于分子扩散项,随着当量比增加,其值由负向正变化,证明分子扩散作用对预混火焰不稳定影响逐渐增强。

固定式可燃气体和有毒气体检测器布点设计优化

简述了常用气体扩散模型,分析了气体检测器的工程设计标准、规格参数等。采用PHAST软件,以液化石油气(LPG)和H_(2)S为例计算泄漏扩散,得到可燃气体和有毒气体浓度随时间、空间的变化关系,确定了固定点式可燃气体检测器和固定式H_(2)S检测器设置的有效空间区域。在选取的介质参数、泄漏场景和气象条件下,固定点式可燃气体检测器距释放源的水平距离不应超过8.4 m;固定式H_(2)S检测器距释放源的水平距离不应超过5.4 m;如果要在距H_(2)S释放源4 m范围内检测到一级报警值(体积分数0.005‰),则泄漏气体中H_(2)S初始体积分数达到0.75‰以上时就应设置固定式H_(2)S检测器。

内燃机车车顶高温浮射流扩散规律的数值研究

内燃机车在高海拔偏远山区的非电气化铁路中得到了广泛应用,然而其在运行过程中,车顶产生的高温浮射流将紧贴车顶表面流动,导致列车车顶局部过热,从而影响列车的运行安全。基于实车试验验证的数值模拟方法,对高海拔地区运行的5辆编组列车(包括2节内燃机车)进行仿真研究,并分析了不同运行速度和射流入射角度对高温浮射流扩散特性的影响。研究结果表明:随着运行速度的提高,射流运动轨迹线降低,导致高温气流更贴近列车车顶,特别是当内燃机车以最高运行速度160 km/h运行时,列车车顶的高温区域达到最大;增大射流入射角度能够有效减轻高温浮射流受到的来流冲击作用,进而提高射流轨迹线并降低车顶表面温度,当高温浮射流的入射角度达到45°时,列车车顶最高温度下降51.6%。本研究的发现为降低高海拔铁路上内燃机车车顶设备损坏风险提供了重要的参考。

采空区注液氮降温对煤自燃热物理特性的影响研究

为了研究注液氮降温对煤自燃的影响,选取亭南煤矿二盘区和三盘区煤样进行热物性实验。首先通过LFA457激光闪射仪对煤样进行预处理,再测定煤样30~300℃范围内的热物性参数,得到注液氮降温后煤样热物性参数随温度的变化规律,对比分析注液氮前后影响煤样热物理性质的因素。结果表明:注液氮处理前后的煤样,二者的热扩散系数都随着温度的升高而降低,比热容与导热系数随着温度的升高而上升;在30~200℃范围内,注液氮处理后煤样的热物性参数平均变化率高于原煤样,说明注液氮处理会增加煤样对温度的敏感性;此外,在相同温度下,注液氮处理后煤样热物性参数相较原煤样均有不同程度的上升,热扩散系数平均增长率最高,表明注液氮处理后的煤样在氧化升温过程中热扩散能力增强。

A flamelet model for turbulent diffusion combustion in supersonic flow

In order to develop a turbulent diffusion combustion model for supersonic flow, the physical argument of the extension of the flamelet model to supersonic flow was presented, and the flow field of a hydrogen/air diffusion combustion generated by axisymmetric supersonic jets was numerically simulated by employing the flamelet model. Using the experimental data, value of the model coefficient of scalar dissipation in the flamelet model was revised specifically for supersonic flow. The computational results of the modified flamelet model were compared with the experimental results, and it was indicated that the precision of the modified flamelet model was satisfying. Based on the numerical results and flamelet theory, the influence mechanisms of turbulence fluctuation on the average state equation and chemical reaction rate were studied for the first time. It was found that the fluctuation correlation of species mass fractions and temperature has little effect on the averaged gas state equation; the temperature fluctuation decreases the product of H2O, but its effect is small; the fluctuation of species mass fractions increases the product of H2O in the region close to oxidizer while decreases the product of H2O in other regions; the fluctuation correlation of species mass fractions and temperature largely decreases the product of H2O.

The impact of combustion characteristics and flame structure on soot formation in oxy-enhanced and oxy-fuel diffusion flames

Based on a detailed chemical mechanism, impacts of combustion characteristics and flame structure on soot formation in opposed-flow diffusion ethylene flames was studied with different stoichiometric mixture fractions in O2/N2and O2/CO2atmospheres. The results showed the followings. 1) In both atmospheres, with the increase of stoichiometric mixture fraction, the flame structure changed significantly. The stagnation plane shifted toward the oxidizer side. Furthermore, there were less C2H2 but more O and OH to occur in the soot inception zone, therefore the amount of soot in the flame decreased. 2) Compared withN2, CO2had a suppression effect on soot formation, which was mainly due to thermal and direct chemical interaction effects of CO2. This is because the specific heat capacity of CO2is higher than that of N2, which will cause the flame temperature to drop,and mole fractions of C2H2, H, O, OH and main PAHs to decrease. Soot oxidation played a dominant role, while soot surface growth was attributed to the secondary position. Meanwhile, when CO2 abounded in the flame, OH concentration was increased through the backward reaction of CO+OH=CO2+H, and this would be conducive to the oxidation of soot precursor and incipient soot particles. In addition, the results of maximum particle density indicated the thermal effect of CO2on soot for-mation is more important than the direct chemical interaction effect.

Numerical Investigation of Effect of Porosity and Fuel Inlet Velocity on Diffusion Filtration Combustion

Methane-air diffusion filtration combustion in a radiative round-jet burner was numerically investigated in this work.The purpose of this study was focused on the effects of porous media porosity and gas velocity on temperature distribution and CO and NO_(x)emissions.Reduced chemical kinetics was used where air and methane were assumed to be at their stoichiometric ratio,while thermo-physical properties were varied per the solid matrix porosity variation.Combustion characteristics were evaluated based on conduction and radiation as the two primary heat transfer modes within the solid matrix.Numerical simulations were carried out based on a packed bed with 3 mm alumina pellets.Results show that combustion temperature increases while the temperature gradient decreases with the increase in porosity,yielding higher NO_(x),and lower CO emissions.Furthermore,the combustion temperature is the lowest and most uniformly distributed with 1 m/s and 3 m/s gas velocities,wherewith 3 m/s gas velocity,combustion occurs outside of the porous zone.The corresponding NO_(x)and CO emissions are the lowest with 1 m/s gas velocity and increase with the increase in gas velocity from 1 m/s to 10m/s.

EFFECTIVE SOLUTION METHOD OF CHEMICAL REACTION KINETICS WITH DIFFUSE

The time integration method with four-order accuracy, self-starting and implicit for the diffuse chemical reaction kinetics equation or the transient instantaneous temperature filed equation was presented. The examples show that both accuracy and stability are better than Runge-Kutta method with four-order. The coefficients of the equation are stored with sparse matrix pattern, so an algorithm is presented which combines a compact storage scheme with reduced computation cost. The computation of the competitive and consecutive reaction in the rotating packed bed, taken as examples, shows that the method is effective.

Pressure Analysis of the Initial Process of Diffusion Combustion Surge in a 350 kW Gas Boiler

In order to meet the increasingly stringent requirements for nitrogen oxides(NOx)emissions from gas boilers,flue gas recirculation(FGR)technology is commonly used to achieve ultra-low NOx emissions.However,under some ultra-low NOx combustion conditions with FGR,a surge phenomenon occurs in the boiler,which causes a flameout and should be avoided.In this study,the diffusion combustion surge of gas boiler with a rated power of 350 k W and equipped with FGR device was investigated.Pressure characteristic analysis results of the initial process of combustion surge showed that the high-frequency component of pressure is closely related to combustion stability and its change can provide reference for the occurrence of surge.Besides,the initial process of surge was analyzed by wavelet packet entropy method.Results indicated that the wavelet packet entropy of pressure signals could effectively reflect the stability of combustion in the furnace,and it could also be used to study the occurrence of surge.

不同变质程度煤样活性基团变化与传热特性研究

为了探究不同变质程度煤样中活性基团与传热性质的变化与联系,利用红外光谱技术和激光导热技术研究了4种不同变质程度煤样的活性基团和热物性参数变化。结果表明:随着煤变质程度的增高,煤中的芳香族化合物和脂肪族化合物的百分含量逐渐升高,含氧官能团的百分含量逐渐降低;煤中的含氧官能团以醇、酚和醚为主;随着温度的升高,煤的热扩散系数先降后升,而比热容和导热系数整体呈不断升高的趋势;煤的热物性与煤的变质程度和工业分析数据有关。皮尔逊相关系数计算结果表明,—C=C—、—CH_(3)、—CH_(2)—、脂肪—CH与热扩散系数和导热系数的负相关性较强,而—C=O与热扩散系数和导热系数的正相关性较强,—OH则与比热容存在良好的负相关关系。

东海某平台可燃气体冷放空扩散安全评估研究

以东海某平台为例,采用数值模拟的方法研究不同工况条件下可燃气体冷放空的扩散规律,选用k-epsilon模型和Species Transport模型分别描述气相湍流运动和可燃气体扩散过程。结果表明:冷放空排放气体扩散受环境风向影响较小;冷放空排放气体扩散受风速条件和泄放放空速率的影响明显,随着环境风速的变大,火炬头上方形成的可燃气体团越小,可燃气体团中心距离火炬头越来越近;随着放空速率的变大,火炬头上方形成的可燃气体团越大,可燃气体团中心距离火炬头越来越远;意外熄灭工况、火灾工况和阻塞工况条件下,对应的最大扩散距离分别为15.69 m、20.62 m和28.48 m;直升机远离火炬头安全飞行的距离分别为16 m、21 m和29 m。建议平台加强可燃气体探测系统维护,确保能够及时探测到冷放空气体。

储油罐可燃气体泄漏扩散行为研究

设定不同的环境条件,通过数值模拟研究不同油罐结构内不同油品类型的可燃气体扩散规律。结果表明,轻质油在固定顶罐和外浮顶罐中的最大泄漏量分别达到重质油的65.8倍和48.2倍。对于轻质油,固定顶罐的泄漏性远大于浮顶罐结构,与固定顶罐相比,内浮顶罐和外浮顶罐的泄漏量分别减少约98%和35%;三种油罐结构对于重质油的存放安全性均相对较高。温度越高,可燃气体扩散得越快,0,20,40℃的可燃气体泄漏量与-20℃相比分别增加10%、23%、28%。环境风影响可燃气体挥发和被稀释的速度,风速越大,作用越明显,且正向风对可燃气体挥发和稀释的促进效果最强。

高压下氢气-乙醇球形膨胀火焰的层流燃烧速度和火焰不稳定性研究

在初始温度为400 K、不同的初始压力(0.1 MPa、0.4 MPa)、氢气比例(70%、80%)和当量比(0.7~1.4)条件下进行氢气-乙醇预混燃烧实验,使用高速纹影技术记录火焰传播图像。对氢气-乙醇球形膨胀火焰中的层流燃烧速度(LBV)进行实验研究,发现LBV随着氢气比例的增加而增加,压力升高却有着负影响。对火焰发展不同阶段的火焰形貌进行了研究。当火焰表面的大裂纹分裂出现小裂纹并且导致新细胞再生时,火焰变得不稳定。通过热膨胀比、火焰厚度和刘易斯数等参数考察了流体动力学效应和热扩散效应对火焰固有不稳定性的影响。结果表明,流体动力不稳定性随着压力的增加而增加,热扩散不稳定性对压力变化的敏感性较低。此外,增加氢气比例或初始压力会导致火焰更早遭受不稳定。