乙烷含量对天然气、煤层气燃烧速率和火焰稳定性的影响

本文在定容燃烧弹中,研究了高温高压(0.75 MPa,450 K)下甲烷-乙烷-空气预混合气火焰传播规律,并系统分析了当量比、混合气中乙烷含量对混合气层流燃烧及火焰稳定性的影响.实验结果表明:随着混合气中乙烷含量的增加,不同当量比下无拉伸火焰燃烧速率均增大,马克斯坦长度增大,表明火焰稳定性增强.在实验范围内,无拉伸火焰...     

富燃料丙烷/空气预混火焰特性的微重力实验研究

地面常重力(1g)条件下,丙烷/空气预混火焰向上传播的富燃极限为9.2%C_3H_8,而向下传播时的富燃极限仅为6.3%C_3H_8,二者之间存在明显差距。利用微重力条件下的实验,对燃料浓度从6.5%到8.6%(微重力实验中测定的可燃极限)范围内的丙烷/空气预混火焰特性进行了研究。实验发现,重力对近极限丙烷/空气火焰的传播有显著影响,影响程度随着当量比的增加而增大。微重力下丙烷/空气的富燃极限为8.6%C_3H_8(φ=2.24),明显高于1g条件下向下传播火焰的可燃极限,略低于向上传播火焰的可燃极限。随着当量比的增大,根据压力变化曲线计算的火焰层流燃烧速度从8.5cm/s逐渐减小到2.7 cm/s,可燃极限处的层流燃烧速度与前人实验数据一致。     

低热值燃料的滑动弧稳燃实验研究

利用旋流实验台进行了滑动弧稳燃低热值燃料的研究,并探究了滑动弧对低热值燃料的火焰特性及熄火极限的影响规律。实验结果表明：低热值燃料燃烧随着当量比变化可以分为五种典型火焰形态。滑动弧可缩短火焰长度,增大火焰张角,使火焰驻定位置靠近角涡回流区和剪切层,从而增强燃烧稳定性。随着滑动弧的加入,角涡火焰间歇消失的不稳定过渡形态得到了极大的改善。随着空气流量的增加,滑动弧的稳燃效果逐渐减弱。滑动弧可有效拓宽低热值燃料的熄火极限。在空气流量40L/min时,稳燃极限当量比最大拓宽了0.35,熄火极限最大拓宽了0.33。提高滑动弧的输入电压对低热值燃料的熄火极限拓宽明显。     

激波与火焰作用的实验与理论研究

采用高速摄影技术拍摄了等当量比的甲烷/空气预混气环境下,火焰与激波相互作用的时序照片,对实验结果进行了分析讨论。使用基于带化学反应的N-S方程和热力学数据,利用改进的VLS格式,对等当量比条件下甲烷/空气预混气中激波与火焰的相互作用进行了数值模拟,并利用光学知识,进行了计算光学的数值模拟。实验结果与数值计算结果进行了比较,两者符合得较好。     

较高当量比氢气空气预混合气的燃烧特性研究

利用纹影法,在定容燃烧弹中研究了较高当量比和不同初始压力下氢气空气预混合气的燃烧特性,分析了两参数对其燃烧特性的影响。试验结果表明,本实验条件下的氢气空气预混合物燃烧过程中,主火焰两侧出现挤流火焰,且挤流火焰的传播明显快于主火焰;根据出现挤流火焰与否、两侧挤流火焰相遇与否、实验时的热力参数、燃料浓度等条件,燃烧过程可分为四个阶段;在本文的实验条件下随着当量比增加,挤流火焰燃烧速度加快,其倾向于自燃时的多点燃烧;随着初始压力降低,挤流火焰逐渐出现在主火焰层流燃烧阶段。     

微型摆式发动机内丙烷/空气单次燃烧实验研究

在厘米尺度百瓦级微型摆动式发动机样机上进行了单次燃烧实验,燃用当量比φ=0.9~1.2的丙烷/空气预混合气时,对燃烧室内的火焰传播形态、气体动态压力和摆臂运动进行测量,获得了平均火焰传播速度、燃烧持续时间、燃料质量燃尽率、压力和摆臂止点角度随当量比变化的规律特性。结果表明:在进气初始温度300 K、压力0.13 MPa条件下,φ=1.0~1.2工况时,微摆发动机内燃烧为湍流燃烧,燃烧持续时间在5 ms以内,压力峰值高于8个大气压;随当量比增加,燃烧持续时间缩短、平均火焰传播速度加快和压力峰值升高,更接近定容燃烧,有利于提高输出功率。     

微尺度扩散火焰特性的数值解析

本文以均匀空气流中圆管形成的甲烷射流扩散火焰为对象,用数值解析的方法研究了微尺度扩散火焰的火焰结构和燃烧特性。燃烧反应采用甲烷/空气一步总包反应,喷管壁面采用绝热条件。在Re一定情况下,改变喷口尺寸和喷口流速考察了微扩散火焰的结构和火焰熄灭的尺度效应。数值结果表明,随着喷口直径的增大,微火焰的上方出现回流; Re=12条件下,在喷口直径=0.07 mm时存在熄灭极限;稳定燃烧区的最小发热率约为0.5 W;微尺度条件下,Da数对火焰结构和火焰的熄灭有一定的影响。     

近贫燃极限甲烷/空气火焰的层流燃烧速度研究

利用微重力条件下向外传播的球形火焰,对贫燃极限附近甲烷/空气预混火焰的层流燃烧速度进行了测量,得到当量比从0.512(本文微重力实验中测定的可燃极限)到0.601范围内的零拉伸层流燃烧速度,并与前人实验数据和使用3种化学反应动力学模型的计算结果进行了比较.本文实验结果与已有的微重力实验数据非常接近,而其他研究者在常重力...     

喷管直径对微尺度扩散火焰特性的影响

对均匀空气流中微尺度甲烷扩散燃烧进行了数值模拟,重点考察微喷管内的流动和传热传质对微尺度燃烧特性的影响.研究结果表明,在保持燃料喷出速度一定的条件下,随着喷管直径的减小,喷管内与甲烷喷出速度相反方向上发生热量和质量的传递,燃料与空气的混合在喷管内已经发生,火焰的一部分热量回流到喷管内顶热了未燃混合气,同时也增加了火焰的热损失.当管径为0.15 mm时,甲烷在微喷管内就开始发生化学反应,在进行微尺度解析计算时,必须包含一定的喷管区域.     

双模式放电中DBD放电参数对甲烷滑动弧火焰光谱及活性粒子的影响分析

对未燃烧的可燃混合气体进行DBD放电,放电后会产生大量的活性粒子,这些活性粒子可以辅助气体燃烧,达到提高燃料燃烧利用率等目的。以DBD激励氩气、甲烷、空气产生的自由基（CH基和OH基）等强化燃烧的关键活性粒子为探索对象,研究DBD放电激励甲烷对滑动弧火焰的影响。为此,采用自主设计的DBD-滑动弧双模式等离子体激励器,利用同轴介质阻挡放电结构对氩气、甲烷、空气混合气进行放电激励,将激励后的氩气、甲烷、空气混合气通入滑动弧端进行点火。固定氩气流量不变,调整空气流量为4.76 L·min-1,并加入甲烷0.5 L·min-1,保证进气通道内氩气与空气-甲烷的气体体积流量比达到Ar∶（CH₄+Air）=1∶30,其中空气、甲烷这两种气体达到了化学燃烧当量比φ=1,氩气、甲烷、甲烷混合气体能实现均匀而稳定的放电并燃烧。DBD段放电电压在15～20 kV范围变化,放电频率在6～10 kHz范围变化,滑动弧段的电压和频率分别保持4 kV与10 kHz恒定,通过改变DBD段放电电压和放电频率,用高速光纤光谱仪检测滑动弧火焰中自由基种类及其光谱强度,分析放电参数激励甲烷对火焰中自由基（CH基和OH基）的影响。结果表明,DBD段放电电压及放电频率的增加可以促进火焰内部的偶联反应发生,可有效提升甲烷滑动弧火焰内部的活性粒子含量,其中OH基团、CH基团在燃烧链式化学反应进程中发挥着较为重要的作用。甲烷经过DBD激励后,随放电电压和频率的增加,火焰中OH基、CH基等主要活性粒子都随之增加。DBD放电后,活性粒子的光谱强度增大,特征谱线比单模式更加明显;甲烷经过DBD激励后,火焰组成发生了变化,滑动弧段出口处甲烷燃烧反应更加充分,火焰温度越高越容易产生OH基。与单模式滑动弧相比,双模式放电可有效促进火焰内部的链式化学反应进程,促进燃料燃烧。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.