试样宽度对RPU板竖向逆流火蔓延的影响

以2cm厚硬质聚氨酯(RPU)保温板为研究对象,实验研究了试样宽度对竖向逆流燃烧蔓延过程中火焰高度、脉动频率、火焰温度及蔓延速度等特征参量的影响.结果表明,宽度一定时相关特征参量不随时间变化,随着宽度的增加,燃烧程度逐渐加剧,火焰脉动频率先增大后减小,平均火焰高度与火蔓延速度的变化趋势基本一致,均表现为先增大后减小,最终趋于不变,而气相火焰最高温度基本保持不变.     

液化石油气层流燃烧火焰特性分析

应用实验测试的方法对常温常压下不同配比的液化石油气/空气的燃烧特性进行研究,获得了水平管内火焰传播速度、火焰中心温度、火焰高度等随着液化气体积分数的变化规律。结果表明:火焰传播速度随着液化石油气体积分数的增大先增大后减小,最大值出现在体积分数为2. 78%处,即当量比为0. 98;不同燃烧方式火焰中心温度沿高度方向变化规律不同,扩散火焰的温度分布均匀;半预混火焰温度沿高度方向先上升后下降;全预混火焰中心温度随火焰高度的增加而下降;火焰高度随着液化石油气体积分数变化而变化,在当量比小于1时,火焰高度随着液化石油气体积分数的减小而降低,当接近化学当量比时达到最低;当量比大于1后,随着液化石油气体积分数减小,火焰高度增加。     

当量比对锥形燃烧器火焰稳定位置影响

为了探究当量比对锥形燃烧器头部火焰稳定位置及排放特性的影响,采用数值模拟方法对锥形燃烧 器的流动与燃烧特性进行研究。分析讨论了当量比从0. 54增加至0. 78时燃烧器头部的火焰锋面位置与高 温区温度的变化规律,以及不同当量比下火焰指数、NOx与C0排放量的变化趋势。研究结果表明,速度分布 与回流区特征随当量比升高未见明显变化。随着当量比升高,高温区的最高温度逐渐升高,火焰稳定位置向 燃烧器内部移动。当量比增加至0.66时开始发生回火,继续增加当量比时高温区贴近锥形燃烧器头部壁面 与喷嘴,有烧毁燃烧器的危险。NOx排放量随当量比增大而增大,当量比从0. 54增加至0. 66时,NOx排放量 缓慢增加,当量比继续增加至0.78过程中,NOx排放量迅速增加,NOx排放增加了 32.4倍。C0排放量随当 量比的增大先减小后增大,并在当量比为0.66时达到最小值     

生物质燃气预混层流燃烧特性的实验研究

在密闭燃烧容器中对常温、常压环境下的生物质燃气预混层流燃烧特性进行了实验研究,研究了不同燃气组分、不同当量比对生物质燃气预混层流火焰传播速度、火焰表面拉伸率和层流燃烧速度的影响规律。研究结果表明:发酵法制取的生物质燃气中甲烷含量越高,其层流火焰传播速度就越快;相同尺寸的火焰锋面上拉伸率越大,层流燃烧速度则越快;随着当量比的增大,层流火焰传播速度、层流燃烧速度呈现出先增大后减小的趋势。     

预燃室火焰射流对双燃料着火燃烧过程的模拟研究

基于计算流体力学(CFD)程序耦合动力学机理,研究了一台大型低速二冲程船用柴油机改装的柴油-天然气双燃料发动机预燃室系统的布置方案对射流火焰发展过程的影响,以及由此对缸内流动、燃烧和有害污染物氮氧化物(NO_x)生成历程的影响。结果表明:预燃室方案造成射流火焰对撞会对碰撞区域及周围流场产生较大扰动,同时在碰撞区域形成富燃区,抑制该区域内NO_x的生成;射流火焰不碰撞则会增大其贯穿距离,实现更大空间范围的多点着火,放热更集中,同时会因较高的温度使NO_x排放上升;此外射流火焰与缸盖、活塞和缸套等壁面接触会显著降低其流动速度和燃烧温度,造成燃烧效率下降,缸内湍动能减小,在实际应用中应尽可能避免。     

甲烷-空气预混火焰稳定特性的实验研究

基于本生灯实验,测试分析了甲烷-空气预混火焰的稳定燃烧特性。试验研究了预混气体火焰闪回和吹熄极限随燃空当量比的变化关系。研究发现,甲烷-空气混合气体的闪回极限的最大值出现在接近化学当量比处,并且呈现出类似抛物线的变化规律;而火焰的吹熄极限随着当量比的增加而逐渐增大。试验通过采用13 mm和11 mm两种不同口径的本生灯,研究了本生灯孔径对甲烷-空气预混火焰的稳定燃烧区间的影响关系,实验证明,随着孔径的增大,闪回极限将会减小,而吹熄极限随之增大。通过实验获取这些参数,能够为设计和优化燃烧系统提供理论支撑。     

圆周运动下移动火源扩散火焰的图像特性分析

为了预测和控制移动火源扩散火焰的燃烧,对火焰图像特性的影响因素和规律进行研究.通过高速摄像仪,实时记录移动火源扩散火焰在圆周运动下的形态特征,利用力场分析和MATLAB工具,得到火焰面积随火焰线速度的变化规律以及火焰倾角随火焰线速度的变化.研究发现,燃烧产生热量和气流散热两者综合地导致火焰面积随着线速度的递增而先增大后减小;随着火焰线速度的增大,刚开始火焰倾角升幅较快,后趋于平缓;火焰内外温差会影响浮升力的大小,进而影响燃烧的稳定性.     

基于波瓣旋流燃烧器的甲烷燃烧污染物排放特性

贫燃预混燃烧方式是抑制燃烧过程中NO_x生成的方法之一,但易出现燃烧不稳定现象.针对这一问题,试验采用波瓣旋流燃烧器,研究了当量比、预混气分级比、预混气分级形式对NO_x和CO排放规律、燃烧室声压峰值及火焰形态的影响.结果表明,随着当量比的减小,烟气中NO_x浓度减小,而CO浓度上升.旋流侧流量/波瓣内侧流量减小时,烟气中NO_x浓度降低,CO浓度增大.通过调节旋流器和波瓣外侧预混气分级比,NO_x和CO的排放浓度都有所下降,并在旋流侧流量、波瓣内侧流量、波瓣外侧流量分级比为6∶0∶4时浓度较低.燃烧室内声压峰值随当量比的减小而增大.当量比为0.60,预混气分级比为5∶0∶5时,燃烧室声压峰值最低,燃烧较为稳定.     

生物质燃油燃烧特性分析

以小桐子油、小桐子生物柴油、地沟油、地沟油生物柴油、0#柴油作为研究对象,对这5种燃油的黏温特性进行了探究分析,同时在自行搭建的雾化燃烧试验平台研究燃油在炉内燃烧火焰体积、长度及火焰温度变化规律,试验结果表明燃烧温度越高,生物质燃油和0#柴油的运动黏度均减小,地沟油减少幅度最大为81.75%;试验条件相同情况下,0#柴油的火焰长度最大为288.209 mm,地沟油火焰长度的最小为207.814 mm,5种燃油燃烧温度在轴线方向先上升后下降,在径向方向波动较大;在不同工况下,随过量空气系数α或雾化压力p的增大,生物质燃油和0#柴油燃烧火焰体积及火焰长度均呈下降趋势;燃油火焰平均温度的变化趋势随过量空气系数α增大先增大后减小,随氧体积分数的增大一直上升,小桐子油增幅最大为25.90%.     

反应速率对层流扩散火焰特性的影响

为探究燃烧过程中火焰结构和烟黑特性的变化规律,对层流乙烯/空气扩散火焰进行了数值模拟,分析了不同成核过程和表面生长过程中,反应速率常数的指前因子及活化能对层流乙烯/空气扩散火焰温度和烟黑体积分数的影响。结果表明：成核反应速率常数中,指前因子增大,火焰温度降低,烟黑体积分数增大,当指前因子提高50%时,在轴向高度3 cm位置对应的火焰温度峰值减小0.70%,烟黑体积分数的峰值增大37.98%;活化能增加,火焰温度增大,烟黑体积分数减小,当活化能提高50%时,在轴向高度3 cm位置对应的火焰温度峰值增大3.41%,烟黑体积分数的峰值减小78.92%;表面生长反应速率常数中,指前因子增大,火焰温度逐渐减小,烟黑体积分数逐渐增大,当指前因子提高50%时,在轴向高度3 cm位置对应的火焰温度峰值减小2.03%,烟黑体积分数的峰值增大1.65倍;活化能增加,使火焰温度升高,烟黑体积分数减小,当活化能提高50%,在轴向高度3 cm位置对应的火焰温度峰值增大9.61%,当活化能提高12.5%,烟黑体积分数的峰值减小46.68%。     

旋流对天然气高温空气燃烧特性影响的数值模拟

以工业炉的高温空气燃烧技术应用为背景,对一个新型轴向旋流式单烧嘴燃烧室内天然气的高温空气燃烧特性进行了数值研究。采用数值模拟的方法研究了同心式轴向旋流燃烧器（HCASbumer）中螺旋肋片的旋转角度对燃烧特性的影响,其中湍流采用Reynolds应力模型,气相燃烧模拟采用β函数形式的PDF燃烧模型,采用离散坐标法模拟辐射换热过程,NOx模型为热力型与快速型。计算结果表明,对预热空气采用旋转射流时,能明显降低NOx生成量。对于HCAS型燃烧器,随着空气射流旋转角度的增大,燃烧室内的回流区域增大增强,降低了局部的氧体积分数分布,燃烧室中平均温度和最高温度都有所增加,且燃烬程度大幅度提高,而局部高温区缩小,只在靠近入口处出现。总的NOx排放量随着空气射流旋转角度的增大先减小,后增大。因此,适当调整肋片的旋转角度可以降低NOx生成量。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

旋流预混燃烧室燃烧特性及排放特性的数值模拟研究

为了综合考察燃气轮机燃烧室在高稳定性、低排放以及燃料适应性等方面的新要求,基于旋流预混燃烧技术,通过三维数值模拟方法开展了甲烷/空气、丙烷/空气预混燃烧特性及排放特性研究。结果表明：在一定的预混气进气质量流量条件下,当量比增大易引发回火,燃烧温度更高,同时NO_x排放指数增大,增加预混气质量流量,可在一定程度上提高回/熄火极限;当量比固定,增加预混气进气质量流量可避免潜在的回火现象,且NO_x排放指数线性降低;旋流器的旋流数增大能形成强旋流,稳定火焰,降低NO_x排放指数,但过大的旋流强度会引发回火现象;相比于甲烷/空气预混燃烧,丙烷/空气预混燃烧温度偏高,NO_x排放指数较大,但回熄火边界更宽,对应更广阔的稳定燃烧区间。     

零碳燃料对燃气锅炉燃烧过程调控作用

利用小型化模拟炉膛开展了零碳燃料氢气对燃气锅炉燃烧过程调控作用实验研究,研究了掺氢比对炉膛内部预混火焰宏观形态、炉膛温度均匀性、炉膛污染物排放规律的影响,并总结了CO及NO_x的排放规律。实验结果表明：随着预混当量比增加,纯甲烷火焰长度逐渐缩短;对于20%掺氢火焰,随着预混程度的提高,火焰长度降低明显;不同火焰条件下,炉膛温度只由燃烧功率控制;改变燃烧条件时,处于壁面附近位置的温度变化较为平稳,而靠近火焰处温度变化较大;天然气中掺入氢气,燃烧时可以有效降低未燃CO排放;在相同预混程度下,全局当量比减小导致未燃空气增加,热量被稀释,火焰温度降低,热力型NO_x的生成降低;随着掺氢比的增加,燃烧时火焰温度升高,导致热力型NO_x排放增加。     

锅炉燃烧调整对NOx排放和锅炉效率影响的试验研究

在2台典型的1025 t/h锅炉上进行了燃烧调整降低NOx排放浓度的试验研究,通过改变过量空气系数、辅助风配风方式、运行负荷和制粉系统运行方式等,测定了锅炉尾部烟道NOx排放浓度,分析了锅炉运行工况、运行方式对NOx排放的影响.结果表明:降低过量空气系数,烟煤锅炉NOx减排效果比贫煤锅炉好得多;降低负荷,烟煤锅炉的NOx排放量降低值较大;缩腰式配风的NOx排放浓度比均匀配风方式约降低10%,制粉系统的运行方式影响炉内燃料的燃烧状态和温度分布,也影响NOx的生成和排放.在不降低锅炉效率的前提下,调整燃烧工况,可降低锅炉排放NOx浓度1O%～20%.     

The decreasing effect of ammonia enrichment on the combustion emission of hydrogen,methane, and propane fuels

In the present study, non-premixed combustion and NOx emission of H₂, NH₃, C₃H₈, and CH₄ fuels have been studied in a combustion test unit under lean mixture conditions (λ = 4) at 8.6 kW thermal capacity. Furthermore, the combustion and NOx emission of the H₂, C₃H₈, and CH₄ fuels have been investigated for various NH₃ enrichment ratios (5, 10, 20, and 50%) and excess air coefficients (λ = 1.1, 2, 3, and 4) at the same thermal capacity. The obtained results have been compared for each fuel. Numerical simulation results show that H₂ emits intense energy through the reaction zone despite the lowest fuel consumption in mass, among others, due to its high calorific value. Therefore, it has a higher flame temperature than others. At the same time, C₃H₈ has the lowest flame temperature. Besides, NH₃ has the shortest flame length among others, while C₃H₈ has the most extended flame form. The highest level of NOx is released from the NH₃ flame in the combustion chamber, while the lowest NOx is released from the CH₄. However, the lowest NOx emission at the combustion chamber exit is obtained in NH₃ combustion, while the highest NOx emission is obtained with H₂ combustion. It results from the shortest flame length of NH₃, short residence time, and backward NOx reduction to N₂ for NH₃. As for H₂, high flame temperature and relatively long flame, and high residence time of the products trigger NOx formation and keep the NOx level high. On the other hand, excess air coefficient from 1.1 to 2 increases NOx for H₂, CH₄, and NH₃ due to their large flame diameters, unlike propane. Then, NOx emission levels decrease sharply as the excess air coefficient increases to 4 for each fuel. NH₃ fuel also emits minimum NOx in other excess air coefficients at the exit, while H₂ emits too much emission. With NH₃ enrichment, the NOx emissions of H₂, CH₄, and C₃H₈ fuels at the combustion chamber exit decrease gradually almost every excess air coefficient apart from λ = 1.1. As a general conclusion, like renewable fuels, H₂ appears to be a source of pollution in terms of NOx emissions in combustion applications. In contrast, NH₃ appears to be a relatively modest fuel with a low NOx level. In addition, the high amount of NOx emission released from H₂ and other fuels during the combustion can be remarkably reduced by NH₃ enrichment with an excess air combustion.     

燃料掺混方式对天然气柔和燃烧器燃烧性能的影响研究

燃气轮机在更高参数下的低污染排放限制和宽工况范围稳定运行的需求,对燃烧室燃烧提出了新的要求。柔和燃烧作为一种新型燃烧技术,具有燃烧稳定和污染物排放低的优势。高速射流引射掺混是实现柔和燃烧所需条件的一种可行方式。本文主要研究不同燃料掺混方式对柔和燃烧器污染物排放和稳定工作范围的影响。在前期工作基础上设计了可实现燃料不同掺混方式的天然气柔和燃烧器。在常压条件下,通过实验研究了不同当量比、不同燃料/空气掺混方式下天然气柔和燃烧器的污染物排放,并研究了不同掺混方式对燃烧贫燃极限的影响,通过OH~*自发荧光、OH平面激光诱导荧光测量和数值模拟对反应区和流场结构进行了观察和分析。实验结果表明,在相同当量比下,全预混模式下的NO_x排放最低,全预混模式下稳定燃烧的贫熄火当量比为0.57;扩散模式下NO_x排放相对高,但贫熄火当量比可低至0.15,燃烧稳定范围更宽;混合模式下污染物排放水平介于预混和扩散模式之间;非预混模式下较好的贫燃火焰稳定性得益于燃烧室头部扩散燃料周围形成的低速稳定反应区。     

The regulation effect of methane and hydrogen on the emission characteristics of ammonia/air combustion in a model combustor

Ammonia, made up of 17.8% hydrogen, has attracted a lot of attention in combustion community due to its zero carbon emission as a fuel in gas turbines. However, ammonia combustion still faces some challenges including the weak combustion and sharp NOx emissions which discourage its application. It was demonstrated that the combustion intensity of ammonia/air flame can be enhanced through adding active fuels like methane and hydrogen, while the NOx emission issue will emerge in the meantime. This study investigates regulation effect of methane and hydrogen on the emission characteristics of ammonia/air flame in a gas turbine combustor. The instantaneous OH profile and global emissions at the combustion chamber outlet are measured with Planar Laser Induced Fluorescence (PLIF) technique and the Fourier Transform Infrared (FTIR), respectively. The flames are also simulated by large eddy simulation to further reveal physical and chemical processes of the emissions formation. Results show that for NH₃/air flames, the emissions behavior of the gas turbine combustor is similar to the calculated one-dimensional flames. Moreover, the NOx emissions and the unburned NH₃ can be simultaneously controlled to a proper value at the equivalence ratio (φ) of approximate 1.1. The variation of NO and NO₂ with φ for NH₃/H₂/air flames and NH₃/CH₄/air flames at blending ratio (Z_f) of 0.1 are similar to the NH₃/air flames, with the peak moving towards rich condition. This indicates that the NH₃/air flame can be regulated through adding a small amount of active fuels without increasing the NOx emission level. However, when Z_f = 0.3, we observe a clear large NOx emission and CO for NH₃/CH₄/air flames, indicating H₂ is a better choice on the emission control. The LES results show that NO and OH radicals exhibit a general positive correlation. And the temperature plays a secondary role in promoting NOx formation comparing with CH₄/air flame.     

CFD study on influence of fuel temperature on NOx emission in a HiTAC furnace

The influence of the fuel temperature on NOx formation was investigated numerically. For this purpose CFD modeling of NOx emission in an experimental furnace equipped with high temperature air combustion (HiTAC) system was studied. The comparison between the predicted results and measured values have shown good agreement, which implies that the adopted combustion and NOx formation models are suitable for predicting the characteristics of the flow, combustion, heat transfer, and NOx emissions in the HiTAC chamber. Moreover the predicted results show that increase of the fuel temperature results in a higher fluid velocity, better fuel jet mixing with the combustion air, smaller flame and lower NOx emission.     

The CFD Modeling of NOx Emission,HiTAC and Heat Transfer in an Industrial Boiler

NOx emission, heat transfer, and high temperature air combustion (HiTAC) in a boiler of Mobin Petrochemical Complex, Iran was numerically studied. The comparison between the measured values and the CFD predicted results showed good agreement, which implied that the adopted combustion and NOx formation models are suitable for correctly predicting characteristics of the heat recovery steam generation (HRSG) boiler. The predicted results show that NOx emission within the boiler depends highly on temperature, as well as oxygen concentration. Moreover, the influence of the equivalence ratio at a fixed air mass flow rate on the flame temperature and NOx formation has been investigated.