To elucidate the evolution laws of impact velocity of high-pressure pulse water jet and the breakage characteristics of coal under confining condition, a coupled smoothed particle hydrodynamics-finite element (SPH-FEM) algorithm is adopted. A sinusoidal velocity is applied to the plunger inside the pipeline. The evolution laws of water jet velocity inside and outside the nozzle were obtained, and the temporal damage and breakage characteristics of coal under load and unload conditions impacted by pulse water jet were compared and analyzed. The influence of key parameters such as average velocity, pulse amplitude, and pulse frequency on damage and breakage characteristics of coal was revealed. The results show that the velocity evolution of water jet particles inside and outside the nozzle undergoes four stages: a stationary stage and transient acceleration to a low speed in the pipeline, acceleration inside the convergent section of the nozzle, micro-acceleration inside the straight section of the nozzle, and pulse variation speed following a sinusoidal variation after exiting the nozzle. Under the stress free and two-dimensional stress load conditions, the broken pits of coal specimen exhibit an abnormal development, and undergoes from bowl shape to U-shape, respectively. Two-dimensional stress load has a suppressive effect on the derivation and propagation of internal cracks in coal, reducing the rock-breaking efficiency. Besides, pulse water jet has a higher rock-breaking efficiency on loaded coal specimens than that of continuous water jet. The depth and area of coal fragmentation increase exponentially with the increase of plunger’s average velocity or pulse amplitude, and show a trend of initial increase and subsequent decrease with the increase of pulse frequency, indicating the existence of an optimal pulse frequency for coal fragmentation. The research findings could provide a theoretical guidance for improving the rock-breaking efficiency of high-pressure pulse water jet under confining conditions and optimizing the working parameters.

Diamond anvil cell (DAC) is a kind of widely used static-high-pressure device. Benefitting from its wide pressure range, excellent optical applicability and convenience of use, DAC provides a tremendous boost to the development of high-pressure science. However, at high pressures, factors like solidification of pressure transmitting medium may cause destruction of the hydrostatic pressure condition in the DAC sample chamber, leading to the generation of pressure gradients. In this work, a new method of using the technique of picosecond ultrasonics to investigate acoustic signal distribution at various locations within the sample chamber was proposed, which can analyze the pressure distribution via the acoustic observations. Limitations in the continuity of signal acquisition, sample selection, etc. can be overcome in this experimental technique, which could be built and manipulated in an ordinary laboratory. Here, pressure gradient in silicon oil was carried out under compression using this technique, and the results revealed that the pressure gradient in the sample chamber increased from 1.3×10⁻⁴ GPa/μm at 1 GPa to 5.3×10⁻² GPa/μm at 30 GPa. In addition, the anomalous change of standard deviation of the pressure distribution was analyzed by combining it with in-situ Raman spectroscopy, then the possible phase transitions of silicone oil at high pressures were discussed.

In order to improve the ultimate pressure bearing capacity and increase the volume of the cavity of the belt type ultra-high pressure die, a structure of winding discrete type large cavity ultra-high pressure die was proposed. This die is mainly composed of discreted cylinder, supporting ring and steel wire winding layers. The circumferential stress of the monolithic cylinder is eliminated in discrete structure so that there is no need to use large size cemented carbide and supporting ring as high pressure die, which can effectively improves the pressure bearing capacity of high pressure die, reduce the difficulty of its manufacturing, and make it easy to obtain large cavity volume. The key parameters of the structure of high pressure die are designed and calculated to determine the optimal size of the geometry. It is found that under the same working internal pressure loading by comparing numerical simulation methods, the stress of the discrete compression cylinder is lower, and the stress environment on the inner wall of the cylinder is effectively improved. The pressure bearing capacity of the winding discrete large-cavity ultra-high pressure die is predicted. It is found that the pressure bearing capacity of the die gradually increases with the increase of the number of discrete blocks, but the growth rate is slower and slower. Therefore, it is not feasible to increase the pressure bearing capacity of the cylinder by increasing the number of discrete blocks infinitely. The analysis shows that the winding discreted large cavity ultra-high pressure die has higher pressure bearing capacity, longer life and lower operating cost. It provides a new idea and method for the design of high pressure device with large volume and high pressure bearing capacity.

In order to explore the influence of injection pressure on the deflagration characteristics of gasoline in the confined space, a 20 L spherical explosion test device was used to examine the changes of characteristic parameters, i.e., the transient flame propagation and temperature of gasoline mist deflagration under different injection pressures. The results showed that the optimum spraying time was 100 ms, and the maximum explosion pressure and maximum explosion pressure rise rate increased linearly with the increase of injection pressure, while explosion duration decreased linearly. The change of injection pressure had a more significant effect on explosion duration, and the combustion efficiency of gasoline increased significantly with the increase of injection pressure. Based on the colorimetric temperature measurement method, the flame temperature field was reconstructed. It was found that the maximum average temperature had a linear relationship with injection pressure, and the maximum average temperature increased with injection pressure. The influence of injection pressure on the deflagration characteristics of gasoline mist was analyzed through the changes of mist morphology and flame temperature during flame propagation. The outcome of this research can provide theoretical reference for the design of turbocharged direct injection internal combustion engine and the improvement of combustion efficiency and economy of gasoline internal combustion engine.