低温下生物柴油的触变特性研究

触变性是一种重要的流变学性质,这种性质的研究对于生物柴油的输送及安全性有着重要的意义。低温下利用应力控制流变仪分析了剪切速率和剪切时间对不同原料制备的生物柴油粘度的影响,结果表明,低温下生物柴油的粘度不仅与剪切速率有关,且随剪切时间的延长而降低,表现出明显的触变性。以此为基础研究了各种历史条件下生物柴油的初次裂降规律,同时分析了三参数和四参数触变模型对地沟油生物柴油不同温度、不同剪切速率下初次裂降曲线的拟合效果,结果表明,四参数双曲模型的拟合效果最理想。对四参数双曲模型中的参数与温度、剪切速率的关系进行进一步分析,并对最大剪切应力、平衡剪切应力与剪切速率的关系进行了曲线拟合,结果表明,两者与剪切速率呈直线关系。     

Improving the low temperature properties of biodiesel fuel

The use of biodiesel as a diesel fuel extender and lubricity improver is rapidly increasing. While most of the properties of biodiesel are comparable to petroleum based diesel fuel, improvement of its low temperature flow characteristic still remains one of the major challenges when using biodiesel as an alternative fuel for diesel engines. The biodiesel fuels derived from fats or oils with significant amounts of saturated fatty compounds will display higher cloud points and pour points. This paper is aimed to investigate the cold flow properties of 100% biodiesel fuel obtained from Madhuca indica, one of the important species in the Indian context. In this paper, the cold flow properties of biodiesel were evaluated with and without pour point depressants towards the objectives of identifying the pumping and injecting of these biodiesel in CI engines under cold climates. Effect of ethanol, kerosene and commercial additive on cold flow behavior of this biodiesel was studied. A considerable reduction in pour point has been noticed by using these cold flow improvers. The performance and emission with ethanol blended Mahua biodiesel fuel and ethanol–diesel blended Mahua biodiesel fuel have also been studied. A considerable reduction in emission was obtained. Ethanol blended biodiesel is totally a renewable, viable alternative fuel for improved cold flow behavior and better emission characteristics without affecting the engine performance.     

菜籽油及其生物柴油低温流动特性研究

采用燃料低温性能测定仪考察了菜籽油及其生物柴油的冷滤点、凝点和运动粘度,采用旋转粘度计考察了菜籽油及其生物柴油粘温特性的差别,采用示差扫描量热分析仪研究了菜籽油及其生物柴油在低温下的相转变行为.研究结果表明:将菜籽油制备成生物柴油后,其冷滤点和粘度降低,粘温性能得到改善.在低温条件下,菜籽油粘度迅速增大,导致其失去流动性;菜籽油生物柴油在低温下析出固态物质,并逐渐连接成网状结构,将液态生物柴油吸附于其中,使生物柴油整体上失去流动性.     

Dimethyl carbonate mediated production of biodiesel at different reaction temperatures

Methanol was replaced by dimethyl carbonate for biodiesel production. In the process, fatty acid methyl ester (FAME) was produced through transesterification of soybean oil with dimethyl carbonate (DMC) using potassium methoxide as a catalyst. This method produced a more attractive by-product, glycerol carbonate (GC). Factors affecting the reaction such as vegetable oil to DMC molar ratio, catalyst concentration, reaction time and reaction temperature were optimized. Triglyceride conversion of 95.8% was obtained at the optimized condition. This process provided an insight into the reactivity of DMC at different temperature. Co-production of FAME and glycerol carbonate (GC) proceeded through carboxymethylation reaction because methoxyl group and carbonyl group are generated which subsequently attacked the carbonyl moiety in glyceride molecules to form the required products.     

Comprehensive study of biodiesel fuel for HSDI engines in conventional and low temperature combustion conditions

In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for High Speed Direct Injection (HSDI) diesel engines. The scope of this work has been broadened by comparing the combustion characteristics of diesel and biodiesel fuels in a wide range of engine loads and EGR conditions, including the high EGR rates expected for future diesel engines operating in the low temperature combustion (LTC) regime.The experimental work has been carried out in a single-cylinder engine running alternatively with diesel and biodiesel fuels. Conventional diesel fuel and neat biodiesel have been compared in terms of their combustion performance through a new methodology designed for isolating the actual effects of each fuel on diesel combustion, aside from their intrinsic differences in chemical composition.The analysis of the results has been sequentially divided into two progressive and complementary steps. Initially, the overall combustion performance of each fuel has been critically evaluated based on a set of parameters used as tracers of the combustion quality, such as the combustion duration or the indicated efficiency. With the knowledge obtained from this previous overview, the analysis focuses on the detailed influence of biodiesel on the different diesel combustion stages known ignition delay, premixed combustion and mixing controlled combustion, considering also the impact on CO and UHC pollutant emissions.The results of this research explain why the biodiesel fuel accelerates the diesel combustion process in all engine loads and EGR rates, even in those corresponding with LTC conditions, increasing its possibilities as alternative fuel for future DI diesel engines.     

Fabrication of evacuated glazing at low temperature

An indium-based seal augmented with an adhesive, developed to maintain a vacuum between two sheets of glass, avoids the high temperatures required to produce a seal in evacuated glazings to date. An experimentally-validated three-dimensional transient model has been used to predict heat transfer for an indium/adhesive sealed 1 m² area evacuated window with a highly insulating frame. An overall heat loss coefficient of 0.9 W m⁻² K⁻¹, with a midplane value of 0.36 W m⁻² K⁻¹, can be achieved with 0.72 visible transmittance for two 6 mm panes separated by 0.2 mm diameter pillars 40 mm apart. The conduction through a 3 mm edge-seal was 1.14 W m⁻² K⁻¹. Detailed three-dimensional isothermal contour plots through the system are presented.     

甲烷快速部分氧化重整试验研究

采用常规浸渍法制备了Rh/α-Al2O3催化剂,建立了甲烷快速部分氧化重整试验体系。通过控制变量法,考察了甲烷快速部分氧化重整反应中反应条件参数(CH4/O2、反应气体预混合温度、空速)变化对反应物的转化率、反应产物及分布的影响。试验结果表明,在试验条件下,CH4的转化率始终大于85%,O2转化率接近100%,CO的选择性为85%左右,H2的选择性为40%～60%。反应过程大致为催化剂入口处的部分氧化反应和下游的水蒸气重整,大部分的CO由部分氧化产生,而H2的产生受水蒸气重整反应的影响较大;随着反应温度的上升,CH4的转化率上升,CO,H2的选择性也上升;随着空速的增大,H2的选择性减小,表明甲烷催化部分氧化反应是一个受传质控制的反应。     

Stresses in vacuum glazing fabricated at low temperature

This paper reports an experimental and theoretical study of the stresses in and durability of vacuum glazing fabricated at low temperature using an indium based edge seal. For the first time a finite-element model with support pillars incorporated directly, enabled the stresses in the whole structure to be explicitly calculated. Experimental validations of the finite element model predictions were undertaken. Modelling results are presented for a case with American Society of Testing and Materials standard winter boundary conditions. It was found that, for the particular system studied, the predicted stress level in the structure is essentially the same for indium sealed and solder glass sealed vacuum glazing, and the magnitude of stress values in the indium seal is comparable with that dictated by the indium strength characteristics.     

CeO2-promoted BaO-MnOx catalyst for lean methane catalytic combustion at low temperatures: Improved catalytic efficiency and light-off temperature

In this research, the effect of various promoters (Zr, La, Ce, and Y) on the physicochemical features and catalytic activities of the BaO(10)-MnO_x prepared by the mechanochemical preparation route was investigated in the catalytic combustion of lean methane. Incomplete methane combustion as a result of the burning of natural gas in industries is the major reason to use a catalytic system to reduce the pollutants formation (NO_x, CO_x, etc.) and improve the combustion efficiency and proceeds towards complete combustion. In our previous study, we performed the methane combustion reaction on the mechanochemical synthesized BaO(x)-MnO_x catalysts with various contents of BaO (5–20 wt%), and the results indicated that the addition of 10 wt% of BaO to MnO_x could remarkably improve the catalytic efficiency due to the enhance the oxygen mobility and reduction features. In the present study, the structural properties of the synthesized catalysts were specified by XRD, BET, H₂-TPR, O₂-TPD, and SEM techniques. It is observed from the O₂-TPD technique that the addition of promoters into the BaO-MnO_x catalyst resulted in the increase in oxygen mobility, which could rise the catalytic activity. The addition of CeO₂ has a more positive effect on the catalytic activity due to the higher surface area and oxygen storage capacity. The obtained results revealed that the CeO₂(3)-BaO(10)-MnO_x catalyst possessed the superior performance in the methane combustion. The 90% of CH₄ conversion was obtained at about 350 °C over this catalyst. The effect of calcination temperature, feed ratio, GHSV, hysteresis curve, pretreatment atmospheres, and the presence of CO₂ and moisture was evaluated on the catalytic efficiency. After 50 h of continuous reaction at 450 °C, the selected catalyst showed high stability and the catalyst morphology was not significantly altered. Furthermore, CO oxidation was performed over the CeO₂(3)-BaO(10)-MnO_x catalyst, and the results indicated that the CO conversion was reached 100% at 250 °C.     

Effects of additives on the hydrogen generation of Al–H2O reaction at low temperature

Water displacement method is used to study the influence of temperatures (60–80°C), additives (Na₂CO₃, NaCl, Na₂CO₃/NaCl) and concentrations on the reaction characteristics and kinetics of Al–H₂O. Results show that the reaction rate and the hydrogen yield are enhanced with the increase of the temperature or by adding Na₂CO₃. The reaction rate is decreased by adding NaCl, but which has less effect on the hydrogen yield. For the mixture additive, Na₂CO₃ plays a key role in improving the hydrogen yield and the reaction rate. The influence degree of different factors is analyzed by orthogonal method. The most obvious factor is additive, but additive concentration has a minimum influence. The solid products are collected and analyzed by X‐ray diffraction and transmission electron microscopy. Al, Al(OH)₃ and AlO(OH) are detected. The spherical particles are obviously found at the initial reaction stage. However, they change to flocs at the end of reaction. Kinetic analysis shows that the reaction mechanism of Al–H₂O is changed by adding Na₂CO₃ or mixture, but it is not affected by adding NaCl. Moreover, the apparent activation energy of Al–H₂O is 74.49 kJ mol^?1, while it is only 43.03 kJ mol^?1 for Al–H₂O with 5 wt% Na₂CO₃ addition. Copyright © 2017 John Wiley & Sons, Ltd.     

One-step synthesis of Ni3S2 nanowires at low temperature as efficient electrocatalyst for hydrogen evolution reaction

Ni₃S₂ is an emerging cost-effective catalyst for hydrogen generation. However, a large amount of reported Ni₃S₂ was synthesized via multi-step approaches and few were fabricated based on the one-step strategies. Herein, we report a facile one-step low-temperature synthesis of Ni₃S₂ nanowires (NWs). In this strategy, a resin containing sulfur element is recommended as a sulfur resource to form Ni₃S₂ NWs. It presents a plausible explanation on the vapor–solid–solid (VSS) growth mechanism according to the results of this experiment and reported in literature that has been published. The Ni₃S₂ NW exhibits a potential ∼199 mV at 10 mA cm⁻² and the long-term durability over 30 h at 20 mA cm⁻² HER operation, better than other reported Ni₃S₂. More importantly, according to replace transition metal foam as the initial metal, other transition metal sulfide can be readily synthesized via this original approach.     

Glucose decomposition at high temperature, mild acid, and short residence times

Glucose is an intermediate product in the conversion of biomass to liquid fuels and chemicals via H₂SO₄ hydrolysis and subsequent fermentation. Unfortunately, glucose is destroyed as well as formed in this reaction. This study of glucose decomposition kinetics can be used to more accurately determine the kinetics of glucose formation from cellulosic biomass. The results demonstrate the importance of parallel reversion reactions in explaining the higher rates of disappearance of glucose found in this study as compared to earlier studies. An heuristic set of decomposition rate constants, applicable to conditions likely to be found in a flow reactor, are presented.     

Research on reaction conditions and mechanism for simultaneous removal of NO and Hg0 over CuFe modified activated carbon at low temperature

In this study, modified microwave coconut shell activated carbon (CuFe/MCSAC) was used to simultaneously remove NO and Hg⁰ in the industrial tail gas. The influences of reaction condition were investigated, such as NH₃ concentration, O₂ content, gas hourly space velocity (GHSV), resistance of SO₂ and H₂O. Under the optimal reaction conditions (600 ppm NH₃, 3% O₂ and 30000 h⁻¹ GHSV), CuFe/MCSAC showed high NO conversion rate (86%), high Hg⁰ conversion rate (61%) and low N₂O concentration (81 ppm) at 225 °C. NH₃ was conducive to the removal of NO, but it had a competitive adsorption effect for Hg⁰. O₂ promoted oxidation of NO and Hg⁰, and led to the formation of N₂O. Low GHSV had the external diffusion effect, which affected the reaction rate. High GHSV could not provide enough reaction time. H₂O and SO₂ were not conducive to the selectivity of SCR reaction and oxidation of Hg⁰.     

Widegap a-Si:H films prepared at low substrate temperature

Wide bandgap hydrogenated amorphous silicon (a-Si:H) films have been prepared by the PECVD method at a low substrate temperature (80°C) controlling the incorporation of hydrogen (bonded with silicon) into the film. Optimizing the deposition parameters viz. hydrogen dilution, rf power, a-Si:H film with E_g ∼ 1.90 eV and σ_ph ≥ 10⁻⁴ Scm⁻¹ has been developed. This film exhibited better optoelectronic properties compared to a-SiC:H of similar optical gap. The quantum efficiency measurement on the Schottky barrier solar cell structure showed a definite enhancement of blue response. Surface reaction as well as structural relaxation under suitable deposition condition have been claimed to be responsible for the development of such material.     

Enhanced electrocatalytic performance of Cu0.02S0.01/rGO hybrid for oxygen reduction reaction in alkaline medium at low temperature

Graphene, is a carbon allotrope, which is widely used as a substrate for various catalysts due to its interesting physicochemical properties. In the present study, graphene oxide sheets were prepared from graphite, then, the graphene oxide surface was modified by a low-temperature method using sulfur and copper atoms to obtain pseudo-enzyme Cu/S/Graphene prosthetic group. The current density passing through Cu/S/Graphene catalyst was four times higher than that passing through graphite. The novel copper-based catalyst had an extraordinary performance for oxygen reduction reaction (ORR) due to the unique bio-inspired and stoichiometric structure. The results of Raman and Dispersive X-ray spectroscopy confirmed the presence of ultra-low content of copper (2%) and sulfur (1%) atoms on the graphene surface. Thermogravimetric analysis indicated a strong interaction between nanoparticles and graphene layers. The number of electrons transferred for ORR varied from 3.98 to 4.16 in a wide range of over-potentials indicating an effective 4-electron pathway form O₂ to H₂O. The Tafel slopes indicated insignificant amount of formed copper oxide on the catalyst surface. The catalyst showed excellent electrochemical durability and its half-wave potential (E_1/2) was exhibited a negative shift only 8.2 mV after 10000 cycles.     

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

A detailed chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, and methyl palmitate, are large methyl ester molecules, some with carboncarbon double bonds, and kinetic mechanisms for them as a family of fuels have not previously been available. Of particular importance in these mechanisms are models for alkylperoxy radical isomerization reactions in which a CC double bond is embedded in the transition state ring. The resulting kinetic model is validated through comparisons between predicted results and a relatively small experimental literature. The model is also used in simulations of biodiesel oxidation in jet-stirred reactor and intermediate shock tube ignition and oxidation conditions to demonstrate the capabilities and limitations of these mechanisms. Differences in combustion properties between the two biodiesel fuels, derived from soy and rapeseed oils, are traced to the differences in the relative amounts of the same five methyl ester components.     

中温条件下铝镁锂合金与水反应的动态过程

铝水反应是铝作为新能源的一种主要利用方式。为了探究熔融态下铝水反应的动态传递规律,利用自制的反应器,研究了中温条件下铝镁锂合金与水蒸气反应的动态过程,并对反应器内部的温度、压力、氢产率进行了实时监测。实验结果表明:启动温度为500℃时,通入水蒸气后,反应器内部温度迅速升高,最高温度为791℃;金属反应区的截面温度分布差异较大,存在局部的核心高温区;随着反应的进行,核心高温区自进水口处向外向下传递,传递速率约为0.33 mm/s,该速率主要是由水蒸气扩散速率和热传递速率共同决定的。     

Nanocrystalline silicon thin films deposited by high-frequency sputtering at low temperature

Intrinsic and n-type hydrogenated nanocrystalline silicon thin films (nc-Si:H) were deposited at a temperature as low as 95 °C by high-frequency (HF) sputtering, with hydrogen dilution percentage varying from 31% to 73%. In order to study the properties of the films prepared by this method, the samples were examined by infrared absorption spectroscopy (IR), X-ray diffraction (XRD), SEM, spectroscopic ellipsometry (SE), laser Raman spectrometry and atomic force microscopy (AFM). XRD measurements showed that this film has a new microstructure, which is different from the films deposited by other methods. In addition, an n-type nc-Si:H/p-type c-Si heterojunction solar cell, which has an open circuit voltage (V_oc) of 370 MV and a short-circuit current intensity (J_sc) of 6.5 mA/cm², was produced on the nanocrystalline silicon thin film. After 10 h light exposure under AM1.5 (100 MW/cm²) light intensity at room temperature, radiation degradation has not been found for the device.     

锂离子电池系统低温充电策略

新能源汽车行业正迅猛发展,电动汽车的销量也屡创新高,而电动汽车在冬季低温下如何高效且经济地进行充电,仍是一个亟待解决的问题.基于充电时电池自身内阻产热的原理,提出了一种锂电池系统低温充电的策略,并在此基础上进行了改进.以最小单体电池温度为判断条件,使用多阶段恒流充电技术可以有效缩短充电时间,并保证一定的充电容量.通过研...