Investigation of kerosene combustion characteristics with pilot hydrogen in model supersonic combustors

Experimental investigations on the ignition and combustion stabilization of kerosene with pilot hydrogen in Mach 2.5 airflows were conducted using two test combustors, with cross sections of 30.5 x 30 and 51 x 70 mm, respectively. Various integrated modules, including the combinations of different pilot injection schemes and recessed cavity flameholders with different geometries, were designed and tested. The stagnation pressure of vitiated air varied within the range of 1.1-1.8 NiPa, while the stagnation temperature varied from 1500 to 1900 K. Specifically, effects of the pilot hydrogen injection scheme, cavity geometry, and combustor scaling on the minimally required pilot hydrogen equivalence ratio were systematically examined. Results indicated that the cavity depth and length had significant effects on the ignition and flameholding, whereas the slanted angle of the aft wall was relatively less important. Two cavities in tandem were shown to be a more effective flameholding mechanism than that with a single cavity. The minimally required pilot hydrogen equivalence ratio for kerosene ignition and stable combustion was found to be as low as 0.02. Furthermore, combustion efficiency of 80% was demonstrated to be achievable for kerosene with the simultaneous use of pilot hydrogen and a recessed cavity to promote the ignition and global burning.

Experimental investigation on the cavity-based scramjet model

The present work focused on improving the engine performance with different fuel equivalence ratios and fuel injections. A scramjet model with strut/cavity integrated configurations was tested under Mach 5.8 flows. The results showed that the strut may sreve as an effective tool in a kerosene-fueled scramjet. The integration of strut/cavities also had great effect on stablizing the combustion in a wide range of fuel equivalence ratio. The one-sdimensional analysis method was used to analyze the main characteristics of the model. The two-stage fuel injection should have better performance in increasing the chemical reaction rate in the first cavity region.

Embryo-damage induced nucleation of microcracks in an aluminum-alloy under impact loading

The nucleation of microdamage under dynamic loading was investigated through planar impact experiments accomplished with a light gas gun. The microscopic observation of recovered and sectioned specimens showed that microcracks were nucleated only by cracking of brittle particles inside material. However, for comparison the in situ static tensile tests on the same material conducted with a scanning electron microscope showed that the microcracks were nucleated by many forms those were fracture of ductile matrix, debonding particles from matrix and cracking of brittle particles. The quantitative metallographic observations of the specimens subjected to impact loading showed that most of the cracked particles were situated on grain boundaries of the aluminium matrix. These facts suggested the concept of critical size and incubation time of submicroscopic cavities in the dynamic case and the mechanism of embryo-damage induced nucleation by fracture of brittle particles in the aluminium alloy under impact loading was proposed.

Characteristics and microstructure in the evolution of shear localization in ti-6al-4v alloy

A new interrupting method was proposed and the split Hopkinson torsional bar (SHTB) was modified in order to eliminate the effect of loading reverberation on post-mortem observations. This makes the comparative study of macro- and microscopic observations on tested materials and relevant transient measurement of tau - gamma curve possible. The experimental results of the evolution of shear localization in in Ti-6Al-4V alloy studied with the modified SHTB are reported in the paper. The collapse of shear stress seems to be closely related to the appearance of a certain critical coalescence of microcracks. The voids may form within the localized shear zone at a quite early stage. Finally, void coalescence results in elongated cavities and their extension leads to fracture along the shear band.

Experimental Studies on Model Scramjet in a Mach 6 High Enthalpy Free-Jet Wind Tunnel

A side-wall compression scramjet model with different combustor geometries has been tested in a propulsion tunnel that typically provides the testing flow with Mach number of 5.8, total temperature of 1800K, total pressure of 4.5MPa and mass flow rate of 4kg/s. This kerosene-fueled scramjet model consists of a side-wall compression inlet, a combustor and a thrust nozzle. A strut was used to increase the contraction ratio and to inject fuels, as well as a mixing enhancement device. Several wall cavities were also employed for flame-holding. In order to shorten the ignition delay time of the kerosene fuel, a little amount of hydrogen was used as a pilot flame. The pressure along the combustor has an evident raise after ignition occurred. Consequently thrust was observed during the fuel-on period. However, the thrust was still less than the drag of the scramjet model. For this reason, the drag variation produced by different strut and cavities was tested. Typical results showed that the cavities do not influence the drag so much, but the length of the strut does.

Experimental Studies on Scramjet Tested in a Freejet Facility

Two different type scramjet models with side-wall compression and top-wall compression inlets have been tested in HPTF (Hypersonic Propulsion Test Facility) under the experimental conditions of Mach number 5.8, total temperature 1700K, total pressure 4.5MPa and mass flow rate 3.5kg/s. The liquid kerosene was used as main fuel for the scramjets. In order to get fast ignition in the combustor, a small amount of hydrogen was used as a pilot. A strut with alternative tail was employed for increasing the compression ratio and for mixing enhancement in the side-wall compression case. Recessed cavities were used as a flameholder for combustion stability. The combustion efficiency was estimated by one dimensional theory. The uniformity of the facility nozzle flow was verified by a scanning pitot rake. The experimental results showed that the kerosene fuel was successfully ignited and stable combustion was achieved for both scramjet models. However the thrusts were still less than the model drags due to the low combustion efficiencies.

Bubble Behavior and Heat Transfer in Quasi-Steady Pool Boiling in Microgravity

Pool boiling of degassed FC-72 on a plane plate heater has been studied experimentally in microgravity. A quasi-steady heating method is adopted, in which the heating voltage is controlled to increase exponentially with time. Compared with terrestrial experiments, bubble behaviors are very different, and have direct effect on heat transfer. Small, primary bubbles attached on the surface seem to be able to suppress the activation of the cavities in the neighborhoods, resulting in a slow increase of the wall temperature with the heat flux. For the high subcooling, the coalesced bubble has a smooth surface and a small size. It is difficult to cover the whole heater surface, resulting in a special region of gradual transitional boiling in which nucleate boiling and local dry area can co-exist. No turning point corresponding to the transition from nucleate boiling to film boiling can be observed. On the contrary, the surface oscillation of the coalesced bubble at low subcooling may cause more activated nucleate sites, and then the surface temperature may keep constant or even fall down with the increasing heat flux. Furthermore, an abrupt transition to film boiling can also be observed. It is shown that heat transfer coefficient and CHF increase with the subcooling or pressure in microgravity, as observed in normal gravity.

A Wide Band Strong Acoustic Absorption in a Locally Network Anechoic Coating

Composite materials with interpenetrating network structures usually exhibit unexpected merit due to the cooperative interaction. Locally resonant phononic crystals (LRPC) exhibit excellent sound attenuation performance based on a periodical arrangement of sound wave scatters. Inspired by the interpenetrating network structure and the LRPC concept, we develop a locally network anechoic coating (LNAC) that can achieve a wide band of underwater strong acoustic absorption. The experimental results show that the LNAC possesses an excellent underwater acoustic absorbing capacity in a wide frequency range. Moreover, in order to investigate the impact of the interpenetrating network structure, we fabricate a faultage structure sample and the network is disconnected by hard polyurethane (PU). The experimental comparison between the LNAC and the faultage structure sample shows that the interpenetrating network structure of the LNAC plays an important role in achieving a wide band strong acoustic absorption.

OBSERVATION OF CAVITY QUANTUM-ELECTRODYNAMIC EFFECTS IN A ND-GLASS MICROSPHERE

In a Nd:glass microspherical cavity the enhancement and inhibition of spontaneous-emission processes that are due to cavity QED effects have been observed. The rates of the enhanced spontaneous emission are location dependent and reach a maximum value of more than 10(3) times the free-space value. The large enhancement strongly modifies the decay processes of Nd ions in glass, and the radiative properties of Nd:glass have been changed. As a result a new spectrum including new lasing wavelengths in the Nd:glass sphere has been observed.

基于多台阶反射光栅的飞秒脉冲压缩装置

反射式光栅对是一种具有负色散性质的器件,可用于飞秒激光脉冲的压缩和展宽,具有无材料色散的优点。给出了一种基于多台阶反射光栅的脉冲压缩装置。该装置为倍密度光栅结构,由两个周期分别为40μm和20μm的四台阶反射式光栅组成。实验得到的衍射效率可以达到70%以上,输入脉冲经过两个光栅的衍射后会按原路返回,从而达到色散补偿的效果。利用此压缩装置,脉冲宽度为66.8 fs的输入脉冲压缩至接近傅里叶变换极限脉冲,即46.6 fs,由此证明只要多台阶光栅效率足够高,此装置就有可能成为不同于棱镜对进行飞秒脉冲腔内和腔外压缩的另一种途径。

Instabilities in a grating feedback external cavity semiconductor laser

Output power fluctuations in a grating external cavity diode laser with Littman configuration are described, showing peculiar chaotic behaviors of self-pulsation at the L-I curve kink points. Different spectral characteristics with multiple peaks are observed at upper and lower state of the self-pulsation. It is found also that P-N junction voltage jumps in a same pace with the pulsation. The observed phenomena reflect competition between different longitudinal modes, and transient variation of transverse modes in addition. These experimental results may contain information about the mechanisms of the chaotic instability in strong filtered feedback semiconductor lasers. (C) 2008 Optical Society of America

用于多普勒测风雷达的单频全固态激光器稳频

采用Pound-Drever-Hall技术，对用于多普勒测风雷达的种子注入激光器的主动激光器进行稳频，将其频率锁定在一个特殊设计的法珀腔上。该法珀腔总体采用零膨胀微晶玻璃材料制成，具有极高的温度稳定性。使用计算机采集鉴频信号并且进行处理。锁定后，1秒内激光器的相对频率漂移为±25kHz，一小时内的相对频率漂移为±55kHz，满足多普勒测风雷达的要求。

Efficient laser oscillation of Yb : Y3Al5O12 single crystal grown by temperature gradient technique

Low-threshold and highly efficient continuous-wave laser performance of Yb:Y3Al5O12 (Yb:YAG) single crystal grown by a temperature gradient technique (TGT) was achieved at room temperature. The laser can be operated at 1030 and 1049 nm by varying the transmission of the output coupler. Slope efficiencies of 57% and 68% at 1049 and 1030 nm, respectively, were achieved for 10 at. % Yb:YAG sample in continuous-wave laser-diode pumping. The effect of pump power on the laser emission spectrum of both wavelengths is addressed. The near-diffraction-limited beam quality for different laser cavities was achieved. The excellent laser performance indicates that TGT-grown Yb:YAG crystals have very good optical quality and can be potentially used in high-power solid-state lasers.

白杄花粉管胞吞/胞吐动态及其与细胞壁构建的关系

在有花植物受精过程中，具有顶端极性生长特性的花粉管是雄性生殖单位的载体，同时也是研究细胞生长分子调控机理的理想体系。与被子植物相比，裸子植物花粉具有萌发时间长、花粉管生长缓慢等特点。对于裸子植物花粉萌发和花粉管生长的机理，目前人们尚不十分清楚。本文将以裸子植物白杄（Picea meyeri）花粉为材料，应用不同浓度的分泌系统干扰剂Brefeldin A处理，并通过细胞学和生理生化方法，其中包括普通光学显微镜、荧光显微镜、激光扫描共聚焦显微镜、显微红外光谱（FTIR）和透射电镜（TEM）等技术，对其花粉萌发和花粉管生长过程中胞吞胞吐的调控，以及与细胞壁建成的关系等进行较为系统的研究，旨在为进一步揭示裸子植物花粉管发育的调控机理提供参考。 首先比较观察了各种细胞器在白杄与被子植物花粉管中的分布差异。经FM4-64探针标记结果表明，在正常生长的白杄花粉管顶端存在分泌小泡积累的透明区，但与被子植物比较起来，此透明区在花粉管中所占比例较小，且不呈倒“V”字型。在透射电镜下观察发现，其花粉管顶端透明区内分泌小泡的分布密度远低于被子植物。另外，在白杄花粉管中，线粒体的分布一般靠近细胞壁的地方，高尔基体分布较为分散，而内质网的分布则不具方向性。 其次，研究了BFA对白杄花粉萌发和花粉管生长的影响，特别是对其花粉管生长过程中的胞吐/胞吞作用。通常在正常生长的白杄花粉管中，用FM4-64标记后发现，在其顶端形成与透明区对应的荧光亮区;超微结构显示，在花粉管顶端进行旺盛的胞吐作用，许多分泌小泡正与质膜融合，以及分布有大量显示高分泌活性的壁旁体（PB）等。而经过BFA处理后，花粉的萌发和花粉管的生长均受到严重抑制，花粉管出现了弯曲（波状生长）或顶端膨大等异常形态，同时还干扰了FM4-64在花粉管顶端的标记模式。另外，花粉管顶端分泌小泡数量减少，透明区内充满线粒体、高尔基体和空泡等一些大的细胞器，壁旁体也随之消失，其中高尔基体呈现解体或弯曲的异常形态，在其周围的分泌小泡数量大大减少，内质网出现膨胀和核糖体脱落等;同时胞吐活性标志性酶——酸性磷酸酶的活性也随之降低。通过对FM4-64的染料吸收实验表明，BFA对胞吞有明显的促进作用。由上可见，BFA对白杄花粉管生长过程中的胞吐和胞吞作用起了相反的影响， BFA正是通过扰乱花粉管生长过程中的分泌途径来抑制其花粉管的生长。 最后，检测了白杄花粉管分泌途径紊乱后，管壁物质合成的变化情况。通过FTIR光谱分析表明，BFA处理后花粉管壁化学组分发生了变化，例如蛋白质和多糖含量明显减少，而且与蛋白比较起来，多糖的含量下降更为明显，尤其是在顶端。蛋白和多糖含量的下降导致花粉管壁的组成结构不够致密。由SDS-PAGE的结果显示， BFA抑制后，花粉管壁中糖蛋白的含量下降了60%，同时很多壁蛋白条带在BFA处理后不表达或含量减少。通过对花粉管壁多糖成分的研究表明，BFA处理还导致纤维素含量下降，而胼胝质在花粉管顶端积累。用识别AGPs的LM6和识别酸性果胶的JIM5对花粉管进行标记，发现BFA处理后AGPs的环状分布消失，酸性果胶质在顶端的含量也明显减少，但在胞质内却形成一些小的分隔亮点（compartments）。 综上所述，导致裸子植物白杄花粉管生长缓慢的原因，可能与其顶端透明区较小、分泌小泡数量少等有关。另外，从白杄花粉管的细胞质状态和细胞器分布上看，虽然与被子植物相比差异较大，但在其正常生长中仍能进行旺盛地胞吐和胞吞过程。经BFA处理后引起花粉管内分泌系统的紊乱，致使管壁物质不能正常合成，从而导致花粉管的停滞生长。

A bactericidal homodimeric phospholipases A(2) from Bungarus fasciatus venom

Group IIA secretory phospholipases A(2) (sPLA(2)-II) is generally known to display potent grampositive bactericidal activity, while group IA sPLA(2) (sPLA(2)-I) reportedly is not. In this work, a novel sPLA(2)-I named BFPA was identified from Bungarus fas