bluuebunny/crossref_metadata_2025 huggingface dataset:
Cold hardening induces transfer of fatty acids between polar and nonpolar lipid pools in the Arctic collembollan Megaphorura arctica
Authors: PURAĆ JELENA , POND DAVID W. , GRUBOR‐LAJŠIĆ GORDANA , KOJIĆ DANIJELA , BLAGOJEVIĆ DUŠKO P. , WORLAND MICHAEL ROGER , CLARK MELODY S.
Published: January 2011

Cold hardiness in the Arctic Collembola Megaphorura arctica (Tullberg), formerly Onychiurus arcticus, has been the subject of extensive studies over the last decade. This species employs an unusual strategy known as cryoprotective dehydration to survive winter temperatures as low as −25 °C. To expand knowledge of cryoprotective dehydration in M. arctica, the present study investigates how a reduction in ambient temperature affects the fatty acid composition of the total body lipid content along with polar (mainly membrane phospholipids) and nonpolar (mainly triacylglycerols) lipids. Most ectothermic animals compensate for changes in fluidity by regulating fatty acid composition, a process often described as homeoviscous adaptation. In M. arctica, changes in the fatty acid composition of total body lipid content during cold treatment are only moderate, with no clear pattern emerging. However, the levels of unsaturated fatty acids in the polar lipids increase with cold exposure, largely attributable to 16 : 1(n− 7), 18 : 1(n− 9), 18 : 3(n− 6) and 18 : 3(n− 3), whereas unsaturated fatty acid levels in the nonpolar lipids correspondingly decrease. These results suggest a reallocation of fatty acids between the two lipid pools as a response to a temperature reduction of 6 °C. Because of hypometabolism, a characteristic of cold adaptation, such a mechanism could be less energy demanding than de novo synthesis of fatty acids and may comprise part of an adaptive homeostatic response.
The Process is the Rule and the Punishment is the Process
Authors: Morgan Rod
Published: January 2011

Andrew Ashworth, The Criminal Process: An Evaluative Study, Oxford: Clarendon Press, 1994, 315 pp, hb £45.00, pb £12.95.

Andrew Sanders and Richard Young, Criminal Justice, London: Butterworths, 1994, 496 pp, pb £18.95.
Real Reform or Change for Chumps: Earmark Policy Developments, 2006–2010
Authors: Doyle Richard
Published: January 2011

In response to widespread perceptions of problems associated with congressional earmarks, reform efforts began in late 2006 and continued through 2010. This essay summarizes those problems, explains the distribution of earmarks within Congress, and documents their rise and relative fall between 1991 and 2010 using government and public interest group databases. The author explains and critiques earmark reform policies, including congressional rules, initiatives taken by the congressional appropriations committees, and reforms pursued by the George W. Bush and Barack Obama administrations. Congressional rules and committee‐initiated reforms have been most effective, resulting in significant improvements in earmark transparency and accountability. The number and dollar value of earmarks first dropped noticeably in fiscal year 2007 after an earmark moratorium, and then stabilized as reforms were implemented. It is premature to conclude that these levels will continue or that reforms will alter the policy content of earmarks or their distribution among members of Congress.
Retracted: Bone response to hydroxyapatites with open porosity of animal origin (porcine [OsteoBiol®mp3] and bovine [Endobon®]): a radiological and histomorphometric study
Authors: Ramírez‐Fernández MaPiedad , Calvo‐Guirado Jose Luis , Delgado‐Ruiz Rafael Arcesio , Maté‐Sánchez del Val José Eduardo , Vicente‐Ortega Vicente , Meseguer‐Olmos Luis
Published: January 2011

Purpose: To carry out a radiological and histomorphometric evaluation of bone response to two xenografts of animal origin, one porcine, and the other bovine, inserted in rabbits' tibiae.

Material and methods: Twenty New Zealand rabbits weighing 3900–4500 g were used. Twenty bovine bone grafts (Endobon®) in granulated form of 500–1000 μm granulometry were inserted in the proximal metaphyseal area of the animals' right tibia, and 20 porcine bone grafts (OsteoBiol®mp3) in granulated form of 600–1000 μm granulometry were inserted in the proximal metaphyseal area of the animals' left tibia. Following graft insertion, the animals were sacrificed in four groups of five, after 1, 2, 3 and 4 months, respectively. Anteroposterior and lateral radiographs were taken. Samples were processed for observation under light microscopy. Histomorphometric measurements were presented as mean values ± standard deviations.

Results: At 4 months after treatment, the bone defects displayed radiological images that showed complete repair of osseous defects. Histomorphometric evaluation showed that for the porcine xenograft, the study averages for newly formed bone represented 22.8 ± 1.8%, for residual graft material 23.6 ± 3% and for connective tissue 53.5 ± 2.5%, while for the bovine xenograft newly formed bone represented 23.1 ± 1.8%, residual graft material 39.4 ± 3% and non‐mineralized connective tissue 37.5 ± 2.5%.

Conclusions: The biomaterials assessed in the study were shown to be biocompatible and osteoconductive. Collagenized porcine xenografts proved more resorbable than bovine xenografts. Both can be used as possible bone substitutes without interfering with normal reparative bone processes.

To cite this article:
 Ramírez‐Fernández MP, Calvo‐Guirado JL, Delgado‐Ruiz RA, Maté‐Sánchez del Val JE, Vicente‐Ortega V, Meseguer‐Olmos L. Bone response to hydroxyapatites with open porosity of animal origin (porcine [OsteoBiol®mp3] and bovine [Endobon®]): a radiological and histomorphometric study. Clin. Oral Impl. Res. 22, 2011; 767–773. doi: 10.1111/j.1600‐0501.2010.02058.x
Computed tomography‐based evaluation of template (NobelGuide™)‐guided implant positions: a prospective radiological study
Authors: Vasak Christoph , Watzak Georg , Gahleitner André , Strbac Georg , Schemper Michael , Zechner Werner
Published: January 2011

Objectives: This prospective study was intended to evaluate the overall deviation in a clinical treatment setting to provide for quantification of the potential impairment of treatment safety and reliability with computer‐assisted, template‐guided transgingival implantation.

Material and methods: The patient population enrolled (male/female=10/8) presented with partially dentate and edentulous maxillae and mandibles. Overall, 86 implants were placed by two experienced dental surgeons strictly following the NobelGuide™ protocol for template‐guided implantation. All patients had a postoperative computed tomography (CT) with identical settings to the preoperative examination. Using the triple scan technique, pre‐ and postoperative CT data were merged in the Procera planning software, a newly developed procedure – initially presented in 2007 allowing measurement of the deviations at implant shoulder and apex.

Results: The deviations measured were an average of 0.43 mm (bucco‐lingual), 0.46 mm (mesio‐distal) and 0.53 mm (depth) at the level of the implant shoulder and slightly higher at the implant apex with an average of 0.7 mm (bucco‐lingual), 0.63 mm (mesio‐distal) and 0.52 mm (depth). The maximum deviation of 2.02 mm was encountered in the corono‐apical direction. Significantly lower deviations were seen for implants in the anterior region vs. the posterior tooth region (P<0.01, 0.31 vs. 0.5 mm), and deviations were also significantly lower in the mandible than in the maxilla (P=0.04, 0.36 vs. 0.45 mm) in the mesio‐distal direction. Moreover, a significant correlation between deviation and mucosal thickness was seen and a learning effect was found over the time period of performance of the surgical procedures.

Conclusion: Template‐guided implantation will ensure reliable transfer of preoperative computer‐assisted planning into surgical practice. With regard to the required verification of treatment reliability of an implantation system with flapless access, all maximum deviations measured in this clinical study were within the safety margins recommended by the planning software.

To cite this article:
 Vasak C, Watzak G, Gahleitner A, Strbac G, Schemper M, Zechner W. Computed tomography‐based evaluation of template (NobelGuide™)‐guided implant positions: a prospective radiological study. Clin. Oral Impl. Res. 22, 2011; 1157–1163. doi: 10.1111/j.1600‐0501.2010.02070.x
Butyrate production in phylogenetically diverse Firmicutes isolated from the chicken caecum
Authors: Eeckhaut Venessa , Van Immerseel Filip , Croubels Siska , De Baere Siegrid , Haesebrouck Freddy , Ducatelle Richard , Louis Petra , Vandamme Peter
Published: January 2011

Sixteen butyrate‐producing bacteria were isolated from the caecal content of chickens and analysed phylogenetically. They did not represent a coherent phylogenetic group, but were allied to four different lineages in the Firmicutes phylum. Fourteen strains appeared to represent novel species, based on a level of ≤ 98.5% 16S rRNA gene sequence similarity towards their nearest validly named neighbours. The highest butyrate concentrations were produced by the strains belonging to clostridial clusters IV and XIVa, clusters which are predominant in the chicken caecal microbiota. In only one of the 16 strains tested, the butyrate kinase operon could be amplified, while the butyryl‐CoA : acetate CoA‐transferase gene was detected in eight strains belonging to clostridial clusters IV, XIVa and XIVb. None of the clostridial cluster XVI isolates carried this gene based on degenerate PCR analyses. However, another CoA‐transferase gene more similar to propionate CoA‐transferase was detected in the majority of the clostridial cluster XVI isolates. Since this gene is located directly downstream of the remaining butyrate pathway genes in several human cluster XVI bacteria, it may be involved in butyrate formation in these bacteria. The present study indicates that butyrate producers related to cluster XVI may play a more important role in the chicken gut than in the human gut.
Improving Efficiency, Extending the Maximum Load Limit and Characterizing the Control-Related Problems Associated With Higher Loads in a 6-Cylinder Heavy-Duty Natural Gas Engine
Authors: Kaiadi Mehrzad , Tunestal Per , Johansson Bengt
Published: January 2011

High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition Natural Gas engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. Most of the heavy duty NG engines are diesel engines which are converted for SI operation. These engine’s components are in common with the diesel-engine which put limits on higher exhaust gas temperature. The engines have lower maximum load level than the corresponding diesel engines. This is mainly due to the lower density of NG, lower compression ratio and limits on knocking and also high exhaust gas temperature. They also have lower efficiency due to mainly the lower compression ratio and the throttling losses. However performing some modifications on the engines such as redesigning the engine’s piston in a way to achieve higher compression ratio and more turbulence, modifying EGR system and optimizing the turbocharging system will result in improving the overall efficiency and the maximum load limit of the engine. This paper presents the detailed information about the engine modifications which result in improving the overall efficiency and extending the maximum load of the engine. Control-related problems associated with the higher loads are also identified and appropriate solutions are suggested.
The Effects of Biodiesel Fuel Blends on Exhaust Emissions From a General Electric Tier 2 Line-Haul Locomotive
Authors: Osborne Dustin , Fritz Steve , Glenn Doug
Published: January 2011

This paper documents exhaust emission test results from a Tier 2 General Electric ES44DC line-haul locomotive with 3,280 kW rated traction power, and the impact of biodiesel fuel blends on regulated exhaust emissions. Baseline exhaust emission testing was performed with a test fuel containing a sulfur concentration of approximately 400 ppm, and was followed by testing of fuel blends containing 2%, 10%, 20%, and 100% soybean derived biodiesel (B2, B10, B20, B100). Gaseous and particulate emissions were sampled per Title 40 of the United States Code of Federal Regulations, Part 92. Test results indicate particulate matter (PM) reductions occurred over the EPA Locomotive Line-Haul and Switch Duty Cycles for each biodiesel blend tested, as compared to the base fuel. The bulk of the PM reduction benefit was present with the 10% biodiesel blend, with comparatively small additional amounts of PM reductions found with increased amounts of biodiesel. PM reduction associated with biodiesel was greater over the Switch Duty Cycle than for the Line-Haul Duty Cycle. The change in cycle weighted oxides of nitrogen (NOx) for B2, B10, and B20 were not greater than the expected test measurement variation; however, B100 increased NOx by nearly 15% over the line-haul cycle. Changes in hydrocarbon (HC) emissions over the duty cycles were within normal test measurement variation except for neat biodiesel, where HC was reduced by 21% and 24% over the Line-Haul and Switch cycles. Carbon Monoxide (CO) reductions of 17% and 24% over the Line-Haul cycle were measured for B20 and B100, as compared to the base fuel. Volumetric fuel consumption increased about 1% for both B2 and B10 blends. Just over 2% increase in volumetric fuel consumption was observed at B20 and nearly 7% increase in volumetric fuel consumption at B100.
A New Valve Lift Control Technique in Electrohydraulic Variable Valve Actuation Systems
Authors: Pournazeri Mohammad , Khajepour Amir , Fazeli Amir
Published: January 2011

Besides valve timings and opening duration control, several benefits could be achieved in engine operation if the valve actuation system could control the maximum valve displacement during a particular engine condition. Typically, in most electro-hydraulic variable valve actuation systems (VVA), the maximum valve lift along with valve opening/closing events are adjusted simultaneously by precise control of the spool travel in servo-valves. However, at high engine speeds, concurrent control of timings and peak valve lift becomes difficult and sometimes even impossible due to servo-valve response time limitations. In this paper, a new lift control technique is proposed using a control-valve located in the hydraulic supply line. Using this technique, it is possible to precisely control the valve lift even at high engine speeds. With this mechanism, the control-valve flow area could be adjusted using a low-speed actuator such as an electric motor. In contrast to conventional approaches, where maximum lift is repeatedly controlled within each cycle, valve lift in this technique can be adjusted after few engine cycles, thereby reducing control signal fluctuations and also eliminating the need for ultra-high-speed actuators. The proposed hydraulic VVA system is mathematically modeled, and a non-linear sliding mode controller is designed based on the derived equations. Finally, the performance of the proposed lift control technique is verified under different operating conditions.
Study on NOx Emission of Medium Speed Micro Pilot Gas Engine With Pre-Combustion Chamber
Authors: Goto Satoru
Published: January 2011

Over the past decade, improved performance has given advanced gas engines a special role in numerous applications. High-density gas engines with BMEP values exceeding 2MPa and power generation efficiency exceeding 45% are now widely available. The performance parameters of advanced lean burn gas engines such as thermal efficiency and BMEP now nearly equal those of diesel engines. Despite higher thermal efficiency, these designs have successfully maintained low emissions, particularly NOx emissions. Nevertheless, problems associated with knocking, misfires, and spark plug service life have grown more serious with increasing BEMP. Micro pilot engines offer the advantage of fast and stable combustion over conventional spark ignition systems and represent a technical solution for such problems. They also provide long maintenance intervals. Niigata Power Systems has already introduced the 22AG series and 28AG micro pilot gas engines to the Japanese market. The five models in the 22AG series (namely 6, 8L and 12, 16, 18V) cover the power range from 1 to 3MW. The output of the 18V28AG is 6MW. The first delivered 8L22AG has operated daily and continuously from 2002, with no serious issues encountered to date over a total time of operation of roughly 60,000 hours, with minimum engine stops for scheduled maintenance every 4,000 hours. Environmental issues, cost effectiveness, energy conservation, and the ability to use waste alternative fuels are major concerns worldwide. Micro pilot gas engines can contribute in these areas by using refuse and synthesis gas—very low heat energy sources—as fuel. Synthesis gas contains hydrogen and carbon monoxide as combustible components. Micro pilot engines offer major potential advantages, making an examination of their NOx emission characteristics worthwhile. This paper discusses issues related to the NOx emissions of micro pilot gas engines.
On Comparative Performance Testing of Prechamber and Open Chamber Laser Ignition
Authors: Joshi Sachin , Loccisano Frank , Yalin Azer P. , Montgomery Dave T.
Published: January 2011

Laser ignition is a potential ignition technology to achieve reliable lean burn ignition in high brake mean effective pressure (BMEP) internal combustion engines. The technology has the potential to increase brake thermal efficiency and reduce exhaust emissions. This submission reports on engine testing of a Caterpillar G3516C stationary natural gas fueled engine with three types of ignition approaches: i) non-fueled electric prechamber plug with electrodes at the base of the prechamber (i.e., conventional ignition), ii) non-fueled laser prechamber plug with laser spark in the middle of the prechamber, and iii) open chamber plug with laser spark in the main chamber. In the second configuration, a stock non-fueled prechamber plug was modified to incorporate a sapphire window and a focusing lens to form a laser prechamber plug. A 1064 nm Q-switched Nd:YAG laser was used to create laser sparks. For these tests, a single cylinder of the engine was retrofitted with the laser plug while the remaining cylinders were run with conventional electric ignition system at baseline ignition timing of 24 degree before Top Dead Center (BTDC). The performances of the three plugs were compared in terms of Indicated Mean Effective Pressures (IMEP), Mass Burn Fraction Duration and Coefficient of Variation (COV) of IMEP, and COV of Peak Pressure Location. Test data show comparable performance between electric and laser prechamber plugs, albeit with a lower degree of variability in engine’s performance for electric prechamber plug compared to the laser prechamber plug. The open chamber plug exhibited poorer variability in engine performance. All results are discussed in the context of prechamber and engine fluid mechanics.
Development and Application of Advanced Combustion Modeling Tools for Heavy Duty Gaseous Fueled Industrial Spark Ignition Engines
Authors: Juneja Harmit , LaPointe Leon A. , Ntone Francois , Lyford-Pike Edward J. , Qin Xiao
Published: January 2011

This paper covers the development and application of advanced combustion modeling tools to meet the stringent design objectives of heavy duty gaseous fueled industrial spark ignition engines. Extensive literature survey and validation work was conducted to identify the best available chemical mechanism to represent natural gas and its variations. Mechanism reduction using the Simulation Error Minimization (SEM) approach was undertaken to reduce the chemistry mechanism to a reasonable size for practical computational turn around times. Laminar flame speed (LFS) correlations were also developed using the identified chemistry mechanism. These fundamental elements were then integrated into a level set method (G-equation) based combustion model to predict heat release rate, exhaust gas composition, and the onset and intensity of autoignition (knock). The developed combustion modeling tools can handle lean or stoichiometric operation, presence of high levels of EGR, and variations in natural gas fuel composition. Detailed experimental data was available in the form of a spark timing sweep covering a non-knocking to a highly knocking operating condition for different fuel compositions. The intake flow modeling process was validated with available flow rig data at different valve lifts. Accurate modeling of the intake and compression process generates precise initial conditions for combustion modeling. Results are shown for conventional natural gas, natural gas containing 9% propane by mass, and natural gas containing 12% hydrogen mass fraction, at stoichiometric operating conditions. Excellent agreement with the measured data was observed in predicting heat release rate and the onset and intensity of knock for these different fuel compositions. The modeling tools developed in this study offer a robust methodology to design and optimize combustion systems for heavy duty gaseous fueled industrial spark ignition engines.
An Assessment of the Relative Benefits of Miller Cycle and Turbocompounding on a Medium Speed Diesel Engine Using Second Law Analysis
Authors: Lavertu Thomas M. , Primus Roy J. , Akinyemi Omowoleola C.
Published: January 2011

The relative benefit of a power turbine as a means of exhaust energy recovery (i.e., turbocompounding) being used in conjunction with altered intake valve closure timing (Miller cycle) on a medium speed diesel engine has been investigated. An assessment of the impact of these different engine architectures on the various loss mechanisms has been performed using second law analysis. The Miller and turbocompounding cycle modification as well as the combination of the two features were studied and their relative benefits are compared and discussed. Results show the corresponding decrease in effective compression ratio achieved with Miller cycle leads to lower pre-turbine exhaust availability, which decreases the potential benefit of turbocompounding.
Numerical Study of Piston Skirt-Liner Elastohydrodynamic Lubrication and Contact by the Multigrid Method
Authors: Meng Xianghui , Xie Youbai
Published: January 2011

The cylinder liner-piston system of internal combustion engines is one of the key friction pairs running at the most rigor working conditions. Under the influence of elastohydrodynamic lubrication and contact between the piston skirt and the liner, the dynamic process of piston is a nonlinear and stiff problem difficult to be analyzed accurately and easily. To reach a stable and rapid convergence in analysis, the MEBDF method and the multigrid method are used to solve the piston-skirt elastohydrodynamic lubrication and contact problem. Firstly the solving process of the piston dynamics is analyzed based on the MEBDF method. Then the residual equations for the elastohydrodynamic lubrication pressure are built based on the multigrid method. And the solving method of the nonlinear residual equations is presented based on the quasi Newton-Raphson method. Finally the numerical simulation program is developed based on the MEBDF method and the multigrid method. The elastohydrodynamic lubrication and contact problem of the piston skirt-liner system is simply analyzed based on the simulation. The study in this paper can provide an effective method for tribological analysis and optimization of piston–liner system in the future.
In-Cylinder Optical Diagnostics in a Laser Ignited Natural Gas Fired Reciprocating Engine
Authors: Bihari Bipin , Gupta Sreenath B. , Biruduganti Munidhar S. , Sekar Raj R.
Published: January 2011

In-cylinder combustion gas temperature and rate of heat release are important combustion metrics in internal combustion engines. Such metrics play an important role in the development of strategies for reduced emissions and improved engine performance. The traditional practice has been to measure in-cylinder pressures and deduce the metrics using simple thermodynamic treatments. However, with the availability of improved optics, especially in the field of fiber-optics, optical access to in-cylinder combustion becomes possible. Two diagnostics that measure spectral emission from CO2* and OH* species within the combustion environment of a natural gas fueled IC engine were evaluated. The combustion temperatures were varied by operating the engine over an EQR of 0.6–1.0 and different levels of exhaust gas recirculation. CO2* emission does not lend itself to prediction of crank-angle resolved combustion metrics. However its peak values in a combustion cycle correlated well with both rate of heat release as well as peak combustion temperature during the cycle. In contrast temperatures derived from curve fitting to OH* emission spectra enabled measurement of crank angle resolved in-cylinder temperatures.
Investigation of the Roles of Flame Propagation, Turbulent Mixing, and Volumetric Heat Release in Conventional and Low Temperature Diesel Combustion
Authors: Kokjohn Sage L. , Reitz Rolf D.
Published: January 2011

In this work, a multi-mode combustion model, that combines a comprehensive kinetics scheme for volumetric heat release and a level-set-based model for turbulent flame propagation, is applied over the range of engine combustion regimes from non-premixed to premixed conditions. Model predictions of the ignition processes and flame structures are compared to measurements from the literature of naturally occurring luminous emission and OH planar laser induced fluorescence (PLIF). Comparisons are performed over a range of conditions from conventional diesel operation (i.e., short ignition delay, high oxygen concentration) to a low temperature combustion mode (i.e., long ignition delay, low oxygen concentration). The multi-mode combustion model shows excellent prediction of the bulk thermodynamic properties (e.g., rate of heat release), as well as local phenomena (i.e., ignition location, fuel and combustion intermediate species distributions, and flame structure). The results of this study show that even in the limit of mixing controlled combustion, the flame structure is captured extremely well without considering sub-grid scale turbulence-chemistry interactions. The combustion process is dominated by volumetric heat release in a thin zone around the periphery of the jet. The rate of combustion is controlled by transport of reactive mixture to the reaction zone and the dominant mixing processes are well described by the large scale mixing and diffusion. As the ignition delay is increased past the end of injection (i.e., positive ignition dwell), both the simulations and optical diagnostics show that the reaction zone spans the entire jet cross-section. In this combustion mode the combustion rate is no longer limited by transport to the reaction zone, but rather by kinetic timescales. Although comparisons of results with and without consideration of flame propagation show very similar flame structures and combustion characteristics, the addition of the flame propagation model reveals details of the edge or triple-flame structure in the region surrounding the diffusion flame at the lift off location. These details are not captured by the purely kinetics based combustion model, but are well represented by the present multi-mode model.
Predictive Analytics and Diagnostics Drive Effectiveness in Condition Based Monitoring
Authors: Snyder Tim , Ali Asma
Published: January 2011

Large industrial internal combustion engines employ a wide range of analytical techniques in order to improve their availability and fuel efficiency, and to decrease their maintenance expense. When viewed in context of reliability centered maintenance programs, most industrial engines rely on one of the following systems: • Time-based preventive maintenance analyses, • Continuous monitoring systems that have first-principles deterministic models, or • Run until failure operating philosophy. Predictive analytics using empirically-derived pattern recognition algorithms can enhance problem detection and increase the effectiveness of an organization’s monitoring program. With robust early detection that has few false alarms, equipment operators can remove time-dependent randomness from their ability to discover problems. Skilled equipment analysts and technicians will no longer spend time devoted to analyzing healthy equipment. When a company has numerous engine installations, scalability and cost-effectiveness becomes increasingly more important. Empirically-derived pattern recognition speeds fleet deployment across a wide range of equipment types and models. This reduces the dependence on the expertise that is required to establish and maintain a first-principles based system. Predictive analytics enables a bridge between the depth of coverage of a permanently installed full analytical system and the versatility of portable analyzers and preventive maintenance analyses. Equipment operators can use early detection from predictive analytics to focus their technicians on analyzing the right equipment at the right time. This paper will describe the predictive analytics modeling philosophy around frame mechanics, combustion, and emissions. One or more case studies will show the processes of even detection, diagnostics, collaboration, and information consolidation. The extension of predictive analytics is predictive diagnostics which combines detection with the context of how equipment operates. Equipment operators can extend run times and maintenance intervals by using predictive analytics as a foundation. The observations, diagnoses, and feedback will then roll up into a total asset management system and bridge major gaps that occur in many reliability programs. Predictive diagnostic methodologies enable equipment owners to extend run times and to decrease maintenance effort with confidence.
Validation of a Lagrangian Ignition Model in SI Engine Simulations
Authors: Forte Claudio , Bianchi Gian Marco , Corti Enrico
Published: January 2011

Ignition process plays a key role in flame kernel formation and heavily affects further combustion development. The paper aim is to present a 1D lagrangian ignition model and to validate it against real engine configurations. A lump model for the electrical circuit of the spark plug is used to compute breakdown and glow energy. At the end of shock wave and very first plasma expansion, a spherical kernel is deposited inside the gas flow at spark plug location. A simple model allows computing initial flame kernel radius and temperature based on physical mixture properties and spark plug characteristics. The sphere surface of the kernel is discretized by triangular elements which move radially according to a lagrangian approach. Expansion velocity is computed accounting for both heat conduction effect at the highest temperatures and thermodynamic energy balance at relatively lower temperatures. Turbulence effects and thermodynamic properties of the air-fuel mixture are accounted for. Restrikes are possible depending on gas flow velocity and mixture quality at spark location. CFD solver and 1D/lagrangian ignition model are closely coupled at each time step. The model proves to strongly reduce the grid sensitivity. The CFD model validation phase is crucial for a correct representation of both kernel formation and combustion development: the operation has been carried out by means of an accurate statistical analysis of experimental in-cylinder pressure data in real engine configurations.
Soot Modeling for Advanced Control of Diesel Engine Aftertreatment
Authors: Mulone V. , Cozzolini A. , Abeyratne P. , Littera D. , Thiagarajan M. , Besch M. C. , Gautam M.
Published: January 2011

Diesel Particulate Filters (DPFs) are well assessed aftertreatment devices, equipping almost every modern diesel engine on the market to comply with today’s stringent emission standards. However, an accurate estimation of soot loading, which is instrumental to ensuring optimal performance of the whole engine-after-treatment assembly is still a major challenge. In fact, several highly coupled physical-chemical phenomena occur at the same time, and a vast number of engine and exhaust dependent parameters make this task even more daunting. This challenge may be solved with models characterized by different degrees of detail (0-D to 3-D) depending on the specific application. However, the use of real-time, but accurate enough models, may be of primary importance to face with advanced control challenges, such as the integration of the DPF with the engine or other critical aftertreatment components (Selective Catalytic Reduction (SCR) or other NOx control components), or to properly develop model-based OBD sensors. This paper aims at addressing real time DPF modeling issues with special regard to key parameter settings, by using the 1D code ExhAUST (Exhaust Aftertreatment Unified Simulation Tool), developed jointly by the University of Rome Tor Vergata and West Virginia University. ExhAUST is characterized by a novel and unique full analytical treatment of the wall that allows faithful representation with high degree of detail the evolution of soot loading inside the porous matrix. Numerical results are compared with experimental data gathered at West Virginia University (WVU) engine laboratory using a Mack heavy-duty diesel engine coupled to a Johnson Matthey CCRT (DOC, Diesel Oxidation Catalyst+CDPF, Catalyzed DPF) aftertreatment system. To that aim, the engine test bench has been equipped with a DPF weighing setup to track soot load over a specifically developed engine operating procedure. Obtained results indicate that the model is accurate enough to capture soot loading and back pressure histories with regard to different steady state engine operating points, without needing any tuning procedure of the key parameters. Thus, the use of ExhAUST for application to advanced after-treatment control appears promising at this stage.
Performance of a Large Bore Natural Gas Engine With Reformed Natural Gas Prechamber Fueling
Authors: Ruter Matthew D. , Olsen Daniel B. , Scotto Mark V. , Perna Mark A.
Published: January 2011

Lean combustion is a standard approach used to reduce NOx emissions in large bore natural gas engines. However, at lean operating points, combustion instabilities and misfires give rise to high total hydrocarbon (THC) and carbon monoxide (CO) emissions. To counteract this effect, precombustion chamber (PCC) technology is employed to allow engine operation at an overall lean equivalence ratio while mitigating the rise of THC and CO caused by combustion instability and misfires. A PCC is a small chamber, typically 1–2% of the clearance volume. A separate fuel line supplies gaseous fuel to the PCC and a standard spark plug ignites the slightly rich mixture (equivalence ratio 1.1 to 1.2) in the PCC. The ignited PCC mixture enters the main combustion chamber as a high energy flame jet, igniting the lean mixture in the main chamber. Typically, natural gas fuels both the main cylinder and the PCC. In the current research, a mixture of reformed natural gas (syngas) and natural gas fuels the PCC. Syngas is a broad term that refers to a synthetic gaseous fuel. In this case, syngas specifically denotes a mixture of hydrogen, carbon monoxide, nitrogen, and methane generated in a natural gas reformer. Syngas has a faster flame speed and a wider equivalence ratio range of operation. Fueling the PCC with Syngas reduces combustion instabilities and misfires. This extends the overall engine lean limit, enabling further NOx reductions. Research results presented are aimed at quantifying the benefits of syngas PCC fueling. A model is developed to predict equivalence ratio in the PCC for different mixtures and flowrates of fuel. An electronic injection valve is used to supply the PCC with syngas. The delivery pressure, injection timing, and flow rate are varied to optimize PCC equivalence ratio. The experimental results show that supplying the PCC with syngas improves combustion stability by 16% compared to natural gas PCC fueling. Comparing equivalent combustion stability operating points between syngas mixtures and natural gas shows a 40% reduction in NOx emissions when fueling the PCC with syngas mixtures compared to natural gas fueling.
Mass and Momentum Flux Measurements With a High Pressure Common Rail Diesel Fuel Injector
Authors: Johnson Samuel E. , Nesbitt Jaclyn E. , Naber Jeffrey D.
Published: January 2011

The combined optimization of diesel engine power, fuel consumption, and emissions output significantly drives the development and tuning of engines. One leading subsystem that continues to receive major development and advancement is the fuel system. High pressure common rail systems lead fuel injection technology and utilize both solenoid and piezoelectric actuated injectors with a wide range of pressure and injection scheduling control. To optimize engine operation the fuel system’s capability is implemented through complex fuel scheduling coupled with charge preparation. With the number of parameters to control, fuel delivery (including dynamic flow characteristics) is one that must be well understood. Most rate of injection systems provide mass flow rate; however, studies have shown that momentum flux is a critical parameter controlling spray entrainment and penetration. To obtain the mass flow rate and momentum flux for a high pressure common rail diesel fuel injector, a rate of injection meter was designed, constructed, and tested allowing for the dynamic measurement of fuel injection with the capability of in-situ operation in a combustion vessel. Measurements were obtained by recording the force signal from a fuel spray jet impinging on the anvil of a force transducer. Combining the force signal with a measure of cumulative injected mass enables calculation of mass and momentum dynamics. The injection system consisted of a Bosch Generation 2 CRIP 2.2 solenoid controlled fuel injector with a single hole 0.129 mm diameter injector nozzle, driven by a custom programmable injector driver from Southwest Research Institute. Testing control variables were injection pressure and injection duration while using #2 ULSD fuel. Initial results showed high repeatability with a COV of less than 1.1 percent for all injection parameters with an average Cd of 0.92 and Ca of 0.97 for a mean injection pressure of 852 bar. A six point injection pressure sweep from 1000 to 1810 bar showed a 1.74 mg/ms overall increase in injection rate and a 0.16 ms overall decrease in fuel discharge duration. A six point injection duration sweep from 0.25 ms to 1.50 ms showed a 3.36 mg/ms total injection rate increase and a 0.68 ms overall increase in fuel discharge time while maintaining a consistent start-of-injection delay. The results show that this injection rate apparatus provides needed information on injection characteristics to assist engine manufacturers with achieving goals of high power with minimal emissions. Furthermore, it has been shown that this system is versatile for future injector characterizations over a wide range of pressures and durations, along with fuel type and injector parameters including nozzle hole diameter.
An Experimental-Numerical Procedure for Stuffing Box Packing Characterization
Authors: Diany Mohammed , Bouzid Abdel-Hakim
Published: January 2011

The sealing of valve stems is ensured by the traditional systems of packed stuffing boxes. The performance of this type of sealing system used also in rotating equipment is dependent on the radial contact pressures generated by the packing axial compression. The mechanical behavior of a packing seal is characterized by the transmission ratio of the axial stress over the radial stress known as the lateral pressure coefficient which is one of the required characteristic used to select packing seals. However, the modeling of the packed stuffing box requires the knowledge of some mechanical characteristics other than the lateral pressure coefficient. In this paper, the mechanical characteristics of packing seals are obtained using a hybrid experimental-numerical procedure. The experimental study is carried out on an instrumented stuffing box packing test bench. The tests results of the experiments are coupled to the ones obtained by a finite element simulation of the test rig to determine the packing seal mechanical characteristics. Two packing types are used; one based on Teflon and the other one based on flexible graphite.
Optimization of Stuffing Box Stem Sealings in Valves by Means of Surface Treatment and Coating
Authors: Ottens Werner , Roos Eberhard , Kockelmann Hans , Hahn Rolf
Published: January 2011

The optimization of the frictional behavior of valve stems in stuffing box sealing systems by means of stem surface treatment and coating is subject of a research project carried out at MPA Stuttgart. Low friction should lead to a high compression and densification of the packing already during assembly resulting in a reduced drop of packing stress with service time and improved tightness. Several surface treatment and coating technologies (Nitrogen and Boron Hardening, inductive coat, Si- and Me-DLC, AlTiN, Chromium-Nitride Multilayer, Tungsten-Carbide and Chromium-Carbide) were examined. Friction tests were carried out at 400 °C followed by leakage tests (160 bar, test fluid Nitrogen) on simulated stuffing box sealings with usual graphite packings and coated or surface treated stems in comparison to a “standard” stem without coating and surface treatment. These combined friction and leakage tests were accompanied by mechanical, technological and metallographical investigations. Visual inspection of the stems after the friction tests suggests a classification in 3 categories depending on the graphite adhesion to the stem surface. Some coatings caused a deterioration (increase of leakage rate) compared to the standard stem (without any coating or surface treatment). In the other cases the leakage rates were comparable to that of the standard stem. Most favorable behavior was observed for the stem with inductive coat. This technology can be seen as a repair technology for damaged stems.
Degradation of Mechanical Properties in Austenitic Stainless Steel Pipe and Fittings for Corrosive Refinery Applications
Authors: Colwell Richard L. , Messer Barry , Hu Jing
Published: January 2011

Recent tests and data analysis have shown a correlation between the degree of hot working and elevated temperature mechanical properties of austenitic stainless steel piping and fittings, independent of the final solution anneal temperature and grain size. While this phenomenon is shown to occur in stabilized stainless steels by data in this paper, it has also been observed in non-stabilized austenitic stainless steel grades. It is understood that work-hardening results in higher material strength, and that annealing results in lower strength, as well as promoting dissolution of carbides and intermetallic phases. The “as-fabricated” mechanical properties of hot formed product are affected by the competition between strain-hardening, and softening due to recovery and recrystallization during hot working and subsequent solution annealing. It has been shown that increasing the amount of hot forming lowers the yield strength of austenitic stainless steel at elevated temperatures. Data is presented that calls into question the common belief that the solution anneal substantially eliminates strain-hardening resultant of prior forming. This paper discusses strengthening mechanisms, provides case histories, suggests mitigation practices, and stresses the importance of proper alloy characterization, and using conservative Code allowable safety factors.
Vibration Loosening Model for Preloaded Countersunk-Head Bolts
Authors: Zaki A. M. , Nassar S. A. , Yang X.
Published: January 2011

A nonlinear mathematical model is developed for studying the self-loosening behavior of preloaded countersunk threaded fasteners that are subjected to cyclic transverse loads. This paper investigates the effect of thread and bearing friction coefficients on the rate of loosening. Torque components acting on the bolt are divided into pitch and resistance torque components; the net torque determines whether or not the bolt will rotate loose under the external excitation. The accumulation of the differential amount of loosening rotation increments is converted into gradual loss of bolt tension/clamp load. Model prediction of the self-loosening behavior is experimentally validated.
Drag Coefficient and Two-Phase Friction Multiplier on Tube Bundles Subjected to Two-Phase Cross-Flow
Authors: Sim W. G. , Njuki W. Mureithi
Published: January 2011

An approximate analytical model for upward two-phase cross-flow through horizontal bundles, to predict drag coefficient on a cylinder and two-phase Euler number, has been developed. To verify the model, two sets of experiments were performed for various pitch mass fluxes of air-water mixture with void fraction. The experiments were undertaken with rotated triangular array of cylinders. The pitch to diameter ratio is 1.5 and the cylinder diameter 38 mm. The void fraction model proposed by Feenstra et al. (2000) is utilized to estimate the void fraction for the cross-flow in the tube bundle. An important variable on the drag coefficient is the two-phase friction multiplier. An empirical formulation of non dimensional pressure drop (Euler number) for single phase flow in tube bundles was proposed by Zukauskas et al. (1988) and two-phase friction multiplier in duct flow was formulated by various researchers. Considering the formulations, the present model was developed. It is found that Marchaterre’s model (1961) for two-phase friction multiplier is applicable to air-water mixtures. The analytical results agree well with experimental drag coefficients and Euler numbers in air-water mixtures for a sufficiently wide range of pitch mass fluxes and qualities. This model will allow researcher to provide analytical estimates of the drag coefficient, which is related to two-phase damping.
Design Limits for Buckling in the Creep Range
Authors: Jawad Maan , Griffin Donald
Published: January 2011

A methodology is introduced for calculating the allowable buckling stress in equipment operating in the time-dependent (creep) range. Norton’s equation coupled with various procedures such as the stationary stress method, classical creep buckling equations, and the isochronous stress-strain diagrams are utilized to obtain a practical design approach for equipment operating in the time-dependent range. Various components are investigated such as slender columns, cylindrical shells, spherical components, and conical transition sections.
Effect of Pressure on Plastic Collapse Under the Combined Bending and Torsion Moments for Circumferentially Surface Flawed Pipes
Authors: Li Yinsheng , Ida Wataru , Hasegawa Kunio , Bezensek Bostjan , Hoang Phuong H.
Published: January 2011

When a crack is detected in a stainless steel pipe during in-service inspection, the failure estimation method given in the codes such as ASME Boiler and Pressure Vessel Code Section XI or JSME S NA-1-2008 Appendix E-8 can be applied to evaluate the integrity of the pipe. In the current editions of these codes, the failure estimation method is provided considering bending moment and pressure. Torsion load is assumed to be relatively small and not considered in the method. In this paper, finite element analyses are carried out for 24-inch stainless steel pipe with a circumferential surface crack under the multi-axial loads including internal pressure. Based on the analysis results, the failure estimation method for cracked pipe subjected to the combined bending and torsion moments is developed considering the effect of internal pressure.