Combustion characteristics of methanol–air and methanol–air–diluent premixed mixtures at elevated temperatures and pressures

Combustion characteristics of the methanol–air premixed mixtures were studied in a constant volume bomb at different equivalence ratios, initial pressures and temperatures, and dilution ratios. The results show that the combustion pressure, the mass burning rate and the burned gas temperature get the maximum value at the equivalence ratio of 1.1 while the flame development duration and the combustion duration get the minimum value at the equivalence ratio of 1.1. The flame development duration, the combustion duration and the peak combustion pressure decrease with the increase of the initial temperature, while the maximum burned gas temperature increases with the increase of the initial temperature. The peak combustion pressure and temperature increase with the increase of the initial pressure. The flame development duration and combustion duration increase with the increase of the dilution ratio, while the peak combustion pressure and temperature decrease with the increase of the dilution ratio.     

Crystallographic and electrochemical characteristics of melt-spun Ti–Zr–Ni–Y alloys

Ti₄₅Zr₃₀Ni₂₅Y_x (x = 1, 3, 5 and 7) alloys were prepared by melt-spinning at wheel velocity of 20 m s⁻¹. The effect of additive Y on phase structure and electrochemical performance of melt-spun alloys was investigated. Ti₄₅Zr₃₀Ni₂₅Y_x melt-spun alloys were composed of I-phase and amorphous phase. The amorphous phase increased with increasing x value, indicating amorphous forming ability improved with increasing Y content. The maximum discharge capacity and high-rate dischargeability decreased with increasing x value, which may be ascribed to the decrease of nickel content. Cycling stability first increased with increasing x from 1 to 3, and then decreased when x increased to 7, which was resulted from the combined effect of the decrease of nickel content and the increase of amorphous phase.     

Synthesis and electrochemical properties of layered Li–Ni–Mn–O compounds

An attempt to prepare solid solutions in the system of LiNiO₂, LiMnO₂ and Li₂MnO₃ was performed by heating metal acetates. The solid solutions between end members LiNiO₂ and Li₂MnO₃ can be successfully prepared in the overall compositional ranges. Both the structure and capacity were compared based on Rietveld analysis and electrochemical investigation on solid solutions between LiNiO₂ and Li₂MnO₃. The result showed that the cationic disorder as well as capacity was closely related to the ratio of Li, Mn and Ni in formula. The investigation of chronopotentiogram and ex situ XRD on the solid solutions indicated that the complex phase transitions in LiNiO₂ during delithiation were strongly suppressed with low Mn content (Mn/(Mn+Ni) ratio was 0.1 or 0.2) and completely suppressed with the ratio more than 0.5.     

Crystallographic and electrochemical characteristics of Ti–Zr–Ni–Pd quasicrystalline alloys

Ti₄₅Zr₃₅Ni_20−xPd_x (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dischargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni.     

A DMFC stack operating with hydrocarbon blend membranes and Pt–Ru–Sn–Ce/C and Pd–Co/C electrocatalysts

Direct methanol fuel cell (DMFC) stacks consisting of 5 cells and 20 cells were assembled with low-cost hydrocarbon blend membranes and new electrocatalysts with better methanol tolerance and stability. The hydrocarbon blend membranes consisting of an acidic polymer (sulfonated poly (ether ether ketone), SPEEK) and a basic polymer (polysulfone-2-amide-benzimidazole, PSf-ABIm) exhibited low methanol crossover, high conductivity, and good mechanical stability. The Pt–Ru–Sn–Ce/C anode catalyst exhibited better stability than the commercial PtRu/C catalyst, while the cathode catalyst Pd–Co/C showed better methanol tolerance than the commercial Pt/C catalyst. A maximum power of around 20 W was achieved with a DMFC stack consisting of 20 membrane-electrode assemblies (MEAs) fabricated with the above membranes and electrocatalysts. The results demonstrate the feasibility of utilizing these acid-base blend membranes and novel catalysts for DMFC applications.     

Hydrogenation and electrochemical studies of La–Mg–Ni alloys

La–Mg–Ni alloys are potential candidates for hydrogen storage materials. In this study, mechanical alloying with subsequent annealing under an argon atmosphere at 973 K for 0.5 h, were used to produce La_2-xMg_xNi₇ alloys (x = 0, 0.25, 0.5, 0.75, 1). Shaker type ball mill was used. An objective of the present study was to investigate an influence of amount of Mg in alloy on electrochemical, hydrogenation and dehydrogenation properties of La–Mg–Ni materials. X-ray diffraction analyses revealed formation of material with multi-phase structure. Obtained materials were studied by a conventional Sievert's type device at 303 K. It was observed that electrochemical discharge capacity and gaseous hydrogen storage capacity of La–Mg–Ni alloys increases with Mg content to reach maximum for La_1.5Mg_0.5Ni₇ alloy. Moreover, all of La–Mg–Ni alloys were characterized by improved hydrogen sorption kinetics in comparison to La–Ni alloy.     

Electrochemical behavior of Mg–Li,Mg–Li–Al and Mg–Li–Al–Ce in sodium chloride solution

Mg–Li, Mg–Li–Al and Mg–Li–Al–Ce alloys were prepared and their electrochemical behavior in 0.7 M NaCl solutions was investigated by means of potentiodynamic polarization, potentiostatic current–time and electrochemical impedance spectroscopy measurements as well as by scanning electron microscopy examination. The effect of gallium oxide as an electrolyte additive on the potentiostatic discharge performance of these magnesium alloys was studied. The discharge activities and utilization efficiencies of these alloys increase in the order: Mg–Li < Mg–Li–Al < Mg–Li–Al–Ce, both in the absence and presence of Ga₂O₃. These alloys are more active than commercial magnesium alloy AZ31. The addition of Ga₂O₃ into NaCl electrolyte solution improved the discharging currents of the alloys by more than 4%, and enhanced the utilization efficiencies of the alloys by more than 6%. It also shortened the transition time for the discharge current to reach to a steady value. Electrochemical impedance spectroscopy measurements showed that the polarization resistance of the alloys decreases in the following order: Mg–Li > Mg–Li–Al > Mg–Li–Al–Ce. Mg–Li–Al–Ce exhibited the best performance in term of activity, utilization efficiency and activation time.     

Hydrogen absorption characteristics of mechanically alloyed Ti–Zr–Ni and Ti–V–Ni powders

A first investigation into the production of amorphous and nanostructured Ti-based alloys with nominal compositions Ti_41.5Zr_41.5Ni₁₇, Ti₆₁Zr₂₂Ni₁₇, Ti_41.5V_41.5Ni₁₇ and Ti₆₁V₂₂Ni₁₇ by mechanical alloying (MA) technique is presented. This technique was adopted to produce alloys' powders with high fresh surface area that were active for hydrogen storage. Hydrogen absorption characteristics and structure changes in the alloys after hydrogenation were investigated. Gas phase hydrogenation of the Ti–Zr–Ni alloys, at 573 K and an initial hydrogen pressure of 2 MPa, exhibited good hydriding properties and started at a maximal rate without induction period with a hydrogenation capacity up to 1.2 wt%. However, hydriding of Ti–V–Ni alloys at the same conditions exhibited slower rates. The Ti₆₁V₂₂Ni₁₇ composition showed high hydrogen absorption capacity of 1.8 wt% and exceeded 4 wt% at 345 K. In addition, the Ti–V–Ni alloys showed structure stability after hydrogenation and retained the amorphous structure.     

Laminar convective heat transfer and viscous pressure loss of alumina–water and zirconia–water nanofluids

Laminar convective heat transfer and viscous pressure loss were investigated for alumina–water and zirconia–water nanofluids in a flow loop with a vertical heated tube. The heat transfer coefficients in the entrance region and in the fully developed region are found to increase by 17% and 27%, respectively, for alumina–water nanofluid at 6 vol % with respect to pure water. The zirconia–water nanofluid heat transfer coefficient increases by approximately 2% in the entrance region and 3% in the fully developed region at 1.32 vol %. The measured pressure loss for the nanofluids is in general much higher than for pure water. However, both the measured nanofluid heat transfer coefficient and pressure loss are in good agreement with the traditional model predictions for laminar flow, provided that the loading- and temperature-dependent thermophysical properties of the nanofluids are utilized in the evaluation of the dimensionless numbers. In other words, no abnormal heat transfer enhancement or pressure loss was observed within measurement errors.     

Microstructure and electrochemical properties of Zr–Ti–V–Ni–Mn–LM alloys for application in Ni–MH secondary battery

A series of multi-component Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4; y=0.0,0.02,0.05,0.1,0.2,0.3, LM; lantanum-rich-mischmetal) alloys are prepared and their crystal structure and P–C–T curves are analyzed. The alloys have been modified by adding LM and their gaseous and electrochemical hydrogenation properties are studied to find out the effect of LM elements. Also, the second phase and initial activation performance are investigated. The Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3,0.4; y=0.0,0.02,0.05,0.1,0.2,0.3) alloys have C14 Laves phase hexagonal structure, so the volume expansion ratio of lattice parameters with LM has increased. As the amount of LM in alloy has increased, correspondingly the second phase is also increased. The second phase is LM, Ti and V-rich. The second phase improve the activation of La-rich misch-metal, and also the concentration of elements Ti, V〉LM〉 matrix in alloys.The addition of LM in Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4) alloys have increased the activation rate and hydrogen storage capacity significantly, but the plateau pressure and the discharge capacity have been decreased due to the formation of second phase. For more Zr in electrode alloys, the activation of rate becomes slow.     

Catalytic activity and characterization of Fe–Zn–Mg–Al hydrotalcites in biohydrogen production

Four different M²⁺–Mg–Al hydrotalcite (HT) materials were investigated for their effect on biohydrogen enhancement, where M²⁺ is Fe and/or Zn. HTs were synthesized by the coprecipitation method and characterized by infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The effect of Fe–Zn–Mg–Al HTs dose (0–833 mg/L) on hydrogen production was investigated in batch tests using sucrose-fed anaerobic mixed culture at 37 °C. The best catalytic activity was observed on Mg–Al HT at 167 mg/L with the maximum hydrogen yield of 2.30 ± 0.37 mol H₂/mol sucrose, which was 44% higher than the control. The major metabolites detected in the test were acetic acid (3.6 g/L), butyric acid (4.1 g/L), and lactic acid (0.5 g/L). The basic properties of the different catalysts played an important role in stimulating or inhibiting the activity of hydrogen producing bacteria. Calcined Mg–Al HT did not promote biohydrogen production, suggesting that the catalytic enhancement was related to immobilization of bacteria in the electrostatically charged HT interlayers.     

Preparation and performance of novel Li–Ti–Si–P–O–N thin-film electrolyte for thin-film lithium batteries

Novel Li–Ti–Si–P–O–N thin-film electrolyte was successfully fabricated by RF magnetron sputtering from a Li–Ti–Si–P–O target in N₂ atmosphere at various temperatures. XRD, SEM, EDX, XPS, and EIS were employed to characterize their structure, morphology, composition and electrochemical performances. The films were smooth, dense, uniform, without cracks or voids, and possessed an amorphous structure. Their room temperature lithium-ion conductivities were measured to be from 3.6 × 10⁻⁷ S cm⁻¹ to 9.2 × 10⁻⁶ S cm⁻¹, and the temperature dependence of the ionic conductivities fits the Arrhenius relation. This kind of electrolyte possessed good properties is a promising candidate material for solid-state thin-film lithium batteries.     

Hydrogen absorption and desorption kinetics of Ag–Mg–Ni alloys

The hydrogen absorption/desorption (A/D) kinetics of hydrogen storage alloys Mg_2−xAg_xNi (x=0.05, 0.1) prepared by hydriding combustion synthesis in two-phase (α–β) region in the temperature range of 523–$\text{573}\text{K}$ have been investigated. The hydriding/dehydriding (H/D) reaction rate constants were extracted from the time-dependent A/D curves. The obtained hydrogen A/D kinetic curves were fitted using various rate equations to reveal the mechanism of the H/D processes. The relationships of rate constant with temperature were established. It was found that the three-dimensional diffusion process dominates the hydrogen A/D. The apparent activation energies of 63±5 and $\text{61±7}\text{kJ/mol}\text{H}{}_2$ in Mg_1.95Ag_0.05Ni alloy and $\text{52±2}\text{kJ/mol}\text{H}{}_2$ and of $\text{50±2}\text{kJ/mol}\text{H}{}_2$ in Mg_1.9Ag_0.1Ni alloy were found for the H/D processes in two-phase (α–β) coexistence region from 523 to $\text{573}\text{K}$, respectively. With the increasing content of Ag in Ag–Mg–Ni alloys, the apparent energy was decreased and the reaction rate was faster. It is reasonable to explain that the hydriding kinetics of Mg₂Ni was improved by adding Ag.     

Kinetics of hydrogen in Zr–H and Zr–D systems

We measured dependences of the electrical resistance on time of isothermal annealing for Zr rods saturated electrolytically by hydrogen or deuterium. The annealing of samples was carried out at temperatures 305–498 K. The resistance of inhomogeneously saturated samples increased with the time of annealing. The model of diffusion of the hydrogen from the surface of the sample into its volume described this increase adequately. The resistance of homogeneously saturated samples had a minimum at some time of annealing. We showed that the decrease of the resistance during annealing obeyed the exponential law, and that the characteristic time of the decrease obeyed the Arrhenius law with the activation energy about 0.16 eV. We supposed that the resistance decreases due to the formation of the hydride in the saturated layer or on the boundaries of grains.     

Fe–P and Fe–P–Pt co-deposits as hydrogen electrodes in alkaline solution

Fe–P and Fe–P–Pt alloys for use as electrodes for alkaline water electrolysis are prepared by an electroplating technique which employs an acidic complex bath solution. After heat treatment, the plated alloys act as effective electrocatalytic materials by lowering the hydrogen overpotential sufficiently. The improved electrocatalytic activity is due to an increase in effective surface area, a change in surface features upon heat treatment, and the presence of traces of platinum. Electrodes of the plated alloys are stable even in a highly corrosive electrolytic medium (6 M KOH).     

Laminar-burning velocities of hydrogen–air and hydrogen–methane–air mixtures: An experimental study

The laminar burning velocities of hydrogen–air and hydrogen–methane–air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of hydrogen–air and different composition of hydrogen–methane–air mixtures (from 100% hydrogen to 100% methane) have been measured at ambient temperatures for variable equivalence ratios (ER=0.8–3.2$\mathrm{ER}=0.8–3.2$). A modified test rig has been developed from the former Cardiff University ‘Cloud Chamber’ for this experimental study. The rig comprises of a 250 mm length cylindrical stainless steel explosion bomb enclosed at one end with a stainless steel plug which houses an internal stirrer to allow mixing. The other end is sealed with a 120 mm diameter round quartz window. Optical access for filming flame propagation is afforded via two diametrically opposed quartz windows in both sides. Flame speeds are determined within the bomb using a high-speed Schlieren photographic technique. This method is an accurate way to determine the flame–speed and the burning velocities were then derived using a CHEMKIN computer model to provide the expansion ratio. The design of the test facility ensures the flame is laminar which results in a spherical flame which is not affected by buoyancy. The experimental study demonstrated that increasing the hydrogen percentage in the hydrogen–methane mixture brought about an increase in the resultant burning velocity and caused a widening of the flammability limits. This experiments also suggest that a hydrogen–methane mixture (i.e. 30% hydrogen+70% methane) could be a competitive alternative fuel for existing combustion plants.     

Synthesis and hydrogenation properties of Mg–La–Ni–H system by reactive mechanical alloying

We have synthesized Mg–30 mass%LaNi_2.28 composite material and investigated its hydrogenation behaviour. The reactive mechanical alloying process of the mixture of Mg and LaNi_2.28 was studied. It is found that a composite of _MgH2${\mathrm{MgH}}_2$, _La4H12.9${\mathrm{La}}_4{\mathrm{H}}_{12.9}$ and _Mg2NiH4${\mathrm{Mg}}_2{\mathrm{NiH}}_4$ formed after 80 h ball-milling under 3.0 MPa hydrogen. Scanning electron microscopic analysis indicated that these new phases are distributed homogeneously. This composite shows excellent hydriding properties even at moderate temperature. Under 3.0 MPa hydrogen pressure it absorbed more than 80% of its full capacity in the temperature range of 473–553 K within less than 1 min. The maximum hydrogen absorption capacity at 553 K is 5.4 mass%. The enhanced hydriding properties could be attributed to the fine and uniform particles and a synergeticly catalytic effect generated by mechanical milling.     

The effect of hydrogen addition on premixed laminar acetylene–hydrogen–air and ethanol–hydrogen–air flames

In the present work, the laminar premixed acetylene–hydrogen–air and ethanol–hydrogen–air flames were investigated numerically. Laminar flame speeds, the adiabatic flame temperatures were obtained utilizing CHEMKIN PREMIX and EQUI codes, respectively. Sensitivity analysis was performed and flame structure was analyzed. The results show that for acetylene–hydrogen–air flames, combustion is promoted by H and O radicals. The highest flame speed (247 cm/s) was obtained in mixture with 95% H₂–5% C₂H₂ at λ = 1.0. The region between 0.95 < X_H2 < 1.0 was referred to as the acetylene-accelerating hydrogen combustion since the flame speed increases with increase the acetylene fraction in the mixture. Further increase in the acetylene fraction decreases the H radicals in the flame front. In ethanol–hydrogen–air mixtures, the mixture reactivity is determined by H, OH and O radicals. For X_H2 < 0.6, the flame speed in this regime increases linearly with increasing the hydrogen fraction. For X_H2 > 0.8, the hydrogen chemistry control the combustion and ethanol addition inhibits the reactivity and reduces linearly the laminar flame speed. For 0.6 < X_H2 < 0.8, the laminar flame speed increases exponentially with the increase of hydrogen fraction.     

Binary Pt–Pd and ternary Pt–Pd–Ru nanoelectrocatalysts for direct methanol fuel cells

Nano-sized binary and ternary alloys are synthesized by polyol process on Vulcan XC72-R support. Nanostructured binary Pt–Pd/C catalysts are prepared either by co-deposition or by depositing on each other. Ternary Pt–Pd–Ru/C catalysts are prepared by co-deposition. The structural characteristics of the nanocatalysts are examined by TEM and XRD. Their electrocatalytic activity toward methanol oxidation and CO stripping curves were measured by electrochemical measurements and compared with that of commercial Pt/C catalyst. The results show that the binary nanocatalyst prepared by depositing the Pt precursor colloids on Pd-Vulcan XC-72R are more active toward methanol oxidation than that of the co-deposited binary alloy nanocatalyst. The co-deposited ternary Pt–Pd–Ru/C nanocatalyst based membrane electrodes assembly shows higher power density compared to the binary nanocatalysts as well as commercial Pt/C catalyst in direct methanol fuel cell. Significantly higher catalytic activity of the nanocatalysts toward methanol oxidation compared to that of the commercial Pt/C is believed to be due to lower level of catalyst poisoning.