Hypobaric Chamber Assessment (HCA) Kick Off Meeting
The purpose of this kick-off meeting is to provide an overview of the project and establish working structure/expectations for the Hypobaric Chamber Assessment (HCA) project.
Monica Hew↗
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Data Validation for Hosting Capacity Analyses
The usefulness of Hosting Capacity Analysis (HCA) is dependent on users' confidence that the results accurately reflect grid conditions. This report provides the findings and recommendations from research, conducted by The National Renewable Energy Lab (NREL) and The Interstate Renewable Energy Council (IREC), into HCA data validation best practices. The goal is to provide utilities, regulators, and stakeholders best practices for HCA data validation procedures so that future HCA deployments avoid uncertainties and potential mistakes from earlier rollouts and provide useful and accurate data from the day they are published. Utilities can use this report to develop or refine their HCA data validation procedures. Regulators can use the report to inform their oversight of utilities' HCA data validation practices, while stakeholders can use it to evaluate the effectiveness of utility efforts.
14 SOLAR ENERGY↗
Impact of gasoline composition on the effects of nitric oxide on autoignition and knock in a DISI engine
Modern spark-ignition engines use exhaust gas recirculation (EGR) to dilute the charge and suppress knock, enabling the use of higher compression ratios and/or more optimum combustion phasing for higher efficiency. The effectiveness of EGR is affected by the composition of the fuel and its chemical-kinetic interactions with combustion products. Among those, nitric oxide (NO) has been shown to strongly affect autoignition reactivity. However, the impact of fuel composition of the effect of NO on reactivity is not well-understood. Here, in this study, engine experiments were conducted to assess the impact of NO seeded to the intake on knock-limited operation of two gasoline fuels (high cycloalkane content, or HCA, and high olefin content, or HO). Results showed that compositionally-different fuels responded differently to NO. HCA, which was less knock-limited than HO for NO < 200 ppm, became more knock-limited for NO > 200 ppm. Moreover, it was found that differences in knock between fuels were caused by differences in autoignition chemistry and not in the sequential autoignition process of the end gas that occurs due to thermal stratification. Chemical kinetic simulations were performed to better understand the experimental results. For HCA, intermediate-temperature heat release had a greater impact on autoignition reactivity than low-temperature heat release, while the opposite was observed for HO. For both fuels, NO enhances the magnitude of low-temperature heat release via NO + HO 2 → NO 2 + OH. The effect of NO on reactivity was stronger for HCA because OH produced from NO helped to overcome the OH quenching effect of cyclopentane, a main species in HCA. In contrast, HO had relatively strong inherent low-temperature chemistry arising from iso-octane, which reduced the impact of NO on reactivity. For the range of NO mole fractions tested in this study, in-cylinder NO increased fuel’s knock propensity, especially for fuels with mild low-temperature chemistry.
Autoignition↗
Effects of Gasoline Composition and Operating Parameters on the Response of End-Gas Autoignition to Nitric Oxide in a Lean-Burn DI-SI Engine
Lean operation of spark-ignition engines can lead to engine thermal efficiency gains and lower NOx emissions due to reduced combustion temperatures. Yet, lean operation could still face challenges in end-gas autoignition and knock generation due to higher intake pressures and trapped NO in the residual gas. Here, this study evaluates the impact of NO on end-gas autoignition for two gasoline fuels with similar octane rating but different composition: high cycloalkane fuel (HCA) and high olefin fuel (HO). Experiments were performed at stoichiometric and lean (λ = 2) conditions and at two engine speeds of 1400 rpm and 2000 rpm. Accompanying chemical kinetics simulations in CHEMKIN revealed that the mechanisms controlling the effect of NO on autoignition are similar λ = 2 and λ = 1, with NO + HO 2 = NO 2 + OH being the main pathway for enhancing reactivity by promoting low-temperature heat release (LTHR). The compositionally different fuels reacted differently to NO seeding and engine speed, and differences were augmented at λ = 2 compared to λ = 1 as the end-gas autoignition shifted to the low temperature regime. HO, which has inherent low temperature chemistry, was strongly impacted by engine speed at low NO seeding levels, with no noticeable peak of LTHR detected at 2000 rpm. On the other hand, LTHR of HCA was marginally affected by shortened residence time at higher engine speed as NO + HO 2 reaction was not greatly affected by shorter time scales, since HO 2 production was sustained even at 2000 rpm to support OH generation from NO + HO 2 . Contrary to HO, HCA exhibited greater sensitivity to NO seeding, as the increased OH production at higher NO concentrations offset the OH-quenching effect of cyclopentane, which accounts for 28.6% of HCA’s composition. Consequently, a sensitivity analysis revealed that fuels with weak inherent low-temperature chemistry, like HCA, are likely to be more sensitive to variations in NO concentration and charge temperature, whereas fuels with strong low temperature chemistry are more sensitive to variations in end-gas λ and intake pressure.
Energy↗
Cathodes Delivered for Space Station Plasma Contactor System
The International Space Station's (ISS) power system is designed with high-voltage solar arrays that typically operate at output voltages of 140 to 160 volts (V). The ISS grounding scheme electrically ties the habitat modules, structure, and radiators to the negative tap of the solar arrays. Without some active charge control method, this electrical configuration and the plasma current balance would cause the habitat modules, structure, and radiators to float to voltages as large as -120 V with respect to the ambient space plasma. With such large negative floating potentials, the ISS could have deleterious interactions with the space plasma. These interactions could include arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. A plasma contactor system was baselined on the ISS to prevent arcing and sputtering. The sole requirement for the system is contained within a single directive (SSP 30000, paragraph 3.1.3.2.1.8): "The Space Station structure floating potential at all points on the Space Station shall be controlled to within 40 V of the ionospheric plasma potential using a plasma contactor." NASA is developing this plasma contactor as part of the ISS electrical power system. For ISS, efficient and rapid emission of high electron currents is required from the plasma contactor system under conditions of variable and uncertain current demand. A hollow cathode plasma source is well suited for this application and was, therefore, selected as the design approach for the station plasma contactor system. In addition to the plasma source, which is referred to as a hollow cathode assembly, or HCA, the plasma contactor system includes two other subsystems. These are the power electronics unit and the xenon gas feed system. The Rocketdyne Division of Boeing North American is responsible for the design, fabrication, assembly, test, and integration of the plasma contactor system. Because of technical and schedule considerations, the NASA Lewis Research Center was asked to manufacture and deliver the engineering model, the qualification model, and the flight HCA units for the plasma contactor system as government furnished equipment. To date, multiple units have been built. One cathode has demonstrated approximately 28 000-hr lifetime, two development HCA units have demonstrated over 15 000-hr lifetime, and one HCA unit has demonstrated more than 38 000 ignitions. All eight flight HCA's have been manufactured, acceptance tested, and are ready for delivery to the flight contractor.
Patterson, Michael J.↗
Data Validation for Hosting Capacity Analyses: Executive Summary
The usefulness of Hosting Capacity Analysis (HCA) is dependent on users' confidence that the results accurately reflect grid conditions. This report provides the findings and recommendations from research, conducted by The National Renewable Energy Lab (NREL) and The Interstate Renewable Energy Council (IREC), into HCA data validation best practices. The goal is to provide utilities, regulators, and stakeholders best practices for HCA data validation procedures so that future HCA deployments avoid uncertainties and potential mistakes from earlier rollouts and provide useful and accurate data from the day they are published.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Fast Iterative Multi-site Hosting Capacity Analysis for Distribution Systems With Search Space Pruning
Interconnection studies for distributed energy resources (DERs) is a time-intensive process, primarily due to the necessity of solving large number of power flow scenarios. Hosting capacity analysis (HCA) is a time-consuming aspect of interconnection studies that is divided into single-site HCA (SHCA) and multi-site HCA (MHCA). From a computational and understandable standpoint, the industry seeks iteration-based solutions for SHCA, although it doesn't maximize the total DER hosting capacity (DERHC) of the grid, as MHCA does. While non-iterative solutions are available for MHCA, they involve a trade-off between the modeling accuracy of the distribution system, solution quality, and ease of understanding. In this work, we present a fast iterative solution for MHCA, reducing computational complexity by eliminating the need to solve power flows for a large amount of search space, thus making iterative solutions feasible. This iterative approach guarantees both a global optimal solution with sufficient time and a fast, close-to-optimal solution through efficient search space pruning. It also easily integrates with existing utility HCA tools. The results are demonstrated on select locations in the IEEE-123 bus system for community-scale interconnection studies. We highlight the benefits of skipping the need to solve millions of power flows, all while maximizing the grid's total DERHC.
Guddanti, Kishan Prudhvi↗
Space Station Cathode Ignition Test Status at 32,000 Cycles
A plasma contactor system has been baselined for the International Space Station for structural potential control. An ignition procedure was developed for the plasma contactor hollow cathode assembly (HCA). To demonstrate the required 99% HCA ignition reliability over 6,000 cycles, an ignition test was conducted. An accelerated test procedure was employed to rapidly accumulate ignition cycles. The test procedure minimized the differences between accelerated and non-accelerated test results. The development HCA used in this test has achieved 32,000 ignitions to date. The HCA has been qualified for cyclic operation, which could reduce xenon consumption and extend the life of the plasma contactor system.
Zakany, James S.↗
H-Canyon Jumper Gasket Sealing Evaluation
H-Canyon Documented Safety Analysis approved December 2019 credits the leak integrity of H-Canyon (HCA) process tanks, piping, and jumpers in preventing the release of radioactive material in a post seismic environment. Demonstration of leak tightness capability for this equipment was achieved through substantial analytical effort. However, one potential weak point that affects leak integrity exists at the gasketed joint between Hanford Connectors (HC) and nozzles. Review of the HCA Crane Log over a three-year period indicates the HCs periodically leak. Savannah River National Laboratory (SRNL) was requested to perform gasket compression tests that evaluate gasket relaxation characteristics, i.e., creep, and provide improvements to the HC installation process that can reduce or eliminate the frequency of leaks at HCs. A HC torque value of 312 ft-lbf is the target value used because it is the minimum torque value, with 95% confidence, when an unlubricated HC is impacted for standard sealing period of 9 seconds. In the HCA pipe-jumper connections are installed remotely by using HCs. HCs inherently add to the uncertainty of a gasketed joint because a calibrated torque value cannot be applied. The gasket material is a special material made of asbestos-fiber impregnated with Teflon. This material has been used for decades and generally performs well but does leak intermittently as gaskets creep and preloaded torque is lost. Gasket types are either snap-ring (SR) or lampshade (LS). Both gasket types cover the same seating area. The SR gasket is designed to remain with the jumper when the jumper is removed leaving the nozzle faces clean of any debris. SR gaskets are initially installed when the jumper is fabricated. Changing gaskets is time consuming and the radioactive environment presents risks to personnel. When jumpers are removed LS gaskets could be used to better seal the connection to reduce down time and ALARA concerns. That is, an LS gasket would be remotely positioned over the nozzle and the HC reinstalled. Testing also included two situations not typical of plant operation. One situation was the use of the non-standard double-layered gaskets (DG), and the other situation was the use of a LS without removal of the installed SR gasket. The DG was used when the supply of LS gaskets ended, so that testing could continue. It was of interest to demonstrate this gasket’s creep response because the DG, which was two gaskets glued together, was thicker than the LS gasket and the thicker material was expected to elicit a greater creep characteristics. The second situation of using two gaskets together by installing an LS gasket without removing the installed gasket is not allowed by the ASME Codes. However, by demonstrating the creep history of such a gasket arrangement it could be considered as an option that could possibly seal a connection while significantly reducing operational down time and personnel risk. Forty tests were conducted, and the overall results demonstrate the initial applied force and how the gasket changes with time. The change in sealing force, in terms of torque, was then measured to obtain a force history as the gaskets creep. This report documents the results of those tests as well as the method used to perform the tests.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Thermal analysis of radiometer containers for the 122m hoop column antenna concept
A thermal analysis was conducted for the 122 Meter Hoop Column Antenna (HCA) Radiometer electronic package containers. The HCA radiometer containers were modeled using the computer aided graphics program, ANVIL 4000, and thermally simulated using two thermal programs, TRASYS and MITAS. The results of the analysis provided relationships between the absorptance-emittance ratio and the average surface temperature of the orbiting radiometer containers. These relationships can be used to specify the surface properties, absorptance and reflectance, of the radiometer containers. This is an initial effort in determining the passive thermal protection needs for the 122 m HCA radiometer containers. Several recommendations are provided which expand this effort so specific passive and active thermal protection systems can be defined and designed.
Dillon-Townes, L. A.↗
28,000 Hour Xenon Hollow Cathode LifeTest Results
The International Space Station Plasma Contactor System requires a hollow cathode assembly (HCA) with a lifetime of at least 18,000 hours. Critical components of the HCA include the hollow cathode and electron emitter. A series of hollow cathode wear tests was performed which included a life test operated at the maximum current of the HCA. This test sought to verify the hollow cathode design and contamination control protocols. The life test accumulated 27,800 hours of operation before failing to ignite. The hollow cathode exhibited relatively small changes in operating parameters over the course of the test. This life test is the longest duration test of a high current xenon hollow cathode reported to date.
Sarver-Verhey, Timothy R.↗
Space Station Cathode Design, Performance, and Operating Specifications
A plasma contactor system was baselined for the International Space Station (ISS) to eliminate/mitigate damaging interactions with the space environment. The system represents a dual-use technology which is a direct outgrowth of the NASA electric propulsion program and, in particular, the technology development efforts on ion thruster systems. The plasma contactor includes a hollow cathode assembly (HCA), a power electronics unit, and a xenon gas feed system. Under a pre-flight development program, these subsystems were taken to the level of maturity appropriate for transfer to U.S. industry for final development. NASA's Lewis Research Center was subsequently requested by ISS to manufacture and deliver the engineering model, qualification model, and flight HCA units. To date, multiple units have been built. One cathode has demonstrated approximately 28,000 hours lifetime, two development unit HCAs have demonstrated over 10,000 hours lifetime, and one development unit HCA has demonstrated more than 32,000 ignitions. All 8 flight HCAs have been manufactured, acceptance tested, and are ready for delivery to the flight contractor. This paper discusses the requirements, mechanical design, performance, operating specifications, and schedule for the plasma contactor flight HCAs.
Patterson, Michael J.↗
Destructive Evaluation of a Xenon Hollow Cathode after a 28,000 Hour Life Test
International Space Station (ISS) plasma contactor system requires a hollow cathode assembly (HCA) with a lifetime of at least 18,000 hours. In order to demonstrate the lifetime capability of the HCA, a series of hollow cathode wear tests was performed which included a life test operated at the maximum current of the HCA. This test sought to verify hollow cathode lifetime capability and contamination control protocols. This hollow cathode accumulated 27,800 hours of operation before it failed during a restart attempt. The cathode was subsequently destructively analyzed in order to determine the failure mechanism. Microscopic examination of the cathode interior determined that relatively small changes in the cathode physical geometry had occurred and barium tungstates, which are known to limit the emission process, had formed over a majority of the electron emitter surface. Because the final state of the insert was consistent with expected impregnate chemistry, the hollow cathode was believed to have reached the end of its usable life under the test conditions.
Sarver-Verhey, Timothy R.↗
Process for Ignition of Gaseous Electrical Discharge Between Electrodes of a Hollow Cathode Assembly
The design and manufacturing processes for Hollow Cathode Assemblies (HCA's) that operate over a broad range of emission currents up to 30 Amperes, at low potentials, with lifetimes in excess of 17,500 hours. The processes include contamination control procedures which cover hollow cathode component cleaning procedures, gas feed system designs and specifications, and hollow cathode activation and operating procedures to thereby produce cathode assemblies that have demonstrated stable and repeatable operating conditions, for both the discharge current and voltage. The HCA of this invention provides lifetimes of greater than 10,000 hours, and expected lifetimes of greater than 17,500 hours, whereas the present state-of-the-art is less than 500 hours at emission currents in excess of 1 Ampere. Stable operation is provided over a large range of operating emission currents, up to a 6:1 ratio, and this HCA can emit electron currents of up to 30 Amperes in magnitude to an external anode that simulates the current drawn to a space plasma, at voltages of less than 20 Volts.
Patterson, Michael J.↗
A Review of Testing of Hollow Cathodes for the International Space Station Plasma Contactor
Since October 2000, two plasma contactors have been providing charge control on the International Space Station (ISS). At the heart of each of the two plasma contactors is a hollow cathode assembly (HCA) that produces the contacting xenon plasma. The HCA is the result of 9 years of design and testing at the NASA Glenn Research Center. This paper summarizes HCA testing that has been performed to date. As of this time, one cathode has demonstrated approximately 28,000 hr of lifetime during constant, high current use. Another cathode, HCA.014. has demonstrated 42,000 ignitions before cathode heater failure. In addition to these cathodes, four cathodes. HCA.006, HCA.003, HCA.010, and HCA.013 have undergone cyclic testing to simulate the variable current demand expected on the ISS. HCA.006 accumulated 8,000 hr of life test operation prior to being voluntarily stopped for analysis before the flight units were fabricated. HCA.010 has accumulated 15,876 hr of life testing, and 4,424 ignitions during ignition testing. HCA.003 and HCA.0 13 have accumulated 12,415 and 18,823 hr of life testing respectively.
Kovaleski, S. D.↗
Design and Manufacturing Processes of Long-Life Hollow Cathode Assemblies
The design and manufacturing processes for Hollow Cathode Assemblies (HCA's) that operate over a broad range of emission currents up to 30 Amperes, at low potentials, with lifetimes in excess of 17,500 hours. The processes include contamination control procedures which cover hollow cathode component cleaning procedures, gas feed system designs and specifications, and hollow cathode activation and operating procedures to thereby produce cathode assemblies that have demonstrated stable and repeatable operating conditions, for both the discharge current and voltage. The HCA of this invention provides lifetimes of greater than 10,000 hours, and expected lifetimes of greater than 17,500 hours, whereas the present state-of-the-art is less than 500 hours at emission currents in excess of 1 Ampere. Stable operation is provided over a large range of operating emission currents, up to a 6:1 ratio, and this HCA can emit electron currents of up to 30 Amperes in magnitude to an external anode that simulates the current drawn to a space plasma at voltages of less than 20 Volts.
Michael J Patterson↗
Comparison of On-Orbit and Ground Based Hollow Cathode Operation
The Plasma Contactor Unit (PCU) was developed by the Rocketdyne division of Boeing to control charging of the International Space Station (ISS). Each PCU contains a Hollow Cathode Assembly (HCA), which emits the charge control electrons. The HCAs were designed and fabricated at NASA's Glenn Research Center (GRC). GRC's HCA development program included manufacture of engineering, qualification, and flight model HCAs as well as wear tests and qualification tests. GRC is currently tracking the on-orbit data for the flight HCAs. This data will be discussed with comparison to operating parameters verified by ground based HCA tests. The flight HCAs continue to operate flawlessly. The first unit has accumulated more than 3650 hours of on-orbit operation and the second unit has accumulated over 5550 hours.
Burke, Tom↗
Design and Manufacturing Processes of Long-Life Hollow Cathode Assembles
A process for testing an impregnated insert of a Hollow Cathode Assembly (HCA) subsequent to every exposure of the HCA to air, and prior to ignition, using a heater and an oil-free assembly having a base pressure of less than 5.0 x 10(exp -6) torr. The process comprises the steps of: installing the HCA in a vacuum; energizing the heater to a particular current level; de-energizing the heater after one-half hour; again energizing the heater to a particular current level; and de-energizing the heater for at least one-half hour.
Michael J Patterson↗