bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Fuel Reactivity on Ignitability and Combustion Phasing in a Heavy-Duty Engine Simulation for Mixing-Controlled and Partially-Premixed Combustion
Authors: Voice Alexander K. , Kumar Praveen , Zhang Yu
Published: December 2016

Light-end fuels have recently garnered interest as potential fuel for advanced compression ignition engines. This next generation of engines, which aim to combine the high efficiency of diesel engines with the relative simplicity of gasoline engines, may allow engine manufacturers to continue improving efficiency and reducing emissions without a large increase in engine and aftertreatment system complexity.

In this work, a 1-D heavy-duty engine model was validated with measured data and then used to generate boundary conditions for the detailed chemical kinetic simulation corresponding to various combustion modes and operating points. Using these boundary conditions, homogeneous simulations were conducted for 242 fuels with research octane number (RON) from 40 to 100 and sensitivity (S) from 0 to 12.

Combustion phasing (CA50) was most dependent on RON and less dependent on S under all conditions. Both RON and S had a greater effect on combustion phasing under partially-premixed compression ignition (PPCI) conditions (19.3°) than under mixing-controlled combustion (MCC) conditions (5.8°). The effect of RON and S were also greatest for the lowest reactivity (RON>90) fuels and under low-load conditions. The results for CA50 reflect the relative ignition delay for the various fuels at the start-of-injection (SOI) temperature. At higher SOI temperatures (>950K), CA50 was found to be less dependent on fuel sensitivity due to the convergence of ignition delay behavior of different fuels in the high-temperature region.

Combustion of light-end fuels in CI engines can be an important opportunity for regulators, consumers and engine-makers alike. However, selection of the right fuel specifications will be critical in development of the combustion strategy. This work therefore provides a first look at quantifying the effect of light-end fuel chemistry on advanced CI engine combustion across the entire light-end fuel reactivity space, and provides a comparison of the trends for different combustion modes.
Modelling and Simulation of an Inverted Brayton Cycle as an Exhaust-Gas Heat-Recovery System
Authors: Chen Z. , Copeland C. D. , Ceen B. , Jones S. , Goya A. A.
Published: December 2016

The exhaust gas from an internal combustion engine contains approximately 30% of the thermal energy of combustion. The exhaust-gas heat-recovery systems aim to reclaim a proportion of this energy in a bottoming thermodynamic cycle to raise the overall system thermal efficiency. The inverted Brayton cycle considered as a potential exhaust-gas heat-recovery system is a little-studied approach, especially when applied to small automotive power-plants. Hence, a model of the inverted Brayton cycle using finite-time thermodynamics (FTT) is presented to study heat recovery applied to a highly downsizing automotive internal combustion engine. IBC system consists of a turbine, a heat exchanger and compressors in sequence. The use of IBC turbine is to fully expand the exhaust gas available from the upper cycle. The remaining heat in the exhaust after expansion is rejected by the downstream heat exchanger. Then, the cooled exhaust gases are compressed back up to the ambient pressure by one or more compressors. In this paper, the exhaust conditions available from the engine test bench data were introduced as the inlet conditions of the IBC thermodynamic model to quantify the power recovered by IBC, thereby revealing the benefits of IBC to this particular engine. It should be noted that the test bench data of the baseline engine were collected by the worldwide harmonized light vehicles test procedures (WLTP). WLTP define a global harmonized standard for determining the levels of pollutants and CO2 emissions, fuel consumption. The IBC thermodynamic model was simulated with the following variables: IBC inlet pressure, turbine pressure ratio, heat exchanger effectiveness, turbomachinery efficiencies, and the IBC compression stage. The aim of this paper is to analysis the performance of IBC system when it is applied to a light-duty automotive engine operating in a real world driving cycle.
3D CFD Modeling and Validation of Ion Current Sensor in a Gen-Set Diesel Engine Using Chemical Kinetic Mechanism
Authors: Badawy Tamer , Henein Naeim
Published: December 2016

The control of the combustion process is becoming a necessity for diesel engines in order to meet the upcoming stringent emission regulations. Ion current sensing technology has the potential to provide real-time feedback of the combustion process while using a fairly inexpensive sensor. 3D computational fluid dynamics (CFD) cycle simulation is becoming more complementary in understanding the complex combustion process in diesel engines. In this paper, a CFD study is focused on investigating the characteristics of the ion current signal produced during the combustion process of a Gen-set turbocharged diesel engine. Multiple virtual ion sensing probes are defined in different locations inside the combustion chamber to understand the influence of sensor location on signal characteristics. The n-heptane reaction mechanism and NO mechanism, combined with an ionization mechanism developed at WSU with 11 species, are used in the model to predict the chemical kinetics of combustion and the mole fraction of ionized species produced during combustion. Since the charge in diesel engines is heterogeneous and due to the sensing nature of the ion sensor, this paper explores the effect of sensor sensing diameter and its protrusion depth inside the combustion chamber on the ion current signal development. The simulation is validated by comparing in-cylinder pressure traces, the rate of heat release, and the ion current signal. Further, the model results are validated under different engine loads and injection pressures. This study utilizes the ionization mechanism to give further understanding of the complex formation of ionization species and their amplitudes, particularly at local sensing locations. This can be very vital to identify the potentials of using the ion current sensing and highlight its viability in feedback closed loop combustion control.
Impact of a Yttria-Stabilized Zirconia Thermal Barrier Coating on HCCI Engine Combustion, Emissions, and Efficiency
Authors: Powell Tommy , O’Donnell Ryan , Hoffman Mark , Filipi Zoran
Published: December 2016

In-cylinder surface temperature has significant impacts on the thermo-kinetics governing the Homogeneous Charge Compression Ignition (HCCI) process. Thermal Barrier Coatings (TBCs) enable selective manipulation of combustion chamber surface temperature profiles throughout a fired cycle. In this way, TBCs enable a dynamic surface temperature swing, which prevents charge heating during intake while minimizing heat rejection during combustion. This preserves volumetric efficiency while fostering more complete combustion and reducing emissions.

This study investigates the effect of a Yttria-Stabilized Zirconia (YSZ) coating on Low Temperature Combustion (LTC) engine combustion, efficiency, and emissions. This is an initial step in a systematic effort to engineer coatings best suited for LTC concepts. A YSZ coating was applied to the top of the aluminum piston using a powder Air Plasma Spray process, Final thickness of the coatings was approximately 150 microns. The coated piston was subsequently evaluated in the single-cylinder HCCI engine with exhaust re-induction.

Engine tests indicated significant advancement of the autoignition point and reduced combustion durations with the YSZ coating. Hydrocarbon and carbon monoxide emissions were reduced, thereby increasing combustion efficiency. The combination of higher combustion efficiency and decreased heat loss during combustion produced tangible improvements in thermal efficiency. When the effects of combustion advance were removed, the overall improvements in emissions and efficiency were lower, but still significant. Overall, the results encourage continued efforts to devise novel coatings for LTC.
Investigation of RCCI Characteristics of Combustion and Emissions With PFI of N-Butanol and Direct Injection of High Linoleic Content Biodiesel
Authors: Soloiu Valentin , Naes Tyler , Muiños Martin , Rivero-Castillo Alejandro , Harp Spencer
Published: December 2016

This study investigated the RCCI (Reactivity Controlled Compression Ignition) of PFI (Port Fuel Injection) of n-butanol with direct injection (DI) of a high linoleic acid content biodiesel, cottonseed (CS100). The experimental omnivorous-fuel engine was operated at 1400 rpm and 6 bar indicated mean effective pressure (IMEP) with 20% cooled EGR. The mass ratio of n-butanol injected comprised of 50% of the total fuel mass.

The dual fueling strategy of RCCI changed the conventional diesel combustion (CDC) apparent heat release profile. With the new fueling strategy the heat release was split into two regions of high temperature heat release when using CS100. The first occurred before top dead center (BTDC) from the high reactivity fuel and the second peak occurred due to the combustion of the low reactivity fuel (n-butanol) after top dead center (ATDC). ULSD did not produce this same split in heat release due to the longer ignition delay.

The ignition delay for CS100 was shortened by 0.15 ms when compared to ULSD because of the high palmitic acid content in the biodiesel. The RCCI process itself extended the ignition delay about 0.17 ms (about 1.4 CAD) suggesting the possibility of controlling combustion phasing for both RCCI fueling strategies of ULSD and CS100. The CA50 occurred similarly at 10° ATDC for ULSD and CS100 however, RCCI shifted the CA50’s (7° and 8° ATDC for CS100 and ULSD respectively). Soot emissions exhibited a decrease with the PFI of n-butanol because of the highly oxygenated nature of the fuel by 80%. In summary, RCCI stratification using n-Butanol as the low reactivity fuel significantly reduced soot emissions when using either a high linoleic acid content biofuel or ULSD while also suggesting control over combustion phasing.
Effect of Fuelling Control Parameters on Combustion Characteristics of Diesel-Ignited Natural Gas Dual-Fuel Combustion in an Optical Engine
Authors: Khosravi Mahdiar , Rochussen Jeremy , Yeo Jeff , Kirchen Patrick , McTaggart-Cowan Gordon , Wu Ning
Published: December 2016

Its inherent economic and environmental advantages as an internal combustion engine fuel make natural gas (NG) an attractive alternative to diesel fuel as the primary energy source for some compression ignition (CI) engine applications. Diesel pilot-ignition of NG is an attractive fueling strategy as it typically requires minimal modification of existing CI engines. Furthermore, this strategy makes use of the highly developed direct injection (DI) diesel fuel systems already employed on modern CI engines for to control dual-fuel (DF) combustion. Despite the increasing popularity of the dual-fuel NG engine concept, the fundamental understanding of the fuel conversion mechanisms and the impact of the fueling parameters is still incomplete. A conceptual understanding of the relevant physics is necessary for further development of fueling and pilot-ignition strategies to address the shortcomings of dual-fuel combustion, such as low-load emissions and combustion stability.

An experimental facility supporting optical diagnostics via a Bowditch piston arrangement in a 2-litre, single-cylinder research engine (Ricardo Proteus) was used in this study to consider the effect of fueling parameters on the fuel conversion process in a dual fuel engine. Fueling was achieved with port injected CH4 and diesel direct injection using a common rail system. Simultaneous, high-speed natural luminosity (NL) and OH* chemiluminescence imaging was used to characterize dual-fuel combustion and the influence of pilot injection pressure (300 bar vs. 1300 bar) and relative diesel-CH4 ratios (pilot ratio, PR), as these have been noted as key operating dual-fuel control metrics.

The pilot injection pressure was observed to have a significant impact on the fuel conversion process. At higher pilot injection pressures, the auto-ignition sites were concentrated around the piston bowl periphery and the reaction zone propagated towards the center of the bowl. At lower pilot injection pressures, ignition initiated in the vicinity of the pilot fuel jet structures and resulted in a more heterogeneous fuel conversion process with regions of intense natural luminosity, attributed to particulate matter. An increase in the pilot ratio (i.e., increased diesel fraction) resulted in a more aggressive combustion event, due to a larger fraction of energy released in a premixed auto-ignition event. This was coupled with a decrease in the fraction of the combustion chamber with significant OH* or NL light emission, indicating incomplete fuel conversion in these regions. The insight to the dual-fuel conversion processes presented in this work will be ultimately used to develop dual-fuel injection strategies, as well as provide much needed validation data for modeling efforts.
Torsional Vibration Solutions for Geared Aviation Diesel Engines: Power Transmission Through the Camshaft or Dedicated Internal Driveshaft
Authors: Nardella Francis A.
Published: December 2016

Aviation gasoline is in limited supply in many parts of the world although jet fuel is widely available. The turbine engine solution, however, is not a viable option for most of general aviation because of cost. Therefore considerable effort has been expended to develop suitable jet fuel burning compression ignition (CI) engines for general aviation. Because of weight and power concerns in aviation, much of the effort has been directed toward the development of geared engines. Many currently certified geared CI engines, however, require frequent gearbox inspections and have relatively low times before replacement or overhaul. The high pressures produced by CI engines generate torsional vibration that can be troublesome for geared engines. The first mode natural frequency of a drive train can be lowered by increasing its length thereby reducing stiffness so that its convergence with dominant engine excitation harmonics occurs at lower rpm below the high power operating range of the engine. This can be accomplished without increasing the length of the engine and with 2:1 gear reduction by using the camshaft in the case of a four-stroke pushrod engine as the power transmission shaft or a dedicated geared internal power transmission shaft at the desired ratio in the case of an engine with overhead camshafts. Simulation studies show that resonance at the lower speed is associated with a marked reduction in torsional vibration.
Development of an Injector Fault Insertion Tool for DI Gasoline and Diesel Engines
Authors: Yapaulo Renato , Viele Matthew , Polk Andrew
Published: December 2016

In order to ensure that every portion of the emission control software in a vehicle works, all fault conditions must be tested. Simply simulating faults in the software of the engine controller and reporting it to the OBD II scanner is inadequate; the fault condition must be injected externally to the Engine Control Unit (ECU). In the case of hard-to-reproduce mechanical failures, this is a challenging task. This paper discusses the development of a system capable of emulating various faults that a fuel injector can have while operating as part of a complete working vehicle. For the ECU to operate properly, all fuel injectors must be present in the vehicle, be fully functional, and must represent an accurate electrical load to the ECU. Then, the induced faults must be seamlessly inserted into the running system in less than 10μs and removed before the subsequent injection event. This was accomplished with a variety of COTS hardware, a simple custom circuit, and the use of a large, flexible FPGA platform.
The Effect of Vibration-Based Ash Cleaning on the Mechanical Strength Properties of Ceramic Diesel Particulate Filters
Authors: Ragaller Paul , Sappok Alexander , Bromberg Leslie , Owolabi Gbadebo , Odeshi Akindele
Published: December 2016

Vibration-based particulate filter cleaning processes have been proposed to enhance the removal of packed ash deposits accumulated in particulate filters. The processes raise concerns regarding their impact on the cellular ceramic filter material. In this study, several new ceramic diesel particulate filters from the same production batch were subjected to differing levels of vibration-based ash cleaning, and their mechanical properties were measured in order to determine the effect, if any, the vibrations have on the overall integrity of the substrate. Samples underwent compressive and three-point bending testing at two different strain rates in order to measure the differences in the ultimate strength and modulus of rupture. The results show no statistically significant differences in the ultimate crushing strength of the vibrated samples as compared to the unvibrated samples at each orientation. Additionally, the three-point bending tests show no statistically significant reduction in the modulus of rupture of the vibrated samples as compared to the unvibrated ones. The results indicate that the vibration-based ash removal approach proposed in this study poses no measurable risk to the integrity of the ceramic substrate.
The Estimation of Nitrogen Oxides Reduction Potential Through Enhanced Heat Release Analysis
Authors: Gao Tongyang , Yu Shui , Xie Kelvin , Jeftic Marko , Wang Meiping , Zheng Ming
Published: December 2016

An enhanced heat release analysis method is proposed to investigate the NOx emission reduction potential in diesel low temperature combustion and the combustion of premixed ethanol ignited by diesel injections. The heat release analysis from the in-cylinder pressure is a commonly applied diagnostic tool to gain insights in various aspects of combustion, such as start of combustion, ignition delay, combustion phasing, and combustion duration. However, these parameters are more qualitative than quantitative when they are correlated to engine efficiency and emissions. The results are often inconsistent at different engine operating conditions, such as different intake pressure levels, EGR rates and engine loads.

In this work, the authors proposed a new parameter named as peak of combustion acceleration, which is the maximum of the first derivative of the heat release rate over an engine cycle. It was observed that the peak of combustion acceleration had a close correlation with the emissions of smoke and NOx at different engine loads and in the combustion of both diesel LTC and premixed ethanol ignited by diesel injections. With the test engine platform, the NOx emission reduced to lower than 50 ppm when the peak of combustion acceleration was less than 25 for diesel LTC and 35 for premixed ethanol ignited by diesel injections. The detailed cylinder pressure sampling and treatment processes were described in this paper. The impact of cycle to cycle variation in the cylinder pressure on the calculation of the peak of combustion acceleration was discussed. The peak of combustion acceleration and the corresponding engine crank angle from each individual engine cycle were calculated and the statistic performance of these parameters was evaluated. The comparison indicated an acceptable consistency between the results from individual engine cycle and from the averaged engine cycles. The proposed peak of combustion acceleration can be potentially integrated in the engine control as an indication of the NOx reduction potential.
Combustion and Emission Characteristics of a CI Engine Operating in Diesel-1-Butanol/CNG Dual Fuel Mode With Low and High CNG Substitution Rates in Light Load Operation
Authors: Meng Xiangyu , Li Yuanxu , Nithyanandan Karthik , Long Wuqiang , Lee Chia-Fon F.
Published: December 2016

Dual-fuel combustion mode with direct injection of diesel as the pilot fuel and port injection of compressed natural gas (CNG) in compression ignition (CI) engines has been widely investigated to comply with the latest emission regulations. The diesel-CNG dual-fuel combustion mode shows some potential to decrease NOx and soot emissions simultaneously, while it reveals a lower thermal efficiency compared to the pure diesel combustion mode under low load condition. The purpose of the current study is to investigate the possibility of using diesel blended with 1-butanol as the pilot fuel to enhance the engine performance and reduce emissions. Three pilot fuels — B0 (pure diesel), B10 (90% diesel and 10% 1-butanol by volume) and B20 (80% diesel and 20% 1-butanol) with the CNG substitution rates of 50% and 80% were compared at an engine speed of 1200 rpm. The experiments were conducted by sweeping the pilot fuel injection timing from −3 to −18 ° CA ATDC with an equivalent total energy (∼5 bar IMEP). The results illustrated that, for the 50% CNG substitution rate, the dual-fuel operation mode revealed a higher indicated thermal efficiency (ITE) under low load conditions, and B10 can significantly improve the ITE due to the shorter combustion duration. The emission results of B10 showed that it obtained lower THC and CO emissions, but a slightly higher NOx emission. For the 80% CNG substitution rate, the results presented lower ITE, higher THC and lower NOx emissions, comparatively.
Return on Investment Calculation for a Heavy Duty Vehicle With a Dual Fuel Diesel-Natural Gas Engine
Authors: Ivanco Andrej , Prucka Robert , Hoffman Mark , Filipi Zoran
Published: December 2016

Advancements in natural gas extraction technology are driving down natural gas prices to much lower levels than diesel fuel. This situation could be advantageous to commercial vehicle operators if they are able to cost-effectively modify their fleets to replace a portion of their diesel fuel usage with natural gas. Dual-fuel retrofit kits are an attractive option since they can use existing vehicles and offer relatively low conversion cost as compared to engine replacement. These systems convert dedicated diesel engines to operate on dual-fuel with the addition of intake fumigated natural gas. Fumigated dual-fuel systems replace a significant portion of diesel fuel energy with natural gas (generally 50% or more by energy content), and produce lower operating costs than diesel-only operation. This research describes a methodology, which can be used to predict the return on investment for a dual fuel vehicle and specify the $/mile gain if the vehicle is fitted with dual fuel technology. As a case study, a generic class 8 vehicle is chosen to evaluate the benefit of dual fuel system integration considering overall return of investment.
Prediction of Flame Burning Velocity at Early Flame Development Time With High Exhaust Gas Recirculation (EGR) and Spark Advance
Authors: Lian H. , Martz J. B. , Maldonado B. P. , Stefanopoulou A. G. , Zaseck K. , Wilkie J. , Nitulescu O. , Ehara M.
Published: December 2016

Diluting Spark-Ignited (SI) stoichiometric combustion engines with excess residual gas improves thermal efficiency, and allows spark to be advanced towards Maximum Brake Torque (MBT) timing. However, flame propagation rates decrease and misfires can occur at high Exhaust Gas Recirculation (EGR) conditions and advanced spark, limiting the maximum level of charge dilution and its benefits.

The misfire limits are often determined for a specific engine from extensive experiments covering a large range of speed, torque and actuator settings. To extend the benefits of dilute combustion while at the misfire limit, it is essential to define a parameterizable, physics-based model capable of predicting the misfire limits, with cycle to cycle varied flame burning velocity as operating conditions change based on driver demand. A cycle averaged model is the first step in this process.

The current work describes a model of cycle averaged laminar flame burning velocity within the early flame development period of 0 to 3 percent mass fraction burned. A flame curvature correction method is used to account for both the effect of flame stretch and ignition characteristics, in a variable volume engine system. Comparison of the predicted and the measured flame velocity was performed using a spark plug with fiber optical access. The comparison at a small set of spark and EGR settings at fixed load and speed, shows an agreement within 30% of uncertainty, while 20% uncertainty equals ± one standard deviation over 2,000 cycles.
Variable Inertia Damper Using MR Fluid
Authors: Matsuoka Taichi , Hiramoto Kazuhiko , Sunakoda Katsuaki , Abe Naoto
Published: December 2016

Inertia damper has an inertia effect by a flywheel which is caused by a quick moving mass. In general, it is difficult to change the inertia mass physically. In order to obtain a variable inertia effect, a new type of inertia damper has a long bypass pipe is proposed in this paper. This type of damper generates a damping effect and inertia effect by the fluid. It is noted that the inertia effect is depended on a density of the fluid, cross sectional areas of cylinder and bypass pipe, and length of the bypass pipe. If the diameter of the bypass pipe can be controlled, it means that a cross sectional area of the bypass pipe can be switched by clustering particles of MR fluid under magnetization, the inertia effect might be artificially controllable. A trial damper with several electromagnets installed along the long bypass pipe is manufactured, and dynamic property is measured when MR fluid inside the bypass pipe is magnetized by the electromagnets. From experimental results, it seems to be that the inertia effect can be switched and depended on amplitude of magnetization. Finally, the calculated results are theoretically approached, and compared with the experimental results.
Mechanistic Studies on Type 300 Stainless Steels Manufactured by Hot Isostatic Pressing: The Impact of Oxygen Involvement on Fracture Behaviour
Authors: Cooper Adam J. , Dhers Jean , Sherry Andrew H.
Published: December 2016

With near-net shape technology becoming an increasingly desirable route toward component manufacture due to its ability to create components with increasingly complex geometries, minimizing the number of potential welded joints, as well as reducing machining time and associated costs, it is important to demonstrate that components fabricated via Hot Isostatic Pressing (HIP) are able to perform to similar standards as those set by equivalent forged materials. Hot Isostatically Pressed (HIP’d) materials are typically accredited with displaying enhanced yield strengths, ultimate tensile strengths, and ductility over their forged counterparts.

In this paper we explore the effects of oxygen, which resides in the austenite matrix during the HIP manufacture process, on a material’s fracture toughness properties. We quantify the influence of different concentrations of oxygen on both the microstructural and mechanical properties of HIP’d 304L and 316L stainless steel, highlighting the benefit of reducing the oxygen as much as possible. Various mechanical tests have been performed on materials containing a range of oxygen contents (between 100 ppm and 200 ppm) and over a large temperature range, including J1C fracture toughness testing, instrumented Charpy, and tensile, and the mechanistic involvement of residual oxygen on the results is discussed. The effects of oxygen become more apparent at cryogenic temperatures, whereas the fracture behavior of HIP’d and forged variants of 304L and 316L at elevated temperatures appears to be comparable.
Life Prediction of Cold-Stretched Austenitic Stainless Steel at High Temperature
Authors: Han Yu , Wang Kesheng
Published: December 2016

With the purpose of long-cycle safe operation of cold stretched austenitic stainless steel pressure vessels to achieve unification of economy and safety, prediction of fatigue life of S31603 austenitic stainless steel at high temperature is systematic studied. Based on the Hull-Rimmer cavity theory, a fatigue life prediction model applicable to stress controlled is developed. Fatigue tests were carried out on the solution annealed and cold stretched S31603 steel at high temperature and corresponding test data is obtained. The fatigue life of the solution annealed and cold stretched materials was predicted by the model and the prediction results are in good agreement with the experimental lives. On this basis, the life prediction model coupled with the strain level of cold stretching is further established. Compared with the test data, the prediction results is found to be very satisfactory with an error band less than ±1.5 times. The fatigue life prediction model suitable for stress control at high temperature is simple in form and has a clear and obvious physical significance which points out a new way to predict fatigue life of metal materials.
Characterisation of Microstructure and Properties of a Transition Weld
Authors: Brayshaw W. J. , Sherry A. H. , Burke M. G. , James P.
Published: December 2016

Transition welds represent a challenge for the assessment of structural integrity of nuclear plant due to the complexity of the microstructure, properties and local stress state. This paper presents the initial findings of a study aimed at characterising the local microstructure and properties of a transition weld between SA508-4N ferritic steel and SS316LN austenitic stainless steel using a nickel-base filler of Alloy 82. The local microstructures and local composition of the material interfaces are characterised using backscattered electron imaging and Energy-dispersive X-ray spectroscopy. The ferritic steel shows significant grain refinement in the heat affected zone compared to the base metal. This refinement is also observed in the heat affected zone of the austenitic stainless steel although not as significant. Micro-hardness testing has also been incorporated to provide an indication of the influence of local microstructure on flow properties across the weld region. The results indicate a hardness range of between 180–340HV across the weld with the highest value in the heat affected zone of the ferritic steel and the lowest in the austenitic stainless steel. Yield and flow properties derived from flat transweld tensile tests incorporating digital image correlation are related to the micro-hardness results and microstructural characterisation, and an initial assessment of the fracture mechanism performed using fractography.
Location of Initiation Sites in Fracture Toughness Testing Specimens: The Effect of Size and Side Grooves
Authors: Wallin Kim , Yamamoto Masato , Ehrnstén Ulla
Published: December 2016

Cleavage fracture initiates usually at single locations in front of the fatigue crack in some position along the crack front. If the crack driving force along the crack front is uniform, one should expect the initiation sites to be randomly located along the crack front. Finite element analyses have, however, shown that the crack driving force varies along the crack front. Thus, the location of the cleavage initiation sites should reflect this variation in crack driving force.

Fracture toughness specimens differ both in geometry and size. Also, the specimens may be side grooved or plane sided. All this can be expected to affect the local crack driving force along the crack front. The local crack driving force for cleavage fracture initiation can be divided into two components. The local KJ value describes the local effective stress intensity, whereas Q or Tstress describes the local constraint. To make things even more complicated, the local constraint is also affected by the local effective stress intensity. All of these are also affected by any ductile tearing occurring prior to cleavage initiation.

The testing standards contain specific limitations on specimen sizes and their measuring capacity in order to ensure that the crack driving force in different specimens is sufficiently similar to make the results from different specimen types and sizes comparable.

Classically, the fracture toughness test specimens have been comparatively large. Recently more and more work has been devoted to diminish the size of the specimens, to save material. One very promising specimen type is the miniature C(T) specimen with a 4 mm thickness and total height of 10 mm. Based on a recent international round-robin, the miniature C(T) specimen appears to provide compatible Master Curve T0 values as large specimens, but further validation regarding the similitude of the cleavage initiation is required, since the Master Curve is based on the assumption that specimen size does not affect this similitude.

In this work, the location of cleavage initiation sites along the crack front are examined for different size and type of fracture toughness specimens, focusing on the miniature C(T) specimen. The location distributions are evaluated in terms of load level, specimen type, size and possible side grooving. It is shown that, as long as the standard requirements are fulfilled, the initiation location distributions for the miniature C(T) specimens are similar to larger conventional specimens. Side grooving is shown to have a minor effect on the initiator locations.
The Influence of a Non-Aligned Semi-Elliptical Surface Crack on a Quarter-Circle Corner Crack in an Infinitely Large Plate Under Uniaxial Tension
Authors: Perl M. , Ma Q. , Levy C.
Published: December 2016

The evaluation of non-aligned multiple cracks is required in various fitness-for-service codes. For non-aligned parallel cracks, on-site inspection needs to decide whether the cracks should be treated as coalesced or separate multiple cracks for Fitness-for-Service. In the existing literature, criteria and standards for the adjustment of multiple nonaligned cracks are very source dependent, and those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the authors previously reported on the effect between an edge and an embedded parallel crack in 2-D scenarios and, more recently, in 3-D scenarios of circular cracks. Since realistic crack configurations detected using non-destructive methods are generally 3-D in nature, the study of 3-D effect of non-aligned cracks with different shapes is deemed necessary in order to obtain more practical guidance in the usage of rules speculated in Fitness-for-Service codes. In this study, a quarter-circle corner crack is considered to interact with a semi-elliptic non-aligned surface flaw in an infinitely large plate under uniaxial tension. While keeping the geometry of the quarter-circle corner crack unchanged, a pair of horizontal (H) and vertical (S) separation distances between the two cracks is chosen followed by a detailed analysis of the effect of crack shape on the 3D SIFs for various embedded semi-elliptical cracks. The analysis is repeated for various combinations of separation distances S and H. The results from this study are collectively significant to the understanding of the correlation between the criteria and standards in Fitness-for-Service community and the consequence of their usage in engineering practice.
Failure of Thin-Walled Pipes With D/T up to 140 and Conclusions for the Design Codes
Authors: Schau Henry , Mkrtchyan Lilit , Johannes Michael
Published: December 2016

The influence of imperfections on the instability bending moment of thin-walled straight pipes with D/t-ratios (D - outside diameter, t - wall thickness) up to 140 is determined using nonlinear Finite Element (FE) analyses. The analyses show that the type and size of the imperfection, the D/t ratio and the material properties have significant influences on the instability moment. The nominal bending stress of pipes (yield stress 500 MPa) with D/t > 70 and an ovality of 0.5% is smaller than the yield stress at the instability point. That means, the failure occurs by buckling in the elastic range of the nominal bending stress. In static analyses the moment decreases abruptly after reaching the instability moment. In the dynamic analyses the pipe jumps abruptly to the state with smaller moment. The obtained results are applied to calculate the B2 index for pipes with D/t ≤ 140. The B2 indices for thin-walled straight pipes with D/t > 40 are considerably higher than 1.0. In general, there is a good agreement between the calculated B2 values and the values of the ASME Code. A correction factor for higher temperatures is not necessary. The allowable moments calculated with the B2 index and the stress intensification factor i are compared. The bending moments from disabled thermal expansion and anchor movements have the same effect on the failure due to (plastic) buckling as the primary moments and must be taken into account.
Efficient Intensity Measures for Probabilistic Seismic Response Analysis of Anchored Above-Ground Liquid Steel Storage Tanks
Authors: Phan Hoang Nam , Paolacci Fabrizio
Published: December 2016

Liquid storage tanks are vital lifeline structures and have been widely used in industries and nuclear power plants. In performance-based earthquake engineering, the assessment of probabilistic seismic risk of structural components at a site is significantly affected by the choice of ground motion intensity measures (IMs). However, at present there is no specific widely accepted procedure to evaluate the efficiency of IMs used in assessing the seismic performance of steel storage tanks. The study presented herein concerns the probabilistic seismic analysis of anchored above-ground steel storage tanks subjected to several sets of ground motion records. The engineering demand parameters for the analysis are the compressive meridional stress in the tank wall and the sloshing wave height of the liquid free surface. The efficiency and sufficiency of each alternative IM are quantified by results of time history analyses for the structural response and a proper regression analysis. According to the comparative study results, this paper proposes the most efficient and sufficient IMs with respect to the above demand parameters for a portfolio of anchored steel storage tanks.
The OECD-NEA Programme on Metallic Component Margins Under High Seismic Loads (MECOS)
Authors: Labbé Pierre B. , Reddy G. R. , Mathon Cedric , Moreau François , Karamanos Spyros A.
Published: December 2016

MECOS is Post-Fukushima OECD/NEA initiative, with the following main objectives:

- To quantify the existing margins in seismic analysis of safety class components and assess the existing design practices within a benchmark activity.

- To make proposals for new design/evaluation criteria of pressurized piping systems, accounting for their actual failure mode under strong input motions.

The first part of MECOS consisted of gathering information on i) current design practices and ii) piping system experimentation carried out around the world that could be suitable for benchmarking. Part 2 is the benchmark itself and Part 3 proposals for new criteria. The purpose of the proposed paper is to present the experimental background and the benchmark exercise.
Fracture Probability Assessment for Embrittled Reactor Pressure Vessels Under Ultimate Response Guideline Operation
Authors: Chou Hsoung-Wei , Huang Chin-Cheng
Published: December 2016

After the Fukushima nuclear accident occurred in Japan on March 11, 2011, the compound disaster beyond design basis which may severely impact the nuclear safety has been noticed and paid much more attention. In addition to the original emergency operating procedures (EOPs) and severe accident management guidance (SAMG) of nuclear power plant, the licensee in Taiwan developed the ultimate response guideline (URG) when EOPs and SAMG cannot be performed effectively due to loss of power and water supply by the Fukushima-like compound disaster. Once the URG procedures are initiated, the operators will conduct reactor depressurization, low pressure water injection and containment venting to strictly prevent the core damage and the release of radioactive material.

In the paper, the fracture probabilities of boiling water reactor (BWR) pressure vessels with incremental levels of radiation embrittlement under URG operation are evaluated by probabilistic fracture mechanics (PFM) analysis. First, the models of PFM FAVOR code concerning the beltline shell welds of reactor pressure vessels (RPVs) associated with a very conservative flaw distribution are built. Then, the hypothetical transients of URG operation obtained from the thermal hydraulic analyses for Taiwan domestic BWRs are applied as the loading condition. The analysis results demonstrate that performing URG operation will not cause significant fracture probability for RPV, even at an extremely embrittled condition. The URG procedures can ensure the prevention of core damage as well as maintenance of structural integrity of RPV in the situation of long-term loss of electric power when suffering from the Fukushima-like accidents.
Risk Based Inspection Planning for Deteriorating Pressure Vessels
Authors: Haladuick Shane , Dann Markus R.
Published: December 2016

Pressure vessels are subject to deterioration processes, such as corrosion and fatigue. If left unchecked these deterioration processes can lead to failure; therefore, inspections and repairs are performed to mitigate this risk. Oil and gas facilities often have regular scheduled shutdown periods during which many components, including the pressure vessels, are disassembled, inspected, and repaired or replaced if necessary.

The objective of this paper is to perform a decision analysis to determine the best course of action for an operator to follow after a pressure vessel is inspected during a shutdown period. If the pressure vessel is inspected and an unexpectedly deep corrosion defect is detected an operator has two options: schedule a repair for the next shutdown period, or perform an immediate unscheduled repair. A scheduled repair is the preferred option as it gives the decision maker lead time to accommodate the added labour and budgetary requirements. This preference is accounted for by a higher cost of immediate unscheduled repairs relative to the cost of a scheduled repair at the next shutdown. Depending on the severity of deterioration either option could present the optimal course of action. In this framework the decision that leads to the minimum expected cost is selected. A stochastic gamma process was used to model the future deterioration growth using the historical inspection data, considering the measurement error and uncertain initial wall thickness, to determine the probability of pressure vessel failure. The decision analysis framework can be used to aid decision makers in deciding when a repair or replacement action should be performed. This method can be used in real time decision making to inform the decision maker immediately post inspection. A numerical example of a corroding pressure vessel illustrates the method.
Effective Method of Measuring the Reliability of the Gas Network
Authors: Feng Chen , Changchun Wu
Published: December 2016

This paper aims at evaluating the gas supply reliability of the gas network, which is meaningful to promote the safe operation of large natural gas transporting system. The solution to solve the problem is put forward by combination of Monte-Carlo method, Random Process Algorithm and hydraulic thermal method.

The reliability of the network depends on the user’s conformance to their requirements and their corresponding degree of gas supply security. Since the matter thing is whether the adequate gas can be sent to the users, the study of gas supply reliability should focus on the common unit states, including the functional state and typical expected failure states. While these familiar states can be obtained by analyzing the historical operating data stored in SCADA system along with the Monte-Carlo simulation, the corresponding failure probability of each state can be achieved. Moreover, the gas flow that expected by the user under various conditions can be performed by the hydraulic and thermal simulation software. Hence, the supply volume of the combined states is defined as the sum of the amount of states to be combined.

This evaluation model can reveal the performance of the gas supply at any time interval and under any degree of gas supply security. Not only can this model develop the classical reliability theory, but also have the benefits for the operation and maintenance of the network.
Application of Probabilistic Fracture Mechanics Analysis on BWR Recirculation Piping Systems
Authors: Shen Yu-Yu , Chou Hsoung-Wei , Huang Chin-Cheng , Liu Ru-Feng
Published: December 2016

In recent years, the probabilistic fracture mechanics (PFM) approach has been widely applied to estimate the fracture risk of nuclear power plant piping systems. In the paper, the probabilistic fracture mechanics code, PRO-LOCA, developed by the Probabilistic Analysis as a Regulatory Tool for Risk Informed Decision Guidance (PARTRIDGE) project, is employed to practically evaluate the fracture probability of the recirculation piping system welds in a Taiwan domestic boiling water reactor (BWR) nuclear power plant. To begin with, the models based on the real situation of the recirculation piping welds are built. Then, the probabilities of through-wall cracking, leak with different rates, and rupture on the welds considering both in-service inspection and leak detection are analyzed. Meanwhile, the effects of probability of detection curves of ISI on the piping are simulated. Further, the efficiencies of performing the induction heating stress improvement and weld overlay are also studied and discussed. The present work could provide a reference of operation, inspection and maintenance for BWR plants in Taiwan.
Study on Intermediate Support of Tall Columns for FPSO Topside Structures
Authors: Nanjo Takanori , Miyashita Toshikazu , Kataoka Shunji , Sato Takuya
Published: December 2016

FPSO (Floating Production, Storage and Offloading) has become used increasingly for off-shore gas fields. Most tall pressure vessels such as columns installed in the FPSO are surrounded by topside structures. In general, columns in on-shore plants are supported only by bottom skirts; on the other hand, some of the tall columns on FPSO hulls require intermediate supports in addition to bottom skirts because of large accelerations they are subject to due to ship motion induced by wave loading. In this paper, the effects of the support were investigated considering acceleration distributions and structure deformation (drift), then the ideal elevation of the support was determined to minimize bending moment throughout the columns under the combined conditions. A dimensionless controlling parameter related to the acceleration, structure drift, and column properties was proposed and graphs (called N-Charts) were proposed to understand effects in reducing the maximum bending moment with respect to the elevation of the guide.
Evaluation of Design Methodologies for High-Pressure Hazard Barricades
Authors: Kostecki Jodi , Edel Matthew , Bingham Barry
Published: December 2016

Operation and testing of high-pressure products and equipment are commonly completed in a variety of industrial applications, including oilfield services, industrial gas manufacturing and supply, heat exchangers, refining, chemical, petrochemical, water jetting, and vessel manufacturing, among others. This daily operation has the potential for high consequence (personnel injury, property damage, and business interruption) due to common accidental tool and equipment failures. An increasing number of companies are seeking assistance in providing a testing environment that focuses on improving safety within the industry.

One method for high-pressure hazard mitigation is to use a barricade as a means of protection. This paper investigates a variety of methodologies used for evaluating steel barricades subjected to impact loads from a projectile that produces a flexural response in the plate (rather than penetration). The investigation covers various approaches in hazard (i.e., load) application and structural analysis. The structural models focus on impact loading of steel plates, and the results are directly compared to test results in terms of structural component response.