Combustion and emission performances of coconut,palm and soybean methyl esters under reacting spray flame conditions

The spray combustion characteristics of coconut (CME), palm (PME) and soybean (SME) biodiesels/methyl esters were compared with diesel by using an axial swirl flame burner. Atomisation of the liquid fuels was achieved via an airblast-type nozzle with varied atomising air-to-liquid ratios (ALR) of 2–2.5. The fully developed sprays were mixed with strongly swirled air to form combustible mixtures prior to igniting at the burner outlet. Under fuel-lean condition, biodiesel spray flames exhibited bluish flame core without the yellowish sooty flame brush, indicating low sooting tendency as compared to baseline diesel. Increasing the atomising air led to the reduction of flame length but increase in flame intensity. Measurements of post-combustion emissions show that SME produced higher NO as compared to CME and PME due to higher degree of unsaturation, while the most saturated CME showed the lowest NO and CO emissions amongst the biodiesels tested across all equivalence ratios. By preheating the main swirl air to 250 °C, higher emissions of NO, CO and CO₂ were observed for biodiesels. Higher ALR led to reduced NO and CO emissions regardless of the fuel used, making it a viable strategy to resolve the simultaneous NOCO reduction conundrum. This work shows that despite different emission characteristics exhibited by biodiesels produced from different feedstock, they are in principle potential supplemental fuels for practical combustion systems. The pollutants emitted can be mitigated by operating at higher ALR in a twin-fluid based swirl combustor.     

基于传输反射法的等离子体相对复介电系数测量

为解决微波激发等离子体参数诊断存在的困难问题,提出利用二端口传输反射法测量微波激励产生的低温等离子体的等效相对复介电系数。使用有限元方法设计了基于BJ22标准波导的样品测试结构,该结构能在较大的介电系数范围内,保证介电系数和端口的|S11|,φS11和|S21|参数保持较好的单调性,避免产生多值问题;通过人工神经网络对计算获得的各介电系数对应的S参数进行训练,达到足够的精确度;最后通过实验,将测量获得的S参数利用神经网络反演获得待测物质的相对复介电系数。该方法对今后测量类似等离子体、复介电系数实部为负的特殊材料的介电常数具有一定的指导意义。     

High performance resonant cavity antenna with non‐uniform metamaterial inspired superstrate

The resonant cavity antenna (RCA) is a class of widely used high gain antennas, but usually suffers from narrow impedance bandwidth owing to its strong resonant property, as well as relatively low aperture efficiency because of its non‐uniform electromagnetic (EM) field distribution on the aperture. This article explores enhancing the RCA's impedance bandwidth and aperture efficiency by designing a non‐uniform metamaterial inspired superstrate, on which the metal patches vary their sizes with respect to their distances to the superstrate's center. After optimized by the Genetic Algorithm, the proposed RCA is designed, fabricated and tested. Measured results agree well with simulated ones and show that in comparison with a RCA with a uniform metamaterial inspired superstrate, this work significantly improves the |S ₁₁| < ?10 dB impedance bandwidth from 2.1% to 6.1%, the gain at the working frequency 10 GHz from 19.07 dBi to 20.55 dBi, and correspondingly the aperture efficiency from 50.5% to 71%. A further analysis estimates that due to the non‐uniform metamaterial inspired superstrate, a more homogeneous distribution for both the amplitude and phase of the EM field is observed on the superstrate's aperture.     

STABILITY OF NONAQUEOUS ELECTROLYTES FOR AMBIENT TEMPERATURE RECHARGEABLE LITHIUM CELLS

Three tests have been used lo determine the stability of solutions of two nonaqueous solvents, propylene carbonate and 2-methyl-tetrahydrofuran and their solutions of LiAlCl₄. LiAsF₆ and LiClO₄ in contact with lithium. The procedures identify the effect of surface layers, open-circuit stand, anodic and cathodic polarization. They employ (1) contact with liquid Li amalgam and solid sheet Li; (2) open circuit potential measurements of cathodic deposits and (3) anodic dissolution of deposits with ramped potential. The stability of solvents is found to depend on the dissolved electrolyte. Polymeric materials containing other products of the reaction between metal and electrolytes have been identified by X-ray diffraction.     

Computer-based virtual reality simulator for phacoemulsification cataract surgery training

Recent research in virtual reality indicates that computer-based simulators are an effective technology to use for surgeons learning to improve their surgical skills in a controlled environment. This article presents the development of a virtual reality simulator for phacoemulsification cataract surgery training, which is the most common surgical technique currently being used to remove cataracts from the patient’s eyes. The procedure requires emulsifying the cloudy natural lens of the eye and restoring vision by implanting an artificial lens through a small incision. The four main procedures of cataract surgery, namely corneal incision, capsulorhexis, phacoemulsification, and intraocular lens implantation, are incorporated in the simulator for virtual surgical training by implementing several surgical techniques. The surgical activity that are applied on the anatomy of the human eye, such as incision, grasping, tearing, emulsification, rotation, and implantation, are simulated in the system by using different types of mesh modifications. A virtual reality surgical simulator is developed, and the main procedures of phacoemulsification cataract surgery are successfully simulated in the system. The simulation results of the training system show that the developed simulator is capable of generating a virtual surgical environment with faithful force feedback for medical residents and trainees to conduct their training lessons via the computer using a pair of force-feedback haptic devices. In addition, the successful simulation of the mesh modifications on the human eyeball with visual realism and faithful force feedback throughout the surgical operation shows that the developed simulator is able to serve as a virtual surgical platform for surgeons to train their surgical skills.     

一种新型连续流生物柴油微波反应器仿真与设计

生物柴油作为一种新型的清洁能源被越来越多人重视。现有利用化学法制备生物柴油方法,普遍存在反应时间长,能耗大,环境污染严重等缺点。针对以上缺点,设计了一种新型连续流的微波反应器用于制备生物柴油,通过COMSOL Multiphysics软件,将电磁场、化学反应动力学、层流和传热传质进行多物理场耦合来模拟反应过程,通过分析反应物流速对温度的影响,盘管匝数、盘管螺旋尺寸以及腔体尺寸对能量利用率的影响,整体优化反应器结构尺寸,实现了93.7%的微波能量利用率。     

一种具有谐波抑制功能的圆极化天线设计

微波能量传输以及无线通信系统中的天线设计,追求剖面低、质量轻,易与平面电路集成。基于此,设计了一种具有谐波抑制功能的单馈背腔圆极化环缝天线。该天线工作在5.8 GHz,采用导波结构基片集成波导(SIW)抑制表面波,提高了天线增益。SIW通过2排金属孔阵列集成在介质板上,在介质板上蚀刻短路圆环缝隙,辐射电磁波。采用50 Ω微带线到SIW过渡的背馈方式,并在馈线上引入并联枝节,有效抑制了高次谐波,且实现了基于基片集成波导天线的谐波抑制。通过加工测试,天线的轴比为0.67 dB,增益为6.9 dBi,阻抗匹配良好,前后比为22 dB,仿真结果与实测结果吻合良好。     

基于磁感应频率跟踪的逆变电源研究与设计

针对近距离高频磁感应能量传输系统中距离改变会使谐振频率发生变化,导致效率降低的问题,提出一种基于74HC4046AD锁相环的频率跟踪驱动方案,该方案可以实现谐振频率的自动跟踪,在proteus环境下对中心频率为100 kHz的逆变电源系统和锁相功能进行仿真。设计并制作基于频率跟踪的逆变电源样机,通过样机对输出情况进行跟踪反馈。仿真实验结果表明,该系统输出性能良好,验证了频率跟踪的有效性,实现了功率管的软开关工作模式。     

混合粉末加载对隔离滤波器性能的影响实验

粉末材料的微波耗散机理不同于块状材料,非磁性的金属与氧化物混合粉末展现出对微波磁场较强的吸收特性。本文针对金属与氧化物混合粉末的电导率和微波磁吸收特性开展研究,并利用特定比例的混合粉末加载基于静磁表面波的隔离滤波器,研究其对非互易滤波器的隔离度和插入损耗的影响。实验结果表明：30%Cu+70%CuO的混合粉末电导率为217.435 mS/m,对微波磁场具有较好的吸收特性;利用此混合粉末加载非互易滤波器后,插入损耗减小,隔离度获得了明显提升,达到了21.56 dB。