乳化液喷雾与微爆现象的激光全息实验研究

本文采用离轴高速多脉冲红宝石激光全息摄影仪研究高温高压环境中乳化液喷雾的雾化和蒸发过程,记录方式为象面全息方式,再现时分别采用激光和白光光源。实验发现:在适当的温度压力条件下,乳化液喷雾可以发生微爆现象,微爆呈团状,又称“团状微爆”,也称为“二次雾化”,微爆能量可以将众多的小液滴及液滴碎片抛出液束区,有效地改善液体与环境气体的混合过程,具有重要的理论意义和实用价值。     

Expansion,injection and micro-explosion phenomena during the full combustion cycle of mixed fuel droplets of ethyl alcohol and biodiesel

In this study, mixed fuel droplets of ethyl alcohol and biodiesel with different volumes or ratios were prepared and the related expansion, injection and micro-explosion phenomena were investigated. During the tests, a mixed-fuel droplet was hung on a high-temperature-resistant Cr-Ni wire, which was transported to the preheating piston for heating and then was ignited automatically. Micro-needles and an infusion set also were employed to prepare mixed droplets with identical ratios but different volumes. Using a single-lens-reflex (SLR) camera, colour videos that captured the combustion process of the mixed droplets were taken and were processed into colour images using Adobe Premiere Pro CC. The colour image series were analysed to determine the ignition delay time, the burnout time and the flame characteristics during combustion of mixed droplets with different ratios. Instantaneous grey images were obtained by means of high-speed photography during combustion of the mixed droplets with different volumes and different ratios, and of droplets of E40 (in which the volume ratio of ethyl alcohol was 40%). Using Image pro plus and Origin software, the variation of normalised mean droplet diameter with time over the whole combustion cycle was calculated and the underlying reasons for various combustion phenomena were analysed.     

Warm dense matter at the bench-top: Fs-laser-induced confined micro-explosion

We report the experimental evidence for creation of Warm Dense Matter (WDM) in ultrafast laser-induced micro-explosion inside a sapphire (Al₂O₃) crystal. We show that the WDM can be formed by a 100 nJ fs-pulse if the following conditions are satisfied: (1) the laser pulse is tightly focused to inside of the bulk of transparent material so the intensity at focus is two orders of magnitude higher than the optical breakdown threshold; (2) the pulse duration is shorter than the electron-ion energy exchange time; and, (3) the absorbed energy density is above the Young’s modulus for the material studied. The empty void created inside a sapphire crystal surrounded by a shell of compressed material provides the direct evidence of the maximum pressure above the Young’s modulus of sapphire (∼400 GPa). Synchrotron X-ray diffraction (XRD) analysis of the shell revealed the presence of novel super-dense bcc-Al crystalline phase predicted at pressures above ∼380 GPa theoretically, which has never been observed experimentally before neither in nature in laboratory experiments. These results show that confined micro-explosion induced by tightly focussed fs-laser inside a transparent solid opens new routes for synthesis of new materials and study of WDM at a laboratory bench-top.     

单滴燃料热壁蒸发、微爆与着火的实验研究

多组分燃料在热板的蒸发与着火规律与空间相比,具有一些新的特点,特别是乳化油的贴壁燃烧现象更有重要意义。本文通过实验将多组分与单组分的燃烧情况进行了对比研究。结果表明：（１）易挥发组分的着火延迟在较低的温度条件下长于不易挥发份,在较高温度时情况相反。混合物则居于其中;（２）对于含水的乳化油,燃烧与微爆发生先后同的外界条件有关,其着火过程极为迅速。（３）乳化油中易挥发燃料含量较高,环境温度也较高时,微爆滞后很明显。     

飞秒激光在石英玻璃中诱导微爆炸的理论研究

利用有限元方法建立了二维模型，研究了飞秒激光作用下石英玻璃中导带电子的产生、激光 能量的沉积、导带电子和能量扩散等微观过程. 计算了导带电子扩散引起的局部净电荷及其 形成的静电场分布，初步揭示了微爆炸的演化过程. 关键词： 雪崩击穿模型 微爆炸 飞秒激光 有限元方法