[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: • Knock suppression of a spark-ignition engine with kerosene is tested. • Effect of water injection is evaluated experimentally and theoretically. • Water injection can suppress the knock and improve the output power. • Too much water injection has a negative effect on the work output. -- Abstract: The four-stroke spark-ignition (SI) internal combustion engine has good fuel economy and high power/weight ratio, making it very suitable for small aircraft. Normally, four-stroke aviation SI engines are fuelled with gasoline. Using kerosene can improve the system safety; However, a four-stroke SI engine fuelled with kerosene suffers from a small indicated mean effective pressure (IMEP) because of the knock limit of kerosene. In this study, water injection is investigated as a method of extending the knock limitation and improving IMEP of a four-stroke SI engine fuelled with kerosene. First, a Rotax 914 engine is retrofitted. Two port-fuel-injection systems supplied with kerosene and water are developed. Then, the combustion characteristics with water injection are studied. The effects of water injection on the in-cylinder pressure and heat-release rate are analysed. Additionally, the extent of knock suppression due to water injection under various engine speeds is evaluated. The results indicate that the knock limit of the four-stroke SI engine with kerosene is extended significantly via water injection. The measured IMEP is improved by 25–28% under different engine speeds. Thus, the requirement for ordinary cruise operation is satisfied. Furthermore, the security is enhanced with water injection.

[en] Objective: To study the equivalence of the Novel Medical NET632 SPECT and the SIEMENS Symbia T16 SPECT/CT in whole-body bone scintigraphy. Methods: A total of 32 cases (21 males and 11 females; aged 60.87 ± 12.25 years) in the Department of Nuclear Medicine of the Affiliated Hospital of Inner Mongolia Medical University from March 2018 to September 2018 were found positive with bone lesions in the whole-body bone scintigraphy using the SIEMENS Symbia T16 SPECT/CT and the Novel Medical NET632 SPECT. Then, the image quality was compared using the same image scoring criteria. The positive lesion involvement area and the number of areas in each patient were determined using the two devices. Results: The image qualities were scored 5, 4, and 3 (including < 3) for 18, 14, and 0 in the Symbia T16 SPECT/CT, and the image qualities were scored 5, 4, and 3 (including < 3) for 16, 16, and 0. A total of 84 positive lesion sites were found in the chest, spine, pelvis, limbs, and skull by using the Symbia T16 SPECT/CT, and the numbers in each location were 19, 24, 20, 16, and 5, respectively. The same number of positive lesions was observed in the same locations for the NET 632 SPECT. Conclusion: The Novel Medical NET632 SPECT and the SIEMENS Symbia T16 SPECT/CT detect the lesions in whole-body bone scintigraphy equivalently. (authors)

[en] Highlights: • Cross-sectional area of spray at the front end becomes larger as the chamber pressure increases from 0.5 bar to 3.5 bar. • Spray penetration and volume decrease significantly with an increase in chamber pressure from 0.5 bar to 3.5 bar. • Liquid-phase penetration decreases with an increase in fuel amount (controlled by fuel injection pulse width). • There is no significant difference in kerosene vapor penetration when the chamber temperature changes from 400 K to 500 K. -- Abstract: The performance of kerosene spray from an air-assisted system was investigated in a constant volume chamber by backlit imaging and shadowgraph technologies over various chamber pressures, temperatures, and fuel amount. The results show that the penetration decreases with the increase in the chamber pressures from 0.5 bar to 3.5 bar due to the reduction in the differential pressure between the air/fuel interface and ambience and the rise in the resistance to penetration as well. Liquid-phase penetration increases with an increase in temperature from 400 K to 500 K both at 1.0 bar and 3.0 bar for decreasing density of ambient gas. When ambient temperature was increased at 1.0 bar, there was no significant change in the vapor penetration. Therefore, increasing ambient temperature by internal EGR cannot reduce wall impingement when GDI engines fueled with kerosene. Furthermore, liquid-phase penetration decreases with the increase in fuel amount, while at the front end of spray the cross-sectional area increases since the spray is increasingly disturbed by the ambient gas.

[en] A one-way coupled spatiotemporally chaotic map lattice is used to construct cryptosystem. With the combinatorial applications of both chaotic computations and conventional algebraic operations, our system has optimal cryptographic properties much better than the separative applications of known chaotic and conventional methods. We have realized experiments to practice duplex voice secure communications in realistic Wired Public Switched Telephone Network by applying our chaotic system and the system of Advanced Encryption Standard (AES), respectively, for cryptography. Our system can work stably against strong channel noise when AES fails to work