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At least 271 records · Page 15

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DOE OSTI2024

H - Ion Source RF Plasma Testing with 13 MHz and 27 MHz at the Spallation Neutron Source (SNS)

The baseline RF-driven H⁻ ion source configuration at the Spallation Neutron Source (SNS) facility uses a continuous wave (CW) 600 W 13 MHz RF system to ignite and maintain a low-density plasma inside the ion source vacuum chamber. After the continuous low-density 13 MHz plasma has been established, a pulsed (typical 1 ms pulse width and 60 Hz pulse repetition rate) 80 kW 2 MHz RF system is used to increase the plasma density to produce the pulsed H⁻ ion beam. Incremental upgrades and improvements to the SNS ion source systems have resulted in the ability to reliably operate an H⁻ ion source for SNS neutron production run cycles that can last up to four months. Conditions inside the SNS H⁻ ion source evolve throughout a four-month run cycle due to changes in impurity levels, sputtering, and erosion. As the internal ion source conditions change during the run cycle, there can also be changes in plasma stability and the 13 MHz RF power level required to ignite the plasma. This paper presents the preliminary results of testing performed on the SNS Ion Source Test Stand (ISTS) system where we looked at plasma ignition and plasma stability using 27 MHz RF in place of the baseline 13 MHz RF system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Multidimensional modeling of non-equilibrium plasma generated by a radio-frequency corona discharge

Low-temperature plasma (LTP) ignition concepts rely on the production of radical and charged species to speed up the onset of combustion in spark-ignition engines. These features are responsible for the superior performance of LTP igniters under extremely dilute combustion operation that is not achievable by conventional spark igniters. Additionally, LTP discharges extend the lifetime of the igniters, due to the avoidance of spark processes. For these reasons, the engine research community and the automotive industry have shown growing interest in this technology in the recent years. As of today, computational fluid-dynamics (CFD) codes typically used by the multi-dimensional engine modeling community do not have reliable models to describe LTP ignition processes. One key missing piece of information is the physical and chemical properties of the plasma and their effect on combustion ignition. Most non-equilibrium plasma simulations reported in literature are based on simplified, canonical geometries, with simple discharge excitation schemes. Here we conduct multi-dimensional modeling of the non-equilibrium plasma generated by an application-relevant radio-frequency (RF) corona discharge in air. Three test cases are simulated, characterized by different environmental pressure levels and peak electrode voltage values at room temperature. Streamer penetration, electron number density, atomic oxygen production, and bulk gas temperature distribution in the first 10 sinusoidal pulses are presented and discussed. This model can be used as a key tool for an in-depth understanding of RF-corona discharge for automotive applications and provides the basis for future implementations of dedicated LTP ignition models in CFD codes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1993

Development and testing of hermetic, laser-ignited pyrotechnic and explosive components

During the last decade there has been increasing interest in the use of lasers in place of electrical systems to ignite various pyrotechnic and explosive materials. The principal driving force for this work was the requirement for safer energetic components which would be insensitive to electrostatic and electromagnetic radiation. In the last few years this research has accelerated since the basic concepts have proven viable. At the present time it is appropriate to shift the research emphasis in laser initiation from the scientific arena--whether it can be done--to the engineering realm--how it can be put into actual practice in the field. Laser initiation research and development at EG&G Mound was in three principal areas: (1) laser/energetic material interactions; (2) development of novel processing techniques for fabricating hermetic (helium leak rate of less than 1 x 10(exp -8) cu cm/s) laser components; and (3) evaluation and testing of laser-ignited components. Research in these three areas has resulted in the development of high quality, hermetic, laser initiated components. Examples are presented which demonstrate the practicality of fabricating hermetic, laser initiated explosive or pyrotechnic components that can be used in the next generation of ignitors, actuators, and detonators.

Kramer, Daniel P.↗

DOE OSTI2019

The use of partial fuel stratification to enable stable ultra-lean deflagration-based Spark-Ignition engine operation with controlled end-gas autoignition of gasoline and E85

Lean operation of Spark-Ignition engines can provide higher thermal efficiency compared to standard stoichiometric operation. However, for a homogeneous lean mixture, the associated reduction of flame speeds becomes an important issue from the perspective of robust ignition and fast flame spread throughout the charge. This study is focused on the use of a lean partial fuel stratification strategy that can stabilize the deflagration, while sufficiently fast combustion is ensured via the use of end-gas autoignition. The engine has a spray-guided Direct-Injection Spark-Ignition combustion system and was fueled with either a high-octane certification gasoline or E85. Partial fuel stratification was achieved using several fuel injections during the intake stroke in combination with a small pilot-injection concurrent with the Spark-Ignition. The results reveal that partial fuel stratification enables very stable combustion, offering higher thermal efficiency for parts of the load range in comparison to well-mixed lean and stoichiometric combustion. The heat release and flame imaging demonstrate that the combustion often has three distinct stages. The combustion of the pilot-injected fuel, ignited by the normal spark, acts as a “super igniter,” ensuring a very repeatable initiation of combustion, and flame incandescence reveals locally rich conditions. The second stage is mainly composed of blue flame propagation in a well-mixed lean mixture. The third stage is the compression autoignition of a well-mixed and typically very lean end-gas. The end-gas autoignition is critical for achieving high combustion efficiency, high thermal efficiency, and stable combustion. Partial fuel stratification enables very effective combustion-phasing control, which is critical for controlling the occurrence and intensity of end-gas autoignition. Comparing the gasoline and E85 fuels, it is noted that achieving end-gas autoignition for the higher octane E85 requires a more aggressive compression of the end-gas via the use of a more advanced combustion phasing or higher intake-air temperature.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS1964

Pyrotechnics.

Pyrotechnic devices describing hot bridgewire, exploding bridgewire systems, mechanical and pressure actuated initiators and Gemini installations

IGNITION SYSTEM↗

NASA NTRS1978

Quick look test report: MPT static firing no. 2 test MPT-S2

The three engine cluster was fired at 70 percent power level for a nominal 15 seconds to evaluate the integrated performance of the main propulsion system. Engine ignition occurred at approximately 1403 with the planned mainstage duration achieved for all three engines. Operation of all systems was as expected with the exception of the recirculation pumps. The pumps were started while the propellant loading was in fast fill, but they cavitated and lost head at the termination of fast fill. The pumps were subsequently restarted after pressurizing the tank and draining back propellant to get good quality. Post test inspection of the engines revealed some discoloration on the inside of the thrust chamber and distorted drain lines for engine #2.

Source record↗

NASA NTRS2004

Tests of Flammability of Cotton Fabrics and Expected Skin Burns in Microgravity

During a shuttle launch and other portions of space flight, astronauts wear specialized flame resistant clothing. However during most of their missions on board the Space Shuttle or International Space Station, astronauts wear ordinary clothing, such as cotton shirts and pants. As the behaviour of flames is considerably different in microgravity than under earth's gravity, fabrics are expected to burn in a different fashion in microgravity than when tested on earth. There is interest in determining how this change in burning behaviour may affect times to second and third degree burn of human skin, and how the results of standard fabric flammability tests conducted under earth's gravity correlate with the expected fire behaviour of textiles in microgravity. A new experimental apparatus was developed to fit into the Spacecraft Fire Safety Facility (SFSF), which is used on NASA's KC-135 low gravity aircraft. The new apparatus was designed to be similar to the apparatus used in standard vertical flammability tests of fabrics. However, rather than using a laboratory burner, the apparatus uses a hot wire system to ignite 200 mm high by 80 mm wide fabric specimens. Fabric temperatures are measured using thermocouples and/or an infrared imaging system, while flame spread rates are measured using real time observations or video. Heat flux gauges are placed between 7 and 13 mm away from the fabric specimen, so that heat fluxes from the burning fabric to the skin can be estimated, along with predicted times required to produce skin burns. In November of 2003, this new apparatus was used on the KC-135 aircraft to test cotton and cotton/polyester blend fabric specimens in microgravity. These materials were also been tested using the same apparatus in 1-g, and using a standard vertical flammability test that utilizes a flame. In this presentation, the design of the test apparatus will be briefly described. Examples of results from the KC-135 tests will be provided, including heat fluxes and skin burn predictions. These results will be compared with results from 1-g tests using the same apparatus and a standard fabric flammability test apparatus. Recommendations for future microgravity fabric flammability tests will also be discussed.

Cavanagh, Jane M.↗

NASA NTRS2004

Tests of Flammability of Cotton Fabrics and Expected Skin Burns in Microgravity

Cavanagh, Jane M.↗

NASA NTRS2014

A Monte Carlo Analysis of the Thrust Imbalance for the Space Launch System Booster During Both the Ignition Transient and Steady State Operation

This paper presents the results of statistical analyses performed to predict the thrust imbalance between two solid rocket motor boosters to be used on the Space Launch System (SLS) vehicle. Two legacy internal ballistics codes developed for the Space Shuttle program were coupled with a Monte Carlo analysis code to determine a thrust imbalance envelope for the SLS vehicle based on the performance of 1000 motor pairs. Thirty three variables which could impact the performance of the motors during the ignition transient and thirty eight variables which could impact the performance of the motors during steady state operation of the motor were identified and treated as statistical variables for the analyses. The effects of motor to motor variation as well as variations between motors of a single pair were included in the analyses. The statistical variations of the variables were defined based on data provided by NASA's Marshall Space Flight Center for the upgraded five segment booster and from the Space Shuttle booster when appropriate. The results obtained for the statistical envelope are compared with the design specification thrust imbalance limits for the SLS launch vehicle.

Foster, Winfred A., Jr.↗

DOE OSTI2014

Using indium tin oxide material to implement the imaging of microwave plasma ignition process

In this paper, a method is introduced to get global observation of microwave plasma ignition process at high pressure. A microwave resonator was designed with an indium tin oxide coated glass at bottom. Microwave plasma ignition was implemented in methane and air mixture at 10 bars by a 2 ms-3 kW-2.45 GHz microwave pulse, and the high speed images of the ignition process were obtained. The images visually proved that microwave plasma ignition could lead to a multi-point ignition. The system may also be applied to obtain Schlieren images, which is commonly used to observe the development of flame kernel in an ignition process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2003

Measuring the Internal Environment of Solid Rocket Motors During Ignition

A new instrumentation system has been developed to measure the internal environment of solid rocket test motors during motor ignition. The system leverages conventional, analog gages with custom designed, electronics modules to provide safe, accurate, high speed data acquisition capability. To date, the instrumentation system has been demonstrated in a laboratory environment and on subscale static fire test motors ranging in size from 5-inches to 24-inches in diameter. Ultimately, this system is intended to be installed on a full-scale Reusable Solid Rocket Motor. This paper explains the need for the data, the components and capabilities of the system, and the test results.

Weisenberg, Brent↗

DOE OSTI2010

Target diagnostic control system implementation for the National Ignition Facility (invited)

The extreme physics of targets shocked by NIF's 192-beam laser is observed by a diverse suite of diagnostics. Many diagnostics are being developed by collaborators at other sites, but ad hoc controls could lead to unreliable and costly operations. A diagnostic control system (DCS) framework for both hardware and software facilitates development and eases integration. Each complex diagnostic typically uses an ensemble of electronic instruments attached to sensors, digitizers, cameras, and other devices. In the DCS architecture each instrument is interfaced to a low-cost WINDOWS XP processor and JAVA application. Each instrument is aggregated with others as needed in the supervisory system to form an integrated diagnostic. The JAVA framework provides data management, control services, and operator graphical user interface generation. DCS instruments are reusable by replication with reconfiguration for specific diagnostics in extensible markup language. Advantages include minimal application code, easy testing, and high reliability. Collaborators save costs by assembling diagnostics with existing DCS instruments. This talk discusses target diagnostic instrumentation used on NIF and presents the DCS architecture and framework.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1947

Investigation of the I-40 Jet-Propulsion Engine in the Cleveland Altitude Wind Tunnel. V - Operational Characteristics: Operational Characteristics - 5

An investigation has been conducted in the Cleveland altitude wind tunnel to determine the operational characteristics of the I-40 jet-propulsion engine over a range of pressure altitudes from 10,000 to 50,000 feet and ram-pressure ratios from 1.00 to 1.76. Engine operational data were obtained with the engine in the standard configuration and with various modifications of the fuel system, the electrical system, and the combustion chambers. The effects of altitude and airspeed on operating speed range, starting, windmilli.ng, acceleration, speed regulation, cooling, and vibration of the standard and modified engines were determined, and damage to parts was noted. Maximum engine speed was obtainable at all altitudes and airspeeds wi th each fuel-control system investigated. The minimum idling speed was raised by increases in altitude and airspeed. The lowest minimum stable speeds were obtained with the standard configuration using 40-gallon nozzles with individual metering plugs. The engine was started normally at altitudes as high as 20,000 feet with all of the fuel systems and ignition combinations except one. Ignition at 70,000 feet was difficult and, although successful ignition occurred, acceleration was slow and usually characterized by excessive tail-pipe temperature. During windmilling investigations of the engine equipped with the standard fuel system, the engine could not be started at ram-pressure ratios of 1.1 to 1.7 at altitudes of 10,000, 20,000 and 30,000 feet. When equipped with the production barometric and Monarch 40-gallon nozzles, the engine accelerated in 12 seconds from an engine speed of 6000 rpm to 11,000 rpm at 20,000 feet and an average tail-pipe temperature of 11000 F. At the same altitude and temperature, all the engine configurations had approximately the same rate of acceleration. The Woodward governor produced the safest accelerations, inasmuch as it could be adjusted to automatically prevent acceleration blow out. The engine speed was held constant by the Woodward governor and the Edwards regulator during simulated dives and climbs at constant throttle position. The bearing cooling system was satisfactory at all altitudes and airspeeds. The engines operated without serious failure, although the exhaust cone, the tail pipe, and the airplane fuselage were damaged during altitude starts.

Golladay, Richard L.↗

DOE OSTI2014

Neutron source reconstruction from pinhole imaging at National Ignition Facility

The neutron imaging system at the National Ignition Facility (NIF) is an important diagnostic tool for measuring the two-dimensional size and shape of the neutrons produced in the burning deuterium-tritium plasma during the ignition stage of inertial confinement fusion (ICF) implosions at NIF. Since the neutron source is small (∼100 μm) and neutrons are deeply penetrating (>3 cm) in all materials, the apertures used to achieve the desired 10-μm resolution are 20-cm long, single-sided tapers in gold. These apertures, which have triangular cross sections, produce distortions in the image, and the extended nature of the pinhole results in a non-stationary or spatially varying point spread function across the pinhole field of view. In this work, we have used iterative Maximum Likelihood techniques to remove the non-stationary distortions introduced by the aperture to reconstruct the underlying neutron source distributions. We present the detailed algorithms used for these reconstructions, the stopping criteria used and reconstructed sources from data collected at NIF with a discussion of the neutron imaging performance in light of other diagnostics.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2022

Exceptional Points in Novel Multiscale Quantum-Nanoplasmonic Materials for Enhanced Sensing and Other Applications

Lossy quantum systems can display fascinating behaviors around singularities known as exceptional points in their complex eigenvalue spaces. Interest in these systems was ignited over two decades ago when Carl Bender and Stefan Boettcher—a LANL Director’s Postdoctoral Fellow at the time—pointed out that many features of conventional lossless quantum systems, such as real operator eigenvalues, could be recovered in lossy systems exhibiting parity- and time-reversal (ΡΤ) symmetry.

36 MATERIALS SCIENCE↗

NASA NTRS2000

Model of ASTM Flammability Test in Microgravity: Iron Rods

There is extensive qualitative results from burning metallic materials in a NASA/ASTM flammability test system in normal gravity. However, this data was shown to be inconclusive for applications involving oxygen-enriched atmospheres under microgravity conditions by conducting tests using the 2.2-second Lewis Research Center (LeRC) Drop Tower. Data from neither type of test has been reduced to fundamental kinetic and dynamic systems parameters. This paper reports the initial model analysis for burning iron rods under microgravity conditions using data obtained at the LERC tower and modeling the burning system after ignition. Under the conditions of the test the burning mass regresses up the rod to be detached upon deceleration at the end of the drop. The model describes the burning system as a semi-batch, well-mixed reactor with product accumulation only. This model is consistent with the 2.0-second duration of the test. Transient temperature and pressure measurements are made on the chamber volume. The rod solid-liquid interface melting rate is obtained from film records. The model consists of a set of 17 non-linear, first-order differential equations which are solved using MATLAB. This analysis confirms that a first-order rate, in oxygen concentration, is consistent for the iron-oxygen kinetic reaction. An apparent activation energy of 246.8 kJ/mol is consistent for this model.

Steinberg, Theodore A↗

NASA NTRS2004

EPS (Electric Particulate Suspension) Microgravity Technology Provides NASA with New Tools

The Electric Particulate Suspension is a fire safety ignition test system being developed at Iowa State University with NASA support for evaluating combustion properties of powders, powder-gas mixtures, and pure gases in microgravity and gravitational atmospheres (quenching distance, ignition energy, flammability limits). A separate application is the use of EPS technology to control heat transfer in vacuum and space environment enclosures. In combustion testing, ignitable powders (aluminum, magnesium) are introduced in the EPS test cell and ignited by spark, while the addition of inert particles act as quenching media. As a combustion research tool, the EPS method has potential as a benchmark design for quenching powder flames that would provide NASA with a new fire safety standard for powder ignition testing. The EPS method also supports combustion modeling by providing accurate measurement of flame-quenching distance as an important parameter in laminar flame theory since it is closely related to characteristic flame thickness and flame structure. In heat transfer applications, inert powder suspensions (copper, steel) driven by electric fields regulate heat flow between adjacent surfaces enclosures both in vacuum (or gas) and microgravity. This simple E-field control can be particularly useful in space environments where physical separation is a requirement between heat exchange surfaces.

Colver, Gerald M.↗

DOE OSTI2022

Computational Fluid Dynamics Modeling of Low Temperature Ignition Processes From a Nanosecond Pulsed Discharge at Quiescent Conditions

Recent interest in nonequilibrium plasma discharges as sources of ignition for the automotive industry has not yet been accompanied by the availability of dedicated models to perform this task in computational fluid dynamics (CFD) engine simulations. The need for a low-temperature plasma (LTP) ignition model has motivated much work in simulating these discharges from first principles. Most ignition models assume that an equilibrium plasma comprises the bulk of discharge kernels. LTP discharges, however, exhibit highly nonequilibrium behavior. In this work, a method to determine a consistent initialization of LTP discharge kernels for use in engine CFD codes like CONVERGE is proposed. The method utilizes first principles discharge simulations. Such an LTP kernel is introduced in a flammable mixture of air and fuel, and the subsequent plasma expansion and ignition simulation is carried out using a reacting flow solver with detailed chemistry. Finally, the proposed numerical approach is shown to produce results that agree with experimental observations regarding the ignitability of methane-air and ethylene-air mixtures by LTP discharges.

33 ADVANCED PROPULSION SYSTEMS↗