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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Hydrodynamic growth and decay of planar shock waves

A model for the hydrodynamic attenuation (growth and decay) of planar shocks is presented. The model is based on the approximate integration of the fluid conservation equations, and it does not require the heuristic assumptions used in some previous works. A key issue of the model is that the boundary condition on the piston surface is given by the retarded pressure, which takes into account the transit time of the sound waves between the piston and any position at the bulk of the shocked fluid. The model yields the shock pressure evolution for any given pressure pulse on the piston, as well as the evolution of the trajectories, velocities, and accelerations on the shock and piston surfaces. An asymptotic analytical solution is also found for the decay of the shock wave.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Tailored Materials for High Efficiency CIDI Engines

The overall goal of the project, Tailored Materials for High Efficiency Compression Ignition Direct Injection (CIDI) Engines, is to enable the implementation of new combustion strategies, such as homogeneous charge compression ignition (HCCI), that have the potential to significantly increase the energy efficiency of current diesel engines and decrease fuel consumption and environmental emissions. These strategies, however, are increasing the demands on conventional engine materials, either from increases in peak cylinder pressure (PCP) or from increases in the temperature of operation. The specific objective of this project is to investigate the application of a new material processing technology, friction stir processing (FSP), to improve the thermal and mechanical properties of engine components. The concept is to modify the surfaces of conventional, low-cost engine materials. The project focused primarily on FSP in aluminum materials that are compositional analogs to the typical piston and head alloys seen in small- to mid-sized CIDI engines. Investigations have been primarily of two types over the duration of this project: (1) FSP of a cast hypoeutectic Al-Si-Mg (A356/357) alloy with no introduction of any new components, and (2) FSP of Al-Cu-Ni alloys (Alloy 339) by physically stirring-in various quantities of carbon nanotubes/nanofibers or carbon fibers. Experimental work to date on aluminum systems has shown significant increases in fatigue lifetime and stress-level performance in aluminum-silicon alloys using friction processing alone, but work to demonstrate the addition of carbon nanotubes and fibers into aluminum substrates has shown mixed results due primarily to the difficulty in achieving porosity-free, homogeneous distributions of the particulate. A limited effort to understand the effects of FSP on steel materials was also undertaken during the course of this project. Processed regions were created in high-strength, low-alloyed steels up to 0.5 in. deep that showed significant grain refinement and homogeneous microstructures favorable to increased fracture toughness and fatigue performance. The final tasks of the project demonstrated that the FSP concept can be applied to a relevant part geometry by fabricating diesel piston crowns with FSP regions applied selectively to the edge of the bowl rim. This area of the piston typically suffers from conditions at high PCP that cause severe thermal fatigue issues. It is expected that, given the data from coupon testing, the durability of pistons modified by FSP will allow much higher fatigue lifetime and potentially also greater resistance to elevated stress-level effects on fatigue.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRSDate not supplied

A Study on Effect of Tuning Capacitor in Dynamic Radioisotope Power Systems

This study presents the effect of the tuning capacitor on stability and electrical power output of a gas-bearing based free-piston Stirling convertor (FPSC) when operating on a fixed-frequency type controller. It has been widely accepted that the tuning capacitor is an important circuit component of the FPSC to stabilize piston amplitude and maximize electrical power output by correcting the power factor. Models suggest the stability of the FPSC is strongly coupled to the tuning capacitance, while the coupling to the electrical power output is weak. This applies to cases where the operating frequency of the FPSC is fixed by a fixed-frequency controller and other operating conditions, such as the hot-end and cold-end temperatures, piston amplitude, and pressure are constant. To verify the modeling analysis results, an Advanced Stirling Convertor (ASC) was controlled by an AC power supply and the piston amplitude, hot-end temperature, cold-end temperature, and pressure are actively controlled to 4.3mm, 760˚C, 40˚C and 485psig, respectively, while the tuning capacitor value was changed from 840μF to 1040μF and 1240μF. Furthermore, the vibration test results of the ASC with different tuning capacitor values are also presented to show the effect of the tuning capacitor on stability. The experimental test results verified that the effect of tuning capacitor on electrical power output is negligible while the effect on stability is rather noticeable. Therefore, the ideal tuning capacitor value should be selected based on required stability of the FPSC.

Free-Piston Stirling Convertor Controller↗
NASA NTRSDate not supplied

A Study on Effect of Tuning Capacitor in Dynamic Radioisotope Power Systems

This study presents the effect of the tuning capacitor on the stability and electrical power output of a gas spring-based free-piston Stirling convertor (FPSC) when the FPSC runs on a forced-oscillation type controller. It has been widely accepted that the tuning capacitor is an important circuit component of the FPSC to stabilize piston amplitude and maximize electrical power output by correcting the power factor. Recent modeling analysis, however, suggests that while the effect on the stability is significant, the effect on the electrical power output is almost negligible as long as the operating frequency the FPSC is fixed by a forced-oscillation controller and operating conditions, such as the hot-end/cold-end temperatures, piston amplitude, and pressure, are unchanged. To verify the modeling analysis results, Advanced Stirling Convertor (ASC) is controlled by an AC power supply and the piston amplitude, hot-end temperature, cold-end temperature, and pressure are actively controlled to 4.3mm, 760˚C, 40˚C and 485psig, respectively, while the tuning capacitor value is changed from 840μF to 1040μF and 1240μF. Furthermore, the vibration test results of the ASC with the three tuning capacitor values are also presented to show the effect of the tuning capacitor on stability. The test results suggest that when the FPSC operates at a fixed frequency, the effect of tuning capacitor on electrical power output is negligible while the effect on stability is rather significant. Therefore, the tuning capacitor value should be selected toward the highest stability.

Free-Piston Stirling Convertor Controller↗
DOE OSTI2019

MODELING AND OPTIMIZATION STUDY OF A TIGHTLY INTEGRATED ROTARY ELECTRIC MOTOR-HYDRAULIC PUMP

To meet the growing trend of electrification of mechanical systems, this paper presents a compactly integrated electric motor and hydraulic pump. The proposed application for this machine requires high flow rates at low pressure differentials and four quadrant operation. The hydraulic pump architecture selected for this machine is a radial ball piston pump. An inside impinged version of this architecture allows for efficient filling of the chambers and is radial balanced, both of which allow high- speed operation for increased power density. The radial ball piston pump is less expensive to manufacture and is radially more compact than a standard radial cylindrical piston pump. A model of the pump and the integrated electric motor have been created to study scaling relationships and drive detailed design and optimization. The scaling study considers how displacement is affected by pump diameter, and how the diameter and required torque change with angular velocity. The detailed model considers the effect of valve timing, piston-cylinder clearance, and pump geometry on the efficiency. The model is then exercised in an optimization of the machine parameters.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

A Moving Embedded Boundary Approach for the Compressible Navier-Stokes Equations in a Block-Structured Adaptive Refinement Framework

A computational technique has been developed to perform compressible flow simulations involving moving boundaries using an embedded boundary approach within the block-structured adaptive mesh refinement (SAMR) framework of AMReX [1], [91], [92]. We leverage the SAMR capability to obtain quantitatively accurate results whilst using robust, second-order finite volume schemes. A conservative, unsplit, cut-cell approach is utilized and a ghost-cell approach is developed for computing the flux on the moving, embedded boundary faces. A third-order least-squares formulation has been developed to compute the wall velocity gradients, and was found to significantly improve the performance of the solver in terms of the quantitative comparison of surface quantities such as the skin friction coefficient. Various test cases are performed to validate the method, and compared with analytical, experimental, and other numerical results in literature. Inviscid and viscous test cases are performed that span a wide regime of flow speeds - acoustic (harmonically pulsating sphere), smooth flows (expansion fan created by a receding piston) and flows with shocks (shock-cylinder interaction, shock-wedge interaction, pitching NACA 0012 airfoil and shock-cone interaction). A closed system with moving boundaries - an oscillating piston in a cylinder, showed that the percentage error in mass within the system decreases with refinement, demonstrating that the numerical scheme is conservative with grid refinement, but is not discretely conservative. Viscous test cases involve that of a horizontally moving cylinder at Re = 40, an inline oscillating cylinder at Re = 100, and a transversely oscillating cylinder at Re = 185. The judicious use of adaptive mesh refinement with appropriate refinement criteria to capture the regions of interest leads to well-resolved flow features, and good quantitative comparison is observed with the results available in literature.

adaptive refinement↗
DOE OSTI2017

High-Mach number, laser-driven magnetized collisionless shocks

Collisionless shocks are ubiquitous in space and astrophysical systems, and the class of supercritical shocks is of particular importance due to their role in accelerating particles to high energies. While these shocks have been traditionally studied by spacecraft and remote sensing observations, laboratory experiments can provide reproducible and multi-dimensional datasets that provide complementary understanding of the underlying microphysics. We present experiments undertaken on the OMEGA and OMEGA EP laser facilities that show the formation and evolution of high-Mach number collisionless shocks created through the interaction of a laser-driven magnetic piston and magnetized ambient plasma. Through time-resolved, 2-D imaging we observe large density and magnetic compressions that propagate at super-Alfvenic speeds and that occur over ion kinetic length scales. Electron density and temperature of the initial ambient plasma are characterized using optical Thomson scattering. Measurements of the piston laser-plasma are modeled with 2-D radiation-hydrodynamic simulations, which are used to initialize 2-D particle-in-cell simulations of the interaction between the piston and ambient plasmas. The numerical results show the formation of collisionless shocks, including the separate dynamics of the carbon and hydrogen ions that constitute the ambient plasma and their effect on the shock structure. Furthermore, the simulations also show the shock separating from the piston, which we observe in the data at late experimental times.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Direct Observations of Particle Dynamics in Magnetized Collisionless Shock Precursors in Laser-Produced Plasmas

We present the first laboratory observations of time-resolved electron and ion velocity distributions in magnetized collisionless shock precursors. Thomson scattering of a probe laser beam was used to observe the interaction of a laser-driven, supersonic piston plasma expanding through an ambient plasma in an external magnetic field. From the Thomson-scattered spectra we measure time-resolved profiles of electron density, temperature, and ion flow speed, as well as spatially resolved magnetic fields from proton radiography. We observe direct evidence of the coupling between piston and ambient plasmas, including the acceleration of ambient ions driven by magnetic and pressure gradient electric fields, and deformation of the piston ion flow, key steps in the formation of magnetized collisionless shocks. Even before a shock has fully formed, we observe strong density compressions and electron heating associated with the pileup of piston ions. Furthermore, the results demonstrate that laboratory experiments can probe particle velocity distributions relevant to collisionless shocks, and can complement, and in some cases overcome, the limitations of similar measurements undertaken by spacecraft missions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Optimization of spray breakup model parameters for predicting fuel spray and film characteristics in gasoline direct injection engines

This study investigated the behavior of gasoline direct injection (GDI) sprays using computational fluid dynamics (CFD). The authors developed an approach to identify optimal spray breakup model parameters by evaluating an error function across numerous simulations, with the goal of minimizing discrepancies from experimental data. Using the optimal setup, the simulated spray matched well with projected liquid volume distributions, liquid penetration, and spray width measured in a constant-pressure continuous-flow chamber. To further validate the approach, the same setup was tested across various fuels, injectors, and operating conditions. Subsequently, the optimal setup, along with a recently developed spray-wall interaction model, were applied to a direct-injection spark-ignited engine under late-injection conditions to predict and evaluate fuel film formation and evolution at varying engine coolant temperatures. Here, with the centrally mounted injector directing the spray toward the piston, simulations indicated that the spray tends to impinge on the piston surface. The proposed simulation framework also accurately captured the aggregate film area on the piston surface, aligning with previously published experimental results. Moreover, simulations showed that increasing the coolant temperature from cold start conditions (333 K) to warm conditions (363 K) reduced the fuel mass deposited on the piston by roughly 50%. Furthermore, for the spray-guided engine configuration studied in this work, the CFD model predicted minimal film deposition on the spark plug electrodes regardless of the coolant temperatures due to a relatively weak in-cylinder flow during the compression phase.

Computational fluid dynamics (CFD)↗
DOE OSTI2022

MBARI-WEC September and October 2022 Field Data

This data is needed to simulate a model of the MBARI-WEC (Monterey Bay Aquarium Research Institute, Wave Energy Converter device) in a simulation environment (e.g. Gazebo) for 56 observation dates in the time between September and October 2022, and to compare the simulation outputs to the corresponding field data of the physical MBARI-WEC. There were 50 observations chosen in Sept and 6 observations in Oct. To help understand terms below, a summary of the system can be found at the github link in the downloads section below. The Gazebo MBARI-WEC model is also provided, should users wish to simulate using this platform. There are 4 *mat files included. ................................................................................................................................................................................................................................... Spectrum and Simulation Inputs: September2022_spectrum_siminputs.mat and October2022_spectrum_siminputs.mat has data needed for simulation inputs in table format. These include the ocean spectrum for an observation and operating parameters of the MBARI-WEC during that observation. They are organized as rows representing an observation and columns representing data. For example, for the September *mat there are 50 rows. The first 7 columns are Datetime, sig_waveheight, peak_period, mean_period, heaveconedoor_status, pistonpos_mean, and scale_factor: - Datetime is the date and time the observation occurred in PST - sig_waveheight is the significant wave height of the ocean spectrum during that observation in meters - peak_period is the peak period of the ocean spectrum during that observation in seconds - mean_period is the mean period of the ocean spectrum during that observation in seconds - heaveconedoor_status is the status of the heave cone doors where 0 represents the doors are open and 1 represents they are closed - pistonpos_mean is the mean position of the PTO ram (piston) in meters - scale_factor is an additional factor of 0.5 --1.4 applied to a default damping relationship The next columns are data needed to represent the ocean spectrum. First are the frequencies [Hz] labeled as "f0-f38", then the variance density [m2/Hz] labeled as "vardens0-vardens38". October2022_spectrum_siminputs.mat follows as a similar format as above, but includes a larger amount of ocean spectrum frequencies and variance density elements. ................................................................................................................................................................................................................................... Field data: The field data is found in MBARIWEC_septdata.mat and MBARIWEC_octdata.mat for the observations of September and October, respectively. These contain data in a struct format. The struct contains the following fields for each observation: PC_BattCurr, PC_LoadCurr, PC_RPM, PC_Voltage, SC_Range, SC_Velocity, DateTime, where: - PC_BattCurr is the current flowing to or from the onboard batteries in Amps - PC_LoadCurr is the current flowing to the load dump in Amps - PC_RPM is the electric/hydraulic motor shaft speed (directly coupled) in RPM - PC_Voltage is the bus voltage at the power converter in Volts - SC_Range is the PTO ram (piston) position in meters where 0 is fully retracted and 2.03 is fully extended - SC_Velocity is the PTO ram (piston) velocity in meters/sec - DateTime is the date and time of the sampled field data in each observation in PST - Electric Power is equal to: PC_Voltage*(PC_BattCurr + PC_LoadCurr) in Watts For example, upon loading MBARIWEC_octdata.mat, the aforementioned fields would be loaded, each with {6x1} cells for the 6 observations chosen in October. Within the first cell of e.g. SC_Range would be sampled data representing the field data of the MBARIWEC PTO piston position for say, one hour, of the first October observation. The corresponding field DateTime would...

16 TIDAL AND WAVE POWER↗
DOE OSTI2013

30-kW Maintenance-Free Stirling Engine for High-Performance Dish Concentrating Solar

This final report summarizes the final results of the 30-kW Maintenance-Free Stirling Engine for High-Performance Dish Concentrating Solar project performed by Infinia Corporation for the U.S. Department of Energy under contract DE-FC36-08GO18032 during the project period of March 1, 2008 – March 31, 2012. Over the course of the project, Infinia Corporation achieved substantial progress in the design, fabrication, assembly, testing and evaluation of a 30-kW multi-cylinder, free-piston Stirling engine (MCFPSE) prototype. In this effort, prior MCFPSE conceptual design approaches were adapted for the development of a 30-kW design, thereby producing a cohesive design package and detailed performance specifications. Numerical analysis using the Stirling Engine Analysis and Optimization Code (SAGE) was completed culminating in the selection of a fully balanced 6-cylinder configuration composed of two 3-cylinder engine modules. The model was refined throughout the program to include all wall conduction losses, piston and rod seal losses, appendix, shuttle and pumping losses, and piston radiation loss to closely represent the real system. Performance mapping of the engine was then completed using the detailed model. Based on knowledge and experience from its existing commercial products, and using the results from the extensive numerical modeling discussed above, Infinia successfully fabricated, assembled and tested two sets of 30-kW engine modules. One of these configurations was driven by an external power supply and operated as a cooler in order to verify the mechanical integrity of the system. In the engine configuration, induction heaters provided the energy to the heater head to operate the engine. Considerable effort was expended on correcting problems associated with contact and rubbing of internal components, identification and subsequent elimination of internal leaks, and undesirable amounts of piston bias. Many details concerning the fabrication and testing efforts are considered proprietary. As a result, those findings are not disclosed herein but rather can be found in proprietary reports supplied to the DOE on a periodic basis. The prototype did not fully demonstrate performance nor did it realize the projected cost targets. Furthermore, the basis of the mechanical and electrical architecture of the 30-kW multi-cylinder prototype design is now at least two generations old. Alternatively, Infinia’s 8-kW Bonneville generator, which was successfully demonstrated in April 2012, and is slated to enter commercial production in late 2013, offers immediate benefits of lower cost and significantly higher power density such that the generator will likely meet DOE’s Sunshot LCOE target goal of $\$$0.07-0.10/kWh by 2015 and $\$$0.05-0.07/kWh by 2020. Therefore, the design of a 30-kW Stirling engine as disclosed in the project will not be pursued further. However, Infinia remains keenly interested in developing higher power Stirling machines in the future based on the new Bonneville mechanical design.

14 SOLAR ENERGY↗
DOE OSTI2016

MODELING SNR CASSIOPEIA A FROM THE SUPERNOVA EXPLOSION TO ITS CURRENT AGE: THE ROLE OF POST-EXPLOSION ANISOTROPIES OF EJECTA

The remnants of core-collapse supernovae (SNe) have complex morphologies that may reflect asymmetries and structures developed during the progenitor SN explosion. Here we investigate how the morphology of the supernova remnant Cassiopeia A (Cas A) reflects the characteristics of the progenitor SN with the aim of deriving the energies and masses of the post-explosion anisotropies responsible for the observed spatial distribution of Fe and Si/S. We model the evolution of Cas A from the immediate aftermath of the progenitor SN to the three-dimensional interaction of the remnant with the surrounding medium. The post-explosion structure of the ejecta is described by small-scale clumping of material and larger-scale anisotropies. The hydrodynamic multi-species simulations consider an appropriate post-explosion isotopic composition of the ejecta. The observed average expansion rate and shock velocities can be well reproduced by models with ejecta mass M {sub ej} ≈ 4 M {sub ⊙} and explosion energy E {sub SN} ≈ 2.3 × 10{sup 51} erg. The post-explosion anisotropies (pistons) reproduce the observed distributions of Fe and Si/S if they had a total mass of ≈0.25 M {sub ⊙} and a total kinetic energy of ≈1.5 × 10{sup 50} erg. The pistons produce a spatial inversion of ejecta layers at the epoch of Cas A, leading to the Si/S-rich ejecta physically interior to the Fe-rich ejecta. The pistons are also responsible for the development of the bright rings of Si/S-rich material which form at the intersection between the reverse shock and the material accumulated around the pistons during their propagation. Our result supports the idea that the bulk of asymmetries observed in Cas A are intrinsic to the explosion.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Solar wind helium enhancements following major solar flares

The observations of solar wind helium enhancements following major solar flares are reviewed, and the hypothesis that helium enhancements often mark flare piston plasma is confirmed. Helium enhancements were observed during each of the three periods (March 1966, July 1966, August/September 1966) of major solar activity that occurred from October 1965 to October 1966. No enhancements were seen during the long quiet periods that occurred that year. At 1 AU, the helium-enhanced plasma pistons had slowed so that the velocity was 80 percent of the mean transit velocity, in general agreement with theoretical models of the propagation of flare disturbances. A qualitative model, in which the piston plasma is accelerated from the flare site deep in the corona, is discussed briefly. If the model is valid in general outline, the piston plasmas provide samples of material from the lower levels of the corona.

Hirshberg, J.↗
NASA NTRS1973

Foot pedal operated fluid type exercising device

A foot pedal operated exercising device is reported that contains a dynamometer formed of a pair of cylinders each containing a piston. The pistons are linked to each other. The upper portions of the two cylinders are joined together by a common opening to provide a common fluid reservoir and each piston is provided with a one way check valve to maintain an adequate supply of working fluid. Fluid from the driven cylinder is transmitted to the other cylinder through separate constant force spring biased valves each valve takes the predominant portion of the pressure drop thereby providing a constant force hydraulic dynamometer. A device is provided to determine the amount of movement of piston travel.

Crum, G. W.↗
NASA NTRS1981

Hot gas engine with dual crankshafts

A hot gas engine, such as a Stirling engine is described which comprises a displacer portion and an expander portion with a heat exchanger connected between them. The expander portion has a piston which is operatively connected to and rotates an expander crankshaft. In like manner, the displacer portion is provided with a piston which is also operatively connected to and rotates with a separate displacer crankshafts. The two crankshafts are synchronized with respect to each other preferably by means of an idler gear. Banks of displacer pistons can also be provided for operation on a common displacer crankshaft and banks of cooperating expander pistons also can be provided for operation on a common expander crankshaft.

Mcdougal, A. R.↗
NASA NTRS1981

Reciprocating engines

An intake valve arrangement for positively controlling the opening and closing of the poppet valve in a hot gas cylinder in a hydrazine powered engine is described. The poppet valve is operated by the piston and gas pressure only. The poppet valve uses a pneumatic spring which holds the poppet valve against the piston while the valve is opened and closed. To accomplish this, a poppet valve is slidably mounted in a pneumatic spring chamber which reaches a pressure approaching the gas supply pressure and, during the opening of the valve, the spring chamber retains enough pressure to hold the poppet valve onto the piston. In addition, the bottom of the poppet valve can have a suction cup type configuration to hold the poppet valve on the piston during the down stroke.

Akkerman, J. W.↗
NASA NTRS1982

Solar engine

A solar engine is disclosed in which a fluid, which is first heated and then cooled, forces a piston outward as the fluid is heated, and then draws the piston inward as the fluid is cooled. The piston is connected to a shaft and produces work as it moves outward and inward. A displacer plate moves between an absorber plate and a cooling plate to form an air space between the displacer and one or the other of these two plates for heating and cooling the fluid. The displacer plate is moved from one plate to the other by the displacer push ring as the piston nears the midpoint of its travel on the outward stroke and again on the inward stroke.

Jensen, R. N.↗
NASA NTRS1983

A 10 deg K triple-expansion Stirling-cycle cryocooler

The design of a triple expansion closed cycle Stirling cryocooler optimized for a cooling load of 50 mW at 10 K is described. The cooler was designed with the objectives of low power, low weight, compactness, low mechanical motion, low electromagnetic noise, and low output temperature fluctuations. The design employs a direct drive linear motion piston motor and a triple expansion free displacer. Piston motion is controlled by feedback from an optical position transducer. Mechanical vibrations are attenuated with a passive resonant counterbalance. Electromagnetic noise is attenuated with layered high permeability magnetic shielding. The regenerators move with the displacer within a thin titanium cold finger. The piston and displacer oscillate at 8.33 Hz on bearings and seals of reinforced Teflon. The cooler is designed to provide the desired 50 mW of cooling at 10 K with a power input of less than 100 W. The piston can be driven at a greater stroke to produce up to 200 mW of cooling with an input power of 250 W. A lead and copper cold tip heat exchanger will limit temperature fluctuations to within 0.01 K.

Newman, W.↗