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[en] The hydraulic free-piston engine integrates the internal combustion engine with a hydraulic pump. The piston of an HFPE is not connected to the crankshaft and the piston movement is determined by the forces that act upon it. These features optimize combustion and make higher power density and efficiency increase. In this paper, a detailed thermodynamic and energy saving analysis is performed to demonstrate the fundamental efficiency advantage of an HFPE. The thermodynamic results show that the combustion process can be optimized to an ideal engine cycle. The experimental results show that the HFPE combustion process is a nearly constant-volume process; the efficiency is approximately 50%; the piston displacement and velocity curves for a cycle are the same at any frequency, even at a 1.25 Hz. The maximum velocities are of the same value at high or low frequencies. Similarly, pump output flow is not influenced by frequency. The independent cyclic characteristics of HFPE determine that it should work in higher frequencies when the vehicle runs in Japanese 10–15 road conditions. It indicates that a higher working frequency will lead to the starting frequency of HFPE, and a lower frequency will decrease the pressurized pressure of the hydraulic accumulator. - Highlights: • The thermodynamic and energy saving benefits of the HFPEs was investigated. • The approach of combustion optimization was obtained by adjusting the injection timing and compression ratio. • The high efficiency area of HFPE was given as a function of injection timing and compression pressure. • The maximum efficiency of HFPE of 50% was obtained from the prototype. • The method of energy saving with adjusting the piston frequency was examined.
[en] Highlights: • A hydraulic electronic unit injector in HFPE is developed and the test bench is established. • Effect of drive pressure on injection delay of hydraulic electronic unit injector are investigated. • Cycle fuel injection quantity is tested online and off-line engine operation. • The BDC control results in HFPE based on feed-forward compensation are acceptable. • The energy flow in HFPE is analyzed and the hydraulic output energy is optimized. - Abstract: The fuel injection system in two stroke engine is very important, therefore the hydraulic electronic unit injector system is developed and the injection characteristics of hydraulic electronic unit injector are investigated. Firstly the HFPE and the hydraulic electronic unit injector working principle are analyzed, and then PID control strategy is built by engine demand. In order to validate the feasibility of hydraulic electronic unit injector, the prototype test bench is established. The specific measurement principle is presented. Further the injection characteristics, such as the effect of injection pressure on injection delay and the effect of engine frequency on injection delay, are analyzed. In order to optimize the engine stability performance, the BDC control based on fuel injection control is investigated. The load control based on fuel injection is also discussed and the BDC feedforward control with the load variation is investigated. Experiment results of stead engine operation shows that the hydraulic electronic unit injector system based on PID control can be satisfied with the engine operation demand. In addition, cycle fuel injection quantity is tested online and off-line engine operation. It is obvious that the fuel injection quantity is affected by the hydraulic pressure. The fuel injection quantity variation can be improved with decreasing the fluctuation of drive pressure or adopting more suitable oil common rail instead of connected with exhaust valve hydraulic drive oil-way. The energy flow in HFPE is analyzed and the hydraulic output energy can be optimized by selecting suitable hydraulic valves parameters. The fuel injection quantity should be designed by the energy balance and the stable operation requirement in spite of the higher thermal efficiency.
[en] The cold start characteristic of hydraulic free piston diesel engine may affect its stable operation. Therefore the specific cold start characteristics, such as BDC or TDC positions, pressure in-cylinder, heat release rate, should be investigated in detail. These parameters fluctuate in some regularity in the cod start process. With the development of the free piston engine prototype and the establishment of test bench, the results are obtained. For the dynamic results, the fluctuation range of TDC and BDC positions is 8 mm and decreases with time. The thermodynamic results show that the combustion process is not stable and the pressure in-cylinder fluctuates largely in the cold start process. In addition, the combustion is rapid and knock happens inevitably. In order to investigate the reasons, a CFD model is established for temperature analysis in-cylinder and heat transfer conditions. It is found that higher start wall temperature will lead to more uniform temperature distribution. The delay period may decreases and heat release will move forward. This reason is analyzed by thermodynamic derivation based on the first law of thermodynamics. Finally, the improvement suggestions of cold start strategy are proposed. - Highlights: • The cold start behaviors of HFPE are investigated in detail. • CFD method is used for simulating temperature distribution in start process. • Thermodynamic derivation uncovers the compression temperature distribution. • The improvement suggestions of cold start strategy are proposed.
[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] Under a large signal drive level, a frequency domain black box model of the nonlinear scattering function is introduced into power FETs and diodes. A time domain measurement system and a calibration method based on a digital oscilloscope are designed to extract the nonlinear scattering function of semiconductor devices. The extracted models can reflect the real electrical performance of semiconductor devices and propose a new large-signal model to the design of microwave semiconductor circuits.
[en] This paper reports a cylindrical shear-mode magnetoelectric (ME) composite developed based on a Pb(Zr,Ti)O3 (PZT) tube bonded with an NdFeB permanent magnet for magnetic coupling. The existence of a significant ME effect originating from the superior d15 electromechanical response of the piezoelectric phase is theoretically predicted and experimentally observed with a voltage coefficient of 28.8 mV/Oe (RMS) outside resonance and a maximum power density of 4.56 μW (cm3·Oe2)−1 at resonance, which are much higher than previous shear-mode ME composites without bias field in the literature. These suggest broad application prospects of this particular ME composite as magnetic sensors, transducers and energy harvesters. (paper)
[en] Si nano-well arrays, with precisely controlled undercut Si sidewall profiles and flat bottomed pockets, enable uniform nanoscale pattern transfer from resists to metal deposits without degradation of the initial lithographic resolution, as verified by the formation of arrays of Au nano-dots with 10 nm diameter. An additional functionality of the Si nano-wells as local nano-reactors, where the patterned material is enclosed in a Si pocket during high temperature reaction, is demonstrated by thermally inducing a phase transformation of the as-deposited A1 phase of FePt nano-dots to the high coercivity, chemically ordered L10 phase.
[en] Isoscaling and isobaric yield ratio difference (IBD) methods are used to study Δμ/T (Δμ being the difference between the chemical potentials of the neutron and proton, and T being the temperature) in the measured 1 A GeV 124Sn + 124Sn, 112Sn + 112Sn, 136Xe + Pb and 124Xe + Pb reactions. The isoscaling phenomena in the 124Sn/112Sn and 136Xe/124Xe reaction pairs are investigated, and the isoscaling parameters α and β are obtained. The Δμ/T determined by the isoscaling method (IS-Δμ/T) and the IBD method (IB-Δμ/T) in the measured Sn and Xe reactions are compared. It is shown that in most fragments, the IS- and IB-Δμ/T are consistent in the Xe reactions, while the IS- and IB-Δμ/T ones are only similar in the less neutron-rich fragments in the Sn reactions. The shell effects in IB-Δμ/T are also discussed. (paper)
[en] A simple and universal pathway to produce free multilayer synthetic nanoparticles is developed based on lithography, vapor phase deposition and a tri-layer resist lift-off and release process. The fabrication method presented in this work is ideal for production of a broad range of nanoparticles, either free in solution or still attached to an intact release layer, with unique magnetic, optical, radioactive, electronic and catalytic properties. Multi-modal capabilities are implicit in the layered architecture. As an example, directly fabricated magnetic nanoparticles are evaluated to illustrate the structural integrity of thin internal multilayers and the nanoparticle stability in aggressive biological environments, which is highly desired for biomedical applications.
[en] The porous platelet-shaped α-Bi2O3 photocatalyst was successfully synthesized by a novel hydrothermal–calcination method assisted with ethylenediamine and polyvinylpyrrolidone. The physical and chemical properties of α-Bi2O3 photocatalyst were characterized based on XRD, XPS, SEM, TEM, EDS, UV–Vis DRS, and PL techniques. The influence of preparation conditions on the formation of α-Bi2O3 photocatalyst was investigated, and the effect of catalyst dosage and pH value on the EE2 removal rate was also investigated. The synthesized porous platelet-shaped α-Bi2O3 photocatalyst exhibited excellent photocatalytic activity for 17α-ethynylestradiol (EE2), and 97.8% of EE2 was removed after 75 min of visible light irradiation using α-Bi2O3 as photocatalyst. The reaction rate constant over the porous platelet-shaped α-Bi2O3 photocatalyst was 11.6 and 11.4 times of that of traditional α-Bi2O3 and N-TiO2, respectively. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The porous platelet-shaped α-Bi2O3 was a stable and efficient photocatalyst, proving that it is a promising photocatalyst.