Search Results (13)

High-entropy coatings based on CoCrFeNiMn obtained by thermal spraying have demonstrated the potential to improve the wear resistance of traditional materials used in extreme conditions. The aim of the work was to study the effect of the oxygen/fuel ratio when using kerosene as fuel in the HVOF process on the microstructural characteristics of CoCrFeNiMn coatings, including phase composition, microhardness, elastic modulus, and wear resistance. Phase and microstructural transformations in gas-atomized powder during HVOF spraying were analyzed using XRD, SEM, and EDS methods. The tribological and mechanical properties of the coatings obtained were also evaluated. The results obtained are consistent with thermodynamic predictions based on the Scheil model for non-equilibrium conditions. The data obtained indicate the high potential of high-entropy CoCrFeNiMn alloys for use as protective coatings for industrial purposes. In addition, the results of the study emphasize the promise of using thermodynamic prediction of high-entropy alloys using Thermo-Calc software. The best mechanical and tribological properties were obtained in the HVOF 1 regime, which provided a maximum microhardness of 783.8 HV and a minimum wear rate of 7.45 × 10⁻⁵ mm³ × N⁻¹ × m⁻¹. Full article

Samples of refined petroleum fuels from the three major oil-marketing companies (GOIL Company Limited, Total Energies Ghana Limited and Shell Vivo Ghana Limited) in Ghana have been analysed for elemental concentrations using an X-ray fluorescence facility at the National Nuclear Research Institute, Ghana Atomic Energy Commission. The samples were acquired from seven different fuel service stations where customers directly purchase refined petroleum fuels such as diesel, petrol and kerosene. The X-ray fluorescence method was considered for the study because sample preparation does not require the addition of reagents, and the fluorescence measurements involve a direct electron transition effect. The fluorescence study was carried out to estimate the concentrations of sulphur and other contaminants in the major refined petroleum fuel products patronised in Ghana. The average sulphur concentration in the samples of diesel products were 17.543, 25.805 and 26.813 ppm in DFS, DE and DXP samples compared to 22.258, 22.623 and 15.748 ppm in petrol samples of PE, PXP and VP. Also, the sulphur concentration of sample KE, kerosene products, is 33.250 ppm. Among the diesel samples, DE and DXP recorded the highest but most comparable average concentration of elemental contaminants, and DFS the least, while PXP recorded the least among the petrol samples. The study estimated the concentrations of four heavy metal elements that are toxic to biological life (Hg, Pb, Cr and Mn) to be less than 10.0 ppm, except Cr. The study concluded that most of the elemental contaminants of heavy metals in the samples were relatively less than ultra-low levels. Therefore, exhaust emissions may have little impact on the environment. Also, the content of the ash-producing metal elements in each sample of the seven refined fuel products is between 10.0 and 50.0 ppm. Since the concentration of sulphur and a few other elemental contaminants could not meet the internationally accepted standard (<10.0 ppm), the imported refined fuel products used in Ghana may be considered relatively good but not environmentally safe. Full article

A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray, atomization, and combustion efficiency. In this study, a micro-turbojet engine equipped with a micro-orifice fuel injector was developed that operated under low injection pressure (P_inj), that is, at a low Reynolds number (Re). Given the paucity of cavitation studies conducted under such conditions, the current study experimentally and numerically investigated the cavitation and spray characteristics of water and kerosene in a micro-orifice injector with a diameter of 0.3 mm. The results indicated that the water and kerosene exhibited no cavitation, cavitation, supercavitation, and hydraulic flip. However, the discharged jet was unaffected by internal flows, and the jet angles remained nearly constant, indicating that the cavitation in micro-orifice injectors at a low Re is less important than that at a high Re. Because cavitation in micro-orifice injectors under a low Re has no positive effects on the atomization and spray, determining the geometry of a micro-injector is essential. The injector with a length-to-diameter (L/D) ratio of 3 exhibited an approximately 25% higher discharge coefficient (C_d) than those of injectors with L/D ratios of 6 and 8 and, thus, is recommended for injectors in micro-turbojet engines. Full article

In this paper, an 80-ton thrust liquid rocket engine (hereinafter referred to as an LRE) with a gas generator cycle, a 5:1 thrust throttling ratio, and an integrated flow regulator/gas generator (hereinafter referred to as an IFRGG) is analyzed. This LRE can be used during the first stage of launching, second-stage and upper-stage space missions, and moon/mars low-orbit hovering and soft landing, and it can also be used with various near-space multipurpose flight vehicles. The thermal performance model of the variable-thrust LRE is established, the influence of the main LRE design parameters on the performance optimization is analyzed, and an optimal selection of the design parameters under certain constraints is completed. A performance evaluation was successfully conducted, and we determined the main structural parameters at the sea-level design point; additionally, we evaluated the LRE performance, matched the system parameters under a 100–20% variable-thrust operation, and conducted an analysis on the LRE operating characteristics under a wide range of variable-thrust operations. The LOX/kerosene propellants were selected, and the vacuum-specific impulse of the LRE decreased from 303.2 s to 289.2 s; this followed an approximate linear law, with a decrease of about 4.62% when the thrust was varied in the wide range of 100–20%. The variable-thrust LRE still had a better vacuum performance under a very deep throttling condition. The reason why the specific impulse was low under the deep throttling condition is that it was greatly affected by the different atmospheric pressure that was caused by the varying flight height and the insufficient atomization and combustion of the propellant; however, because of its wide range of variable-thrust working abilities, it is suitable for various special flight missions. Full article

Due to its important environmental role, the analysis of trace metals in natural waters is attracting increasing attention; consequently, faster and more accurate analytical methods are now needed to reach even lower limits of detection. In this work, we propose the use of electro-membrane extraction (EME) to improve analytical methods based on hollow fiber liquid phase micro-extraction (HFLPME). Specifically, an EME-based method for the determination of trace Ni in seawater has been developed, using an HFLPME system with di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as a chemical carrier, followed by instrumental determination by graphite furnace atomic absorption spectroscopy (GFAAS). Under optimum conditions, Ni was pre-concentrated 180 ± 17 times after 15 min, using sample pH = 5.5, the concentration of DEHPA 0.9 M in the liquid membranes, and 1.9 M HNO₃ in the acceptor solution, as well as an electric potential of 25 V with the sample being stirred at 500 rpm. When compared with other HFLPME systems for pre-concentration of trace Ni in seawater in the absence of electric potential, the enrichment factor was improved 2.2 times, while the time of extraction was reduced an 89%. The limit of detection of the new method was 23.3 ng L⁻¹, and both its applicability and accuracy were successfully evaluated by analyzing Ni concentration in a seawater-certified reference material (BCR-403), showing the reliability of EME for sample preparation in the determination of trace metals in marine water samples. Full article

An unsteady numerical simulation method was used in order to explore more efficient atomization methods for liquid fuel in scramjet combustors and to study the influence of different shock wave incident positions on the atomization characteristics of kerosene in crossflow. The wedge compression surface was used to generate the incident shock wave, and the incident position of the shock wave on the fuel jet was controlled by changing the angle of the wedge surface. The inlet Mach number was 2.01; the total temperature was 300 K, and the momentum ratio was 12. The research results show that as the incident position of the shock wave moves upstream, the penetration depth of the jet is essentially unchanged, but the inner edge trajectory of the jet is closer to the wall. Because the shock wave affects the Kelvin–Helmholtz instability of the jet, the unsteadiness of the jet root is strengthened, and the unsteadiness downstream of the jet is weakened. The atomization of the jet and the stability of the particle-size distribution are, thus, realized more quickly. The incident shock wave reduces the Sauter mean diameter of the jet section and makes the droplet distribution more uniform. The incident shock wave makes the atomization angle of the jet along the flow direction increase first and then decrease. The changes in the jet characteristics are determined by the changes in the reflux region, momentum transport, and pressure distribution caused by the incident shock wave. Full article

In order to achieve the effective separation of copper-molybdenum in the presence of xanthate and kerosene, carrageenan was explored as a novel environmentally friendly molybdenite depressant in this work. The flotation behavior of molybdenite was studied by micro-flotation tests, and the depression mechanism was investigated through zeta potential, Fourier Transform Infrared Spectroscopy (FTIR) and atomic force microscope (AFM) analysis. The flotation results showed that molybdenite was significantly depressed by carrageenan in the pH range of 6–12 even in the presence of xanthate and kerosene. Zeta potential, FTIR and AFM measurement demonstrated that carrageenan could adsorb strongly on the molybdenite surface and change the surface wettability of molybdenite, thus significantly reducing the floatability of molybdenite. Full article

Fe-based amorphous coatings are typically fabricated by high-velocity oxygen-fuel spraying using industrial raw materials. The bonding mode between the coating particles and the corrosion mechanism of the coating in the chloride-rich environment were studied. The results indicate that some fine crystallites such as α-Fe and Fe₃C tend to precipitate from the amorphous matrix as the kerosene flow rate increases or the travel speed of spraying gun decreases. Moreover, some precipitates of the (Cr, Fe)₂O₃ nanocrystal were detected in the metallurgical interfaces of the amorphous coating. The relationship among the amorphous volume fraction, porosity, and spraying parameters, such as the kerosene flow rate and the travel speed of the spray gun, were established. Due to an oxidation effect during spraying process, atomic diffusion, crystallite precipitation and regional depletion of Cr occur in the area along the pre-deposited side near the metallurgical bonding interface, leading to the initiation of pitting. A model of pitting initiation and expansion of Fe-based amorphous coatings is proposed in this paper. Full article

Wind direction and speed are the most important factors that determine the degree of damage caused by a jet fire. In this study, the metal hose used to extract/supply fuel was identified as the component with the highest risk for a jet fire occurring at an aerospace facility. A risk assessment was performed to evaluate the individual risk of a jet fire from the metal hose according to the wind direction and speed. HSE failure data was applied for calculating the jet fire probability including metal hose failure, ignition frequency, and jet fire frequency. Which was 3.0 × 10⁻⁴. The individual risk of different fatality probabilities was calculated according to the wind rose data for the aerospace facility. The individual risk from jet fire in the aerospace facility was calculated with a maximum risk of 3.35 × 10⁻⁵ and a minimum risk of 1.49 × 10⁻⁶. The individual risk satisfied HSE ALARP criteria. In addition, firewalls, extinguishing systems, and an emergency shut off system were enhanced, and it was thought that the risk from jet fire could satisfy acceptable criteria. Full article

HVAF (High Velocity Air Flame) flame spraying can generate supersonic high-temperature gas jets, enabling thermal spraying at unprecedented speeds. However, there is a problem with the energy cost of this device. This study focused on combustors that used cheap liquid fuel (kerosene) as the fuel for HVAF. In this research, we have developed a compact combustor with a narrow channel as a heat source for the HVAF heat atomizer. Using this combustor, the stability of the flame formed in the combustor, the morphology of the flame, and the temperature behavior in the combustion chamber were investigated in detail. As a result, the magnitude of the swirling airflow had a great influence on the structure of the flame formed in the combustor, and the stable combustion range of the combustor could be determined. As the swirling air flow rate changes, the equivalent ratio of the entire combustor changes significantly, and the flame structure also transition from the premixed flame to the diffusion flame. From this study, it was confirmed that the temperature inside the combustor has great influence on the flame structure. Full article

To improve our understanding of the interactive effects in combustion of binary multicomponent fuel droplets at sub-atmospheric pressure, combustion experiments were conducted on two fibre-supported RP-3 kerosene droplets at pressures from 0.2 to 1.0 bar. The burning life of the interactive droplets was recorded by a high-speed camera and a mirrorless camera. The results showed that the flame propagation time from burning droplet to unburned droplet was proportional to the normalised spacing distance between droplets and the ambient pressure. Meanwhile, the maximum normalised spacing distance from which the left droplet can be ignited has been investigated under different ambient pressure. The burning rate was evaluated and found to have the same trend as the single droplet combustion, which decreased with the reduction in the pressure. For every experiment, the interactive coefficient was less than one owing to the oxygen competition, except for the experiment at L/D₀ = 2.5 and P = 1.0 bar. During the interactive combustion, puffing and microexplosion were found to have a significant impact on secondary atomization, ignition and extinction. Full article

One of the major challenges in the removal of organic pollutants is to design a material with high efficiency and high flux that can remove both cationic and anionic dyes, oil-in-water (O/W) emulsion and heavy metal ions. Herein, we constructed novel chemically stabilized MgAl-layered-double-hydroxide/sepiolite (MgAl-LDH/Sep) composite membranes via 3D hierarchical architecture construction methods. These membranes were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), etc. Benefiting from the presence of hydrophilic functional groups on the surface of the film, the membranes show an enhanced water flux (~1200 L·m⁻² h⁻¹), while keeping a high dyes rejection (above 99.8% for anionic and cationic dyes). Moreover, the CA membrane coupled with MgAl-LDH/Sep exhibits a multifunctional characteristic for the efficient removal of mesitylene (99.2%), petroleum ether (99.03%), decane (99.07%), kerosene (99.4%) and heavy metal ion in water due to the layer-by-layer sieving. This hierarchical architecture is proved to have excellent environmental and chemical stability. Therefore, the membrane has potential in the treatment of sewage wastewater. Full article

This paper aims to understand the fundamental interaction mechanism between molybdenite and kaolinite in gypsum solution using kerosene as collector. Micro-flotation tests were conducted to study the effect of gypsum solution on the flotation performance of mixed −74 μm molybdenite and −10 μm kaolinite mineral. The results showed that the recovery of molybdenite decreased from 86% to 74% while the gypsum solution concentration increased from 0 to 800 mg/L, indicating the detrimental effect of kaolinite on molybdenite flotation could be enhanced by gypsum solution. This is mainly caused by the slime coating of kaolinite on molybdenite through dissolved calcium ion of gypsum solution. In order to confirm the slime coating phenomenon, zeta potential distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were used to investigate interaction characteristics and mechanisms. The zeta potential distribution results revealed that mixed samples had the value between signal molybdenite and kaolinite samples in gypsum solution, which proved the coating phenomenon of kaolinite on molybdenite. Moreover, the coating phenomenon was becoming more and more obvious with the gypsum solution concentration. The coating phenomenon of kaolinite on molybdenite surface was also directly observed from SEM results. The AFM results provided further evidence for the possibility of slime coating, as the adhesion force increased with the gypsum solution concentration, which means the aggregates of molybdenite and kaolinite were becoming more stable. Full article