Yi Guo

The emerging ionic liquid compressor represents advanced compression technology for high-pressure hydrogen refueling stations. The self-acting valve is the core component in the cylinder of the reciprocating compressor, as it directly affects the operational performance of the ionic liquid compressor; however, the influence of the valve structure on the two-phase flow and compressor performance is unknown. This study combined a two-phase flow model with valve motion to explore the two-phase compression characteristics influenced by self-acting valves. The liquid fluctuation and gas velocity field in the compression chamber were analyzed when different structural self-acting valves that have different valve Mach numbers were arranged on the compression chamber, and then the valve motion and fluid suction and discharge performance were investigated. The results indicated that considering the pressure loss through the valve and the accuracy of opening and closing of the valve disk, the lowest possible Mach number is preferable; however, in terms of hydrogen exhaust temperature and loss of ionic liquid in the discharge procedures, larger Mach number is better. This research provides a foundation for optimizing the valve design of the ionic liquid compressor suitable for two-phase compression and guides future research on improving compressor performance and energy efficiency.

As an important piece of equipment for hydrogen energy application, the hydrogen internal combustion engine is helpful for the realization of zero carbon emissions, where the aluminum connecting rod is one of the key core components. A semi-solid forging forming process for the 7075 aluminum alloy connecting rod is proposed in this work. The influence of process parameters, such as the forging ratio, sustaining temperature, and duration time, on the microstructures of the semi-solid blank is experimentally investigated. The macroscopic morphology, metallographic structure, and physical properties of the connecting-rod parts are analyzed. Reasonable process parameters for preparing the semi-solid blank are obtained from the experimental results. Under the reasonable parameters, the average grain size is 41.48~42.57 μm, and the average shape factor is 0.80~0.81. The yield strength and tensile strength improvement ratio of the connecting rod produced by the proposed process are 47.07% and 20.89%, respectively.

With the wide application potential of wrought aluminium alloy in aerospace, automobile and electronic products, high-quality aluminium bars prepared by the radial forging (RF) process have received extensive attention. Penetration performance refers to the depth of radial plastic deformation of forgings, which is the key factor in determining the quality of forging. In this work, the penetration performance of the radial forging process for 6063 wrought aluminium bars is investigated by simulation using FORGE software. The minimum reduction amount of the hammer is calculated based on the forging penetration theory of forging. The influence of process parameters including forging ratio (FR) and billet temperature on the effective stress and hammer load in the RF process are investigated. The RF-deformed billet is then produced with the optimal process parameters obtained from the simulation results. The average grain size of aluminium alloy semi-solid spherical material is used to evaluate the forging penetration. Simulation results showed that the effective strain at the edge and the centre of the RF-deformed billet gradually increases, but the increasing speed of the effective strain at the edge becomes low. The hammer load first decreases quickly and then gradually maintains stability by increasing the FR. It is found that low billet temperature and high FR should be selected as appropriate process parameters under the allowable tonnage range of RF equipment. Under an isothermal temperature of 630 °C and a sustaining time of 10 min, the difference in the average grain dimension between the edge and the centre positions of the starting extruded blank is 186.43 μm, while the difference in the average grain dimension between the edge and the centre positions of the RF-deformed blank is 15.09 μm. The improvement ratio of penetration performance for the RF-deformed blank is obtained as 91.19%.

Liquid slugging is a fatal fault for large process compressors, leading to transient overpressure, the deformation and fracture of vital pressure-bearing parts, and even gas leakage or explosion. In the study reported here, to reveal the mechanism of overpressure formation, numerical simulations were conducted by means of the volume-of-fluid method to explore the dynamic evolution characteristics of the two-phase flow pattern. Then, high-speed photography was applied to capture the dynamic changes of the liquid boundary in the modified cylinder from different views, thus realizing the validation of the numerical model. This study reveals the significant influence of increased rotational speed on fluid flow patterns, impeding liquid discharge and exacerbating overpressure events. Additionally, changes in pressure waveform and a distinctive waveform feature were identified as effective diagnostic indicators for detecting fluid slugging. Next, a nondestructive pressure monitoring reconstruction method based on measuring bolt strain was proposed. The strain-based pressure showed good agreement with the simulated results, thereby validating its effectiveness and feasibility as an early warning indicator for liquid slugging. This study offers new perspectives on the failure mechanism of liquid slugging in reciprocating compressors by delving into the behavior of two-phase flow, with the potential to enhance the theoretical foundation of compressor condition monitoring and fault diagnosis.

Ensuring the reliability of process gas compressors is critical for underground gas storage, as piston rod fractures can lead to serious accidents, such as natural gas leaks or explosions. On-time monitoring and early detection play a vital role in preventing catastrophic consequences, minimising costs, and reducing production losses due to unplanned downtime. This study presents a novel accelerated life-testing method designed to replicate the fracture events of reciprocating compressor piston rods. By accelerating the induced crack initiation and propagation to the final fracture, comprehensive analyses of the fracture results are performed to reveal the piston rod fracture mechanism and the resulting secondary damage to the unit. The research further presents an innovative approach for identifying piston rod crack propagation by means of acoustic emission. Through kinetic analysis and time–frequency domain analysis, the study elucidates two mechanisms responsible for triggering crack signals during the compressor operation: the contact impact between the crosshead pin and the bearing due to the piston rod load reversal, and crack propagation occurring before the maximum tensile load is reached. In addition, the study identifies the piston rod crack expansion signal frequency band and achieves a high-sensitivity identification of crack dynamic growth by extracting signal sub-band features associated with crack propagation. Then, a prediction model of the fatigue crack growth rate was established based on the AE energy release rate, which provides a quantitative assessment of dynamic crack propagation during compression. This method aims to provide a maintenance strategy for piston rod fractures, thereby increasing the operational safety of critical dynamic equipment in underground gas storage.

The ionic compressor is a new and prospective technology applied for hydrogen storage which adopts a hydraulic system in which the hydraulic drive unit is a solid piston in the compression cavity. Controlling the trajectory of the solid piston is critical for achieving the designed thermodynamic process of compression. However, a strategy for controlling the position of a piston in an ionic compressor has not been reported in the open literature. In this paper, three valve-controlled methodologies are proposed for the effective control of a piston’s trajectory in an ionic compressor. A transient numerical model of the entire compression system was built using AMESim 2021 software. The performances of the proposed control methods were simulated and compared. The results show that the maximum isothermal efficiency, 50.28%, was obtained in the system using Position-P control, for which the highest hydrogen discharge mass for a single compression cycle of 1.14 g, a relatively low specific energy consumption of 2395.17 J/g, and a relatively small velocity control error of 0.32 m/s were observed. Although the lowest specific energy consumption was found in the case of the Dual-PS control method, the smallest mass product was also found for this case. Therefore, the Position-S control strategy was identified as the optimal method for a hydraulically driven ionic liquid compressor system.

As a new and promising compression technology for hydrogen gas, the ionic liquid compressor inherits the advantages of the ionic liquid and the hydraulic system. The liquid density is one of the key parameters influencing the fluid flow field, the sloshing of the bulk liquid, and the movement of droplets generated during the compressor operation. An appropriate selection of the liquid density is important for the compressor design, which would improve the thermodynamic performance of the compressor. However, the density of the ionic liquid varied significantly depending on the specific combination of the cation and anions. This paper proposed the methodology to select the optimal liquid density used in the ionic liquid compressor for hydrogen storage. The gas-liquid interaction in the compression chamber is analysed through numerical simulations under varied liquid density values. Results found that the increase in the liquid density promoted the detachment of the ionic liquid from the cylinder cover during the suction procedure and the contact of the bulk liquid on the compressor cover when the gas is compressed in the cylinder during the compression procedure. Both the droplet size and the dimension of the derived gas vortex decreased when the liquid density increased. The lowest mass transfer of hydrogen through the outlet was obtained at the density of 1150 kg/m³. The density of the ionic liquid from 1300 to 1450 kg/m³ is suggested to the hydrogen compressor, taking into account the transient two-phase flow characteristics, the mass transfer, and the total turbulent kinetic energy.

Aluminum alloys have been widely used in various engineering applications due to their excellent physical properties such as low density, high strength and good cutting capacity. In this paper, the semi-solid thixotropic extrusion forming process is proposed to produce aluminum alloy 6063 shells for mobile phones. The effects of the operating parameters on the equivalent stress distribution, velocity field, temperature field, and the load of the top mould were investigated through numerical simulations. Optimal parameters were identified from the simulation results. The experiment was then conducted at these optimal parameters. The macromorphology and microstructure results of the mobile phone shells produced from the experiment are presented and discussed. It was found that the optimal process parameters for preparing aluminum alloy 6063 shell by the semi-solid thixotropic extrusion process were a billet temperature of 630 °C, mould temperature of 400 °C, and top mould speed of 10 mm/s. It was found that the mobile phone shells fabricated under the optimal operating conditions were fully filled with a clear outline and a smooth surface. The solid grains in the microstructure were small, uniform and nearly spherical. The average grain size of the microstructure for the product was obtained as 76.92 μm and the average shape factor was found as 0.76.