A field operational test on valve-regulated lead-acid absorbent-glass-mat batteries in micro-hybrid electric vehicles. Part I. Results based on kernel density estimation

In March 2007 the BMW Group has launched the micro-hybrid functions brake energy regeneration (BER) and automatic start and stop function (ASSF). Valve-regulated lead-acid (VRLA) batteries in absorbent glass mat (AGM) technology are applied in vehicles with micro-hybrid power system (MHPS). In both part I and part II of this publication vehicles with MHPS and AGM batteries are subject to a field operational test (FOT). Test vehicles with conventional power system (CPS) and flooded batteries were used as a reference. In the FOT sample batteries were mounted several times and electrically tested in the laboratory intermediately. Vehicle- and battery-related diagnosis data were read out for each test run and were matched with laboratory data in a data base. The FOT data were analyzed by the use of two-dimensional, nonparametric kernel estimation for clear data presentation.The data show that capacity loss in the MHPS is comparable to the CPS. However, the influence of mileage performance, which cannot be separated, suggests that battery stress is enhanced in the MHPS although a battery refresh function is applied. Anyway, the FOT demonstrates the unsuitability of flooded batteries for the MHPS because of high early capacity loss due to acid stratification and because of vanishing cranking performance due to increasing internal resistance. Furthermore, the lack of dynamic charge acceptance for high energy regeneration efficiency is illustrated. Under the presented FOT conditions charge acceptance of lead-acid (LA) batteries decreases to less than one third for about half of the sample batteries compared to new battery condition. In part II of this publication FOT data are presented by multiple regression analysis (Schaeck et al., submitted for publication [1]).     

Synthesis and photovoltaic properties of an alternating phenylenevinylene copolymer with substituted-triphenylamine units along the backbone for bulk heterojunction and dye-sensitized solar cells

We have fabricated bulk heterojunction (BHJ) photovoltaic devices based on the as cast and thermally annealed P:[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) blends and found that these devices gave power conversion efficiency (PCE) of about 1.15 and 1.60% respectively. P is a novel alternating phenylenevinylene copolymer which contains 2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid units along the backbone and was synthesized by Heck coupling. This copolymer was soluble in common organic solvents and showed long-wavelength absorption maximum at 390-420 nm with optical band gap of 1.94 eV. The improvement of PCE after thermal annealing of the device based on the P:PCBM blend was attributed to the increase in hole mobility due to the enhanced crystallinity of P induced by thermal treatment. In addition, we have fabricated BHJ photovoltaic devices based on the as cast and thermally annealed PB:P:PCBM ternary blend. PB is a low band gap alternating phenylenevinylene copolymer with BF₂-azopyrrole complex units, which has been previously synthesized in our laboratory. We found that the device based on this ternary blend exhibited higher PCE (2.56%) as compared to either P:PCBM (1.15%) or PB:PCBM (1.57%) blend. This feature was associated with the well energy level alignment of P, PB and PCBM, the higher donor-acceptor interfaces for the exciton dissociation and the improved light harvesting property of the ternary blend. The further increase in the PCE with thermally annealed ternary blend (3.48%) has been correlated with the increase in the crystallinity of both P and PB. Finally, we used copolymer P as sensitizer for quasi solid state dye-sensitized solar cell and we achieved PCE of approximately 3.78%.     

On the validity of a design method for a solar-assisted ejector cooling system

A solar-assisted ejector cooling system is simulated in order to investigate the validity of a design methodology. Hourly simulation results allow for computing the solar fraction, in cases when the cooling capacity of the ejector cycle is kept constant during daily periods. The computed solar fraction is compared with estimates obtained from the method based on the utilizability concept. An equivalent minimum temperature for the utilizability of the solar system is found, which proves to be different, but close to, the vapor generator temperature of the ejector cycle. It is shown that the solar fraction derived from the utilizability concept based on the monthly means of the global solar radiation is applicable to solar-assisted ejector cooling cycles, in cases when the minimum temperature at which solar heat is supplied to the load is determined. Good agreement is found between the solar fraction results obtained from the simulations and those obtained by the method.     

On various modeling approaches to radiative heat transfer in pool fires

Six computational methods for solution of the radiative transfer equation in an absorbing-emitting, nonscattering gray medium were compared for a 2-m JP-8 pool fire. The emission temperature and absorption coefficient fields were taken from a synthetic fire due to the lack of a complete set of experimental data for computing radiation for large and fully turbulent fires. These quantities were generated by a code that has been shown to agree well with the limited quantity of relevant data in the literature. Reference solutions to the governing equation were determined using the Monte Carlo method and a ray-tracing scheme with high angular resolution. Solutions using the discrete transfer method (DTM), the discrete ordinates method (DOM) with both S₄ and LC₁₁ quadratures, and a moment model using the M₁ closure were compared to the reference solutions in both isotropic and anisotropic regions of the computational domain. Inside the fire, where radiation is isotropic, all methods gave comparable results with good accuracy. Predictions of DTM agreed well with the reference solutions, which is expected for a technique based on ray tracing. DOM LC₁₁ was shown to be more accurate than the commonly used S₄ quadrature scheme, especially in anisotropic regions of the fire domain. On the other hand, DOM S₄ gives an accurate source term and, in isotropic regions, correct fluxes. The M₁ results agreed well with other solution techniques and were comparable to DOM S₄. This represents the first study where the M₁ method was applied to a combustion problem occurring in a complex three-dimensional geometry. Future applications of M₁ to fires and similar problems are recommended, considering its similar accuracy and the fact that it has significantly lower computational cost than DOM S₄.     

Mathematical modeling of MILD combustion of pulverized coal

MILD (flameless) combustion is a new rapidly developing technology. The IFRF trials have demonstrated high potential of this technology also for N-containing fuels. In this work the IFRF experiments are analyzed using the CFD-based mathematical model. Both the Chemical Percolation Devolatilization (CPD) model and the char combustion intrinsic reactivity model have been adapted to Guasare coal combusted. The flow-field as well as the temperature and the oxygen fields have been accurately predicted by the CFD-based model. The predicted temperature and gas composition fields have been uniform demonstrating that slow combustion occurs in the entire furnace volume. The CFD-based predictions have highlighted the NO_x reduction potential of MILD combustion through the following mechanism. Before the coal devolatilization proceeds, the coal jet entrains a substantial amount of flue gas so that its oxygen content is typically not higher than 3-5%. The volatiles are given off in a highly sub-stoichiometric environment and their N-containing species are preferentially converted to molecular nitrogen rather than to NO. Furthermore, there exists a strong NO-reburning mechanism within the fuel jet and in the air jet downstream of the position where these two jets merge. In other words, less NO is formed from combustion of volatiles and stronger NO-reburning mechanisms exist in the MILD combustion if compared to conventional coal combustion technology.     

On the spectral bands measurements for combustion monitoring

In this work, spatial–spectral experimental issues affecting the detection of radical emissions in a natural gas flame are discussed and studied by a radiometric analysis of the flame spectral emission. As results of this analysis, Local and Global Spectral Radiation Measurements (LSRM and GSRM respectively) techniques are proposed, and guidelines for selecting the radical emission bands and spatial location of photodetectors are given. Two types of experiments have been performed in order to demonstrate the reliability of the GSRM technique for combustion characterization. In the first experiment, the LSRM and the GSRM have been implemented by using a home made sensor array, based on silicon photodiodes, for sensing the excited CH^∗ and radicals in a natural gas flame. It has been experimentally demonstrated that by using the GSRM, the signal’s dispersion can be reduced to about 86% for the CH^∗ and 76% for the with respect to the obtained values with LSRM methodology. In the second experiment, the GSRM technique has been applied for sensing the CH^∗ and radicals, where it has been found that the signals emissions ratio /CH^∗ provides a good indicator of the thermal combustion efficiency and the CO pollutants emissions, with small dispersion. Thus, the GSRM technique has corroborated the usefulness of that ratio for combustion monitoring.     

Study of the performance of three micromixing models in transported scalar PDF simulations of a piloted jet diffusion flame (“Delft Flame III”)

Numerical simulation results are presented for a turbulent nonpremixed flame with local extinction and reignition. The transported scalar PDF approach is applied to the turbulence-chemistry interaction. The turbulent flow field is obtained with a nonlinear two-equation turbulence model. A C₁ skeletal scheme is used as the chemistry model. The performance of three micromixing models is compared: the interaction by exchange with the mean model (IEM), the modified Curl's coalescence/dispersion model (CD) and the Euclidean minimum spanning tree model (EMST). With the IEM model, global extinction occurs. With the standard value of model constant C?=2, the CD model yields a lifted flame, unlike the experiments, while with the EMST model the correct flame shape is obtained. However, the conditional variances of the thermochemical quantities are underestimated with the EMST model, due to a lack of local extinction in the simulations. With the CD model, the flame becomes attached when either the value of C? is increased to 3 or the pilot flame thermal power is increased by a factor of 1.5. With increased value of C? better results for mixture fraction variance are obtained with both the CD and the EMST model. Lowering the value of C? leads to better predictions for mean temperature with EMST, but at the cost of stronger overprediction of mixture fraction variance. These trends are explained as a consequence of variance production by macroscopic inhomogeneity and the specific properties of the micromixing models. Local time stepping is applied so that convergence is obtained more quickly. Iteration averaging reduces statistical error so that the limited number of 50 particles per cell is sufficient to obtain accurate results.     

Combustion of hydrogen in a bubbling fluidized bed

The combustion of hydrogen in a hot, bubbling bed of quartz sand fluidized by air has been studied for the first time, by injecting hydrogen just above the distributor, via six horizontal fine tubes of Cr/Ni. Overall the fluidizing gas was oxygen-rich, with the composition varying from nearly stoichiometric to very lean mixtures. With the bed initially fluidized at room temperature, combustion (after ignition by a pilot flame) occurs in a premixed flame sitting on top of the bed. When the sand warms up, combustion becomes explosive in bubbles leaving the bed, exactly as with a hydrocarbon as fuel. However, in contrast to hydrocarbons, it is clear that when the bed reaches 500-600 °C, heat is produced both above the top of the bed (because of H₂ bypassing the bed) and very low down in the bed. In fact, with hydrogen as fuel, the location of where bubbles ignite descends abruptly to low in the sand; furthermore, the descent occurs at ∼500 °C, which is ∼100 K below the ignition temperature predicted by well-established kinetic models. However, the kinetic models do reproduce the observations, if it is assumed that the Cr/Ni hypodermic tubes, through which the fuel was injected, exert a catalytic effect, producing free H atoms, which then give rise to HO₂ radicals. In this situation, kinetic modeling indicates that bubbles ignite when they become sufficiently large and few enough to have a lifetime (i.e. the interval between their collisions) longer than the ignition delay for the temperature of the sand. The amounts of NO found in the off-gases were at a maximum (24 ppm), when the bed was at ∼500 °C for λ=[O₂]/stoich[O₂]=1.05. The variations of [NO] with [air]/[H₂] and also temperature indicate that NO is produced, at least partly, via the intermediate N₂H. In addition, the air-afterglow emission of green light (from NO+O→NO₂+hν) was observed in the freeboard, indicating the presence there of both NO and free atoms of oxygen for 1.05<λ<1.1.     

Reliability analysis of solar photovoltaic system using hourly mean solar radiation data

This paper presents the hourly mean solar radiation and standard deviation as inputs to simulate the solar radiation over a year. Monte Carlo simulation (MCS) technique is applied and MATLAB program is developed for reliability analysis of small isolated power system using solar photovoltaic (SPV). This paper is distributed in two parts. Firstly various solar radiation prediction methods along with hourly mean solar radiation (HMSR) method are compared. The comparison is carried on the basis of predicted electrical power generation with actual power generated by SPV system. Estimation of solar photovoltaic power using HMSR method is close to the actual power generated by SPV system. The deviation in monsoon months is due to the cloud cover. In later part of the paper various reliability indices are obtained by HMSR method using MCS technique. Load model used is IEEE-RTS. Reliability indices, additional load hours (ALH) and additional power (AP) reduces exponentially with increase in load indicates that a SPV source will offset maximum fuel when all of its generated energy is utilized. Fuel saving calculation is also investigated. Case studies are presented for Sagardeep Island in West Bengal state of India.     

Simulation of methane conversion to syngas in a membrane reactor: Part I A model including product oxidation

A one-dimensional dense membrane reactor (DMR) model has been developed to simulate the partial oxidation of methane to syngas. A combustion–reforming mechanism was adopted and the oxidation of reforming products, i.e. H₂ and CO, was considered. The performance of the DMR and a conventional fixed-bed reactor was compared and discussed. The results show that the incorporation of the product oxidation steps has a significant effect on the simulation results of a DMR and provides a reasonable explanation of the experimental data. The model is therefore more reasonable than those ignoring the product oxidation reactions.     

International passenger transport and climate change: A sector analysis in car demand and associated emissions from 2000 to 2050

The paper provides global regionalized projections of passenger car demand, use and associated CO₂ emissions from 11 world regions. The study is based on empirical data that have been originally collated from international sources for the purpose of modeling region-specific car stock demand. Derived demands serve as indicator of car related fuel consumption and associated CO₂ emissions, which are calculated on the basis of behavioral and technological scenarios. The obtained CO₂ emission paths are sectoral baseline scenarios that identify region-specific potentials of growth in car induced CO₂ emissions assuming that current trends continue to prevail. The study adopts a multi-model approach to car demand by applying two methodologies rooted in the economics of consumption: utility maximization and single equation models. The utility maximization method for modeling car demand is driven by the preferences of the representative consumers of each world region, subject to exogenous price and income trajectories. The latter is adopted from an optimal growth model. This is a novel approach to projecting global regionalized sectoral car demands. The study is complemented by the application of single equation income–consumption models based on logistical Gompertz functions and non-linear regression techniques to compare model results.     

A theoretical study of the electronic structure and bonding of the monoclinic phase of

The electronic properties of the Mg₂NiH₄ monoclinic phase are calculated using a density functional approach calculation. The crystalline parameters and interatomic distances calculated are close to the experimental values within a 3% error. We also evaluate the density of states (DOS) and character of the chemical bonding for the hydrogen's located in their equilibrium positions. While the Ni–Mg interaction is dominant in the pure alloy, in the hydride the hydrogen atoms present a bonding much more developed with Ni than with Mg. The principal bonding interaction is Ni sp–H s. Moreover, a small bonding between Ni d_eg and H 1s is observed. Up the Fermi level, the Ni–H interaction is slightly antibonding. The Mg–Ni bonding interactions are weaker in the hydride phase when compared with the pure Mg₂Ni alloy. The present study is potentially useful because the alloys Mg–Ni are good materials for hydrogen storage.     

A wide range modeling study of formation and nitrogen chemistry in hydrogen combustion

The chemistry of nitrogen species and the formation of NO_x in hydrogen combustion are analyzed here on the basis of a large set of experimental measurements.The detailed kinetic scheme of H₂/O₂ combustion was updated and upgraded using new kinetic and thermodynamic measurements, and was validated over a wide range of temperatures, pressures and equivalence ratios. The mechanism's performance at high pressures was greatly improved in particular by adopting higher rate parameters for the H+OH+M=H₂O reaction.The NO_x sub-mechanism was further validated and updated. The kinetic parameters of the NO₂+H₂=HONO+H and N₂H₂+NO=N₂O+NH₂ reactions were updated in order to improve model predictions in specific conditions.Sensitivity analyses were carried out to determine which reactions dominate the H₂/O₂ and H₂/NO_x systems at particular operating conditions.Good overall agreement was observed between the model and the wide range of experiments simulated.     

Activation characteristics and microstructure of composite hydrogen storage alloys prepared by two-step re-melting

In the present work, novel composites (x=0,5,10,30) for hydrogen storage were prepared by two-step re-melting and their activation characteristic and microstructure were investigated. The influence of Mg₂Ni content on the activation characteristics was analyzed by electrochemical method. With the increasing content of Mg₂Ni, activation characteristics and maximum discharge capacities of composites increase first and then decrease. The composite with 5% Mg₂Ni has the least cycle number for activation and the highest discharge capacity. It is activated after only 6 cycles (C_n=6) at room temperature and its maximum discharge capacity (C_max) reaches 274.4 mAh/g. However, the composite contained 30 wt% Mg₂Ni is difficult to be activated at room temperature. It is also found that it is easier to be activated for the composites at and than that at and , but their discharge capacity decay slightly at the condition of and . The XRD and SEM analysis show that, with the increasing Mg₂Ni content, the microstructure of the composites varies gradually from lamellar (x=5), acicular (x=10) to massive (x=30), and the activity of the composite declines as a result of the grain size of phase Mg₂Ni grows up.     

Investigation on microstructures and electrochemical performances of hydrogen storage alloys

In order to improve the cycle stability of La–Mg–Ni system (A₂B₇-type) alloy electrode, a small amount of Co was added in the La_0.75Mg_0.25Ni_3.5 alloy. The effects of Co content on the microstructures and electrochemical performances of the alloys were investigated in detail. The results by XRD and SEM show that the alloys have a multiphase structure which is composed of the LaNi₅, (La,Mg)₂Ni₇ two major phases and a small amount of the LaNi₂ phase. The cell volumes of the LaNi₅ and phases enlarge with the increasing Co content in the alloys. With the increasing Co content, some electrochemical properties and kinetic parameters of the alloy, involving the discharge capacity, high-rate discharge ability (HRD), the polarization resistance (R_p), the loss angle (ψ) and the limiting current density (I_L), first increase and then decrease. The addition of Co slightly improves the cycle stabilities of the alloy electrodes. The mechanism of the efficiency loss of the experimental alloy was investigated by means of SEM and X-ray photoelectron spectroscopy (XPS). The results indicate that the fundamental reasons for the capacity decay of the La_0.75Mg_0.25Ni_3.5Co_x (x=0,0.2,0.4,0.6) alloy electrodes are the pulverization of the alloy particle and corrosion/oxidation of La and Mg in alkaline electrolyte.     

Mass production of alloy bulk by isothermal evaporation casting process

An innovative method, isothermal evaporation casting process (IECP), is developed to produce Mg₂Ni alloy for mass production in this work. In the past, high vapor pressure of Mg was considered as a disadvantage for producing pure Mg₂Ni alloy. However, this characteristic was used to develop a refinement procedure to separate primary Mg₂Ni alloy from Mg/Mg₂Ni eutectic matrix. Characteristics of as-cast specimens measured by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and electron probe X-ray microanalyzer (EPMA) reveal that mass production of single phase Mg₂Ni alloy was successfully fabricated by IECP. For every 4.0 kg of raw materials, alloy bulk was extracted at a yield of about 65%. The hydrogen storage capacity of the well-activated Mg₂Ni alloy reaches 3.58 wt% at 300 °C under 40 atm H₂ atmosphere which is close to the theoretical capacity of 3.6 wt%.     

Microstructure and hydrogen storage properties of the laser sintered alloy

The Mg₂Ni hydrogen storage samples were prepared by the laser sintering method. Before laser sintering, the Mg and Ni powders were pre-mixed by pestle milling (sample PM) or ball milling (sample BM). The microstructures and hydrogen storage properties of the laser sintered Mg₂Ni samples were investigated. The sintered samples contained Mg₂Ni and small amount of MgNi₂, Mg, Ni and MgO. Compared with the sample PM, the amounts of Mg₂Ni and MgNi₂ reduced and the amounts of Mg and Ni increased in the sample BM. The laser sintered Mg₂Ni samples can be activated easily at 573 K. The maximum hydrogen storage capacities of the PM and BM samples were 3.23 and 3.44 wt%, respectively.     

Preparation of thin films by sulfurizing sol–gel deposited precursors

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing precursors deposited by the sol–gel method. Copper (II) acetate monohydrate, zinc (II) acetate dihydrate and tin (II) chloride dihydrate were used as the starting materials of the sol–gel method, and 2-methoxyethanol and monoethanolamine were used as the solvent and the stabilizer, respectively. The solution was spin coated on soda lime glass substrates and dried at . The coated glasses were sulfurized by annealing at in a hydrogen sulfide-containing atmosphere. The annealed thin films showed X-ray diffraction peaks attributed to the single phase CZTS. The chemical composition of the films was almost stoichiometric and the band gap energy was at room temperature.     

Carrier collection in Cu(In,Ga)Se2 solar cells with graded band gaps and transparent ZnO:Al back contacts

Cu(In,Ga)Se₂ Solar cells with graded band gap and efficiencies up to 13% have been fabricated on transparent ZnO:Al back contacts. The back contact structure includes a transparent 10 nm thin Mo interlayer with NaF precursor between the ZnO:Al and the Cu(In,Ga)Se₂ absorber that transforms the blocking ZnO:Al/Cu(In,Ga)Se₂ interface into an Ohmic back contact. To investigate the electronic quality of the back contact, the cells are analyzed by internal quantum efficiency measurements under illumination from front and back side. A new semianalytical model for the quantum efficiency of graded band gap absorbers yields quantitative information about the back contact recombination velocity as well as optical and electronic material parameters of the absorber layer. Band gap grading significantly increases carrier collection. However, in the immediate vicinity of the back contact carrier collection is limited by a high ratio of back contact recombination velocity and diffusion constant .