共查询到20条相似文献,搜索用时 15 毫秒
1.
S.M. Sarathy C.K. Westbrook M. Mehl W.J. Pitz C. Togbe P. Dagaut H. Wang M.A. Oehlschlaeger U. Niemann K. Seshadri P.S. Veloo C. Ji F.N. Egolfopoulos T. Lu 《Combustion and Flame》2011,(12):2338-2357
Conventional petroleum jet and diesel fuels, as well as alternative Fischer–Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed and reduced chemical kinetic mechanism for singly methylated iso-alkanes (i.e., 2-methylalkanes) ranging from C7 to C20. The mechanism also includes an updated version of our previously published C8–C16n-alkanes model. The complete detailed mechanism contains approximately 7200 species 31400 reactions. The proposed model is validated against new experimental data from a variety of fundamental combustion devices including premixed and non-premixed flames, perfectly stirred reactors and shock tubes. This new model is used to show how the presence of a methyl branch affects important combustion properties such as laminar flame propagation, ignition, and species formation. 相似文献
2.
The effect of unsteady strain on n-heptane autoignition at elevated pressure is studied numerically with detailed chemistry and transport in the counterflow configuration. Specifically, fuel and air temperatures are chosen so that two-stage ignition occurs, as is typical, in the negative temperature-coefficient regime, and the strain perturbations are selected to rapidly rise and fall to mimic rapid turbulent strain-rate fluctuations. For these rapid fluctuations, the response of the mixing layer is unsteady. Small to moderate strain-rate fluctuations result in a small increase in the ignition delay. For sufficiently large strain rates such that the critical scalar dissipation rate is exceeded, the ignition delay is substantially greater. The latter delay results from both the time required for the dissipation rate to decay to below its critical value and the longer ignition delay time for systems with dissipation rates near the critical dissipation rate. For all magnitudes of strain-rate fluctuation, there is evidence that the second stage of the two-stage ignition is more sensitive to inhibition by higher dissipation rates. For sufficiently large dissipation rates, the heat losses force the second stage to the border between the low- and intermediate-temperature chemistries. 相似文献
3.
4.
Dehydrogenation of organic chemical hydrides has been improved by reconstructing the catalyst in the form of hierarchical porous structure nanocatalyst, in which the economical Ni was adopted as catalytic component and nano Al2O3–TiO2 hybrid composite as support. The Al2O3–TiO2 composite was prepared by spontaneous self-assembly of nano Al2O3 and TiO2 aggregates by hydrolysis of tetra-n-butyl-titanate under continuous agitation. The multi-scaled distribution of Al2O3–TiO2 aggregates with hierarchy could be observed in dynamic light scattering spectrometer. The aggregates are comprised of nano-sized γ-Al2O3 and anatase TiO2 crystallites with sizes of about 5 and 7 nm, respectively. The surface modulation by TiO2 could be verified in FTIR Spectra. The migration of Ti species and crystallite growth were hindered by the Al2O3 skeleton and the hierarchical porous structure was sustained during the thermal related process. The multi-scaled distributed pores were confirmed by both TEM analysis and N2 adsorption results. The results of dehydrogenation experiments showed that the hierarchical porous structure nano Ni/Al2O3–TiO2 exhibited superior catalytic performance to Ni/Al2O3 with the optimum conversion of 99.9% at 400 °C, while the catalyst of Ni/Al2O3 exhibited only 16.5% under the same condition. 相似文献
5.
The spinel LiNi0.5Mn1.5O4 has been surface modified separately with 1.0 wt.% ZrO2 and ZrP2O7 for the purpose of improving its cycle performance as a cathode in a 5-V lithium-ion cell. Although the modifications did not change the crystallographic structure of the surface-modified samples, they exhibited better cyclability at elevated temperature (55 °C) compared with pristine LiNi0.5Mn1.5O4. The material that was surface modified with ZrO2 gave the best cycling performance, only 4% loss of capacity after 150 cycles at 55 °C. Electrochemical impedance spectroscopy demonstrated that the improved performance of the ZrO2-surface-modified LiNi0.5Mn1.5O4 is due to a small decrease in the charge transfer resistance, indicating limited surface reactivity during cycling. Differential scanning calorimetry showed that the ZrO2-modified LiNi0.5Mn1.5O4 exhibits lower heat generation and higher onset reaction temperature compared to the pristine material. The excellent cycling and safety performance of the ZrO2-modified LiNi0.5Mn1.5O4 electrode was found to be due to the protective effect of homogeneous ZrO2 nano-particles that form on the LiNi0.5Mn1.5O4, as shown by transmission electron microscopy. 相似文献
6.
S. Vranckx K.A. Heufer C. Lee H. Olivier L. Schill W.A. Kopp K. Leonhard C.A. Taatjes R.X. Fernandes 《Combustion and Flame》2011,158(8):1444-1455
Despite considerable interest in butanol as a potential biofuel candidate, its ignition behaviour at elevated pressures still remains largely unexplored. The present study investigates the oxidation of n-butanol in air at pressures near 80 bar. Ignition delays were determined experimentally in the temperature range of 795–1200 K between 61 and 92 bar. The time of ignition was determined by recording pressure and CH-emission time histories throughout the course of the experiments. The results display the first evidence of the influence of negative temperature coefficient (NTC) behaviour which was not observed in earlier ignition studies. The high-pressure measurements show that NTC behaviour is enhanced as pressures are increased. The experimental results were modelled using an improved chemical kinetic mechanism which includes a simplified sub-mechanism for butyl-peroxy formation and isomerisation reactions currently incompletely accounted for in n-butanol kinetic models. The detailed mechanism validated with the high-pressure ignition results for realistic engine in-cylinder conditions can have significant impact on future advanced low-temperature combustion engines. 相似文献
7.
The purpose of this study was to investigate the NOx formation and reduction mechanisms in staged O2/CO2 combustion and in air combustion. A flat CH4 flame doped with NH3 for fuel-N was formed over the honeycomb, and NOx formation characteristics were investigated. In addition, chemiluminescence of OH* distribution was measured, and CHEMKIN-PRO was used to investigate the detailed NOx reduction mechanism. In general, the NOx conversion ratio decreases with decreasing primary O2/CH4 ratio, whereas NH3 and HCN, which are easily converted to NOx in the presence of O2, increases rapidly. Therefore, a suitable primary O2/CH4 ratio exists in the staged combustion. Our experiments showed the primary O2/CH4 ratio, which gave the minimum fixed nitrogen compounds in O2/CO2 combustion, was lower than in air combustion. The NOx conversion ratio in O2/CO2 combustion was lower than in air combustion by 40% in suitable staged combustion. This could be explained by high CO2 concentrations in the O2/CO2 combustion. It was shown that abundant OH radicals were formed in O2/CO2 combustion through the CO2 + H → CO + OH, experimentally and numerically. OH radicals produced H and O radicals through H2 + OH → H + H2O and O2 + H → OH + O, because a mass of hydrogen source exists in the CH4 flame. O and OH radicals formed in the fuel-rich region enhanced the oxidation of NH3 and HCN. NOx formed by the oxidation of NH3 and HCN was converted to N2 because the oxidation occurred in the fuel-rich region where the NOx reduction effect was high. In fact, the oxidation of NH3 and HCN in the fuel-rich region was preferable to remaining NH3 and HCN before secondary O2 injection in the staged combustion. A significant reduction in NOx emission could be achieved by staged combustion in O2/CO2 combustion. 相似文献
8.
The n-CdZn(S1−xSex) and p-CuIn(S1−xSex)2 thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S1−xSex)2 and p-CuIn (S1−xSex)2 thin films fabricated by same technique. The n-CdZn(S1−xSex)2 thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S1−xSex)2 thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S1−xSex)2 and p-CuIn(S1−xSex)2 thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S0.5Se0.5)2 and CdZn(S0.5Se0.5)2 thin films, respectively. J–V characteristic was measured for the n-CdZn(S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films under light illumination. The device parameters Voc=474.4 mV, Jsc=13.21 mA/cm2, FF=47.8% and η=3.5% under an illumination of 85 mW/cm2 on a cell active area of 1 cm2 have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S0.5Se0.5)2/p-CuIn(S0.5Se0.5)2 heterojunction thin films. 相似文献
9.
The paper presents numerical studies on forced (spark) ignition in a temporally evolving mixing layer between a fuel (mixture of hydrogen and nitrogen) and air. The research was performed in the framework of low Mach number approximation using implicit large eddy simulation (ILES) approach with detailed chemistry for hydrogen combustion (9 species, 19 reactions) for which the filtered source terms were computed directly using filtered quantities. The computations were performed applying a high-order numerical code on a numerical mesh with cell sizes close to the Kolmogorov scale, thus ensuring that the ILES results were credible. The spark was modelled by an energy deposition model and we considered various sizes and energies of the sparks. We analyzed the impact of these parameters on a success of ignition and flame development process. In case of successful ignition events we observed that depending on the spark locations and its characteristic the maximum temperature during the spark deposition (0.5 ms) varied in the range 2000 K4000 K and stabilized around 1800K shortly after the spark has been switched-off. It was found that the location of the spark in the flow region characterized by low turbulence intensity and proximity of the stoichiometric regimes almost always resulted in successful ignition, independently of the spark parameters (the energies 1mJ-4.5 mJ and sizes 1.2mm-3.3 mm). On the other hand, in the regions of high turbulence the maximum energy of the spark had to be large to ignite the flow. From this point of view it was observed that in the cases in which the total amount of energy supplied to the sparks was defined a priori, the sparks which were smaller but more intense were more effective than the sparks larger in size but weaker. We found that development of the flame and its growth after switching-off the spark cannot be directly related to the maximum temperature levels during the ignition. It was shown that in this respect the locations of the sparks relative to vortical structures play much more important role. 相似文献
10.
Bin Lin Mingjun Hu Jianjun Ma Yinzhu Jiang Shanwen Tao Guangyao Meng 《Journal of power sources》2008,183(2):479-484
A stable, easily sintered perovskite oxide BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (BCZYZn) as an electrolyte for protonic ceramic membrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ (BSZF) perovskite cathode was investigated. The BCZYZn perovskite electrolyte synthesized by a modified Pechini method exhibited higher sinterability and reached 97.4% relative density at 1200 °C for 5 h in air, which is about 200 °C lower than that without Zn dopant. By fabricating thin membrane BCZYZn electrolyte (about 30 μm in thickness) on NiO–BCZYZn anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.00 V, a maximum power density of 236 mW cm−2, and a low polarization resistance of the electrodes of 0.17 Ω cm2 were achieved at 700 °C. This investigation indicated that proton conducting electrolyte BCZYZn with BSZF perovskite cathode is a promising material system for the next generation solid oxide fuel cells. 相似文献
11.
Xingbao Zhu Zhe Lü Bo Wei Kongfa Chen Mingliang Liu Xiqiang Huang Wenhui Su 《Journal of power sources》2009,190(2):326-330
The optimization of electrodes for solid oxide fuel cells (SOFCs) has been achieved via a wet impregnation method. Pure La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCrM) anodes are modified using Ni(NO3)2 and/or Ce(NO3)3/(Sm,Ce)(NO3)x solution. Several yttria-stabilized zirconia (YSZ) electrolyte-supported fuel cells are tested to clarify the contribution of Ni and/or CeO2 to the cell performance. For the cell using pure-LSCrM anodes, the maximum power density (Pmax) at 850 °C is 198 mW cm−2 when dry H2 and air are used as the fuel and oxidant, respectively. When H2 is changed to CH4, the value of Pmax is 32 mW cm−2. After 8.9 wt.% Ni and 5.8 wt.% CeO2 are introduced into the LSCrM anode, the cell exhibits increased values of Pmax 432, 681, 948 and 1135 mW cm−2 at 700, 750, 800 and 850 °C, respectively, with dry H2 as fuel and air as oxidant. When O2 at 50 mL min−1 is used as the oxidant, the value of Pmax increases to 1450 mW cm−2 at 850 °C. When dry CH4 is used as fuel and air as oxidant, the values of Pmax reach 95, 197, 421 and 645 mW cm−2 at 750, 800, 850 and 900 °C, respectively. The introduction of Ni greatly improves the performance of the LSCrM anode but does not cause any carbon deposit. 相似文献
12.
MgH2 is one of the most promising materials for hydrogen storage. However, its rather slow hydrogen absorption and desorption kinetics and high dissociation temperature essentially limit its application in this field. Nevertheless mixing Mg or MgH2 with small amount of transition metals or their oxides remarkably accelerates the hydrogen kinetics. Recently a series of new hydrides Mg7TiHx, Mg6.5NbHx and Mg6VHx of Ca7Ge type structure has been synthesized. The hydrogen desorption properties have been found to be better than for pure MgH2. Here, we report on the results of our theoretical study of the electronic structure of these new hydrides carried out within the framework of the full-potential, self-consistent linearized augmented plane-wave method. We use these results, along with calculations of the heat of formation and relative stability, to discuss the bonding of these materials and their hydrogen-storage properties. 相似文献
13.
Thin film solar cells with chalcopyrite CuInSe2/Cu(InGa)Se2 (CIS/CIGS) absorber layers have attracted significant research interest as an important light-to-electricity converter with widespread commercialization prospects. When compared to the ternary CIS, the quaternary CIGS has more desirable optical band gap and has been found to be the most efficient among all the CIS-based derivatives. Amid various fabrication methods available for the absorber layer, electrodeposition may be the most effective alternative to the expensive vacuum based techniques. This paper reviewed the developments in the area of electrodeposition for the fabrication of the CIGS absorber layer. The difficulties in incorporating the optimum amount of Ga in the film and the likely mechanism behind the deposition were highlighted. The role of deposition parameters was discussed along with the phase and microstructure variation of an as-electrodeposited CIGS layer from a typical acid bath. Related novel strategies such as individual In, Ga and their binary alloy deposition for applications in CIGS solar cells were briefed. 相似文献
14.
Undoped MnO2 thin films have been prepared by a modified spray pyrolysis technique under various deposition conditions and the effects of different variables on electrical and optical properties have been studied in detail. It is found that substrate temperature, spray rate, solution concentration, carrier air pressure and post-deposition heat-treatment, spray outlet to substrate distance play important role in obtaining optimum films.Electrical conductivity study shows an anomaly in conductivity at a temperature 323 K and its thickness dependent resistivity follows Fuchs–Sondheimer theory. The Hall effect and thermoelectric studies indicate that the deposited sample is an n-type semiconductor. Optical study in the entire wavelength 0.3–2.5 μm range exhibits a high transmittance in the visible as well as in the near infrared. Calculation from optical data, the sample exhibits a band gap at 0.28 eV, which also supports the value obtained from the Hall effect study. These studies may be of importance for the applications of this material in energy efficient surface coating devices. 相似文献
15.
Rui JinShengli Zhang Yonghong Zhang Shiping Huang Peng WangHuiping Tian 《International Journal of Hydrogen Energy》2011,36(15):9069-9078
The structure, vibration, and electronic structure of H2 molecule adsorbed on (ZrO2)n (n = 1-6) clusters were investigated with density functional theory. We found that H2 is easily absorbed on the top Zr atoms of (ZrO2)n (n = 1-6) clusters. The Zr5O10H2 cluster has the lowest binding energies in the ZrnO2nH2 (n = 1-6) clusters. By analyzing vibrational frequency and Mulliken charge, the H-O and Zr-H bonds were found to be formed in different sized ZrnO2nH2 clusters. The dissociation mechanism of H2 shows that the charge transfers from (ZrO2)n cluster to H2 due to the important role of the orbital hybridization between the cluster and H2 molecule. With increasing the number of H2 molecule adsorbed on (ZrO2)n clusters, the adsorption favors to the sites with low coordinate number, and these adsorption modes present a symmetrical tendency. 相似文献
16.
Chang-Yeoul Kim Seong-Geun Cho Tae-Young Lim 《Solar Energy Materials & Solar Cells》2009,93(12):2056-8
We fabricated an electrochromic full cell device adopting WO3 as a working electrode, and 1 M LiClO4 in PC with 3% water addition as an electrolyte and CeO2·TiO2 with various thicknesses as an ion storage layer. CeO2·TiO2 with less than 100 nm shows large charge density but the long-term cyclability is not good due to lithium ion diffusion into ITO thin film. Therefore, the thickness of CeO2·TiO2 ion storage layer should be coated at more than 200 mm/min. Long-term cycle test results show that CeO2·TiO2 ion storage layer with more than 150 nm thickness and two time coating enhance the long-term stability. SIMS analysis results show that the degradation is due to the remaining lithium ion in the working electrode, WO3. 相似文献
17.
The Ni-H3PW12O40/nano-hydroxyapatite catalyst with H3PW12O40 (HPW) loading was prepared by impregnation method and performed through hydrocracking of Jatropha oil in a fixed-bed reactor. The catalyst was characterized by N2 adsorption–desorption, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia (NH3-TPD), thermogravimetric analysis (TGA). The conversion of Jatropha oil over Ni-HPW (30 wt%)/nHA was 100%, the liquid yield of liquid product was 83.4%, the ratio of i/n-paraffins was 1.64 at 360 °C, 3 MPa, H2/oil (v/v) = 600 and LHSV = 2 h−1. The pour point of final product oil was −28 °C and the catalyst was used without sulfurization. 相似文献
18.
The full composition range CuIn(SxSe1−x)2 alloy system has been studied using 40 mm length crystal cuts from 10 mm diameter ingots grown by the classical Bridgman method. X-ray diffraction diffractographs show that the CuIn(SxSe1−x)2 compounds have a chalcopyrite structure for each composition x, they exhibit an expansion on the unit cell characteristics by the tetragonal distortion which depends linearly on the electronegativity of the atoms. The photoluminescence spectra is investigated as a function of various compositions, temperature and excitation intensities. Photoluminescence spectra shows a wide variation in the dominant peak location and an overall blue shift with the increase of sulphur content. Photoluminescence CuInS2 and CuIn(S0.72Se0.28)2 have been studied in detail. 相似文献
19.
Bulk conduction and relaxation of the [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions were studied using impedance spectroscopy at intermediate temperatures (200-500 °C). The bulk conductivity as a function of x shows a “V-shape” variation which is a competitive effect of the defect associates and the lattice parameter. In the ZrO2-rich region (x < 0.5) CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5) the increase of x increases the lattice parameter which enlarges the free channel for oxygen vacancy migration. Further analysis indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions. When doping YSZ with other tetravalent dopant with similar ionic radius with Zr4+, e.g., Hf4+, such “V-shape” composition dependence of the bulk conductivity cannot be observed. 相似文献
20.
Role of CO2 in the CH4 oxidation and H2 formation during fuel-rich combustion in O2/CO2 environments
The effect of CO2 reactivity on CH4 oxidation and H2 formation in fuel-rich O2/CO2 combustion where the concentrations of reactants were high was studied by a CH4 flat flame experiment, detailed chemical analysis, and a pulverized coal combustion experiment. In the CH4 flat flame experiment, the residual CH4 and formed H2 in fuel-rich O2/CO2 combustion were significantly lower than those formed in air combustion, whereas the amount of CO formed in fuel-rich O2/CO2 combustion was noticeably higher than that in air. In addition to this experiment, calculations were performed using CHEMKIN-PRO. They generally agreed with the experimental results and showed that CO2 reactivity, mainly expressed by the reaction CO2 + H → CO + OH (R1), caused the differences between air and O2/CO2 combustion under fuel-rich condition. R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO2 was to advance CH4 oxidation during fuel-rich O2/CO2 combustion. Under fuel-rich combustion, H2 was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H2O production. In fact, these hydrocarbon reactions were competitive. With increasing H/OH ratio, H2 formed more easily; however, CO2 reactivity reduced the H/OH ratio by converting H to OH. Moreover, the OH radicals reacted with H2, whereas the H radicals did not reduce H2. It was shown that OH radicals formed by CO2 reactivity were not suitable for H2 formation. As for pulverized coal combustion, the tendencies of CH4, CO, and H2 formation in pulverized coal combustion were almost the same as those in the CH4 flat flame. 相似文献