Decrease In Compression Ratio Research Articles

Simulation and Experimental Study on Sealing Characteristics of Hydro-Pneumatic Spring GS Seal Rings

Hydro-pneumatic springs often work under high pressure and alternating load conditions, which can easily cause seal damage, leakage, and serious failure. Relevant studies have shown that the dynamic seal failure of hydro-pneumatic springs is the main cause of hydro-pneumatic spring failure, and the sealing performance of GS sealing rings directly determines the service life of hydro-pneumatic springs. The influence of different sealing structure parameters on the sealing performance of GS sealing of hydro-pneumatic springs has been studied, which can provide effective theoretical guidance for the design of sealing structures related to hydro-pneumatic springs. However, the existing research on hydro-pneumatic springs mainly focuses on the characteristics of damping and stiffness; there is a relative lack of research on sealing performance and sealing structure, and the performance change law of GS seals under different working conditions is unclear. In this paper, a GS seal ring is selected as the main seal of the hydro-pneumatic spring, the material parameters of the GS seal ring are obtained via the single-axis compression test, and the finite element simulation method is used to establish the sealing model under different compression ratios of 10–30% and different pressure impacts of 5–30 MPa. By doing so, the stress nephogram, sealing ring shape, and sealing contact pressure of the GS sealing ring under different simulation parameters are obtained. From the test results, the decrease in compression ratio after the wear of the sealing ring is the main reason for the seal leakage of the hydro-pneumatic spring. The maximum contact stress of the sealing ring occurs at the lip of the step ring, and the maximum sealing pressure of the sealing ring is determined by the contact pressure of sealing surfaces II and III. The sealing performance of the GS-type combination sealing ring is affected by the compression ratio of the sealing ring and the impact pressure; when the compression ratio of the sealing ring is 15%, the sealing ring can meet the sealing work needs below 25 MPa. The research results provide a theoretical basis for the design of GS sealing of hydro-pneumatic springs and the effective improvement of the life and reliability of related equipment.

Low-Overhead Compressibility Prediction for High-Performance Lossless Data Compression

As big data has evolved over the past few years, a lack of storage space and I/O bandwidth has become one of the most important challenges to overcome. To mitigate these problems, data compression schemes reduce the amount of data to be stored and transmitted at the cost of additional CPU overhead. Many researchers have attempted to reduce the computational load imposed on the CPU by data compression using specialized hardware. However, space savings through data compression often comes from only a small portion of data. Therefore, compressing all data, regardless of data compressibility, can waste computational resources. Our work aims to decrease the cost of data compression by introducing a selective data compression scheme based on data compressibility prediction. The proposed compressibility prediction method provides more fine-grained selectivity for combinational compression. Additionally, our method reduces the amount of resources consumed by the compressibility predictor, enabling selective compression at a low cost. To verify the proposed scheme, we implemented a DEFLATE compression system on a field-programmable gate array platform. Experimental results demonstrate that the proposed scheme improves compression throughput by 34.15% with a negligible decrease in compression ratio.

An experimental investigation on the performance, combustion and emission characteristics of a variable compression ratio diesel engine using diesel and palm stearin methyl ester

An attempt has been made to use biodiesel prepared from non-edible portion of palm oil as fuel of a conventional mono-cylinder compression ignition engine. The present experimental investigation takes into account the combined effect of using blends of diesel–palm stearin biodiesel as fuels and the compression ratio on different performance, combustion and emission characteristics of the said engine. The experiments have been carried out on a single-cylinder, direct injection diesel engine at varying compression ratio of 16:1–18:1 in four steps. It is observed that the brake thermal efficiency reduces by 7.9% when neat biodiesel is used instead of diesel. But, it increases with the increase in compression ratio for all the blends. Brake specific fuel consumption and exhaust gas temperature increase with the addition of biodiesel to diesel and also with the increase in compression ratio. Heat release rate decreases with biodiesel, and it is minimum at the rated compression ratio of 17.5:1 for all the fuels considered here. On the other hand, ignition delay is found to be more with neat diesel, and it increases with the decrease in compression ratio. Significant reductions in emissions of carbon monoxide (CO), hydrocarbon (HC) and smoke are observed with biodiesel, while the emissions of oxides of nitrogen (NOx) and carbon dioxide (CO2) increase. The decrease in compression ratio increases the emissions of CO, HC and smoke, but the emissions of NOx and CO2 decrease with the decrease in compression ratio.

Needle fir wood modified by surface densification and thermal post-treatment: hygroscopicity and swelling behavior

Needle fir (Abies nephrolepis) wood was surface densified at two compression ratios (16.1 and 21.7 %), two hot-pressing temperatures (160 and 180 °C) for a pressure holding duration of 10 min. Subsequently, it was thermally treated at two temperatures (180 and 200 °C) for 1 h. The equilibrium moisture content responses and radial swelling strain ratios were calculated for thirteen types of adsorption specimens under adsorption and water soaking, respectively. Compared with untreated (control) specimens and densified but non-thermally treated ones, the hygroscopicity of thermally post-treated specimens was significantly decreased. Both hot-pressing temperature and compression ratio showed insignificant influence on the hygroscopicity of all treated specimens. Under the current test conditions, with the increase of thermal post-treatment temperature and the decrease of compression ratio among the thermally post-treated specimens, the radial swelling deformation was significantly decreased. The impact of increasing hot-pressing temperature on the radial swelling was insignificant according to the statistical analysis.

Experimental investigations on ejector refrigeration system with ammonia

A vapor ejector refrigeration system has been designed and developed to operate with ammonia. In this paper, performance of ejector refrigeration system has been experimentally studied with three different area ratio ejectors by varying operational parameters namely generator, condenser and evaporator temperatures. Effect of non-dimensional parameters like compression ratio, expansion ratio and area ratio on the system performance is studied. Entrainment ratio and coefficient of performance of the system increase with increase in ejector area ratio and expansion ratio and they increase with decrease in compression ratio.