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As a typical difficult-to-machine composite material, the microfabrication process of printed circuit board (PCB) is widely studied, especially the micro-hole drilling. However, multi-layer PCBs composed of flat glass fiber reinforced polymer and high-hardness ceramic particle fillers exhibit different tool wear behavior during the micro-hole drilling. The results showed that the abrasive wear on the chisel edge and main cutting edge are observed in the drilling of multi-layer PCB, while fracture of the main cutting edge only occurred in the drilling of ceramic particle filled GFRPs. Increasing the feed rate or spindle speed could effectively reduce tool wear. The cold air auxiliary drilling can effectively reduce the flank wear of the micro-drill, especially in the drilling of multi-layer PCBs.

Interfacial energy storage contributes a new mechanism to the emergence of energy storage devices with not only a high-energy density of batteries but also a high-power density of capacitors. In th...

In this paper, biodiesel was used to upgrade bio-oil by extracting the high-quality fuel fractions in bio-oil through solvent extraction. After the extraction, the upper layer blends of biodiesel and the high-quality bio-oil components, also called the “extraction phase liquid”, was obtained and denoted as EPBB. Firstly, Thermogravimetric (TG) and Fourier transform infrared (FTIR) analyses indicated that the light components originally in bio-oil, such as alcohols, ethers, ketones and carboxylic acids were extracted from bio-oil to biodiesel and formed the EPBB. Then the fuel properties of EPBB were measured at different temperatures. The results showed that the density of EPBB was higher, while its viscosity, surface tension and lower heating value (LHV) were lower than those of biodiesel. Accordingly, EPBB revealed better atomization and evaporation characteristics as compared to biodiesel. Finally, the engine performance of EPBB was tested on an unmodified direct-injection diesel engine. When compared with biodiesel, the ignition delay of EPBB was longer, the premixed combustion duration was longer, while the total combustion duration was shorter. The fuel economy of EPBB was comparable to that of biodiesel, and the NOx, soot, CO and UHC emissions of EPBB were all lower than those of biodiesel.

Hybrid lithium-ion supercapacitors combine the advantages of both the high power density of capacitors and the high energy density of lithium batteries, where activated carbon serves as a critical ...

Intercalation of carbon nanosheets into two-dimensional (2D) inorganic materials could enhance their properties in terms of mechanics and electrochemistry, but sandwiching these two kinds of materi...

Aqueous supercapacitors represent an extremely attractive candidate for next-generation energy storage devices, attributed to their excellent high-power density, low cost, nonflammability and environmental friendliness. Nonetheless, compared with their nonaqueous counterparts, the main challenge of aqueous supercapacitors lies in their narrow operating cell voltages and lower energy densities. Here we demonstrate that such issues can be overcome via optimizing the electrolyte and electrode materials by using high concentration “water-in-salt” electrolyte and low electrocatalytic activity all-pseudocapacitive metal-oxide electrodes, respectively. The high operating voltage of 2.2 V can be achieved for hybrid supercapacitor with MnO2 and Fe3O4 as positive and negative electrode, combining with a “water-in-salt” electrolyte. This hybrid supercapacitor exhibits a maximum specific energy of 35.5 Wh kg total − 1 at a specific power of 151.9 W kg total − 1 based on the mass of total activate materials. In addition, the hybrid system retains 87% of its initial specific energy even after 3000 charge/discharge cycles.

A skeletal chemical kinetic model for the simulation of auto-ignition and flame propagation characteristics of primary reference fuel (PRF) was developed. Coupled with this model, 3D simulations were applied to investigate the influence of lubricant oil droplets on pre-ignition in a turbocharged direct-injection spark-ignition (DISI) engine at low-speed high-load operating conditions. First, a simulation study on the influence of a lubricant oil droplet on auto-ignition of gasoline substitute and air mixture was performed in a constant-volume chamber. The results revealed that with an increase of the lubricant oil droplet diameter, the ignition delay time for the air/fuel mixture initially decreased and then increased. The ignition delay time was further shortened with the increase of the temperature of the lubricant oil droplet and the temperature and pressure of the mixture. Moreover, it was found that when n-heptane (n-C7H16) was used as a substitute for the direct evaporation product of the lubricant oil droplet, the shortening of the ignition delay time for the air/fuel mixture caused by lubricant oil evaporation was not enough to initiate pre-ignition. When octyl hydrogen peroxide ketone (C8KET) was chosen as a representative of the accumulated stable reactive radicals, the ignition delay time was significantly shortened and was short enough to trigger pre-ignition. Therefore, pre-ignition may not be induced by the direct evaporation product of an lubricant oil droplet but by the accumulated stable reactive radicals. A simulation study on auto-ignition and flame propagation of the air/fuel mixture with the presence of a lubricant oil droplet was then conducted in a turbocharged DISI engine. The results successfully predicted the auto-ignition of the air/fuel mixture near the lubricant oil droplet before the spark ignition timing. Finally, a more convincing mechanism for pre-ignition induced by lubricant oil droplets is proposed to provide some clues for further investigation.

By coupling the Wu-Faeth (WF) turbulent primary breakup theory with the classical Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) aerodynamic instability theories, the influences of nozzle-generated turbulence and aerodynamic force on the GDI spray atomization were both modeled in this study. The developed WF-KH-RT model was applied to the spray simulation of a six-hole GDI injector. The model calibration showed that with a simple tuning of a few model parameters, the WF-KH-RT model could predict the spray morphology, spray tip penetration (STP) and Sauter Mean Diameter (SMD) under various injection pressure and ambient pressure conditions with a high fidelity. The influences of specific WF-KH-RT model parameters on the spray simulation were also studied. The results revealed that increasing the KH characteristic time constant B1, WF characteristic length constant Csx and RT characteristic length constant CRT will lead to the increase of STP and SMD under most conditions. As the ratio of fuel density to ambient density ρ f / ρ g decreases, the aerodynamic effect is enhanced while the turbulent effect is weakened in the primary breakup, as a result the sensitivity of STP and SMD to B1 increases, while that to Csx declines. In summary, the results of this study can provide an insight into the relationship between different mechanisms affecting the fuel spray atomization, and an instruction of calibrating the proposed novel atomization model in GDI engine spray simulations.

Poor rate capability and cyclability are the major barriers to using TiO2 as the next generation anode material for high-performance lithium-ion batteries. In this study, a sandwich-like composite consisting of atomically defined two-dimensional (2D) carbon nanosheet is constructed by the confined synthesis in the galleries of layered TiO2 nanosheet with the superior cycling and rate performances as the anode material for lithium-ion batteries. It is first experimentally revealed that the interfacial charge storage between unilamellar TiO2 nanosheet and carbon nanosheet in the Carbon/TiO2 nanosheet stack and the excellent structure stability during the discharge/charge process contribute to the superior performance of the composites. The resultant composite exhibits a high specific capacity (568 mAh g−1) with a specific energy of 407.4 Wh kg−1 at a specific power of 71.7 W kg−1, and remains 88.0 Wh kg−1 at a specific power of 9.0 kW kg−1. Apart from promising lithium-ion battery anode, this 2D Carbon/TiO2 composite also has immense potential for applications in other areas such as sodium/potassium-ion batteries, supercapacitor, and catalysis.

In this study, we report the fabrication of garnet-structure composited solid-state electrolyte with high compactness as a water-proof interlayer for multilayer water-proof protected-lithium-anode. It is revealed that with the addition of Li3BO3 into the sintering precursor, the cubic phase garnet Li6.75La3Zr1.75Nb0.25O12 with high lithium ion conductivity and compactness can be achieved at a low temperature of 1000 °C with a “binder-like” Li3BO3 glassy molten phase in the grain boundary, indicating Li3BO3 plays an important role on the densification of grain boundary and the improvement of the relative density. 50 mol % Li6.75La3Zr1.75Nb0.25O12–Li3BO3 pellet shows a high lithium ion conductivity of 2.08 × 10−4 S cm−1 and a good chemical stability in 21 m LiTFSI “water-in-salt” electrolyte at 25 °C. Hybrid lithium ion capacitor using this garnet-ceramic electrolyte as interlayer for water-proof protected-lithium-anode, 21 m LiTFSI electrolyte and commercial activated carbon as the cathode shows a high working voltage of 4.0 V and a high energy density of 228.9 Wh (kg-carbon)−1 at a power density of 1343.2 W (kg-carbon)−1.

In this work, an experimental study on the effects of the impingement geometry, the cross-flow intensity and the wall temperature on the characteristics of an impinging port fuel injection (PFI) spray was conducted. The transient development of the impinging spray was recorded by a high-speed camera with Mie scattering. Based on the high-speed images, the spray tip penetration (S) and the impinged spray height (Hw) were obtained. The results show that with the increase of the impingement distance (Lw), S increases and Hw decreases at the same time after the impingement. As the impingement angle (θw) increases, S decreases while Hw first increases and then decreases. With the increase of the cross-flow velocity (Uc), less part of the spray impinges onto the wall, and S significantly increases. As the wall temperature (Tw) rises, S does not show much variation. However, Hw increases gently for Tw lower than 420 K, and it increases sharply for Tw higher than 420 K due to the Leidenfrost mechanism. The effects of the above factors (Lw, θw, Uc, Tw) on S and Hw were finally evaluated and compared through the introduction of a contribution index.