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1.
Yohannes Ghermay John Mantzaras Rolf Bombach 《Proceedings of the Combustion Institute》2011,33(2):1827-1835
The hetero-/homogeneous combustion of fuel-lean CO/H2/O2/N2 mixtures over platinum is investigated at pressures up to 5 bar, inlet temperatures (TIN) up to 874 K, and a constant CO:H2 molar ratio of 2:1. Experiments are performed in an optically accessible channel-flow catalytic reactor and involve planar laser induced fluorescence (LIF) of the OH radical for the assessment of homogeneous (gas-phase) ignition and 1-D Raman measurements of major gas-phase species concentrations over the catalyst boundary layer for the evaluation of the heterogeneous (catalytic) processes. Simulations are carried out with an elliptic 2-D model that includes detailed heterogeneous and homogeneous chemical reaction schemes. The predictions reproduce the Raman-measured catalytic CO and H2 consumption, and it is further shown that for wall temperatures in the range 975 ? Tw ? 1165 K the heterogeneous pathways of CO and H2 are largely decoupled. However, for wall temperatures below a limiting value of 710–720 K and for the range of pressures and mixture preheats investigated, CO(s) blockage of the surface inhibits the catalytic conversion of both fuel components. The homogeneous ignition distance is well-reproduced by the model for TIN > 426 K, but it is modestly overpredicted at lower TIN. Possible reasons for these modest differences can be the values of third body efficiencies in the gas-phase reaction mechanism. The sensitivity of homogeneous ignition distance on the catalytic reactions is weak, while the H2/O2 subset of the CO/H2/O2 gaseous reaction mechanism controls the onset of homogeneous ignition. Pure hydrogen hetero-/homogeneous combustion results in flames established very close to the catalytic walls. However, in the presence of CO the gaseous combustion of hydrogen extends well-inside the channel core, thus allowing homogeneous consumption of H2 at considerably shorter reactor lengths. Finally, implications of the above findings for the design of syngas-based catalytic reactors for power generation systems are discussed. 相似文献
2.
Ccile Coh Christian Chauveau Iskender Gkalp Dilek Funda Kurtulu 《Proceedings of the Combustion Institute》2009,32(2):1803-1810
An experimental study on CH4–CO2–air flames at various pressures is conducted by using both laminar and turbulent Bunsen flame configurations. The aim of this research is to contribute to the characterization of fuel lean methane/carbon dioxide/air premixed laminar and turbulent flames at different pressures, by studying laminar and turbulent flame propagation velocities, the flame surface density and the instantaneous flame front wrinkling parameters. PREMIX computations and experimental results indicate a decrease of the laminar flame propagation velocities with increasing CO2 dilution rate. Instantaneous flame images are obtained by Mie scattering tomography. The image analysis shows that although the height of the turbulent flame increases with the CO2 addition rate, the flame structure is quite similar. This implies that the flame wrinkling parameters and flame surface density are indifferent to the CO2 addition. However, the pressure increase has a drastic effect on both parameters. This is also confirmed by a fractal analysis of instantaneous images. It is also observed that the combustion intensity ST/SL increases both with pressure and the CO2 rate. Finally, the mean fuel consumption rate decreases with the CO2 addition rate but increases with the pressure. 相似文献
3.
C. Renard 《Proceedings of the Combustion Institute》2009,32(1):631-637
Structures of several premixed ethylene-oxygen-argon rich flat flames burning at 50 mbar have been established by using molecular beam mass spectrometry in order to investigate the effect of CO2, or NH3, or H2O addition on species concentration profiles. The aim of this study is to examine the eventual changes of profiles of detected hydrocarbon intermediates which could be considered as soot precursors (C2H2, C4H2, C5H4, C5H6, C6H2, C6H4, C6H6, C7H8, C6H6O, C8H6, C8H8, C9H8 and C10H8). The comparative study has been achieved on four flames with an equivalence ratio (f) of 2.50: one without any additive (F2.50), one with 15% of CO2 replacing the same quantity of argon (F2.50C), one with 3.3% of NH3 in partial replacement of argon (F2.50N) and one with 13% of H2O in replacement of the same quantity of argon (F2.50H). The four flat flames have similar final flame temperatures (1800 K).CO2, or NH3, or H2O addition to the fresh gas inlet causes a shift downstream of the flame front and thus flame inhibition. Endothermic processes CO2 + H = CO + OH and H2O + H = H2 + OH are responsible of the reduction of the hydrocarbon intermediates in the CO2 and H2O added flames through the supplementary formation of hydroxyl radicals. It has been demonstrated that such processes begin to play at the end of the flame front and becomes more efficient in the burnt gases region.The replacement of some Ar by NH3 is responsible only for a slight decrease of the maximum mole fraction of C2H2, but NH3 becomes much more efficient for C4H2 and C5 to C10 species. Moreover, the efficiency of NH3 as a reducing agent of C5 to C10 intermediates is larger than that of CO2 and H2O for equal quantities added. 相似文献
4.
Thermally induced phase transitions (20-1000 °C) in the substrates and binary mixtures of CH3COOLi·2H2O(1)-MgHPO4·3H2O(11) have been analysed. Changes taking place on dehydration and thermal dissociation of binary mixtures prepared with percent molar ratios of 90-10% were studied by differential thermal analysis (TG, DTG, DTA), IR-spectroscopy and WAXS.The above-mentioned substrates changed their structure when heated for 1 h at 500 or 1000 °C. CH3COOLi·2H2O(1) (ID: 23-1171) changed the structure at 500 °C to that of Li2CO3 (ID: 22-1141), while at 1000 °C the structure was impossible to analyse as the compound reacted both with porcelain and with platinum (crucible materials). MgHPO4·3H2O(11) (Newberyite, ID: 35-780, 19-762) changed its structure at 500 °C to amorphous phase and at 1000 °C to Mg2P2O7 (ID: 32-626).The following compounds were assayed in the respective binary mixtures heated at 500 °C for 1 h: 70% (1)-30%(11): LiMgPO4 (ID: 18-735), MgO (ID: 4-829); 50%(1)-50%(11): LiMgPO4 (ID: 18-735), Li3PO4 (ID: 25-1030); 30%(1)-70%(11): LiMgPO4 (ID: 32-574); binary mixtures heated at 1000 °C contained the following compounds: 70%(1)-30%(11): LiMgPO4 (ID: 32-574,18-735), Li3PO4 (ID: 15-760,25-1030), MgO (ID: 4-829); 50%(1)-50%(11): LiMgPO4 (ID: 32-574, 18-735), MgO (ID: 4-829); 30%(1)-70%(11): LiMgPO4 (ID: 18-735, 32-574), Mg2P2O7 (ID: 22-1152, 8-38), Li4SiO4 (37-1472). 相似文献
5.
We report the experimental Raman spectra of the ν2 band of H2O, D2O, and HDO in the vapor phase at room temperature. A complete interpretation of the Raman intensities is carried out employing the variational rovibrational wavefunctions obtained from a Hamiltonian in Radau coordinates and an ab initio polarizability surface at 514.5 nm. We show the importance of the rotation-vibration coupling to obtain the correct line intensities. Several tables with the assignments of the individual rotational-vibrational transitions and their Raman scattering strengths are reported. From these tables, the ν2 Raman spectra can be simulated up to 2000 K for H2O, and up to 300 K for D2O and HDO. 相似文献
6.
We report the experimental rotational Raman spectra of H2O, and of a mixture of D2O and HDO in the vapor phase at room temperature, and their interpretation in terms of rotational–vibrational energies, wavefunctions, and transition moments of the molecular polarizability. These transition moments are based on high-level ab initio calculations of the wavelength dependent polarizability surface, and on wavefunctions where the rotational–vibrational coupling is considered in detail. As a byproduct of this analysis several tables have been compiled including scattering strengths and assignments for individual rotational transitions of the three species. From these tables the rotational Raman spectra can be simulated over the range of temperatures up to 2000 K for H2O, and up to 300 K for D2O and HDO. 相似文献
7.
Niina Jalarvo Camilla Haavik Camilla Kongshaug Poul Norby Truls Norby 《Solid State Ionics》2009,180(20-22):1151-1156
The hydrated oxygen deficient complex perovskite-related materials Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O were studied at high water vapour pressures over a large temperature range by electrical conductivity measurements, thermogravimetry (TG), and X-ray powder diffraction (XRPD). In humid atmospheres both materials are known to exhibit protonic conductivity below dehydration temperatures, with peak-shaped maxima at about 500 °C. In this work we show that the peaks expand to plateaus of high conductivity from 500 to 700 °C at a water vapour pressure of 1 atm. However, in situ synchrotron XRPD of Sr4(Sr2Nb2)O11·nH2O as a function of temperature shows that these observations are in fact coincident with melting and dehydration of a secondary phase Sr(OH)2. The stability of Sr4(Sr2Nb2)O11·nH2O and Sr4(Sr2Ta2)O11·nH2O in humid atmospheres is thus insufficient, causing decomposition into perovskites with lower Sr content and SrO/Sr(OH)2 secondary phases. This, in turn, rationalizes the observation of peaks and plateaus in the conductivity of these materials. 相似文献
8.
Reaction pathways of CO2 reforming of CH4 on Ni(1 1 1) were investigated by using density functional theory calculation. The computed kinetic parameters agree with the available experimental data, and a new and simplified mechanism was proposed on the basis of computed energy barriers. The first step is CO2 dissociation into surface CO and O (CO2 → CO + O) and CH4 sequentially dissociation into surface CH and H (CH4 → CH3 → CH2 → CH). The second step is CH oxygenation into CHO (CH + O → CHO), which is more favored than its dissociation into C and hydrogen (CH → C + H). The third step is the dissociation of CHO into surface CO and H (CHO → CO + H). Finally, H2 and CO desorb from Ni(1 1 1) and form free H2 and CO. The rate-determining step is the CH4 dissociative adsorption, and the key intermediate is surface adsorbed CHO. Parameters, which might modify the proposed mechanism, have been analyzed. In addition, the formation, deposition and elimination of surface carbon have been discussed accordingly. 相似文献
9.
Yongkui Yin Fenghua Yang Yong Yang Zibao Gan Zengming Qin Song Gao Baibin Zhou Xiaoxia Li 《Superlattices and Microstructures》2011
Shape-controlled synthesis of BaWO4 hierarchical nanostructures has been successfully achieved by exploiting oriented attachment in a mixture of water and ethanol. A controlled change in the volume ratio of C2H5OH and H2O or the concentration of initial reagents has resulted in the synthesis of products of various morphologies, such as shuttle-like, ellipsoid-like, and flower-like ones. The obtained products are characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The altered nucleation and growth rates of primary particles that assembled to the final hierarchical nanostructures through oriented attachment are the main cause of the evolution of their morphologies. The room-temperature photoluminescent intensities of the products strongly depend on their morphology. 相似文献
10.
We report the OH and OD stretching regions of the vapor phase Raman spectra of H2O, and of a D2O/HDO mixture, at room temperature. Also, the corresponding spectrum of H2O at ∼2000 K in a methane/air flame is reported. These spectra are interpreted in terms of transition moments of the molecular polarizability, based on high-level ab initio calculations of the polarizability surface, and on variational wavefunctions considering the rotational-vibrational coupling in full. As a byproduct of this analysis several tables have been compiled including scattering strengths and assignments for individual rotational transitions of the three species. From these tables the Raman spectra in the OH/OD stretching regions can be simulated over the range of temperatures up to 2000 K for H2O, and up to 300 K for D2O and HDO. 相似文献
11.
H. E. Radford K. M. Evenson F. Matushima L. R. Zink G. P. Galvao T. J. Sears 《International Journal of Infrared and Millimeter Waves》1991,12(10):1161-1166
The frequencies of 26 laser lines with wavelengths between 57 and 534 m have been measured in the optically pumped laser gases CH3OD and N2H4. A pair of stabilized cw 12CO
2 lasers was used as a frequency standard for the heterodyne frequency measurements. Seven of the 26 lines are new. 相似文献
12.
M. Vangvichith H. Tran J.-M. Hartmann 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(18):2212-2216
The absorption by O2–CO2 mixtures in the region of the oxygen A-band near 760 nm has been measured in the laboratory at room temperature and for total pressures up to about 80 atm. As done in our previous studies for O2–N2 mixtures the contribution of the “allowed” A-band transitions have been calculated both accounting for line-mixing effects and disregarding this process. The differences between computed spectra and measured values enable extraction of the collision induced absorption (CIA) contribution, which, after removal of the O2–O2 contribution, provides, for the first time, the O2–CO2 CIA. It is shown that neglecting line-mixing overestimates absorption in the wings and underestimates absorption at the P and R branch peaks, and that the O2–CO2 CIA has an integrated intensity, in the A-band region, about 1.5 times larger than that of for pure O2 and almost 10 times greater than for O2–N2. 相似文献
13.
The electron spin resonance spectra (characterized by g factors g, g⊥ and hyperfine structure constants A and A⊥) of Ba2Zn(HCOO)6(H2O) (BZFA): VO2+ crystal are calculated from high order perturbation formulas. The calculated results are in good agreement with the observed values. The local structure parameters of [VO(H2O)5]2+ clusters are also obtained from the calculation. The magnitudes of the metal-ligand distances parallel and perpendicular to the C4-axis are, respectively, R≈0.163 nm and R⊥≈0.210 nm. It is shown that the local structure around the V4+ ion possesses a compressed tetragonal distortion along C4-axis. 相似文献
14.
Bernard A. Baldwin Jim Stevens James J. Howard Arne Graue Bjorn Kvamme Erick Aspenes Geir Ersland Jarle Husebø David R. Zornes 《Magnetic resonance imaging》2009
Magnetic resonance imaging was used to monitor and quantify methane hydrate formation and exchange in porous media. Conversion of methane hydrate to carbon dioxide hydrate, when exposed to liquid carbon dioxide at 8.27 MPa and ∼4°C, was experimentally demonstrated with MRI data and verified by mass balance calculations of consumed volumes of gases and liquids. No detectable dissociation of the hydrate was measured during the exchange process. 相似文献
15.
Ok Ja Yoon Hyun Jung Lee Yeong Mi JangHyun Woo Kim Won Bok LeeSung Su Kim Nae-Eung Lee 《Applied Surface Science》2011,257(20):8535-8541
The O2 and N2/H2 plasma treatments of single-walled carbon nanotube (SWCNT) papers as scaffolds for enhanced neuronal cell growth were conducted to functionalize their surfaces with different functional groups and to roughen their surfaces. To evaluate the effects of the surface roughness and functionalization modifications of the SWCNT papers, we investigated the neuronal morphology, mitochondrial membrane potential, and acetylcholine/acetylcholinesterase levels of human neuroblastoma during SH-SY5Y cell growth on the treated SWCNT papers. Our results demonstrated that the plasma-chemical functionalization caused changes in the surface charge states with functional groups with negative and positive charges and then the increased surface roughness enhanced neuronal cell adhesion, mitochondrial membrane potential, and the level of neurotransmitter in vitro. The cell adhesion and mitochondrial membrane potential on the negatively charged SWCNT papers were improved more than on the positively charged SWCNT papers. Also, measurements of the neurotransmitter level showed an enhanced acetylcholine level on the negatively charged SWCNT papers compared to the positively charged SWCNT papers. 相似文献
16.
In this study several complementary methods as XRD, HRTEM, O2 and H2 adsorption, as well as H2-O2 titration were used for characterization of the metallic phase in 0.5-3.0 wt.% Pt/ZnAl2O4 catalysts. Three nanocrystalline ZnAl2O4 spinels used as a supports were prepared by the solvothermal and co-precipitation method. It was found that irrespective of the preparation method they form very good support materials with a high capacity to achieve high platinum dispersion. O2 and H2 chemisorption data showed metal dispersion up to 90% and good correspondence with HRTEM results was observed. The H2-O2 titration method may be applied for determination of Pt dispersion only in the high-loaded Pt/ZnAl2O4 catalysts. The catalytic performances of Pt supported on the prepared spinels were evaluated in the propane total oxidation reaction. 相似文献
17.
M. Inguscio S. Marchetti A. Moretti F. Strumia 《International Journal of Infrared and Millimeter Waves》1982,3(1):97-116
The optoacoustic spectrum of CH3Br around 10 m band lines of a tunable cw waveguide CO2 laser is investigated. Several new infrared absorptions are observed and most of the correspond ing molecular transitions are assigned. Far infra red laser action is reported by pumping with the same CO2 laser: pump offsets are given using the Transferred Lambs dip (TLD) technique. A new FIR laser emission is obtained and assigned. An optoacoustic Laser Stark spectroscopy technique is used to investigate off resonance infrared tran sitions. 相似文献
18.
Eyk Boesche Piet Stammes 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(3):223-239
We study the intensity and degree of linear polarization of reflected solar radiation at the top of the atmosphere within two carbon dioxide bands and one oxygen absorption band in the near-infrared. In particular, we are interested in the sensitivity of the degree of linear polarization and intensity to changes of aerosol and cirrus cloud layer heights, microphysical properties, and surface albedo. For the simulations we use spectral response functions representative of the Orbiting Carbon Observatory (OCO). Inside the O2A band at 760 nm and strong CO2 band at 2060 nm we find a strong influence of the aerosol and cirrus cloud layer height on the degree of linear polarization. An increase of the aerosol or cirrus cloud layer height can lead either to a decrease or increase of the polarization within the band, depending on the microphysical and optical properties of the scatterers, surface albedo, and absorption strength in the bands. The results for the O2A band also indicate that even over land OCO enables an estimation of the height of an aerosol or cirrus cloud layer. Inside the weak CO2 band at 1610 nm the influence of aerosol or cirrus cloud layer heights is lower as compared to the O2A band and CO2 band at 2060 nm, due to the relatively stronger surface influence. Here an increase of aerosol or cirrus cloud layer height leads to an increase of the degree of linear polarization even in case of low surface albedo and for weakly polarizing scatterers. For the weak CO2 band at 1610 nm we also study the influence of the aerosol or cirrus cloud layer height on the column CO2 estimate and the errors resulting from ignoring polarization in simulations of backscatter measurements by space-based instruments such as OCO. Depending on the surface albedo, misinterpretations of the height of atmospheric scatterers might strongly affect the column CO2 estimates. 相似文献
19.
The fracture toughness property (K1C) of Si3N4 and ZrO2 engineering ceramics was investigated by means of CO2 and a fibre laser surface treatment. Near surface modifications in the hardness were investigated by employing the Vickers indentation method. Crack lengths and the crack geometry were then measured by using the optical microscopy. A co-ordinate measuring machine was used to investigate the diamond indentations and to measure the lengths of the cracks. Thereafter, computational and analytical methods were employed to determine the K1C. An increase in the K1C of both ceramics was found by the CO2 and the fibre laser surface treatment in comparison to the as-received surfaces. The K1C of the CO2 laser radiated surface of the Si3N4 was over 3% higher in comparison to that of the fibre laser treated surface. This was by softening of the near surface layer of the Si3N4 which comprised of lowering of hardness, which in turn increased the crack resistance. The effects were not similar in ZrO2 ceramic to that of the Si3N4 as the fibre laser radiation in this case had produced an increase of 34% compared to that of the CO2 laser radiation. This occurred due to propagation of lower crack resulting from the Vickers indentation test during the fibre laser surface treatment which inherently affected the end K1C through an induced compressive stress layer. The K1C modification of the two ceramics treated by the CO2 and the fibre laser was also believed to be influenced by the different laser wavelength and its absorption co-efficient, the beam delivery system as well as the differences in the brightness of the two lasers used. 相似文献
20.
C. Gastaud M. Redon P. Belland A. Kreisler M. Fourrier 《International Journal of Infrared and Millimeter Waves》1985,6(1):63-70
A systematical study of optical pumping by CO2 and N2O lasers using a FIR metallic waveguide has been undertaken in vinyl cyanide. 97 new FIR laser lines are reported in the wavelength range 400 m–1,5 mm.Unité associée au CNRS (UA 836). 相似文献