Prediction of B20 Storage Tank Precipitate Removal Based on Biodiesel Monoglyceride Content

Precipitate in B20 fuel stored in storage tanks can accumulate at the bottom level of the tank and affect the fuel filter, clogging in the fuel distribution and engine system. This study examines the precipitate formation prediction in B20 fuel based on the monoglyceride content in biodiesel. This research used a modified CSFT method of ASTM D7501 for the precipitation test. Monopalmitin was added to biodiesel with a variation of monoglyceride content. Each biodiesel sample was then blended with petroleum diesel fuel to produce two groups of samples. Each sample was separately soaked in the cooling chamber at constant and room temperature for 21 days. The bottom layer of each B20 fuel sample stored in the measuring cylinder was then pipetted and filtered, washed with petro-ether, vacuum-dried, and weighed for a constant amount of precipitate retained on the filter. The simulation results show that the ratios between the amount of collected precipitate at the bottom layer of the 2-liter measuring cylinder and the total amount of collected precipitate for the 2-liter measuring cylinder increased with the monoglyceride content biodiesel. This ratio was used to predict the amount of accumulated sludge for a given volume of B20 fuel loaded into the storage tank. This study shows the effect of monoglyceride content on the precipitation behaviour in the storage tank concerning general tank storage dimension parameters and B20 loading frequency. This approach can be applied to estimate the sludge removal frequency for biodiesel storage.

Laboratory Study on Changes in Gas Desorption Properties of Anthracite after Cyclic Loading

Coal mass is subjected to cyclic loading during pulsating hydraulic fracturing (PHF), and changes in its gas desorption properties affect gas drainage. Therefore, it is of great importance to correctly understand the influences of cyclic loading on the gas desorption properties of coal mass. Firstly, loading tests with different frequencies and amplitudes were performed on anthracite from Qinshui Basin (Shanxi Province, China) using a fatigue testing machine. Secondly, gas desorption tests were performed to determine the associated curves for each test group at different equilibrium pressures, and the initial desorption capacity and diffusion coefficient of the gas were calculated. Finally, the influence of different loading conditions on the gas desorption laws were analyzed. The test results demonstrate that a greater loading frequency increases the ratio of the initial desorption capacity so that the desorption rate of coal samples is higher, and the gas desorption properties become increasingly better in the initial stage. However, variations in the amplitude have minimal impact on the ratio of the initial desorption capacity. When the amplitude is too large in the initial stage, the diffusion coefficient decreases and the gas desorption properties worsen. In addition, the above test results are used to discuss the selection of the amplitude and frequency in the PHF process from a macroperspective. The contained research results provide an important theoretical basis for the field application of PHF technologies in coal mines.

Investigation of the Influence of Moisture Content on Fatigue Behaviour of HPC by Using DMA and XRCT

High-performance concrete (HPC) is a topic of current research and construction projects, due to its outstanding compressive strength and durability. In particular, its behaviour under high-cycle fatigue loading is the focus of current investigations, to further pave the way to highly challenging long-lasting constructions; e.g., bridges or offshore buildings. In order to investigate the behaviour of HPC with different moisture contents in more detail, a mixture of silica sand and basalt aggregate with a maximum grain size of 8 mm was investigated with three different moisture contents. For this purpose, cyclic compressive fatigue tests at a loading frequency of 10 Hz and different maximum stress levels were performed. The main focus was the moisture influence on the number of cycles to failure and the development of concrete temperature and strain. In a further step, only the mortar matrix was investigated. For this purpose, the mixture was produced without basalt, and the moisture influence was investigated on smaller-sized test specimens using dynamic mechanical analysis (DMA) and X-ray computed tomography (XRCT). It was shown that the moisture content of HPC had a significant influence on the fatigue damage behaviour due to the number of cycles to failure decreasing significantly with increased moisture. In addition, there was also an influence on the temperature development, as well as on the strain development. It was shown that increasing moisture content was associated with an increase in strain development. XRCT scans, in the course of the damage phases, showed an increase in internal cracks, and made their size visible. With the help of DMA as a new research method in the field of concrete research, we were also able to measure damage development related to a decrease in sample stiffness. Both methods, XRCT and DMA, can be listed as nondestructive methods, and thus can complement the known destructive test methods, such as light microscopy.

Experimental Investigation on the Behavior of Gravelly Sand Reinforced with Geogrid under Cyclic Loading

In view of the dynamic response of geogrid-reinforced gravel under high-speed train load, this paper explores the dynamic characteristics of geogrid-reinforced gravel under semi-sine wave cyclic loading. A number of large scale cyclic triaxial tests were performed on saturated gravelly soil reinforced with geogrid to study the influence of the number of reinforcement layers and loading frequencies on the dynamic responses of reinforced gravelly sand subgrade for high speed rail track. The variation of cumulative axial and volumetric strains, excess pore pressure and resilient modulus with number of loading cycles, loading frequency, and reinforcement arrangement are analyzed. The test results reveal that the cumulative axial strain decreases as the number of reinforcement layers increases, but increases with loading frequency. The resilience modulus increases with the number of reinforcement layers, but decreases as the loading frequency increases. The addition of geogrid can reduce the excess pore water pressure of the sample, but it can slightly enhance the rubber mold embedding effect of the sand sample. As the loading frequency increases, the rubber mold embedding effect gradually weakens.

SIGNIFICANCE OF DX-CENTERS FOR ACOUSTIC INDUCED RECONSTRUCTION PROCESSES OF DEFECTS IN GaN/AlGaN

The experimental results of amplitude effects are compared (from an ultrasonic wave deformation amplitude – a tension τUS) for electron concentration and changes of the lattice parameter on the same sample GaN/Al0.2Ga0.8N/GaN/AlN. It has been experimentally established that at ultrasonic loading (frequency 5–10 MHz, amplitude – towards 2·104 W/m2) there is a nonlinear increase in the effective electron concentration and an increase in the lattice parameter; at the same time, the mobility of electrons decreases and μН(τUS) ~ |τUS|. The energy parameters of the acoustic activation charge carriers process are calculated from the approximation of experimental amplitude changes – Еа ≈ 50 meV and γn(300 K) ≈ 2,5·10-27 m3. The amplitude dependences (increase) of the relative lattice parameter change (ΔС/С) from the tension τUS have been investigated experimentally at different frequencies. The energy of DX-center transition UDX ≈ 108 meV and the activation volume of this transition γDX ≈ 6,6·10-27 m3 are calculated from the approximation of the experimental amplitude changes. The revealed correlation of the magnitude of acoustic induced effects in different experiments allows to build a quantitative energy model of the acoustic action process based on the properties of metastable DX centers. It is shown that the acoustic induced process occurs due to the dimensional displacement of the DX-center atom (a background impurity of silicon atoms) from the non-central position to the centrally symmetric one; herewith DX-center is ionized, one goes into the d0-state. It is believed that the changes are most likely to occur near penetrating dislocations in the barrier layer Al0.2Ga0.8N – acoustic modulated oscillations of the distance between the possible positions of the donor atom lead to a decrease in the barrier to the displacement of the defect.