颗粒堆积吸附床内三维数值传热计算

吸附床内传热过程的分析和计算是吸附式制冷研究的重要基础内容之一.在对颗粒堆积吸附床内传热过程分析的基础上,通过对吸附床内复杂传热过程进行合理简化,建立了吸附床内部三维非稳态无内热源传热数学模型,并以硅胶-水工质对为例进行了求解,计算所得吸附床换热系数数值与根据相关文献中提供的实验数据所推算山的数值十分接近.同时,根据计算结果分析了吸附床内部传热过程,为颗粒堆积吸附床的设计和优化提供了一种简单而有效的理论方法.     

惰性多孔介质内过滤燃烧特性分析

以惰性堆积床内甲烷/空气低速过滤燃烧为例,因次分析系统特征尺度,基于修正的单温度模型,提出一种封闭的耦合解析方法,对燃烧过程进行理论分析.研究了燃烧波波速、火焰传播速率、最高燃烧温度等燃烧特性参数,将计算结果与实验结果以及前人的理论结果进行对比.     

堆积床内甲烷/空气预混燃烧的理论分析

在多孔介质内组织预混燃烧,燃气与多孔介质有强烈的换热作用,燃烧过程伴随着化学反应和热输运的强烈耦合。本文以惰性氧化铝球堆积床内的甲烷/空气预混燃烧为例,提出解析模型,对燃烧过程进行理论分析,给出温度分布的解析解,发现了超绝热火焰温度燃烧现象。     

堆积床内非驻定过滤燃烧的一维研究

多孔介质内气体过滤燃烧不同于自由流中燃烧,燃气与多孔介质强烈换热.热波波速和燃烧波波速是燃烧过程的特征参数.以惰性堆积床内的甲烷/空气的低速过滤燃烧为例,提出一维解析模型,用摄动理论推导出燃烧波波速,用直接求解方法和格林函数方法给出充分发展后的和瞬态的燃烧温度分布,并进行计算验证.     

非驻定过滤燃烧的均相模拟

基于一维层流反应流模型,构建了新的准稳态均相模型,并对堆积床内充分发展后的低速过滤贫燃过程进行数值模拟.将计算结果与传统双相模型进行比较,分析弥散效应和化学反应机理等对计算结果的影响,并开展输运项分析;将均相模型的数值结果与准稳态和瞬态的理论结果进行比较,验证理论方法.     

双层多孔介质内预混燃烧的实验和二维数值模拟

对双层多孔介质燃烧器内丙烷/空气预混燃烧进行实验和数值研究.实验对多孔介质燃烧器内固体温度场分布进行测量分析;数值计算利用商业软件FLUENT6.2,通过添加用户自定义标量方程和用户自定义函数,对有壁面散热的双层多孔介质内预混燃烧进行了二维模拟,并与实验结果进行了比较.结果表明,双层多孔介质燃烧器具有良好的稳定燃烧范围和较低的污染物排放;壁面散热对多孔介质燃烧的影响不可忽视.     

蓄冷球堆积床动态放冷性能研究

根据蓄冷球和载冷剂之间的能量平衡,并考虑载冷剂与蓄冷球之间的换热系数变化、载冷剂的导热、蓄冷球堆积床热损失的影响,建立了蓄冷球堆积床放冷过程的数理模型。采用数值计算方法模拟了蓄冷球堆积床的放冷过程,并讨论载冷剂流速、载冷剂入口温度以及堆积床孔隙率对放冷过程中载冷剂出口温度和放冷量的影响。     

氚增殖剂球床内氦气流动特性的数值模拟

通过计算流体力学(CFD)数值模拟方法,对氚增殖剂球床内部的氦气流动特性进行了初步研究。分析了球床流通长度和流通截面对提氚气体压降的影响,获得了不同入口流速下规则堆积球床和随机堆积球床的压降和阻力系数。      

基于稳态电热拉曼技术的碳纳米管纤维导热系数测量及传热研究

利用稳态电热拉曼技术测量了碳纳米管纤维对流换热环境下的导热系数. 该方法基于材料拉曼信号与温度之间的关系, 实时探测一维材料在不同电加热(内热源)下的中心点温度, 利用对流环境下的稳态导热模型推导出材料的导热系数, 实现了一维微纳材料热物性的无损化和非接触式测量. 实验发现: 碳纳米管纤维的导热系数远低于单根碳纳米管的导热系数, 但高于碳纳米管堆积床的导热系数. 这表明碳纳米管体材料的热物性主要取决于内部管束的列阵和管束间的接触热阻.     

蓄冷球堆积床动态充冷性能模拟

根据蓄冷球和载冷剂之间的能量平衡,建立了蓄冷球堆积床充冷过程的数理模型。该模型考虑了载冷剂与蓄冷球之间的换热系数变化、载冷剂的导热、相变蓄冷材料的过冷度以及蓄冷球堆积床热损失的影响。采用数值计算方法模拟了蓄冷球堆积床的充冷过程,讨论了载冷剂入口温度、初始温度和流速对充冷过程蓄冷材料温度、载冷剂温度和蓄冰率的影响。     

Differences between PREMIER combustion in a natural gas spark-ignition engine and knocking with pressure oscillations

PREMIER (PREmixed Mixture Ignition in the End-gas Region) combustion occurs with auto-ignition in the end-gas region when the main combustion flame propagation is nearly finished. Auto-ignition is triggered by the increases in pressure and temperature induced by the main combustion flame. Similarly to engine knocking, heat is released in two stages when engines undergo this type of combustion. This pattern of heat release does not occur during normal combustion. However, engine knocking induces pressure oscillations that cause fatal damage to engines, whereas PREMIER combustion does not. The purpose of this study was to elucidate PREMIER combustion in natural gas spark-ignition engines, and differentiate the causes of knocking and PREMIER combustion. We applied combustion visualization and in-cylinder pressure analysis using a compression–expansion machine (CEM) to investigate the auto-ignition characteristics in the end-gas region of a natural gas spark-ignition engine. We occasionally observed knocking accompanied by pressure oscillations under the spark timings and initial gas conditions used to generate PREMIER combustion. No pressure oscillations were observed during normal and PREMIER combustion. Auto-ignition in the end-gas region was found to induce a secondary increase in pressure before the combustion flame reached the cylinder wall, during both knocking and PREMIER combustion. The auto-ignited flame area spread faster during knocking than during PREMIER combustion. This caused a sudden pressure difference and imbalance between the flame propagation region and the end-gas region, followed by a pressure oscillation.     

Vortex dynamics in different combustion regions of a cavity-based scramjet

A hybrid RANS/LES study of a cavity-based scramjet was performed and reasonable agreements were found between simulation results and experimental measurements. In the current case, the flame was stabilized by the subsonic cavity shear layer and propagated downstream into the supersonic flow. The vortex dynamic in the flow, mixing, and combustion regions was comparatively investigated. The averaged vorticity in the combustion regions was lower by 55% compared to the mixing region, primarily due to dilatation as a result of the heat release. Furthermore, the combustion zone was decomposed into four regions based on premixed/diffusion flame and subsonic/supersonic combustion. Then the vorticity and its transport in the four regions were compared. The averaged vorticity in the premixed combustion regions was only slightly larger than that in the diffusion combustion regions. However, the averaged heat release rate was nearly 3 times larger in the premixed regions, leading to higher contributions of dilatation and baroclinic torque in the premixed regions, with an overall weak positive impact on the vorticity generation. In the subsonic combustion regions, the vorticity was three times larger than that in the supersonic combustion regions, despite similar heat release rates on average. It could be explained by the relatively large magnitude of dilatation and baroclinic torque in the supersonic flow. Vortex stretching and dilatation were comparable in the supersonic flame but the former became two times larger than the latter in the subsonic flame. Moreover, the baroclinic torque had larger contributions than diffusion in the supersonic flame whereas the opposite trend was found in the subsonic flame. The results highlight that the subsonic combustion regions in the cavity shear layer and near the walls significantly contribute to the vortex dynamics and mixing process, in addition to flame stabilization.     

燃料敏感性对内燃机部分预混燃烧(PPC)光谱特性的影响研究

在一台光学发动机上,利用火焰高速成像技术和自发光光谱分析法,研究了燃料敏感性(S)为0和6时对发动机缸内火焰发展和燃烧发光光谱的影响。试验过程中,通过改变喷油时刻 (SOI=-25,-15和-5°CA ATDC) 使燃烧模式从部分预混燃烧过渡到传统柴油燃烧模式。通过使用正庚烷、异辛烷、乙醇混合燃料来改变燃料敏感性。结果表明,在PPC模式下(-25°CA ATDC),火焰发展过程是从近壁面区域开始着火,而后向燃烧室中心发展,即存在类似火焰传播过程,同时在燃烧室下部未燃区域也形成新的着火自燃点。敏感性对燃烧相位影响较大,对缸内燃烧火焰发展历程影响较小;高敏感性燃料OH和CH带状光谱出现的时刻推迟,表明高敏感性燃料高温反应过程推迟,且光谱强度更低,表明碳烟辐射强度减弱。在PPC到CDC之间的过渡区域(-15°CA ATDC),燃烧火焰发光更亮,燃烧反应速率比-25°CA ATDC时刻的反应速率更快。高、低敏感性燃料对缸压放热率的影响规律与-25°CA ATDC相近,此时的燃烧反应更剧烈,放热率更高,碳烟出现时刻更早。该喷油时刻下的光谱强度高于PPC模式下的光谱强度,说明此时的CO氧化反应与碳烟辐射更强。在CDC模式下(-5°CA ATDC),由于使用的燃料活性较低,燃烧放热时刻过于推迟,放热量很小,缸内燃烧压力低,因此燃料敏感性对缸压和放热率的影响不明显,但从燃烧着火图像中可以看到高敏感性燃料的火焰出现时刻较低敏感性燃料推迟。低敏感性燃料的燃烧初期蓝色火焰首先出现在燃烧室中心,着火火焰出现时刻更早,之后蓝色火焰从中心向周围扩散,呈现火焰传播为主导的燃烧过程;燃烧后期,局部混合气过浓区导致亮黄色火焰面积逐渐增大并向周围扩散。高敏感性燃料的火焰发展趋势与低敏感性燃料类似,黄色火焰的亮度与面积更小。尽管高、低敏感性燃料的OH和CH带状光谱的出现时间相近,但高敏感性燃料的光谱强度仍更低。综合分析,火焰发展结构与自发光光谱特征主要受喷油时刻的影响,燃料的敏感性主要影响着火时刻和火焰自发光光谱强度,且高敏感性燃料的光谱强度更低。     

NH3/H2预混旋流火焰稳定性及燃烧极限实验研究

采用叶轮型旋流燃烧器,选取氢气作为燃料添加剂,研究了掺氢比对氨气旋流火焰稳定性的影响,分析了不同旋流数、叶片数、当量比以及预混气总流量条件下,旋流火焰形态变化。测定并分析了不同参数对旋流火焰燃烧极限范围的影响。结果表明,随掺氢比的增大,火焰逐渐由“V”型转化为稳定的“M”型,燃烧反应愈发充分;高旋流数(1.27)或低叶片数(6片)相比低旋流数(0.42)或高叶片数(8片)更有利于旋流火焰的稳定和燃烧的充分进行;相比富燃,贫燃有利于形成稳定的旋流火焰;预混气总流量较大时,火焰高度较高.对于燃烧极限,掺氢比越高,极限范围越大;总流量的变化对贫燃极限影响较小,对富燃极限影响较大;高旋流数(1.27)条件下,燃烧极限范围较大。     

Combustion of partially premixed spray jets

Gas turbines, liquid rocket motors, and oil-fired furnaces utilize the spray combustion of continuously injected liquid fuels. In most cases, the liquid spray is mixed with an oxidizer prior to combustion, and further oxidizer is supplied from the outside of the spray to complete diffusion combustion. This rich premixed spray is called “partially premixed spray.” Partially premixed sprays have not been studied systematically although they are of practical importance. In the present study, the burning behavior of partially premixed sprays was experimentally studied with a newly developed spray burner. A fuel spray and an oxidizer, diluted with nitrogen, was injected into the air. The overall equivalence ratio of the spray jet was set larger than unity to establish partially premixed spray combustion. In the present burner, the mean droplet diameter of the atomized liquid fuel could be varied without varying the overall equivalence ratio of the spray jet. Two combustion modes with and without an internal flame were observed. As the mean droplet diameter was increased or the overall equivalence ratio of the spray jet was decreased, the transition from spray combustion only with an external group flame to that with the internal premixed flame occurred. The results suggest that the internal flame was supported by flammable mixture through the vaporization of fine droplets, and the passage of droplet clusters deformed the internal flame and caused internal flame oscillation. The existence of the internal premixed flame enhanced the vaporization of droplets in the post-premixed-flame zone within the external diffusion flame.     

用光谱诊断技术测定高能单元推进剂的温度分布

采用光谱诊断技术中的相对强度法测定了单元推进剂六硝基六氮杂异伍兹烷(HNIW)在3 MPa和5 MPa两种压力下的燃烧火焰温度分布。结果表明,相对强度法能准确地测出单元推进剂HNIW在整个燃烧过程的温度分布曲线,测得的最高燃烧火焰温度低于相应压力下的理论计算温度;测量压力升高,最高燃烧火焰温度更接近于理论计算温度。此实验结果说明：在较高压力条件下,用相对强度法能够准确地测定高能高燃速推进剂的燃烧火焰温度分布。     

一种测量发光火焰温度的数据处理方法研究

火焰温度是燃烧诊断的重要参数之一,它对研究各种燃烧过程具有重要价值。根据多光谱辐射测温所用的参考温度数学模型,提出了一种基于遗传算法的新的数据处理方法。该方法对火焰发射率与波长的关系依次进行了三点直线拟合,并通过遗传算法进行了优化,从而得到了发光火焰的温度和发射率。采用多波长高温计测量了某种固体推进剂燃烧火焰的自辐射光谱,并进行了数据处理。计算结果表明:火焰温度计算值与理论值之差在±100K以内;这种基于遗传算法的新的数据处理方法是测量发光火焰温度的一种可行性方法。     

CS2燃烧火焰光谱辐射模型的构建与特征污染产物浓度反演研究

CS₂在当今化工等领域占据了重要地位,而CS₂火灾污染事故危害性极大。通过研究CS₂燃烧火焰光谱辐射以探究其火灾污染特性极为必要。搭建了CS₂燃烧火焰光谱测试平台,采用黑体辐射源对VSR仪器进行了标定,通过多用途傅里叶变换(VSR)红外光谱辐射仪测试了5,10和20 cm三种燃烧尺度下CS₂燃烧的火焰光谱,并通过热电偶测试了整个燃烧时间段内不同燃烧时刻下的火焰温度,以及在火焰上方安装了烟气分析仪对火焰中的燃烧产物浓度进行监测。测量了CS₂整个燃烧时间段内火焰温度,以及不同燃烧时间、不同燃烧尺度下的火焰光谱、燃烧产物组分信息。测试结果表明,CS₂火焰中主要含有高温SO₂,CO₂,CO气体和空气中卷入的H₂O分子,并获取了特征污染产物SO₂的浓度。由于现有光谱仪测量分辨率有限,室内实验测量的火焰尺度有限,为了能实现火灾在线监测需要建立一个火焰光谱辐射模型来反演CS₂火灾时的污染物浓度相关信息。基于HITRAN数据库可知在2.7 μm附近为高温水蒸气的发射峰,4.2 μm附近特征峰为高温CO₂气体的发射峰,4.7 μm附近有CO微弱的发射峰,在7.4 μm附近特征峰为高温SO₂气体的发射峰,并获得了CS₂燃烧时产生的SO₂,CO₂,CO和H₂O气体在火焰燃烧相同温度下的吸收系数,通过计算得到了CS₂燃烧时产生的SO₂,CO₂,CO和H₂O混合气体的透过率与发射率,并结合气体辐射传输方程、气体吸收系数等方程,创建了CS₂燃烧的火焰光谱辐射模型。利用该光谱辐射模型反演了不同燃烧时间下特征污染产物SO₂的浓度,并与实验测得的数据进行了对比分析。结果表明,该模型精度高,可用于燃烧产物浓度的定量化反演,SO₂分子含量在燃烧时间20,40,60和80 s时的反演精度分别是89.5%,82.5%,85.6%和86.5%。为遥感反演CS₂型大尺度火灾中燃烧产物的浓度奠定基础。     

低功率电弧放电辅助甲烷燃烧的实验研究

利用低功率电弧放电辅助甲烷燃烧,研究了在不同甲烷/空气比例的情况下,等离子体对甲烷燃烧的影响。采用发射光谱仪进行光谱诊断,比较有/无等离子体辅助甲烷燃烧火焰发射光谱的异同,讨论了等离子体辅助燃烧可能发生的过程和机理。比较有/无等离子体辅助甲烷燃烧火焰温度的变化。利用气相色谱和烟气分析仪对甲烷燃烧产物中的CH₄、CO 和O₂ 进行分析。实验结果表明,加等离子体后,火焰的温度升高,尾气中的可燃性成分减少,氧气含量降低,在很大程度上提高了甲烷的燃烧效率;甲烷/空气的比例越低,燃烧效率的提高越明显;甲烷的富燃燃烧极限从16%调高到21%。     

湿空气扩散燃烧火焰结构特性研究

利用二维粒子成像速度仪(PIV)对钝体燃烧器中的甲烷／湿空气扩散燃烧的速度场进行测量,考察其火焰的结构特性及其内部流动状况。通过对湿空气燃烧流场与普通燃烧流场的对比分析表明,湿空气燃烧情况下,两种燃烧状态的火焰(回流燃烧火焰和中心射流主导火焰)相互转换的燃空速度比(γ)值要比普通燃烧的小;湿空气燃烧使得喷嘴后的同流空气的速度降低,空气的回流作用减弱,燃料更容易冲出回流区,火焰的稳定性能变差。