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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Advanced Materials Development under NASA’s Hybrid Thermally Efficient Core (HyTEC) Project

The Hybrid Thermally Efficient Core (HyTEC) project aims to develop small core turbofan engine technologies that will enable fuel burn reductions, additional use of electric airplane systems through power extraction, and to advance engine operability and compatibility with sustainable aviation fuels. As such, a portfolio of technologies that contribute to raising the pressure, temperature and efficiency of turbofan engine cores needs developed. Included in HyTEC’s technology portfolio to enable these advancements are enhanced combustor liner materials and higher temperature capable turbine blades and vanes manufactured using ceramic matrix composites (CMCs) and environmental barrier coatings (EBCs). These technologies are being developed and tested in laboratory-scale relevant environments to advance the technology readiness level (TRL) to 4 or 5, before moving into an engine core demonstrator to raise the TRL to 6. A new natural gas/oxygen burner rig facility will be used to simulate turbine engine relevant environments at the laboratory/coupon scale. In addition, improvements to enable sub-element, and more complex component testing in NASA Glenn’s combustor facility (CE-5) will be presented.

Ceramic Matrix Composites (CMCs)↗
NASA NTRSDate not supplied

A Fundamental Study of Bifurcation Acoustic Treatment Effects on Aft-Fan Engine Noise

Increasing air traffic and more stringent aircraft noise regulations continue to expand requirements on aircraft noise levels for conventional and unconventional aircraft configurations. A major component of the overall aircraft noise is the sound associated with the propulsion system mounted in the engine nacelle. Acoustic liners mounted in the aircraft engine nacelles provide a significant portion of the current fan noise reduction. However, they must be further optimized if challenging noise reduction goals are to be achieved. One location within the aft bypass duct that may be an excellent candidate for increased attention is the acoustic treatment on the engine bifurcations (i.e., engine pylon and lower bifurcation). This paper presents the continuation of a fundamental study of the effects of bifurcation treatment on simulated aft fan noise and the validation of numerical tools to predict such effects. Five bifurcation configurations (four treated and one hardwall) were fabricated and tested in the NASA Langley Curved Duct Test Rig. Results show that mode scattering may occur due to both the presence of the bifurcation, as well as variable impedance distributions on the bifurcation surface. Future work will also include optimization of bifurcation treatments for testing in the Curved Duct Test Rig. These initial results are promising and this work provides valuable information for further study and improvement of the performance of bifurcation acoustic treatments.

bifurcation effects↗
NASA NTRSDate not supplied

A Fundamental Study of Bifurcation Acoustic Treatment Effects on Aft-Fan Engine Noise

Increasing air traffic and more stringent aircraft noise regulations continue to expand requirements on aircraft noise levels for conventional and unconventional aircraft configurations. A major component of the overall aircraft noise is the sound associated with the propulsion system mounted in the engine nacelle. Acoustic liners mounted in the aircraft engine nacelles provide a significant portion of the current fan noise reduction. However, they must be further optimized if challenging noise reduction goals are to be achieved. One location within the aft bypass duct that may be an excellent candidate for increased attention is the acoustic treatment on the engine bifurcations (i.e., engine pylon and lower bifurcation). This paper presents the continuation of a fundamental study of the effects of bifurcation treatment on simulated aft fan noise and the validation of numerical tools to predict such effects. Five bifurcation configurations (four treated and one hardwall) were fabricated and tested in the NASA Langley Curved Duct Test Rig. Results show that mode scattering may occur due to both the presence of the bifurcation, as well as variable impedance distributions on the bifurcation surface. Future work will also include optimization of bifurcation treatments for testing in the Curved Duct Test Rig. These initial results are promising and this work provides valuable information for further study and improvement of the performance of bifurcation acoustic treatments.

bifurcation effects↗
NASA NTRSDate not supplied

A Fundamental Study of Bifurcation Acoustic Treatment Effects on Aft-Fan Engine Noise

Increasing air traffic and more stringent aircraft noise regulations continue to expand requirements on aircraft noise levels for conventional and unconventional aircraft configurations. A major component of the overall aircraft noise is the sound associated with the propulsion system mounted in the engine nacelle. Acoustic liners mounted in the aircraft engine nacelles provide a significant portion of the current fan noise reduction. However, they must be further optimized if challenging noise reduction goals are to be achieved. One location within the aft bypass duct that may be an excellent candidate for increased attention is the acoustic treatment on the engine bifurcations (i.e., engine pylon and lower bifurcation). This paper presents the continuation of a fundamental study of the effects of bifurcation treatment on simulated aft fan noise and the validation of numerical tools to predict such effects. Five bifurcation configurations (four treated and one hardwall) were fabricated and tested in the NASA Langley Curved Duct Test Rig. Results show that mode scattering may occur due to both the presence of the bifurcation, as well as variable impedance distributions on the bifurcation surface. Future work will also include optimization of bifurcation treatments for testing in the Curved Duct Test Rig. These initial results are promising and this work provides valuable information for further study and improvement of the performance of bifurcation acoustic treatments.

bifurcation effects↗
NASA NTRSDate not supplied

The Two-Cavity Method for Characterizing Acoustical Materials—an Interlaboratory Study

This study focuses on understanding the sound absorption characteristics of porous acoustic materials, which are determined by two key parameters independent of material thickness: characteristic impedance and propagation constant. These parameters can be characterized by testing a porous sample concept in a normal incidence impedance tube using either the two-thickness or the two-cavity method. In the two-thickness method, two samples of varying thicknesses are required. In contrast, the two-cavity method requires testing one sample at two different air cavity depths behind the porous material. This method is particularly advantageous for materials that are costly or challenging to fabricate. This interlaboratory study evaluates the variability of characteristic properties determined using the two-cavity method. Porous acoustic materials were additively manufactured and tested in the Liner Technology Facility(LTF)at NASA Langley Research Center and the Mechanics, Acoustics and Dynamics Lab (MADLab) at Michigan Technological University. The characteristic properties derived from various cavity depth combinations were used to predict the surface impedance of the sample with a rigid backing. The prediction was then compared the measured impedance spectrum. It was also found that the combinations of cavity depths can significantly influence the accuracy of the deduced properties.

acoustic liners↗
DOE OSTI2015

Progress of the Enhanced Hanford Single Shell Tank (SST) Integrity Project

To improve the understanding of the single-shell tanks (SSTs) integrity, Washington River Protection Solutions, LLC (WRPS), the USDOE Hanford Site tank contractor, developed an enhanced Single-Shell Tank Integrity Project (SSTIP) in 2009. An expert panel on SST integrity, consisting of various subject matters experts in industry and academia, was created to provide recommendations supporting the development of the project. This panel developed 33 recommendations in four main areas of interest: structural integrity, liner degradation, leak integrity and prevention, and mitigation of contamination migration. In late 2010, seventeen of these recommendations were used to develop the basis for the M-45-10-1 Change Package for the Hanford Federal Agreement and Compliance Order, which is also known as the Tri-Party Agreement.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Evaluation of the concrete shield compositions from the 2010 criticality accident alarm system benchmark experiments at the CEA Valduc SILENE facility

In October 2010, a series of benchmark experiments were conducted at the French Commissariat a l'Energie Atomique et aux Energies Alternatives (CEA) Valduc SILENE facility. These experiments were a joint effort between the United States Department of Energy Nuclear Criticality Safety Program and the CEA. The purpose of these experiments was to create three benchmarks for the verification and validation of radiation transport codes and evaluated nuclear data used in the analysis of criticality accident alarm systems. This series of experiments consisted of three single-pulsed experiments with the SILENE reactor. For the first experiment, the reactor was bare (unshielded), whereas in the second and third experiments, it was shielded by lead and polyethylene, respectively. The polyethylene shield of the third experiment had a cadmium liner on its internal and external surfaces, which vertically was located near the fuel region of SILENE. During each experiment, several neutron activation foils and thermoluminescent dosimeters (TLDs) were placed around the reactor. Nearly half of the foils and TLDs had additional high-density magnetite concrete, high-density barite concrete, standard concrete, and/or BoroBond shields. CEA Saclay provided all the concrete, and the US Y-12 National Security Complex provided the BoroBond. Measurement data from the experiments were published at the 2011 International Conference on Nuclear Criticality (ICNC 2011) and the 2013 Nuclear Criticality Safety Division (NCSD 2013) topical meeting. Preliminary computational results for the first experiment were presented in the ICNC 2011 paper, which showed poor agreement between the computational results and the measured values of the foils shielded by concrete. Recently the hydrogen content, boron content, and density of these concrete shields were further investigated within the constraints of the previously available data. New computational results for the first experiment are now available that show much better agreement with the measured values.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Hanford double-shell tank ultrasonic test examinations - 15287

Washington River Protection Solutions, LLC (WRPS) under contact from the US DOE is responsible for assessing the condition of the double-shell tanks (DSTs) of the Hanford Nuclear Site. WRPS contracted AVERA Federal Services, LLC to perform the ultrasonic testing inspections of the primary tank wall in 28 DSTs to access the condition of the tanks, judge the effects of past corrosion control practices, and satisfy a regulatory requirement to periodically (eight to ten year frequency) assess the integrity of the tanks per Brookhaven National Laboratory (BNL) guidelines for structural integrity programs for tank systems. The major requirements for the Ultrasonic Testing (UT) of each tank are to detect, characterize (identify, size and locate), and record measurements made of any wall thinning, pitting or cracks that might be present in the wall of the primary tank. The UT program examines representative areas of the primary tank and secondary liner by deploying equipment in the annulus of the tank through two 24-inch diameter risers approximately 180 deg. apart. From 1996 to 2006 the first-round of ultrasonic test inspections for all DSTs were completed utilizing a Pulse-Echo (P-Scan) system. The second round of ultrasonic test inspections have continued since 2007 and are complete for 26 of 28 tanks. The two remaining tanks will receive the second inspections during fiscal year 2015. Currently, the ultrasonic testing comparison results between the first and second rounds of inspection have identified no structural integrity concerns at action levels specified in the BNL guidelines. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

A summary of the Hanford single-shell tank structural analysis of record - 15526

Washington River Protection Solutions, LLC (WRPS), the US DOE Hanford Site tank contractor, developed an enhanced Single-Shell Tank Integrity Project (SSTIP) in 2009 to better understand the integrity of the single-shell tanks (SSTs). A panel of experts from industry and academia was created to recommend project activities in four main areas: structural integrity, liner degradation, leak integrity and prevention, and contamination migration. One of the panel's primary recommendations was to perform a detailed structural integrity analysis of the SSTs. WRPS and the U.S. Department of Energy, Office of River Protection commissioned the Pacific Northwest National Laboratory (PNNL) to perform this structural integrity analysis of record for the Hanford single shell tanks. This is one of seventeen panel recommendations that form the M-45-10-1 Change Package for the Hanford Federal Agreement and Compliance Order; also known as the Tri-Party Agreement. Finite element analysis was used to predict the structural response of the SSTs to the historical thermal and operating loads, plus design basis seismic loads. Bounding thermal histories were established from waste temperature records and applied to the model to include the thermal degradation of concrete modulus and strength, plus cracking due to differential thermal expansion while under in situ static loading conditions. PNNL contracted with Becht Engineering to evaluate the dynamic response of the tanks to a design basis earthquake. The degraded stiffness of the reinforced concrete was also incorporated in the seismic analysis. The combined response to static and seismic loads was then evaluated against the design requirements of the American Concrete Institute standard, ACI-349-06, for nuclear safety-related concrete structures. Specific analyses were performed for the four major tank designs.This paper presents an overview of the analysis methods used and it summarizes the major analytical findings that are common to the tanks and others that are specific to the individual tank designs. The analyses of record determined that including the bounding effects of their operating histories, each tank design currently satisfies the ACI-349-06 structural integrity design requirements. Although leak tightness is not directly addressed in the structural integrity analysis, this analysis will be a key input in the formal tank integrity assessment due in 2018. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Hanford building 324 REC hot cell decommissioning approach - 15484

The 324 Building is a facility located at the Hanford Site and is undergoing decontamination and demolition (D and D) activities by Washington Closure Hanford (WCH). In October 1986, an in-cell leak of approximately 1.3 million curies occurred with a substantial fraction being lost into the subsurface soil beneath the floor of a large hot cell complex. Sampling under the hot cell floor revealed hot spots in the soil and cobble reading in excess of 10,000 R. In January of 2014, WCH contracted an AREVA lead team with Kurion as primary design agent to remove the B-Cell floor and highly contaminated underlying soils. The objective of this project is to remove the contaminated debris and soil and repackage them into the existing adjacent hot cells for final disposition as monoliths. The approach to this project uses an innovate combination of existing cell equipment, commercial equipment, and special tools to perform a series of completely remote operations. Also, a novel waste handling approach allows all the highly radioactive waste to remain within the existing cells. The remote handling approach to this project is to use customized off-the-shelf excavators which are mounted and operated remotely inside the cell. These can be moved and replaced remotely with a -Plug-and-Play- connection method. All the cables and utilities for the excavator and tools are managed through this cell connection with connections in a worker-accessible gallery space. The remote excavators are wall-mounted, which frees up the floor for the excavator work. The design also includes a transfer barrier which allows the B-Cell door to remain open during waste transfers while preventing spread of contamination between cells. The project balances the use of existing cell equipment such as cranes and shield doors, with the use of new remote equipment Existing equipment will be removed from the floor of the hot cell to adjacent cells. The concrete floor and stainless steel liner will then be remotely cut and removed, revealing the contaminated soil beneath the cell. The contaminated soil will be mixed with grout in the cell using the excavators and then placed in rigid bins. These bins will then be placed in the adjacent cells using existing overhead cranes. The waste containers allow optimal utilization of the limited adjacent hot cell space and improve the characteristics of the final waste monolith package. The system will use each bin once which significantly decreases the risk of contamination spread. The project includes a full-scale mockup facility in which all installation and operational activities will be tested and proven prior to hot cell construction activities. The mockup facility will also be used for operator training before actual hot work starts. This facility will remain available for use during operations with a full set of spares for redundancy and to support operations modeling during construction and remediation activities. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Fluor Idaho Technical Investigation-ARP V Lid Ejection Reactants and Mechanism - 19521

In April 2018, four 208.2-L (55-gal) drums containing transuranic waste at the Idaho National Laboratory Site became over-pressurized, resulting in lid ejection and expulsion approximately 50% of the contents. The parent drums were part of a retrieval effort and were exhumed from a portion of Subsurface Disposal Area Pits 11 and 12 beginning in 1974 and ending in 1978. Drums were later retrieved from the cargo containers, characterized using real-time radiography and nondestructive assay, and opened. The contents were visually inspected and repackaged into new 'daughter' drums within the Accelerated Retrieval Project V facility. Lid ejection occurred 7-12 hours after repackaging. The lid ejections were accompanied by significant heat generation. Empirical evidence of heat generation was observed in each reacted drum. The heat generated was sufficient to warp the high-density polyethylene liner (< 122 to 137 deg. C) in three of the drums and char the drum paint (∼400 deg. C) on one drum. To determine the potential reactant(s), a comprehensive chemical analysis was performed by two independent laboratories, Southwest Research Institute and Savannah River National Laboratory, on the reacted drum contents, ejected drum material, and related drums. A comprehensive chemical compatibility analysis was performed, and the most likely reactant(s) were identified. The oxidation of depleted uranium was the source of the heat generation. The presence of depleted uranium in the daughter drums and its chemical behavior (reactive properties and lack of visual indicators during packaging) are consistent with the event. The heat generated was sufficient to accelerate secondary chemical reactions leading to significant gas formation sufficient to generate pressures well in excess of the pressures needed to eject the lid and contents. These reactions fall into two categories: (1) simple volatilization of organics and water present in the drum and (2) hydrolysis of beryllium carbide, which generated significant quantities of methane gas. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Development of a Semi-autonomous Miniature Rover for Inspection of Double Shell Tank Floors - 19575

Leaks in the primary liner of double-shell tank (DST) 241-AY-102 at Hanford have prompted the need for the development of inspection tools that are able to access confined spaces around and underneath the tanks. Last year, Florida International University (FIU) has continued to improve inspection tools that were developed in the previous years, to ensure that the resultant tools are able to overcome the challenges posed by the DSTs. Experimental testing conducted last year at the full-scale sectional mock-up of the DST's refractory slots revealed some shortcomings of the miniature rover, particularly in traversing over weld seams of different heights. The weld seams are the results of welded steel plate-joints for the DST. It was advised by the site engineers that the weld seams height could range from 6.35 mm - 9.525 mm (1/4 to 3/8 inches), and with 12.7 mm (1/2 inches) width. As the rover traverses over a weld seam, the gap between the rover's magnets and tank surface increases, causing the adhesive force to drop. The rover loses its surface contact if this adhesive force drops below its weight, jeopardizing the inspection tasks. In this paper, we present the numerical studies to calculate the minimum magnetic force required for the miniature rover to traverse over weld seams with different heights and the corresponding modifications to the rover design. Initial bench scale tests were conducted using a steel bar with 5 welds of varying heights. The testing validated the results from the simulation studies and established the rover's capability in traversing weld seams. Another challenge for the miniature rover is the use of a joystick or keypad for manual control. Utilizing these controls will likely be difficult for the operators due to the tight channels underneath the tank. Having a semi-autonomous navigational capability would alleviate the complexity of the inspection tasks and allow the operator to focus on the channel inspection. The goal is to implement lane-keeping capability, akin to that of a driverless car, for the inspection tool, so that it will maintain its relative position with respect to the wall of the channels. Am image processing pipeline has been developed using both the Robot Operating System (ROS) and OpenCV to process the image stream coming from the onboard camera, for the purpose of lane identification. Additionally, a PID controller has been implemented to navigate the miniature rover along the central location of the detected lane, while allowing the operator to control the tool's forward and backward motion. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

An Overview of R and D on Retrievability and Retrieval Technology in Germany - 20462

Retrievability is a term that is included in most radioactive waste management programs around the world. Although national definitions vary, the overall understanding of retrievability concerns the ability to recover waste packages from the repository mine after their emplacement. Different countries may implement retrievability in very different ways, ranging from a built-in reversibility into the emplacement process to the stipulation that retrievability may in no way impede passive safety in the post-closure phase. Germany takes a middle course such that retrievability in a HLW repository (repository for high level radioactive waste) may have no significant detrimental effect on passive safety. In Germany, the current siting process considers rock salt, clay rock, and crystalline rock as potential host rocks. Therefore, Research and Development (R and D) has been investigating repository concepts and retrievability in all host rocks. After introduction of retrievability in 2010, existing repository concepts were modified to facilitate retrieval. The changes made comprised, for example, equipping boreholes with steel liners, developing new technologies, and modifying existing emplacement devices. Apart from retrieval of HLW, retrieval of other wastes from underground repositories that were designed and operated without retrievability in mind, poses major technical and scientific challenges. Currently, studies are under way to investigate the feasibility and costs of partial retrieval of waste from an underground repository for hazardous and highly toxic waste in France, Stocamine. With regard to retrieval, the rock-mechanical conditions are deteriorating rapidly, so time is of the essence. In the Asse II mine in Germany, about 126,500 waste casks with low and intermediate level waste await retrieval. The repository mine suffers from difficult rock-mechanical conditions and inflow of brine, locally into emplacement areas. The Federal Company for Radioactive Waste Disposal (BGE) is legally required to retrieve all wastes from the Asse. Due to the specific challenges, R and D is needed to develop technical solutions for the safe retrieval from each of the emplacement chambers. R and D on retrievability and retrieval technology does not only address challenges in radioactive or toxic waste retrieval but may also help to germinate innovation to better master complex underground situations in general, e.g. in deep mining, tunneling, or repository construction. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Characterizing friction in sliding isolation bearings

Summary The force–displacement behavior of the Friction Pendulum™ (FP) bearing is a function of the coefficient of sliding friction, axial load on the bearing and effective radius of the sliding surface. The coefficient of friction varies during the course of an earthquake with sliding velocity, axial pressure and temperature at the sliding surface. The velocity and axial pressure on the bearing depend on the response of the superstructure to the earthquake shaking. The temperature at an instant in time during earthquake shaking is a function of the histories of the coefficient of friction, sliding velocity and axial pressure, and the travel path of the slider on the sliding surface. A unified framework accommodating the complex interdependence of the coefficient of friction, sliding velocity, axial pressure and temperature is presented for implementation in nonlinear response‐history analysis. Expressions to define the relationship between the coefficient of friction and sliding velocity, axial pressure, and temperature are proposed, based on available experimental data. Response‐history analyses are performed on FP bearings with a range of geometrical and liner mechanical properties and static axial pressure. Friction is described using five different models that consider the dependence of the coefficient of friction on axial pressure, sliding velocity and temperature. Frictional heating is the most important factor that influences the maximum displacement of the isolation system and floor spectral demands if the static axial pressure is high. Isolation system displacements are not significantly affected by considerations of the influence of axial pressure and velocity on the coefficient of friction. Copyright © 2014 John Wiley & Sons, Ltd.

Kumar, Manish↗
DOE OSTI2015

Mitigation of wind tunnel wall interactions in subsonic cavity flows

In this study, the flow over an open aircraft bay is often represented in a wind tunnel with a cavity. In flight, this flow is unconfined, though in experiments, the cavity is surrounded by wind tunnel walls. If untreated, wind tunnel wall effects can lead to significant distortions of cavity acoustics in subsonic flows. To understand and mitigate these cavity–tunnel interactions, a parametric approach was taken for flow over an L/D = 7 cavity at Mach numbers 0.6–0.8. With solid tunnel walls, a dominant cavity tone was observed, likely due to an interaction with a tunnel duct mode. Furthermore, an acoustic liner opposite the cavity decreased the amplitude of the dominant mode and its harmonics, a result observed by previous researchers. Acoustic dampeners were also placed in the tunnel sidewalls, which further decreased the dominant mode amplitudes and peak amplitudes associated with nonlinear interactions between cavity modes. This then indicates that cavity resonance can be altered by tunnel sidewalls and that spanwise coupling should be addressed when conducting subsonic cavity experiments. Though mechanisms for dominant modes and nonlinear interactions likely exist in unconfined cavity flows, these effects can be amplified by the wind tunnel walls.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A numerical investigation on methane combustion and emissions from a natural gas-diesel dual fuel engine using CFD model

Natural gas (NG)-diesel dual fuel engines have been criticized for their high emissions of unburned methane. The past research on methane emissions from dual fuel engines has focused on the measurement of methane concentration in exhaust gases. The development of approaches capable of minimizing methane emissions requests the detailed spatial distribution of methane in-cylinder during the combustion and post combustion processes. However, it is difficult to experimentally measure the spatial distribution of methane in-cylinder. Here this research presents a numerical study on the combustion process of a NG-diesel dual fuel engine using the computational fluids dynamics (CFD) model CONVERGE coupled with a reduced primary reference fuel (PRF) mechanism. The model was validated against the heat release process and the emissions of nitrogen oxide, methane and carbon monoxide measured in a single cylinder dual fuel engine. The validated CFD model was applied to investigate the combustion of methane and n-heptane and the spatial distribution of methane in the dual fuel engine. This is most likely the first attempt to visualize the spatial distribution of methane in dual fuel engines using CFD. The objective of this study is to numerically simulate the methane combustion process, especially the methane present outside the pilot spray, quantify the methane combustion in each combustion stage, and visualize the spatial methane distribution in cylinder. The results showed that the momentum produced by the pilot fuel injection and combustion pushed the combustion products of pilot fuel and methane within the pilot spray plume toward the unburned methane-air mixture. Such a movement enhanced the mixing of the hot combustion products and the relatively cold unburned methane-air mixture during the main combustion process and dominated the combustion of methane presented outside the pilot fuel spray plume. Based on the simulation results at a low load condition (4.05 bar), the main combustion process consumed 43–53% of the methane fumigated into the intake mixture. The post-combustion oxidation process consumed 17–29% of the intake methane, which was 36.2–51.8% methane that survived the main combustion process. In comparison, 27–35% methane emitted the engine without participating the combustion process. The unburned methane at exhaust valve opening was mainly observed at the center of the cylinder. In comparison, the contribution of the crevice and boundary layer around the cylinder liner to methane emissions was relatively small. The slip of methane through the dual fuel engines was due to the fact that the premixed mixture was too lean to support the propagation of the turbulent flame initiated by the pilot fuel and the lack of pilot fuel vapor reaching the center of the combustion chamber because of the geometric limitations of the fuel injection system and the reduced mass of pilot fuel injected into the cylinder. The approaches aiming to enhance the combustion of methane and minimize methane emissions from dual fuel engines should focus on those capable of increasing the volume of pilot fuel vapor formed after injected into the cylinder.

42 ENGINEERING↗
DOE OSTI2014

Comparison of Cu, Ti and Ta interlayer explosively fabricated aluminum to stainless steel transition joints for cryogenic pressurized hydrogen storage

Fabrication of a bimetallic joint to facilitate a material transition from a 6061-T651 aluminum pressure vessel liner to stainless steel tubing in cryogenic pressure vessels is explored using three different dissimilar metal interlayers with an explosive welding (EXW) process. Due to difficulties in directly EXW joining aluminum (Al) 6061 to 304 stainless steel, interlayers are used to prevent interaction of the aluminum and stainless steel, thus minimizing brittle intermetallic phase formation. Titanium (Ti), copper (Cu), and tantalum (Ta) were selected as the dissimilar metal interlayer materials; each having advantages and disadvantages. Further, titanium is a commonly used interlayer for this joint, but can microcrack during EXW if the bonding parameters are not correct. Copper has the advantage that it is compatible with hydrogen, but is also known to form brittle intermetallics with aluminum. Tantalum is ductile and bonds well to both Al and stainless steel, and is a high temperature metal that does well to prevent interdiffusion and intermetallic phase formation. However Ta is the most expensive metal of the three. Results of the characterization of the three interlayer bonds showed that Ti produced the highest strength joints, Ta produced the most ductile joints, and Cu produced a joint that failed with low ductility at the Al/Cu interface. Based on these results, the Cu-interlayer joint is not recommended for this application, while the Ti and Ta interlayer bonds both appear to have sufficient strength and ductility for the intended use.

08 HYDROGEN↗