Detailed measurements of transient two-stage ignition and combustion processes in high-pressure spray flames using simultaneous high-speed formaldehyde PLIF and schlieren imaging

This study investigates the low- and high-temperature ignition and combustion processes in a high-pressure spray flame of n-dodecane using simultaneous 50-kHz formaldehyde (HCHO) planar laser-induced fluorescence (PLIF) and 100-kHz schlieren imaging. The PLIF measurements were facilitated through the use of a pulse-burst-mode Nd:YAG laser, producing a 355-nm pulse-train with 300 pulses at 70 mJ/pulse, separated by 20-µs, in a 6-ms burst. The high-speed HCHO PLIF signal was imaged using a non-intensified CMOS camera with dynamic background emission correction. The acquisition rate of this HCHO PLIF diagnostic is unique to the research community, and when combined with high-speed schlieren imaging, provides unprecedented opportunity for analysis of the spatiotemporal evolution of fuel jet penetration and low- and high-temperature ignition processes relevant to internal combustion engine conditions. The present experiments are conducted in the Sandia constant-volume preburn vessel equipped with a new Spray A injector. The influences of ambient conditions are examined on the ignition delay times of the two-stage ignition events, HCHO structures, and lift-off length values. Consistent with past studies of traditional Spray A flames, the formation of HCHO is first observed in the jet peripheries where the equivalence ratio (Φ) is expected to be leaner and hotter and then grows in size and in intensity downstream into the jet core where Φ is expected to be richer and colder. The measurements demonstrate that the formation and propagation of HCHO from the leaner to richer region leads to high-temperature ignition events, supporting the identification of a phenomenon coined “cool-flame wave propagation” during the transient ignition process. Subsequent high-temperature ignition is found to consume the previously formed HCHO in the jet head, while the formation of HCHO persists in the fuel-rich zone near the flame base over the entire combustion period.     

Ethoxylation of p-chloronitrobenzene using phase-transfer catalysts by ultrasound irradiation: a kinetic study

Ethoxy-4-nitrobenzene was synthesized by the reaction of 4-chloronitrobenzene with potassium ethoxide in a homogeneous system using benzyltriethylammonium chloride (QCl) as a phase-transfer catalyst at 50 degrees C under ultrasound irradiation conditions. The use of phase-transfer catalysts and ultrasound has been compared and demonstrated in this nucleophilic substitution reactions. The kinetics of the reaction depends on the effect of amount of catalyst, quaternary ammonium salts, agitation speed, amount of potassium hydroxide, amount of ethanol, temperature and the frequency of the ultrasound waves on the conversion of the reaction.     

Thermodynamics of Li-N-H system for hydrogen storage: A theoretical and experimental study

In the present work, electronic structure, chemical bonding and thermal stability of Li-N-H system for hydrogen storage were calculated by a first principle approach. On the basis of the thermal analysis of this system, pressure-composition-temperature (PCT) isotherm measurements of hydrogen desorption were performed and analyzed. The theoretical and experimental enthalpies of this system were calculated as −75.67 and −69.17 kJ/mol of H₂, which agree well with other corresponding findings of −73.6 and 66.1 kJ/mol of H₂, respectively. The theoretical and experimental values of desorption enthalpies in this study are reasonably agreeable with each other.     

Isothermal reduction kinetics of nickel oxide using hydrogen: Conventional and Weibull kinetic analysis

The powder sample of nickel oxide was synthesized by sol-gel procedure. The isothermal reduction of nickel oxide using hydrogen was investigated by thermogravimetric analysis at five operating temperatures: 245, 255, 265, 275 and 300 °C. The kinetic triplet (E_a, A and f(α)) was determined using conventional and Weibull kinetic analysis. Both the kinetically procedures show that the reduction process considered can be explained with a two-step kinetic model. It is established that at lower temperatures (245 °C?T?255 °C), the reduction process considered is governed by two-parameter Šesták-Berggren autocatalytic model (first step) and at higher temperatures (T?265 °C), the reduction process is governed by Fn reaction model with different values of parameter n (second step). In this paper, the complex manner of dependence of the Weibull shape parameter (β) on temperature is established. With alterations of Weibull shape parameter from lower temperatures (β>1) to higher temperatures (β<1), it was concluded that isothermal reduction process of NiO using hydrogen can be described by a multistep reaction mechanism. These results are confirmed by the evaluated density distribution functions (ddf) of apparent activation energies (E_a), which show variations in basic characteristics at lower and higher operating temperature regions. Also, in this paper, it was shown that the shape parameter (β) of Weibull distribution function can represent the behaviour index, which indicates the kinetic pattern of the mechanism controlling the process studied.     

Sodium decorated net-Y nanosheet for hydrogen storage and adsorption mechanism: A first-principles study

Using first-principles calculations based on density functional theory(DFT), we investigate the potential hydrogen storage capacity of the Na-decorated net-Y single layer nanosheet. For double-side Na decoration, the average binding energy is 1.54 eV, which is much larger than the cohesive energy of 1.13 eV for bulk Na. A maximum of four H_2 molecules can be adsorbed around each Na with average adsorption energies of 0.25–0.32 eV/H_2. Also, H_2 storage gravimetric of 8.85 wt% is obtained, and this meets the U.S. Department of Energy(DOE) ultimate target. These results are instrumental in seeking a promising hydrogen energy carrier.     

Mesoporous titania-alumina mixed oxide: A preliminary study on synthesis and application in selective catalytic reduction of NOx

Titania-alumina mixed oxide was synthesized hydrothermally using tetrapropylammonium hydroxide (TPAOH) as the template. The dried, calcined and palladium loaded samples were characterized for particle morphology, weight loss, nitrogen adsorption/desorption at liquid nitrogen temperature, texture and metal dispersion. The Pd loaded material was tested for NO reduction in a fixed bed catalytic reactor using a simulated gas mixture closely resembling lean burn engine exhaust. Scanning electron microscopy of the dried and calcined samples revealed a well developed tubular fibrous network of titania-alumina. Thermogravimetry (TG) of the dried sample indicated about 16% weight loss due to decomposition of an oxy-hydroxide structure of the material, mostly boehmite, which was confirmed by X-ray diffraction (XRD) measurements. The boehmite phase changed to poorly crystalline γ-alumina upon calcination where as titania remained as anatase. BET specific surface area, adsorption-desorption isotherms and BJH pore size distributions indicated formation of a mesoporous structure. The surface area of the dried material increased when calcined at 600 °C but the pore size distribution patterns for the dried, calcined and palladium dispersed materials remained unchanged. These observations along with TG and XRD analyses suggest that a thermo-resistant, mesoporous, high surface area, crystalline titania-alumina framework can be prepared using the hydrothermal synthesis route. A peak NOx conversion of 75% with the palladium dispersed catalyst indicates high catalytic activity, possibly due to high dispersion of Pd confirmed by CO chemisorption studies.     

A study of the cobalt sites in cobalt and iron molybdate catalysts by emission Mössbauer spectroscopy

Molybdates samples containing 74MBq (2mCi) of cobalt 57 have been studied by emission Mössbauer spectroscopy. Spectra of⁵⁷CoMoO₄ exhibited the three usual Fe²⁺ doublets corresponding to α and β ferrous phases, and two Fe³⁺ doublets accounting for about one third of the absorption area. The Co²⁺ sites of β⁵⁷CoMoO₄ phase exhibit higher quadrupole splittings, i.e. are more dissymmetrical than Fe²⁺ sites of βFeMoO₄ phase. Cobalt and iron molybdates Fe_x ⁵⁷Co_1?xMoO₄ provided spectra where only one Fe³⁺ doublet appeared and occupied less than 7% of the spectral area. It is concluded that a part of cobalt was present in⁵⁷CoMoO₄ as Co³⁺.     

A kinetic study of the initial oxidation of the Ni(001) surface by RHEED and x-ray emission

Nickel (001) surfaces were prepared by a combination of high temperature oxidation, argon ion bombardment and hydrogen reduction. The oxidation of this surface in pure C₂ to form NiO was studied by reflection high energy electron diffraction (RHEED) and X-ray emission. On exposure to oxygen the “clean” surface was found to chemisorb oxygen to produce a coverage of 0.014 $\text{micro}\text{g}\text{cm}{}^2$ in an ordered c(2 × 2) structure. Within this film there appears to exist a number of nucleation sites dependent on temperature and step density. Growth is by oxygen capture at the periphery of these sites to produce oxide islands approximately three oxygen planes thick which spread to cover the surface. At room temperature this film does not thicken with additional oxygen exposure.     

A kinetic study of the initial oxidation of the Ni(110) surface by RHEED and X-ray emission

Nickel (110) surfaces, prepared by a combination of high temperature oxidation, argon ion bombardment and hydrogen reduction, were oxidized in pure O₂. The structural aspects of this interaction were studied by reflection high energy electron diffraction (RHEED) and the corresponding kinetics determined by electron excited X-ray emission spectroscopy. On exposure to oxygen the surface was observed to go through three ordered two-dimensional structures. These were a (2 × 1), a (3 × 1) and finally a (9 × 4) structure containing 0.015 microg/cm² of oxygen. From this surface NiO was produced in a (001) epitaxy which was compressed 4.5% in the plane of the surface. With oxidation beyond 0.060 microg/cm² the oxide strain was relieved and a complex oxide epitaxy developed which has been tentatively identified as a (117) oxide parallel to the nickel (110) surface. The kinetics have been explained on the basis of three distinct processes. (i) An initial chemisorption stage (0 to 0.015 microg/cm²) associated with the two-dimensional structures, (ii) Oxide nucleation and spreading to cover the surface, associated with the (001)-NiO epitaxy (0.015 to 0.06 microg/cm²), (iii) Logarithmic film thickening above 0.060 0.06 microg/cm² associated with the development of (117) epitaxy.     

Sonoprocessing of wetting of SiC by liquid Al: A thermodynamic and kinetic study

The sonoprocessing of droplet spreading during the wetting process of molten aluminum droplets on SiC ceramic substrates at 700 °C is investigated in this paper. When wetting is assisted by a 20 kHz frequency ultrasonic field, the wettability of liquid metal gets enhanced, which has been determined by the variations in thermodynamic energy and wetting kinetics. Wetting kinetic characteristics are divided into two stages according to pinning and depinning states of substrate/droplet contact lines. The droplet is static when the contact line is pinning, while it is forced to move when the contact line is depinning. When analyzing the pinning stage, high-speed photography reveals the evidence of oxide films being rapidly crushed outside the aluminum droplet. In this work, atomic models of spherical Al core being wrapped by alumina shell are tentatively built, whose dioxide microstructures are being transformed from face-centered cubic into liquid at the atomic scale. At the same time, the wetting experiment reveals that the oxide films show changes in the period of sonoprocessing from 3rd to 5th second.During the ultrasonic spreading behavior in the late stage, there is a trend of evident expansion of the base contact area. The entire ultrasonic process lasts for no longer than 10 s. With the aid of ultrasonic sinusoidal waves, the wettability of metal Al gets a rapid improvement. Both molecular dynamic (MD) investigations and the experiments results reveal that the precursor film phenomenon is never found unless wetting is assisted by ultrasonic treatments. However, the precursor film appears near the triple line after using ultrasonics in the droplet wetting process, whose formation is driven by ultrasonic oscillations. Due to the precursor film, the ultrasonic wetting contact angle is lower than the non-ultrasonic contact angle. In addition, the time-variant effective ultrasonic energy has been quantitatively evaluated. The numerical expressions of thermodynamic variables are well verified by former ultrasonic spreading test results, which altogether provide an intrinsic explanation of the fast-decreasing contact angle of Al/SiC.     

A kinetic modeling study on the oxidation of primary reference fuel-toluene mixtures including cross reactions between aromatics and aliphatics

A detailed chemical kinetic model for the mixtures of primary reference fuel (PRF: n-heptane and iso-octane) and toluene has been proposed. This model is divided into three parts; a PRF mechanism [T. Ogura, Y. Sakai, A. Miyoshi, M. Koshi, P. Dagaut, Energy Fuels 21 (2007) 3233-3239], toluene sub-mechanism and cross reactions between PRF and toluene. Toluene sub-mechanism includes the low temperature kinetics relevant to engine conditions. A chemical kinetic mechanism proposed by Pitz et al. [W.J. Pitz, R. Seiser, J.W. Bozzelli, et al., in: Chemical Kinetic Characterization of the Combustion of Toluene, Proceedings of the Second Joint Meeting of the U.S. Sections of the Combustion Institute, 2001] was used as a starting model and modified by updating rate coefficients. Theoretical estimations of rate coefficients were performed for toluene and benzyl radical reactions important at low temperatures. Cross reactions between alkane, alkene, and aromatics were also included in order to account for the acceleration by the addition of toluene into iso-octane recently found in the shock tube study of the ignition delay [Y. Sakai, H. Ozawa, T. Ogura, A. Miyoshi, M. Koshi, W.J. Pitz, Effects of Toluene Addition to Primary Reference Fuel at High Temperature, SAE 2007-01-4104, 2007]. Validations of the model were performed with existing shock tube and flow tube data. The model well predicts the ignition characteristics of PRF/toluene mixtures under the wide range of temperatures (500-1700 K) and pressures (2-50 atm). It is found that reactions of benzyl radical with oxygen molecule determine the reactivity of toluene at low temperature. Although the effect of toluene addition to iso-octane is not fully resolved, the reactions of alkene with benzyl radical have the possibility to account for the kinetic interactions between PRF and toluene.     

Mössbauer emission studies of Co-Mo/Al2O3 hydrodesulfurization catalysts: Effects of reduction and sulfidation treatments

The effect of the sulfiding temperature on the catalytic and structural properties of Co-Mo/Al₂O₃ catalysts is studied by taking into account the after-effects arising from 57-Co in the alumina. The catalytic activity is shown to be correlated to both MoS₂ or CoMoS and Co₉S₈ phases.     

卡尔曼波滤—分光光度法用于有机反应动力学研究

本文将卡尔曼滤波－分光光度法用于α－羰基烯顺环二硫代缩酮化合物的化学动力学研究。结果表明，用该方法能够有效地消除或减小组分间的干扰，从而进行混合体系中各组分的同时测定。该方法成功地用于１－苯基－２－（１，２－亚忆充基）亚甲基－１，３二本号间硝基苯甲醛的缩合反应动力学研究 中。     

A high-temperature study of 2-pentanone oxidation: experiment and kinetic modeling

Small methyl ketones are known to have high octane numbers, impressive knock resistance, and show low emissions of soot, NO_x, and unburnt hydrocarbons. However, previous studies have focused on the analysis of smaller ketones and 3-pentanone, while the asymmetric 2-pentanone (methyl propyl ketone) has not gained much attention before. Considering ketones as possible fuels or additives, it is of particular importance to fully understand the combustion kinetics and the effect of the functional carbonyl group. Due to the higher energy density in a C₅-ketone compared to the potential biofuel 2-butanone, the flame structure and the mole fraction profiles of species formed in 2-pentanone combustion are of high interest, especially to evaluate harmful species formations. In this study, a laminar premixed low-pressure (p?=?40 mbar) fuel-rich (??=?1.6) flat flame of 2-pentanone has been analyzed by vacuum-ultraviolet photoionization molecular-beam mass-spectrometry (VUV-PI-MBMS) enabling isomer separation. Quantitative mole fraction profiles of 47 species were obtained and compared to a model consisting of an existing base mechanism and a newly developed high-temperature sub-mechanism for 2-pentanone. High-temperature reactions for 2-pentanone were adapted in analogy to 2-butanone and n-pentane, and the thermochemistry for 2-pentanone and the respective fuel radicals was derived by ab initio calculations. Good agreement was found between experiment and simulation for the first decomposition products, supporting the initial branching reactions of the 2-pentanone sub-mechanism. Also, species indicating low-temperature chemistry in the preheating zone of the flame have been observed. The present measurements of a 2-pentanone flame provide useful validation targets for further kinetic model development.     

Similarity of Co-Species in Co and CoMo-sulfide catalysts supported on carbon and alumina. A Mössbauer emission spectroscopic study

It is shown that, irrespective of the application of carbon or alumina as a support, the local structure of the “Co-sulfide” phase formed during sulfidation of Co-and CoMo-catalysts is the same. A relation is found between the quadrupole splitting (Q.S. value) of the “Co-sulfide” phase and its dispersion. The higher the dispersion, the larger the Q.S. value. The so-called “Co-Mo-S” doublet is observed in all cases and it turns out to be related to a highly dispersed “Co-sulfide” phase instead of a Co, Mo and S containing phase.     

Stationary inverted Lyman populations and free-free and bound-free emission of lower-energy state hydride ion formed by an exothermic catalytic reaction of atomic hydrogen and certain group I catalysts

Rb⁺ to Rb²⁺ and 2K⁺ to K + K²⁺ each provide a reaction with a net enthalpy equal to the potential energy of atomic hydrogen. The presence of these gaseous ions with thermally dissociated hydrogen formed a plasma having strong VUV emission with a stationary inverted Lyman population. Significant Balmer α line broadening of 18 and 9 eV was observed from a rt-plasma of hydrogen with KNO₃, and RbNO₃, respectively, compared to 3 eV from a hydrogen microwave plasma. The reaction was exothermic since excess power of about 20 mW/cc was measured by Calvet calorimetry. We propose an energetic catalytic reaction involving a resonance energy transfer between hydrogen atoms and Rb⁺ or 2K⁺ to form a very stable novel hydride ion. Its predicted binding energy of 3.0471 eV with the fine structure was observed at 4071 Å, and its predicted bound-free hyperfine structure lines matched those observed for about 40 lines to within.01 percent. Characteristic emission from each catalyst was observed. This catalytic reaction may pump a CW HI laser.     

Sonochemical synthesized BaMoO4/ZnO nanocomposites as electrode materials: A comparative study on GO and GQD employed in hydrogen storage

Due to poor rate proficiency and electrochemical capacity of transition metal oxides, production electrode materials as operative way to develop the electrochemical performance is a crucial strategy to make sure the great electroactive sites and fast electron/ion diffusion route. In order to solve this problem, carbon-based nanocomposites as conductive substrates are applied. The nanostructured BaMoO₄/ZnO was produced by sonochemical method in the presence of tween 20 as stabilizing agent. Effect of graphene quantum dots (GQDs) and graphene oxide (GO) for developing hydrogen capacity of BaMoO₄/ZnO was studied by providing representative composites of BaMoO₄/ZnO-GQDs and BaMoO₄/ZnO-GO. For this purpose, GQDs was synthesized using green source of Spiraea crenata and the GO provided by commercial company. The structural analysis shows preparation of scales-like morphology of BaMoO₄/ZnO without any impurities through SEM, TEM, XRD, EDS and FT-IR characterization data. Also, the specific surface area for BaMoO₄/ZnO-GQDs (11 m²/g) and BaMoO₄/ZnO-GO (124 m²/g) nanocomposites increased by comparing to BaMoO₄/ZnO (9.1 m²/g). The resultant nanocomposites used as new active compounds for applying in hydrogen storage strategies using cyclic voltammetry and chronopotentiometry tests. Comprehensively, the hydrogen capacitance after 15 cycles was demonstrated on the nanostructured BaMoO₄/ZnO about 129 mAhg⁻¹. It demanded the maximum capacitance for BaMoO₄/ZnO-GQDs and BaMoO₄/ZnO-GO nanocomposites were 284 and 213 mAhg⁻¹ respectively, which was higher than the initial nanostructured BaMoO₄/ZnO. It was exposed from the carbon based structured that; the endorsed electrochemical hydrogen storage (EHS) performance is ascribed to the reaction of the redox pair of Mo⁶⁺ /Mo⁵⁺ at the active sites throughout the EHS procedure. This study delivers a novel plan and potential sorption electrode materials to progress the intrinsic action of conductive compounds.     

High-throughput study of the influence of H2O and CO2 on the performance of nitrogen storage and reduction (NSR) catalysts

This paper describes the application of parallel high-throughput experimentation based on FTIR spectral imaging to a tolerance study for NO_x storage and reduction (NSR) catalysts with respect to CO₂ and H₂O in the feed. It was found that both gases decrease the storage capacity of platinum/barium based NSR catalysts, with H₂O having a stronger effect than CO₂.