310 research outputs found
Experimental investigation on the turbulence flame autoignition characteristics of ammonia in a high-temperature co-flow
No full textAmmonia has a promising future for transportation and industrial power as an innovative zero-carbon fuel because of the harsh emission laws in force and the pressing need of low carbon fuels. Thus, the aim of this work has been to investigate the autoignition characteristics of an ammonia turbulence flame under a high temperature co-flow, on the basis of an experimental platform. The morphology, lift height, and stability of an ammonia jet diffusion flame have been explored under different co-flow regimes (in terms of temperature and velocity) and fuel injection pressures. It was found that when the co-flow temperature augments, the ammonia jet can form a stable lifting flame. Moreover, the combustion stability of the ammonia flame increases significantly and the fluctuation of the lift height of the flame clearly decreases over time. Forming a stable ammonia jet lifting flame under high co-flow velocities and injection pressures requires a high co-flow temperature. The length, area, and perimeter of an ammonia jet diffusion combustion flame increase as the co-flow temperature increases. The distance from the point of autoignition to the central nozzle outlet and the ignition delay both decrease when the co-flow temperature augments. The lift height of an ammonia diffusion combustion flame gradually decreases as the co-flow temperature increases. Moreover, there is a critical temperature of 1173 K beyond which the decline slope of both the lift height and ignition delay decreases
Ammonia-hydrogen blends combustion in turbulent high temperature co-flow
No full textIn response to the stringent vehicle emission regulations, ammonia, with its potential as a carbon-free alternative fuel for reducing carbon emissions, faces application challenges due to higher ignition energy requirements and lower flame stability. Adding hydrogen is one of the effective ways to improve combustion performance of pure ammonia. This study focuses on the auto-ignition characteristics and jet flame stability of ammonia-hydrogen fuel blends under various conditions, such as different injection pressures, co-flow velocities, co-flow temperatures, and hydrogen blending ratios, employing a controllable active thermal atmosphere burner. Hydrogen addition increases flame brightness, area, and crinkly morphology due to enhanced NH2 production and higher combustion temperatures. The flame length increases together to the hydrogen ratio and the co-flow temperature, and it has been verified that it is primarily governed by jet momentum. Above 1073 K of co-flow temperature, the heat transfer becomes dominant for auto-ignition, reducing the effect of hydrogen presence. Combustion efficiency improves for higher co-flow temperatures, while hydrogen enhances propagation until a threshold is reached for XH2 = 20 %, beyond which a sensible increment in propagation cannot be detected. When the injection pressure augments, the flame is enlarged but auto-ignition can be hindered. Hydrogen addition reduces fluctuations, ensuring optimal stability for XH2 = 20 %
Interfacial Compatibility and Anticorrosion Performance of Epoxy Resin Coating Improved by Modified Graphene and Graphene Oxide
No full textEpoxy (EP) coatings containing different mass fraction of modified graphene (G) and graphene oxide (GO) have been successfully prepared on the surface of cast irons. The anticorrosion performance of the coatings was studied by electrochemical polarization curve and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution. The interfacial structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results indicate that both G and GO could improve the anticorrosion performance of EP coatings effectively and their best mass fraction are 0.25% for G and 0.50% for GO. Furthermore, the anticorrosion performance of G-EP composite coating is better than GO-EP composite coating at the same mass fraction. Compare to G, XPS and SEM results indicate that GO exhibits better interfacial compatibility in EP. Finally, the inhibitive mechanism of G and GO was discussed based on the obtained results
Achieving excellent anti-corrosion and tribological performance by tailoring the surface morphology and chemical composition of aluminum alloys
No full textAluminum alloy surfaces with micro/nano-structures were fabricated via a simple chemical etching (CE) method. After chemical modification with perfluorodecyltriethoxysilane (PFDS), n-octadecyltriethoxysilane (OTS) and aminopropyltriethoxysilane (APS), surfaces with different wettability were obtained. The morphology and chemical elements of the as-prepared surfaces were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). In addition, the influence of the surface morphology and chemical modification on the wetting/dewetting properties was investigated. Finally, the anti-corrosion and tribological properties of the as-prepared self-assembled monolayers (SAMs) were characterized using an electrochemical workstation and UMT-3 tribometer. The influence of surface morphology and SAMs on the anti-corrosion and tribological performances is discussed in detail. The results showed that the optimal preparation conditions consisted of a 40% volume fraction of hydrochloric acid with a CE time of 2 min. The corrosion resistance of the surfaces chemically modified with hydrophobic groups was much better than that of those modified with hydrophilic groups. Also, the combination of micro/nano-structures and suitable SAMs on aluminum alloy surfaces could greatly enhance the friction reduction and wear resistance behavior
Designing Surface Morphologies and Anti - corrosion Properties of Anodized Aluminum Alloys via a Chemical Etching Method
No full textTo improve corrosion resistance performance of aluminum alloy,micro/nano - structures were formed by chemical etching and anodic oxidation methods on the surface of aluminum alloy. Then,anodic oxidation films with excellent anti-corrosion performance were obtained after being chemically modified via a self-assembly layer to improve the corrosion resistance of aluminum alloys. The surface morphologies and chemical elements of the as-prepared films were investigated by infrared spectroscopy and SEM. The values of surface roughness were measured by laser scanning confocal microscope. The hydrophilic/hydrophobic and anti-corrosion properties of the films were characterized by optical contact angle meter and electrochemical workstation. The influence of etching time on the surface morphologies and anti-corrosion performance was investigated. The results show that when the etching time is 3 min, the film owns the best corrosion resistance performance, the corrosion potential shifted 0.15 V positively, the corrosion current density decreased two orders of magnitude compared to bare aluminum alloy, and the static contact angle is 152°at its maximum which is due to the intact and suitable ratio of the micro/nano - structure of the films under this preparation condition
铜合金表面巯基官能有机硅溶胶-凝胶涂层中TEOS含量对其防腐性能的影响
No full textOrganic-inorganic hybrid sol-gel coatings with high solid content were prepared on copper surface by means of hydrolysis-condensation reaction. 3-Mercaptopropyltrimethoxysilane (MPTMS), tetraethylorthosilicate (TEOS) and hydrochloric acid were used as organic precursor, inorganic precursor and catalysts respectively. The chemical composition, and the average size of sol particles and the surface- and cross section-morphology of sol-gel coatings were characterized by Fourier transform infrared spectroscopy, dynamic light scattering particle size analyzer and field emission scanning electron microscopy respectively. The adhesion and corrosion performance of sol-gel coatings were investigated by pull-off adhesion tester and electrochemical workstation. The results showed that the thermo-stability of the coatings was significantly improved due to the addition of TEOS. However, the average size of sol particles increased with the increase of TEOS content. Excessive addition of TEOS can induce holes and cracks on the surface of coatings or within the coatings. The coatings owned the best corrosion resistance when the molar ratio of TEOS to MPTMS was 0.6 due to their larger crosslinking density and fewer defects
Comparison of atmospheric infrared sounder temperature and relative humidity profiles with NASA African Monsoon Multidisciplinary Analyses (NAMMA) dropsonde observations
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