Conventional Operating Conditions Research Articles

Improving the performance of a proportional 4/3 water–hydraulic valve by using a diamond-like-carbon coating

Today, there are several water–hydraulic, power-control systems already available on the market. Their components are usually made of stainless steel, which ensures satisfactory performance under mild, conventional operating conditions. However, for more demanding operating conditions and long-term, low-friction and low-wear performance, they do not provide the required performance. One of the possible ways to improve the performance of stainless-steel components in water–hydraulic systems is to coat them with diamond-like carbon (DLC), since this material is well known for its excellent low-friction and low-wear characteristics and also provides very good performance under water-lubrication conditions. In this study, real-scale lifetime tests with 2.3 million cycles were performed on a hydraulic test rig with a proportional 4/3 directional control water–hydraulic valve. Two types of contacts in the valve were tested: the steel-spool/steel-sleeve and the DLC-spool/steel-sleeve. The wear behaviour of the valve was evaluated with a scanning electron microscope (SEM) and internal leakage measurements. In the real-scale lifetime tests the wear and the damage on the DLC-coated spool were significantly lower than on the steel spool. Furthermore, in agreement with this, the internal leakage in the DLC-spool/steel-sleeve valve was almost constant throughout the tests, while in the steel-spool/steel-sleeve valve the leakage slowly, but steadily, increased. The steel/steel and DLC/steel contacts were also separately evaluated in pin-on-disc model tribological tests under water-lubricated conditions for a comparison and for a better understanding of the tribological mechanisms. In agreement with the real-scale tests, the DLC/steel contact showed improved friction and wear performance in comparison with the steel/steel contact.

A further evaluation of the mixing controlled direct chemistry (MCDC) combustion model for diesel engine combustion using large eddy simulation

The local mixing effect at sub-grid scale (SGS) is explored using Large Eddy Simulation (LES) turbulence model with a mixing controlled direct chemistry (MCDC) model. The MCDC model is developed using the computation of chemical kinetics, thermo-chemical equilibrium state and SGS mixing effects by combining a mixing time scale and a kinetic time scale with the integration of direct chemistry solver (DCS) solutions. The mixing time scale is based on the SGS scalar variance and SGS scalar dissipation rate. The kinetic time scale is based on thermal–chemical equilibrium state and the kinetic reaction rate. These two time scales have been previously evaluated in experiments and computations, showed reasonable quantifications of local mixing and kinetic progress, which improved accuracy of combustion modeling.In this study, the conventional diffusion-type operating conditions are represented by a Caterpillar 3401™ single cylinder oil test engine (SCOTE). The cylinder-averaged results are compared between the DCS model, MCDC model and ‘Kong-Reitz’ model. A grid dependence study for the MCDC model on a baseline grid and a coarse grid is performed. The mixing time scale and kinetic time scale analysis for the MCDC model and ‘Kong-Reitz’ model is provided to investigate the differences in predictions. Compared to the DCS model and ‘Kong-Reitz’ model, the MCDC model shows improved capability in modeling mixing effects at the SGS level, which is represented by the improved prediction of combustion phasing and good matching with experimental results.

A mixing controlled direct chemistry (MCDC) model for diesel engine combustion modelling using large eddy simulation

A mixing controlled direct chemistry (MCDC) combustion model with sub-grid scale (SGS) mixing effects and chemical kinetics has been evaluated for Large Eddy Simulation (LES) of diesel engine combustion. The mixing effect is modelled by a mixing timescale based on mixture fraction variance and sub-grid scalar dissipation rate. The SGS scalar dissipation rate is modelled using a similarity term and a scaling factor from the analysis of Direct Numerical Simulation (DNS) data. The chemical reaction progress is estimated from a kinetic timescale based on local internal energy change rate and equilibrium state internal energy. An optical research engine operating at conventional operating conditions and Low Temperature Combustion (LTC) conditions was used for evaluation of the combustion model. From the simulation results, the effect of SGS scalar mixing is evaluated at different stages of combustion. In the context of LES, the new approach provides improved engine modelling results compared to the Direct Chemistry Solver (DCS) combustion model.

Robust Linuron Degradation in On-Farm Biopurification Systems Exposed to Sequential Environmental Changes

On-farm biopurification systems (BPS) treat pesticide-contaminated wastewater of farms through biodegradation. Adding pesticide-primed soil has been shown to be beneficial for the establishment of pesticide-degrading populations in BPS. However, no data exist on the response of pesticide-degrading microbiota, either endogenous or introduced with pesticide-primed soil, when BPS are exposed to expected less favorable environmental conditions like cold periods, drought periods, and periods without a pesticide supply. Therefore, the response of microbiota mineralizing the herbicide linuron in BPS microcosm setups inoculated either with a linuron-primed soil or a nonprimed soil to a sequence of such less favorable conditions was examined. A period without linuron supply or a drought period reduced the size of the linuron-mineralizing community in both setups. The most severe effect was recorded for the setup containing nonprimed soil, in which stopping the linuron supply decreased the linuron degradation capacity to nondetectable levels. In both systems, linuron mineralization rapidly reestablished after conventional operation conditions were restored. A cold period and feeding with a pesticide mixture did not affect linuron mineralization. The changes in the linuron-mineralizing capacity in microcosms containing primed soil were associated with the dynamics of a particular Variovorax phylotype that previously had been associated with linuron mineralization. This study suggests that the pesticide-mineralizing community in BPS is robust in stress situations imposed by changes in environmental conditions expected to occur on farms. Moreover, it suggests that, in cases where effects do occur, recovery is rapid after restoring conventional operation conditions.

Absorption of Water into Organic Solvents Used for Electrochemistry under Conventional Operating Conditions

Many solvents used for electrochemistry can be dried to <1 × 10(-3) M water content by storing the solvents over 3 Å molecular sieves in a nitrogen or argon atmosphere. However, as soon as the solvents are placed in an electrochemical cell, the water content increases significantly. Karl Fischer coulometric titrations were conducted on several predried solvents commonly used for electrochemistry (acetonitrile, dichloromethane, N,N-dimethylformamide, and dimethyl sulfoxide) in a controlled-humidity environment (30%, 50%, and 70% relative humidity) to determine the rate of moisture uptake into the organic solvents when used under typical electrochemical conditions (either in an electrochemical cell under a nitrogen atmosphere or in an electrochemical cell directly exposed to the atmosphere). The results in this study give guidelines for estimating the water content of organic solvents under conventional electrochemical operating conditions.

A Mixed-Mode Combustion Model for Large-Eddy Simulation of Diesel Engines

Present technologies of diesel engine combustion involve various operating conditions that can lead to a broad spectrum of combustion regimes. Existing combustion models for diesel engines usually lack universality across combustion regimes. In this study, a mixed-mode combustion model was developed to cover the major regimes pertaining to diesel engine combustion. The model uses kinetically controlled, quasi-steady homogeneous, quasi-steady flamelet, and partially premixed combustion modes. The combustion regime is identified locally by two combustion indices based on the local chemical and mixing conditions. The combustion model takes advantage of mixing details provided by large-eddy simulation. The model was tested over a wide range of engine conditions including conventional diesel-type and low-temperature combustion operating conditions. The model results compared well with experimental data and exhibited strength in both universality and computational efficiency.

The effect of low concentrations of CO on H 2 adsorption and activation on Pt/C. Part 1: In the absence of humidity

The presence of CO in the H 2-rich gas used as fuel for hydrogen fuel cells has a detrimental effect on PEMFC performance and durability at conventional operating conditions. This paper reports on an investigation of the effect of CO on H 2 activation on a fuel cell Pt/C catalyst close to typical PEMFC operating conditions using H 2–D 2 exchange as a probe reaction and to measure hydrogen surface coverage. While normally limited by equilibrium in the absence of impurities on Pt at typical fuel cell operating temperatures, the presence of ppm concentrations of CO increased the apparent activation energy ( E a) of H 2–D 2 exchange reaction (representing H 2 activation) from approximately 4.5–5.3 kcal mole −1 (Bernasek and Somorjai (1975) [24], Montano et al. (2006) [25]) (in the absence of CO) to 19.3–19.7 kcal mole −1 (in the presence of 10–70 ppm CO), similar to those reported by Montano et al. (2006) [25]. Calculations based on measurements indicate a CO surface coverage of approximately 0.55 ML at 80 °C in H 2 with 70 ppm CO, which coincide very well with surface science results reported by Longwitz et al. (2004) [5]. In addition, surface coverages of hydrogen in the presence of CO suggest a limiting effect on hydrogen spillover by CO. Regeneration of Pt/C at 80 °C in H 2 after CO exposure showed only a partial recovery of Pt sites. However, enough CO-free Pt sites existed to easily achieve equilibrium conversion for H 2–D 2 exchange. This paper establishes the baseline and methodology for a series of future studies where the additional effects of Nafion and humidity will be investigated.

Ion trap mass analysis at high pressure: an experimental characterization

In recent years, it has become increasingly interesting to understand the performance of mass spectrometers at pressures much higher than those employed with conventional operating conditions. This interest has been driven by several influences, including demand for the development of reduced-power miniature mass spectrometers, desire for improved ion transfer into and through mass spectrometers, enhanced-yield preparative mass separations, and mass filtering at the atmospheric pressure interface. In this study, an instrument was configured to allow for the performance characterization of a rectilinear ion trap (RIT) at pressures up to 50 mtorr with air used as the buffer gas. The mass analysis efficiency, mass resolution, isolation efficiency, and collision-induced dissociation (CID) efficiency were evaluated at pressures ranging from 1 to 50 mtorr. The extent of degradation of mass resolution, isolation efficiency and ion stability as functions of pressure were characterized. Also, the optimal resonance ejection conditions were obtained at various pressures. Operations at 50 mtorr demonstrated improved CID efficiency in addition to peak widths of 2 and 5 m/z units (full width at half-maximum, FWHM) for protonated caffeine (m/z 195) and Ultramark (m/z 1521) respectively.

Synchronizing Field and Control-Room Operators for Process Operating Transients

Process systems engineering is rapidly moving from steady state simulation towards operator training simulation, based on dynamic models, automated procedures, and predictive systems. Conventional operating conditions are well-known and easily controlled by field operators as well as control-room operators, whereas other situations are not yet. This is the case of more unusual circumstances, such as plant start-ups as well as planned and emergency shutdowns.The implementation of detailed dynamic mathematical models allows simulating the behavior of single process units as well as industrial plants, with the possibility to study unusual scenarios, especially for two reasons. First of all, it is necessary to train the operator and prepare him/her to face several events. Secondly, there is the need for evaluating the best automatic procedure to manage either unconventional or critical situations, without waiting for them to occur. In this sense, the safety approach is changing from reacting to predicting, thanks to the spread of tools that offer the possibility to simulate accidental events, unit and/or valve malfunctions, and significant process transients.The paper investigates and compares different procedures to control process transients, described by a sequence of actions, in order to coordinate synergistically the actions dictated by control-room operators and the operations to be accomplished manually by field operators. The main objective is to improve process start-up and shutdown reliability as well as the corresponding plant safety of an existing plant-wide control structure, without requiring any structural modification. A propane/butane splitter is adopted as a case study.

MS1-3: Numerical simulation of diesel combustion with high EGR rate(MS: Modeling and Simulation,General Session Papers)

A series calculation method from injector nozzle internal flow to in-cylinder combustion in diesel engines has been developed. In this study, the predicted in-cylinder pressure, heat release rate and NO concentration are compared with the experimental results on several conventional operating conditions and a higher EGR rate condition with high boost pressure and high injection pressure. The pressure and heat release rate histories are in reasonable agreement with the experiments, but the NO concentration is underestimated especially on the higher EGR rate condition. Therefore the investigation for improving the quantitative accuracy of NO concentration is performed. The PDF (probability density function) method is able to estimate the real mean reaction rate containing the reaction rate fluctuation by turbulence. However the PDF calculation is prohibitive on the computer resources. In this study, the PDF method only for the calculation of NO formation is developed for striking a balance between improvement of calculation accuracy and calculation cost. The result shows that the effect of reaction rate fluctuation on NO formation has a little on conventional operating conditions, but increases with decreasing the combustion temperature.

Fundamental processes and implications during in situ aeration of old landfills

Results of investigations from many old landfills in Germany and Europe indicate that significant emissions occur under conventional landfill operating conditions (i.e., anaerobic conditions). Significant emissions via the gas phase are predicted to last at least three decades after landfill closure, while leachate emissions are predicted to continue for many decades, potentially even lasting for centuries [Heyer, K.-U., Stegmann, R., 1997. Langfristiges Gefährdungspotenzial und Deponieverhalten von Ablagerungen; Bericht zum Teilvorhaben TV 4 im BMBF-Verbundvorhaben, “Deponiekörper”, Arbeitsbereich Abfallwirtschaft der TU Hamburg-Harburg, Projektträger PTAWAS (Umweltbundesamt Berlin); Krümpelbeck, I., 2000. Untersuchungen zum langfristigen Verhalten von Siedlungsabfall-deponien. Dissertation; Heft 3 der Veröffentlichungen der Bergischen Universität – Gesamthochschule Wuppertal; Kjeldsen, P., Christophersen, M., 2001. Composition of leachate from old landfills in Denmark. Waste Management and Research, 2001;19(3):249–56]. When considering the specific type and quality, and quite often lack of, protection barriers associated with old landfills, these leachate and gas emissions may result in a significant negative impact on the environment. However, complete sealing of the landfill only temporarily reduces emissions because dry-conservation of the biodegradable waste fraction results, thus not allowing any severe reduction in the emission and hazardous potential of the landfill to occur. If noticeable damage of the surface capping system occurred in these landfills, infiltrating water would restart the interrupted emission formation. In contrast, aerobic in situ stabilization by means of low pressure aeration [AERO flott ®, Stegmann, R., Hupe, K., Heyer, K.-U., 2000. Verfahren zur abgestuften beschleunigten in situ-Stabilisierung von Deponien und Altablagerungen. Patent Nr. 10005243. Deutsches Patent- und Markenamt, München] attempts to stabilize and modify the inventory of organic matter inside the landfill, acting to reduce the emission potential in a more sustainable manner. By enabling faster and more extensive aerobic degradation processes in the landfill (compared with anaerobic processes), the organics (e.g., hydrocarbons) are degraded significantly faster, resulting in an increased carbon discharge via the gas phase, as well as reduced leachate concentrations. Because carbon dioxide (CO 2) is the main compound in the extracted off-gas (instead of methane (CH 4), which dominated under anaerobic landfill conditions), the negative impact of diffuse LFG emissions towards an increased global warming effect may be significantly lowered. With respect to leachate quality, a reduction of organic compounds as well as ammonia-nitrogen can be expected. In addition to these positive ecological effects, aerobic in situ stabilization is associated with significant cost savings potential due to both quantitative and qualitative reductions in the aftercare period. This paper describes the fundamental processes and implications of in situ landfill aeration. Additionally, possible criteria for defining an endpoint of the active aeration process are presented and discussed.

Comparative Study of an Iron Fischer−Tropsch Catalyst Performance in Stirred Tank Slurry and Fixed-Bed Reactors

Fischer-Tropsch synthesis (FTS) was studied on a precipitated iron catalyst in a fixed-bed reactor under both supercritical (propane or n-hexane as supercritical fluids; P = 4.1-7.0 MPa) and conventional operating conditions (P = 1.48 MPa), as well as in a stirred tank slurry reactor (STSR) under conventional conditions. Catalyst activity in the supercritical mode of operation was slightly higher than during conventional FTS in the fixed-bed reactor (FBR). This is attributed to higher diffusivities of reactants in supercritical fluids relative to the conventional mode of operation (pores filled with liquid hydrocarbon wax). Catalyst activity was significantly lower in the STSR than in the FBR, due to incomplete reduction of the catalyst in the STSR. Hydrocarbon selectivities in the FBR were similar in both modes of operation. Methane selectivity in the STSR was lower and C 5 + selectivity higher than in the FBR, due to better temperature control in the former and differences in the extent of mixing and 1-olefin readsorption. Total olefin selectivity of high molecular weight olefins was lower and 2-olefin selectivity was higher in the STSR than in the FBR at similar conversions. This indicates that olefin selectivity is not controlled by intraparticle diffusion. It appears that the olefin selectivity in the STSR is largely determined by the residence time of high molecular weight 1-olefins in the liquid phase, 1-olefin solubility dependence on carbon number, and adsorption/desorption phenomena at the catalyst surface.

Comparison of the standard SM&T sequential extraction method with small-scale ultrasound-assisted single extractions for metal partitioning in sediments.

A single extraction method based on the reagents employed in the SM&T (standards, measurement and testing programme) sequential extraction scheme for partitioning of Cd, Cr, Cu, Ni, and Pb in sediments has been developed. Small-scale extractions adapted to electrothermal atomic absorption spectrometric determinations (i.e. 25 mg mass in 1 mL extractant) have been used for the first time in conjunction with selective reagents using conventional operating conditions (i.e. conductive heating, magnetic stirring) or ultrasound-assisted extraction. Small-scale slurry preparations were implemented for determination of the residual/total metal content. The methodology developed enabled drastic reduction of extraction times, yielding extractable contents in accordance with those obtained by application of the conventional SM&T method, which can be regarded as a standard method. An important saving in the amount of sample and reagents is also achieved with small-scale extractions. Homogeneity of sediments at the mg level proved acceptable - precision was similar for between-batch and within-batch measurements. Method development was performed with CRM BCR 601 lake sediment for which extractable amounts of several metals are known. An application to a "real-world" sediment is also presented.

Diagnostics for Assessing Spectral Quality for X-Ray Microanalysis in Low Voltage and Variable Pressure Scanning Electron Microscopy

There is increasing interest in performing x-ray microanalysis of uncoated insulators while operating in unconventional SEM operating modes such as “low voltage” scanning electron microscopy (LVSEM), where the accelerating voltage is ≤ 5 kV and the pressure is low (&lt;10-4 Pa), or variable pressure environmental SEM (VP-ESEM), where a selected gas is maintained at pressures in the range of 1 Pa -1000 Pa. LVSEM and VP-ESEM as microscopy techniques have proven to be extremely successful for imaging uncoated insulators through various charge dissipation mechanisms that are not available under conventional SEM operating conditions (accelerating voltage ≥ 10 kV and pressure &lt; 10-3 Pa). in LVSEM, surface charging of insulators can often be controlled by careful choice of the accelerating voltage, sample tilt, and scan rate, while in VP-ESEM the charged species in the relatively dense gas (ions, secondary electrons) form a self-neutralizing plasma to provide an additional route for discharging the specimen.

The Nature of the Active Metal Surface of Catalysts for the Clean Combustion of Biogas Containing Ammonia

The nature of the active surface of supported metal catalysts for the clean combustion of ammonia-containing simulated biogas has been investigated to understand the very high N2 selectivity of some catalysts. A comparison of the activities of Al2O3-supported precious group metals has shown that under conventional operating conditions the fuel is fully combusted but NH3 is converted predominantly into NOx. In contrast, it is shown that it is possible by operating under O2-deficient conditions to attain essentially zero emissions of NOx with Rh- or Ir-based catalysts, whereas Pt or Pd gave markedly lower selectivities to N2. These variations in selectivity are attributed to the differences in the state of the metal surface during reaction. For Rh- and Ir-based catalysts it has been shown that under fuel-rich conditions, surface carbon, derived from the dissociative adsorption of CO, results in self-poisoning toward CO and H2 oxidation at low temperatures. However, at higher temperatures a preference toward methanation of the Cads is observed. It is thought that this surface reaction between the Cads and Hads scavenges both reductants so that Oads can react with NH3 in a highly specific manner, to give NOx. The NOx thus formed is subsequently reduced by reaction with excess CO to give N2. A model is presented that shows the way in which the chemistry of the surface of the active metal changes as the reaction parameters are varied.

Separation of proteins and peptides by capillary electrophoresis in acid buffers containing high concentrations of surfactants

Separations of proteins at acid pH in the presence of a high concentration of surfactant [sodium laurylsulfate (SDS), 50 mmol/l] was investigated. The purpose of using high concentrations of SDS as background electrolyte modifier was threefold: First, the surfactant exerts a washing effect upon the capillary wall thus preventing binding of analytes and possible clogging of the capillary. Second, it was revealed that even under very acid conditions (below pH 3) the surfactant is capable of forming associates with protein analytes which still bear considerable negative charge and can be separated on this basis. Third, the system can be applied not only for protein mixtures sufficiently soluble in neutral to alkaline media (leukocyte lysates, standard proteins), but it can be used also with proteins, that are under such conditions virtually insoluble and their solubilization is possible in acid buffers only (eggshell proteins or collagen CNBr fragments). The result was that adsorption to the capillary wall was minimized and the analytes were separated as negatively charged associates with high efficiency. With collagen fragments partition was possible on the affinity differences of the peptides to the surfactant micelles and inner wall of the capillary. Theoretical plate counts approaching 100 000 were easily achieved even with proteins which under the more conventional operation conditions exhibit considerable sticking to the capillary wall. The other feature of this system is that the associates move very rapidly to the anode. Owing to the low pH, endoosmotic flow is negligible, and therefore the system has to be operated at reversed polarity.

Evaluating the impedance field through several transport models: A comparison

The article presents a critical discussion on the evaluation of the impedance field for noise analysis by means of several transport models. The models considered are the drift-diffusion model, the full hydrodynamic model, and the scattered packet method for the direct solution of the Boltzmann transport equation. The comparison is carried out on a canonical Si p+pp+ diode at ambient temperature. The agreement found between the approaches is good, thus suggesting that the evaluation of the impedance field does not require any additional care with respect to other, more conventional operating conditions.

Fast Capillary Gas Chromatography: Comparison of Different Approaches

Savings in analysis time in capillary GC have always been an important issue for chromatographers since the introduction of capillary columns by Golay in 1958. In laboratories where gas chromatographic techniques are routinely applied as an analytical technique, every reduction of analysis time, without significant loss of resolution, can be translated into a higher sample throughput and hence reduce the laboratory operating costs. In this contribution, three different approaches for obtaining fast GC separations are investigated. First, a narrow-bore column is used under conventional GC operating conditions. Secondly, the same narrow-bore column is used under typical fast GC conditions. Here, a high oven temperature programming rate is used. The third approach uses a recent new development in GC instrumentation: Flash-2D-GC. Here the column is placed inside a metal tube, which is resistively heated. With this system, a temperature programming rate of 100°/s is possible. The results obtained with each of these three approaches are compared with results obtained on a column with conventional dimensions. This comparison takes retention times as well as plate numbers and resolution into consideration.

Low-temperature migration of lead, thallium, and selenium onto a palladium modifier during the analysis of solutions and slurries by electrothermal atomic absorption spectrometry

A palladium/magnesium modifier, when premixed with solutions or slurries, stabilizes many analytes to higher pyrolysis and atomization temperatures. Similar behavior was seen when analyte and modifier were physically separated by pipetting them onto opposite sides of a L'vov platform. During the pyrolysis stage of the furnace heating cycle, lead, thallium, and selenium migrated from the platform surface and interacted with the modifier on the opposite side. This behavior explains the consistent stabilization by palladium of analytes in slurry samples. Under conventional operating conditions the modifier is premixed with the slurry, and on drying in the furnace, the analyte and modifier may not make close contact. However, this is unimportant since the analyte will migrate to the palladium on heating. Then the rate-limiting step leading to atomization is the release of analyte from palladium, and it is the same for solutions and slurries. Therefore, aqueous standards can be used for slurry analysis.

Further Study of a Rate Model for Inductively Coupled Plasma Analyte Spectra Using a Monte Carlo Technique

Based on Lovett's model, an attempt has been made to evaluate the effect of a number of processes possibly responsible for the analyte spectra emitted from an analytical ICP (inductively coupled plasma) with a Monte Carlo technique. The simulation results show that under conventional ICP operating conditions, absorption, stimulated emission, atom collisional ionization, atom recombination, autoionization, autoionization recombination, and dielectronic recombination made very little or no contribution to the level population. The Penning ionization process has an important effect on the ionization and excitation of Mn only at number density of metastable Ar greater than 1011/cm−3. Electron collisional processes, radiative recombination, and radiative decay are mainly responsible for Mn ionization and excitation. Using the above-mentioned key processes, together with the spatial distribution of the number density of evaporated analyte particles in the ICP obtained previously, the spatial distribution of the number density of excited or ionized Mn under different conditions is simulated. The simulation program is valid and the mechanisms evaluated are reasonable.