掺混甲烷对预混合乙烯火焰碳烟粒径分布的影响

本文以当量比为1.9、模拟最高火焰温度为1727K的乙烯预混火焰为基准,在燃料中分别掺混5%、20%和35%摩尔分数的甲烷,保持当量比和最高火焰温度不变,采用稳定滞止(Burner Stabilized Stagnation,BSS)火焰小孔采样结合扫描电迁移率粒径谱仪(Scanning Mobility Particle Sizer,SMPS)的实验方法,在不同火焰高度上定量测量其生成碳烟颗粒的粒径分布(Particle Size Distribution Function,PSDF),探究掺混甲烷对乙烯预混火焰成烟特性的影响。实验发现,随着甲烷掺混比的增加,生成碳烟颗粒的成核与长大速度越来越小。在所研究的预混火焰工况条件下,乙烯与甲烷在碳烟生成特性方面并不存在协同效应。     

吸收光谱法冲压发动机隔离段来流质量的流量测量

为实现冲压发动机地面直连试验中来流质量流量的测量校核,研制了吸收光谱法测量系统并开展了台架验证试验。首先,介绍了基于隔离段温度、流速测量计算质量流量的原理,针对台架试验环境适应性、长期工作稳定性问题,介绍了测量系统和光机设计方案,然后介绍了波长标定、温度与流速反演关键算法。在Ma6.5,6.0kg/s流量状态两个独立车次台架试验吸收光谱法计算质量流量的最大偏差为5%,验证了所提出方法的可行性。该方法为吸气式发动机来流状态的精细测量提供了新的方案和技术手段,未来可望用于来流捕获的实时反馈控制。     

隔离段内激波位置对TDLAS测量结果影响规律研究

可调谐半导体激光吸收光谱技术(TDLAS)可以实现流场多组分、多参数的测量,具有其极强的环境适应性,可以用于超燃冲压发动机流场测量。为了研究超燃冲压发动机流场中激波对TDLAS测量的影响,利用计算流体力学方法(CFD)模拟了四种马赫数条件下的斜坡流场分布,采用双谱线测温法获得垂直于流道方向每条光线的平均温度。分析了温度测量结果与激波分布的关系,给出了TDLAS光学探头测量位置的建议。本文得到的结论对TDLAS工程应用和测量结果分析具有重要的参考意义。     

基于TDLAS的同轴扩散火焰温度与CO_2浓度测量

温度与组分浓度的空间分布对火焰中多环芳烃和碳烟生成机理的研究非常重要。本文基于可调谐二极管激光吸收光谱(TDLAS)技术对甲烷同轴扩散火焰温度与CO_2浓度的空间分布进行测量。针对轴对称的同轴扩散火焰,本实验采用4.2μm的中红外带间级联激光器测量了不同火焰高度上路径积分的吸光度谱线,并通过傅里叶分析Abel逆变换方法重建出各点的光谱吸收率谱线。结合HITEMP数据库,通过最小二乘法拟合实验数据得到火焰温度与CO_2浓度,并将TDLAS测量结果同CFD仿真进行比较。发现TDLAS温度与CO_2浓度测量结果与CFD仿真吻合良好,但由于未能全面考虑辐射效应,CFD仿真高估了最大火焰温度,计算的最大CO_2浓度和火焰面高度偏低。     

利用平面激光诱导荧光技术及CH滤镜测量微喷管射流火焰OH及CH基元

微射流火焰形貌观测及火焰中重要基元的准确测量,对利用微尺度火焰燃烧特性研制开发微型燃烧动力系统具有重要意义。本文建立了微喷管射流火焰实验及光学测量系统,对H_2和CH_4微射流火焰进行了实验研究,测量了两种重要基元(CH,OH)的空间分布。首先,探索了相机曝光时间对H_2微射流火焰成像的影响,得到了不同流速下H_2微射流火焰形貌的变化规律。其次,采用平面激光诱导荧光测量技术得到了不同燃料流速下H_2及CH_4微射流火焰中OH基元分布,同时还利用单反相机加CH滤镜通过长时间曝光(30s)的方法获得了CH_4微射流火焰中CH基元的分布。结果表明,火焰图像清晰度随曝光时间增加提高,曝光时间30s时可获得H_2微射流火焰的清晰照片;采用分辨率2 048×2 048的ICCD相机可获得微尺度火焰OH基元分布的清晰图像。微射流火焰形貌及重要基元的实验结果表明相关数值计算方法准确可靠。     

石墨炉原子吸收光谱法固体样品直接分析--重晶石中痕量重金属的测定(续)

3 .4　方法比较　固体进样一石墨炉原子吸收光谱法和微波消解石墨炉原子吸收光谱法或火焰原子吸收光谱法的方法比较。用固体进样 -石墨炉原子吸收光谱法可以在较宽的浓度范围内测定重晶石中的 7种微量元素 ,为克服吸收光谱较窄的“线性工作范围” ,选择灵敏度较低的特征吸收线或在原子化阶段用适中的惰性气体流速 (氩气 ,0 .1 5Ｌ/ｍｉｎ) ,会降低光度计灵敏度。校正是用和重晶石不同基体的固体标准样品 (已认证参考物质ＣＲＭｓ) ,因为没有已知重金属浓度的重晶石标准样品。为寻找合适的校正标准样品和了解基体效应 ,采用两种或两种以上的…     

基于激光吸收光谱的SF_6/N_2混合气分解产物同时检测

针对SF_6分解气中H_2S、CO、HF等3种气体进行在线监测,研制基于激光吸收光谱的SF_6分解气在线监测装置,提出采用时分复用的方案实现多组分气体同时测量,对激光器的波长参数进行分析并测试。针对近红外波段CO和H_2S气体吸收谱线弱的问题,提出独立放大电路方案,研制样机并通入混合组分气体进行验证。根据获得二次谐波曲线和浓度随时间变化曲线表明,该系统目前可以实现的检测限为CO 10 ppm,H_2S 4 ppm,HF 1 ppm,可以满足高灵敏度SF_6分解气在线监测和故障预警需求。     

原子捕集法原子吸收光谱分析

常规火焰原子吸收光谱法具有装置简单、分析速度快、测量精度高、基体效应小等优点,在各个领域中得到广泛应用。但是,由于火焰法的雾化效率低(大约只有10％的溶液进入火焰),原子在火焰中停留时间短(约10~(-3)秒)等原因,限制了火焰原子吸收光谱法的灵敏度。原子捕集是一种在火焰中浓缩待测原子的预富集技术,它能提供极高的原子密度供原子吸收(或荧光)测量。与溶剂萃取或离     

激光气体检测及温压补偿研究

可调谐半导体激光吸收光谱(TDLAS)是一种灵敏度高、分辨力高和响应快速的气体测量技术,基于(TDLAS)的激光气体分析仪具有预处理简单、不受背景气体和粉尘影响的特点,是工业过程气体在线分析理想选择。本文介绍了波长调制的吸收光谱浓度测量原理以及实际工况下浓度的温压补偿方法。     

燃烧加热污染空气对超燃冲压发动机性能影响研究

针对燃烧加热地面试验设备存在的工质污染问题,采用数值模拟方法研究了燃烧加热污染空气对氢燃料超燃冲压发动机性能的影响。以飞行马赫数Ma=6.5,当量油气比ER=0.6为计算基准状态,分别对纯净空气和污染空气来流下氢燃料超燃冲压发动机的整机流场和性能进行了对比计算分析。燃烧化学反应模拟采用了改进的H₂/O₂七组分八方程模型,湍流模型为标准的 k-ε模型,并采用直连式燃烧室试验数据进行了数值方法的验证。研究结果表明:(1)相对于纯净空气来流,污染空气来流下的超燃冲压发动机推力和比冲均有所下降。(2)采用酒精燃烧加热器的前提下,来流参数匹配静温、静压、马赫数时,发动机性能与纯净空气来流下的结果最为接近,而匹配总温、总压、马赫数时相差最大。(3)来流参数匹配总焓、静压、马赫数的前提下,采用氢燃烧加热器时发动机性能与纯净空气来流下的结果最为接近,而采用甲烷燃烧加热器时相差最大。      

Application of dfb diode laser sensor to reacting flow (II) —liquid-gas 2-phase reacting flow—

Diode laser sensor is conducted to measure the gas temperature in the liquid-gas 2-phase counter flow flame. C₁₀H₂₂ and city gas were used as liquid fuel and gas fuel, respectively. Two vibrational overtones of H₂O were selected and measurements were carried out in the spray flame region stabilized the above gaseous premixed flame. The path-averaged temperature measurement using diode laser absorption method succeeded in the liquid fuel combustion environment regardless of droplets of wide range diameter. The path-averaged temperature measured in the post flame of liquid-gas 2-phase counter flow flame showed qualitative reliable results. The successful demonstration of time series temperature measurement in the liquid-gas 2-phase counter flow flame gave us motivation of trying to establish the effective control system in practical combustion system. These results demonstrated the ability of real-time feedback from combustor inside using the non-intrusive measurement as well as the possibility of application to practical combustion system. Failure case due to influence of spray flame was also discussed.     

拉瓦尔式燃料流量调节阀流量特性分析

燃料供给的实时、精确调节是冲压发动机技术研究的重点,对提高发动机的效率、改善发动机的工作性能具有重要的意义。为实现冲压发动机气态燃料在高温下流量的精确调节,提出了一种新型的拉瓦尔式燃料流量调节阀,以对流入发动机燃烧室的高温气态燃料进行流量调节。首先,开发了一种用于燃料供应的高温流量调节阀,然后通过采用有限元分析方法,分析了流经主阀阀口的气态燃料速度及压力的分布,从而找出了流量变化规律。研究结果表明,采用拉瓦尔管状阀口的流量调节阀,在不改变阀芯位移量以及一定入口压力条件下,流经阀口的燃料流量保持不变,且与出口压力无关。     

Application of DFB diode laser sensor to reacting flow (I)- estimation and application to laminar flames -

Diode laser sensor for measuring gas temperature and species concentration in combustion chamber was developed using 2.0 μm distributed teed back lasers. To evaluate the measurement sensitivity of diode laser sensor system, CO₂ survey spectra near 2.0 μm were measured and compared with the calculated one. This diode laser absorption sensor was applied to measure gas temperatures in a premixed flat flame of CH₄-air mixture. Experimental results were in good agreement with the values by an R-type thermocouple within 6.12%. In addition, successful demonstration of measurement of gas temperature and species concentration in a soot flame showed the promising possibility of diode laser absorption sensors for practical combustion system with non-intrusive method.     

Time resolved 2D concentration and temperature measurement using CT tunable laser absorption spectroscopy

In this study, the noncontact and simultaneous 2D temperature and concentration measurement method has been developed to elucidate the reaction characteristics and improve the relevant simulation code. The technique is based on a CT method using absorption spectra of molecules such as H₂O, NH₃ and CH₄. The CT Tunable diode laser absorption spectroscopy (TDLAS) method using 16-path laser beams was applied to measure 2D temperature, NH₃ and CH₄ distributions in engine exhausts and oscillating flames. Simultaneous and time resolved 2D temperature, NH₃ and CH₄ distributions were successfully reconstructed using a set of 16-path absorption spectra. Since CT TDLAS has a potential of kHz response time, this method enables real-time 2D temperature and species concentration measurements in various industrial processes including engine applications.     

基于燃料热力学性质的液冲发动机性能预示

文中针对液体亚燃冲压发动机进行了性能建模,并引入了真实燃料特性和热力计算模型,针对常用的JP-4、JP-5,JP-10,RP-1和Jet-A液体燃料开展了发动机性能对比,分析了燃料当量比以及飞行马赫数和高度对发动机性能的影响规律。研究结果表明:采用JP-4液体燃料的发动机性能比采用其它燃料的好;考虑发动机性能、热防护性能以及燃料本身的裂解和积炭特性,选取0.6~0.7的当量比较合适;无论飞行高度如何,发动机比冲在马赫数3.5附近达到最大,飞行高度增加,比冲性能也会增加。     

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.

     

飞机尾流温度场测量与数值模拟

采用有限体积法,对某型发动机尾喷管三维流场及温度场进行了数值计算,分析了不同发动机状态下尾流温度场特性.结合CFD结果,研制了一套用于测量高温、高速条件下的尾流测温系统,并应用于某型飞机尾流温度场测量试验,测取发动机全加力状态下的尾流温度分布,证实该计算及测量方法具有一定的工程应用价值.     

Piston crevice hydrocarbon oxidation during expansion process in an SI engine

Combustion chamber crevices in SI engines are identified as the largest contributors to the engine-out hydrocarbon emissions. The largest crevice is the piston ring-pack crevice. A numerical simulation method was developed, which would allow to predict and understand the oxidation process of piston crevice hydrocarbons. A computational mesh with a moving grid to represent the piston motion was built and a 4-step oxidation model involving seven species was used. The sixteen coefficients in the rate expressions of 4-step oxidation model are optimized based on the results from a study on the detailed chemical kinetic mechanism of oxidation in the engine combustion chamber. Propane was used as the fuel in order to eliminate oil layer absorption and the liquid fuel effect. Initial conditions of the burned gas temperature and in-cylinder pressure were obtained from the 2-zone cycle simulation model. And the simulation was carried out from the end of combustion to the exhaust valve opening for various engine speeds, loads, equivalence ratios and crevice volumes. The total hydrocarbon (THC) oxidation in the crevice during the expansion stroke was 54.9% at 1500 rpm and 0.4 bar (warmed-up condition). The oxidation rate increased at high loads, high swirl ratios, and near stoichiometric conditions. As the crevice volume increased, the amount of unburned HC left at EVO (Exhaust Valve Opening) increased slightly.     

Visualisation of fuel-lubricant interaction on the cylinder surface in the combustion chamber of SI engines

Visualisation of fuel component penetration and release into the lubricating oil layer covering the combustion chamber wall has been achieved, using a laser-induced fluorescence (LIF) test technique. Experimental data show that fuel component penetration into the oil layer contributes not only to unburnt hydrocarbon emissions in spark ignition (SI) engines, but also to engine oil degradation. Fuel components accumulated in the oil layer are transferred to the bulk in ring belt zones, after a measurable residence time. A significant difference in film thickness between the oil layer on the combustion-chamber wall during the intake/compression sequence, as against the expansion/exhaust sequence, indicates that in the ring belt zones and above, engine oil viscosity, and hence load-carrying capacity, is influenced by fuel absorption/desorption in the engine oil.     

EFFECTS OF INJECTION STRATEGY ON D.I. DIESEL ENGINE COMBUSTION

Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount of fuel injected between two injection pulses and the injection interval is varied keeping the injected fuel quantity constant. Results show that under the 70D90-10 injection pattern, the engine achieves the lower NOx-smoke emissions and BSFC compared with the single injection pattern. The heat release rate and the temperature show that the split injections increase the initial premixed burn and retards the diffusion burn. With the balance of these two effects, the maximum in-cylinder temperature decreases while the 50% heat release point is held at almost the same crank angle. Therefore, both NOx emission and BSFC are improved while keeping the smoke emission at the same level.