Peak Burn Research Articles

Thermonuclear performance variability near ignition at the National Ignition Facility

We describe our current understanding of the variability and degradation mechanisms observed through a series of five indirectly driven inertial fusion implosions fielded at the National Ignition Facility in the fall of 2021, four of which attempted to reproduce the first experiment to achieve Lawson's criterion for ignition with a thermonuclear yield of 1.35 MJ on August 8, 2021. A large number of absolutely calibrated (imaging, time-resolved, and spectrally resolved) x-ray and neutron diagnostics are fielded on the NIF along multiple lines of sight for each experiment. This allows for a reconstruction of the DT fuel and ablator mix injected into the hotspot around peak burn. We show that nuclear yield variations are well reproduced by numerical modeling when the measured low mode asymmetries and mix mass are included. Furthermore, these observed perturbations during burn are linked to small variations in laser delivery and capsule defects. Stringent specifications are then set to achieve robust ignition with the implosion design studied in this paper.

Technique for an improved and time-resolved carbon areal density measurement with a single channel diagnostic for inertial confinement fusion

Measurement of the areal density and velocity of the carbon ablator shell during peak burn in inertial confinement fusion give powerful information on the state of the ablator and where in the trajectory of implosion it reaches peak burn. Detailed comparison of the absolute densities and velocities of the carbon in implosions has been prevented by the limited ability to resolve shot-to-shot variation within a shot series or within a campaign. A new approach using a single, ultra fast (∼10 ps) gamma ray channel can massively reduce uncertainties and will provide insights on improvements to target and drive variables. Small improvements in these experimental design parameters may result in much greater yields.

Quantifying Aspect‐Dependent Snowpack Response to High‐Elevation Wildfire in the Southern Rocky Mountains

AbstractIncreasing wildfire frequency and severity in high‐elevation seasonal snow zones presents a considerable water resource management challenge across the western United States (U.S.). Wildfires can affect snowpack accumulation and melt patterns, altering the quantity and timing of runoff. While prior research has shown that wildfire generally increases snow melt rates and advances snow disappearance dates, uncertainties remain regarding variations across complex terrain and the energy balance between burned and unburned areas. Utilizing paired in situ data sources within the 2020 Cameron Peak burn area on the Front Range of Colorado, U.S., during the 2021–2022 winter, we found no significant difference in peak snow water equivalent (SWE) magnitude between burned and unburned areas. However, the burned south aspect reached peak SWE 22 days earlier than burned north. During the ablation period, burned south melt rates were 71% faster than unburned south melt rates, whereas burned north melt rates were 94% faster than unburned north aspects. Snow disappeared 7–11 days earlier in burned areas than unburned areas. Net energy differences at the burned and unburned weather station sites were seasonally variable, the burned area snowpack lost more net energy during the winter, but gained more net energy during the spring. Increased incoming shortwave radiation at the burned site was 6x more impactful in altering the net shortwave radiation balance than the decline in surface albedo. These findings emphasize the need for post‐wildfire water resource planning that accounts for aspect‐dependent differences in energy and mass balance to accurately predict snowpack storage and runoff timing.

Experimental and Numerical Studies on the Fire Performance of Thin Sustainable Wood-Based Laminated Veneers

Wood and wood-based products are abundantly used, especially in structural applications, due to the impetus for sustainable development. The present work helps highlight the fire performance of plywood, one of the most used wood-based laminated structural components, under three different heat fluxes of 35 kW/m2, 50 kW/m2, and 65 kW/m2. The effects on the various fire reaction properties, namely, time to ignition, heat release rate, peak heat release rate, time to peak heat release rate, time to flameout, total burn time, and mass loss, were observed and reported. The times to ignition (42.2% and 35.4%), peak heat release rate (27.7% and 18.9%), flameout (22.2% and 28.6%), burn time (10.6% and 16.1%), and residual mass (25% and 53.3%) were reduced with the increase in heat flux from 35 kW/m2 to 65 kW/m2, respectively, whereas the peak heat release (21.7% and 2.4%) and ignition temperature (6.5% and 6.6%) were observed to increase. The vertical burning test (UL-94) illustrated the plywood samples to have a V-1 rating, with self-extinguishing capabilities. A numerical predictive model has also been developed based on the Fire Dynamics Simulator to predict the time to ignition, time to flameout, and heat release rate trend along with the peak heat release rate—it is shown to have good agreement with the experimental results, with an average correlation coefficient of 0.87.

Prediction of Mild Cognitive Impairment Status: Pilot Study of Machine Learning Models Based on Longitudinal Data From Fitness Trackers.

Early signs of Alzheimer disease (AD) are difficult to detect, causing diagnoses to be significantly delayed to time points when brain damage has already occurred and current experimental treatments have little effect on slowing disease progression. Tracking cognitive decline at early stages is critical for patients to make lifestyle changes and consider new and experimental therapies. Frequently studied biomarkers are invasive and costly and are limited for predicting conversion from normal to mild cognitive impairment (MCI). This study aimed to use data collected from fitness trackers to predict MCI status. In this pilot study, fitness trackers were worn by 20 participants: 12 patients with MCI and 8 age-matched controls. We collected physical activity, heart rate, and sleep data from each participant for up to 1 month and further developed a machine learning model to predict MCI status. Our machine learning model was able to perfectly separate between MCI and controls (area under the curve=1.0). The top predictive features from the model included peak, cardio, and fat burn heart rate zones; resting heart rate; average deep sleep time; and total light activity time. Our results suggest that a longitudinal digital biomarker differentiates between controls and patients with MCI in a very cost-effective and noninvasive way and hence may be very useful for identifying patients with very early AD who can benefit from clinical trials and new, disease-modifying therapies.

Use of tritium-rich fuel to improve the yield of layered deuterium/tritium inertial fusion capsules

In deuterium–tritium (DT) ice layered implosions, nearly all hot spot mass at peak burn comes from the dense fuel. Accurate prediction of the fuel mass ablation, including the enthalpy associated with mass inflow into the hot spot from the dense fuel, is essential to understanding the energetics and ignition of the hot spot in layered implosions. A recently published boundary layer analysis (Daughton et al., 2023) indicates a faster mass ablation rate than in previous analyses of layered implosions. Inclusion of this effect provides a better match to simulations and leads to a new ignition threshold where the temperature of the dense fuel plays a critical role. This analysis motivates possible new directions for improved capsule performance. Here, the authors present evidence in support of one such approach: the use of tritium-rich ice to decrease 14 MeV neutron scattering and heating of the dense fuel, resulting in less mass ablation and more robust burn of the hot spot. It is found from numerical simulations that despite a less favorable D:T ratio in the ice, the use of a 40:60 D:T ratio leads to an increase in capsule yield of 17% percent compared with that of a 50:50 D:T ratio fuel for capsules resembling those of the recent N210808 ignition experiment on the NIF (Abu-Shawareb et al., 2022) and an increase of 74% compared with that of a 60:40 D:T ratio fuel capsule. These results are potentially important for modeling all layered implosions, since some degree of DT fractionization may arise naturally during the beta layering process. In addition, this physics is important for the feasibility of high-gain capsule designs that seek to minimize tritium usage, as in some inertial fusion energy concepts.

Measurements of fusion reaction history in inertially confined burning plasmas

Direct evidence of inertially confined fusion ignition appears in the abrupt temperature increase and consequent rapid increase in the thermonuclear burn rate as seen in the reaction history. The Gamma Reaction History (GRH) and Gas Cherenkov Detector (GCD) diagnostics are γ-based Cherenkov detectors that provide high quality measurements of deuterium–tritium fusion γ ray production and are, thus, capable of monitoring the thermonuclear burn rate. Temporal shifts in both peak burn time and burn width have been observed during recent high-yield shots (yields greater than 1017 neutrons) and are essential diagnostic signatures of the ignition process. While the current GRH and GCD detectors are fast enough to sense the changes of reaction history due to alpha heating, they do not have enough dynamic range to capture the onset of alpha heating. The next generation of instrumentation, GRH-15m, is proposed to increase the yield-rate coverage to measure the onset of alpha-heating.

Comparing Peak Burn Injury Times and Characteristics in Australia and New Zealand.

Burns are a leading cause of morbidity and mortality worldwide. Understanding when and how burns occur, as well as the differences between countries, would aid prevention efforts. A review of burn injuries occurring between July 2009 and June 2021 was undertaken using data from the Burns Registry of Australia and New Zealand. Peak injury times were identified on a country-by-country basis. Variations in demographic and injury event profiles between countries were compared using descriptive statistics. There were 26,925 admissions recorded across the two countries (23,323 for Australia; 3602 for New Zealand). The greatest number of injuries occurred between 6 PM to 7 PM in Australia (1871, 8.0%) and between 5 PM to 6 PM in New Zealand (280, 7.8%). In both countries, scalds accounted for the greatest proportion of injuries during peak times (988, 45.8%), but a greater proportion of young children (under three years) sustained burns during New Zealand’s peak times. The number of burn injuries associated with the preparation and/or consumption of food offers an opportunity for a targeted prevention program that may yield benefits across the two countries. Age- and mechanism-related differences in the profile of burn-injured patients need to be considered when developing and implementing such a program.

Studies on aluminum powder combustion in detonation environment

The combustion mechanism of aluminum particles in a detonation environment characterized by high temperature (in unit 103 K), high pressure (in unit GPa), and high-speed motion (in units km/s) was studied, and a combustion model of the aluminum particles in detonation environment was established. Based on this model, a combustion control equation for aluminum particles in detonation environment was obtained. It can be seen from the control equation that the burning time of aluminum particle is mainly affected by the particle size, system temperature, and diffusion coefficient. The calculation result shows that a higher system temperature, larger diffusion coefficient, and smaller particle size lead to a faster burn rate and shorter burning time for aluminum particles. After considering the particle size distribution characteristics of aluminum powder, the application of the combustion control equation was extended from single aluminum particles to nonuniform aluminum powder, and the calculated time corresponding to the peak burn rate of aluminum powder was in good agreement with the experimental electrical conductivity results. This equation can quantitatively describe the combustion behavior of aluminum powder in different detonation environments and provides technical means for quantitative calculation of the aluminum powder combustion process in detonation environment.

Spray Auto-ignition Behaviors of Diesel and Jet Fuel at Reduced Oxygen Environments

ABSTRACT Spray auto-ignition behaviors of the RP-3 jet fuel were compared to those of a conventional diesel fuel on a constant-volume combustion chamber. The experiments were conducted at changed ambient temperatures and oxygen concentrations, with adjusted fuel injection pressure and duration as well. Compared to diesel fuel, the RP-3 jet fuel exhibits less auto-ignition propensity and lower burn rate, its ignition delay, and combustion delay times are more sensitive to the change in temperature and oxygen concentration, and more obviously staged heat releases and pressure rises are observed at lower oxygen ambience. Also, the peak heat release rate of diesel fuel exhibits an apparent non-monotonic trend versus increased temperature at high oxygen environments, due to the reduced premixed burn intensity with increased ambient temperature, while this non-monotonic trend for the RP-3 jet fuel is less significant, as the peak burn intensity is less influenced by changed ambient temperature. Finally, both elevated injection pressure and extended injection duration significantly reduce the combustion delay time at lower ambient oxygen concentrations, because the interval between the two-stage pressure rises, that occur at lower ambient oxygen environments, are apparently shortened.

RANS and LES of a Turbulent Jet Ignition System Fueled with Iso-Octane

The behaviour of a homogeneously charged Turbulent Jet Ignition (TJI) system, fueled with iso-octane was investigated numerically using Large Eddy Simulation (LES) and Reynolds Averaged Navier-Stokes (RANS) turbulence models. This study was an attempt to capture the start of autoignition in a lean charge TJI system, numerically, and, validate the results with experimental pressure measurements and OH chemilominescence images recorded during high speed imaging. Experiments were performed in an optically acessible Rapid Compression Machine (RCM) and the effect of auxiliary fuel injection in the prechamber and ignition distribution through various orrifices was investigated in depth through jet induced autoignition analysis. Heat release and pressure trace analysis were completed to capture the onset of autoignition, as well as comparing LES and RANS capabilities in this regard. Results showed that enhanced prechamber fueling leads to an increase in combustion stability while reducing the ignition delay. It was determined that keeping the prechamber mixture near stoichiometric is essential in order to have a more powerful turbulent jet discharged into the main chamber and to enhance ultra-lean main chamber combustion. The predicted flame propagation speed in the lean iso-octane mixtures was found to be slower than that observed in the experimental measurements. Results showed that the LES turbulence model is capable of predicting the start of autoignition more accurately and enhances the accuracy of the calculated peak pressure and burn rates relative to the RANS model. Two detailed iso-octane mechanisms were tested and based on the ignition delay comparisons, the LLNL-v3 mechanism was used in the current study.

A Preliminary Investigation of Filter Mud Dewatering and Its Combustive Properties

In order to evaluate the possibility of making use of the filter mud from sugar mills as a boiler fuel, experiment on dewatering the mud by filter press with expression at elevated temperature was carried out and the combustive properties of the dewatered mud were investigated. The proximate and calorific values of the dewatered mud were determined, and the combustive properties were analyzed through thermogravimetric analysis. The results shown that the filter mud could be dewatered to the moisture content around 50% when expressed under the pressure between 1.6∼2.5MPa at 95 °C. The contents of moisture, ashes, volatile matters and fixed carbon on air dried basis were about 9.4%, 19.8%, 58.9%, 12.0% respectively and the calorific value of dewatered mud was around 8450kJ/kg, indicating that it is an appropriate fuel. The thermogravimetric analysis showed that the pyrolysis and combustion of volatiles took place between 200∼370 °C, where the weight loss accounted for over 50%. The fixed carbon was combusted between 370∼550 °C. The temperatures at ignition, peak burning rate and burn out were 280 °C, 340 °C and 550 °C respectively. The ignition, burnout and comprehensive combustion indexes were 3.8 × 10-5 mg·min-1°C-2, 7.2 × 10-3 min-1, 1.8 × 10-8 mg2min-2°C-3 respectively.

Stable and confined burn in a Revolver ignition capsule

The main burn phase physics in a Revolver ignition capsule is analyzed and found to exhibit a new feature where pusher stagnation is persistent and burn occurs with the fuel at a fixed volume. The pressure and density gradients at the fuel-pusher interface are both positive making it stable to Rayleigh-Taylor growth. Expansion cooling and RT mixing are absent from the Revolver burn during this time. The effect is due to the massive heavy metal pusher shell being compressed during implosion and heated on an inner layer by the Marshak wave. The pusher is driven to a higher pressure than the DT fuel and becomes a fuel confining shell starting at stagnation and continuing past the time of peak burn. This period of persistent stagnation lasts for approximately 100 ps (in the baseline design) with a fuel burnup during stagnation of 40%. This behavior does not occur in any other capsule designs, including the double shell schemes that also employ a heavy metal pusher.

Large eddy simulation of a homogeneously charged turbulent jet ignition system

Transient jet ignition of a homogeneous methane air mixture in a turbulent jet ignition system is studied computationally using a large eddy simulation turbulence model. The jet discharges from a prechamber into a main combustion chamber via one or more orifice(s) and provides a distributed ignition source in turbulent jet ignition. The effect of orifice size and stoichiometry is studied numerically using the Converge computational fluid dynamics code. A reduced kinetic mechanism is used for combustion along with a Smagorinsky sub-model for turbulence modeling. The computed pressure traces are compared with experimental measurements through rapid compression machine tests. Computational fluid dynamics results are in acceptable agreement with the experimental data during compression and the early stage of combustion; however, an over-prediction of peak pressure was reported. Peak pressure error is in the range of 0.1%–4% for Reynolds-averaged Navier–Stokes simulation estimation compared to the experimental measurements. This error is a function of mixture stoichiometry and unburned gas temperature. The error calculation showed that with the large eddy simulation model, 1% and 12% improvements in peak pressure and burn rate estimations, respectively, were achieved compared to Reynolds-averaged Navier–Stokes results. The reduced large eddy simulation error relative to the Reynolds-averaged Navier–Stokes simulations were considered to be in the acceptable range; however, further improvements could be achieved through validation and testing of additional turbulence models. In addition, computational fluid dynamics temperature contours for various nozzle orifices and air–fuel ratios are compared to achieve deeper insight into the turbulent jet ignition combustion process in the rapid compression machine combustion cylinder. The numerical iso-surface temperature contours were obtained which enabled three-dimensional views of the flame propagation, the jet discharge, ignition and extinction events. The heat release process and regeneration of mid-range temperature iso-surfaces (1200 K) were not visible through the experimental images.

Analyzing seasonal patterns of wildfire exposure factors in Sardinia, Italy.

In this paper, we applied landscape scale wildfire simulation modeling to explore the spatiotemporal patterns of wildfire likelihood and intensity in the island of Sardinia (Italy). We also performed wildfire exposure analysis for selected highly valued resources on the island to identify areas characterized by high risk. We observed substantial variation in burn probability, fire size, and flame length among time periods within the fire season, which starts in early June and ends in late September. Peak burn probability and flame length were observed in late July. We found that patterns of wildfire likelihood and intensity were mainly related to spatiotemporal variation in ignition locations, fuel moisture, and wind vectors. Our modeling approach allowed consideration of historical patterns of winds, ignition locations, and live and dead fuel moisture on fire exposure factors. The methodology proposed can be useful for analyzing potential wildfire risk and effects at landscape scale, evaluating historical changes and future trends in wildfire exposure, as well as for addressing and informing fuel management and risk mitigation issues.

On thermonuclear burn propagation in a pre-compressed cylindrical DT target ignited by a heavy ion beam pulse

AbstractThermonuclear ignition and burn propagation in pre-compressed cylindrical deuterium-tritium (DT) targets is studied by two-dimensional radiation hydrodynamics simulations using the code MULTI-2D. Special attention is paid to self-sustained steady burn wave propagation. Peak temperatures and burn wave velocity scale with the density-radius product of the fuel, and wave propagation is obtained for (ρR)DT ≥ 0.45 g/cm2. Radiation transport is identified as the dominant mechanism to drive the wave. Details of ignition by a heavy ion beam pulse are also presented. Limitations in the physics basis of the simulations are pointed out. The results are compared with previous publications found in the literature.

Experimental investigation of performance, emission and combustion characteristics of an indirect injection multi-cylinder CI engine fuelled by blends of de-inking sludge pyrolysis oil with biodiesel

De-inking sludge can be converted into useful forms of energy to provide economic and environmental benefits. In this study, pyrolysis oil produced from de-inking sludge through an intermediate pyrolysis technique was blended with biodiesel derived from waste cooking oil, and tested in a multi-cylinder indirect injection type CI engine. The physical and chemical properties of pyrolysis oil and its blends (20 and 30vol.%) were measured and compared with those of fossil diesel and pure biodiesel (B100). Full engine power was achieved with both blends, and very little difference in engine performance and emission results were observed between 20% and 30% blends. At full engine load, the brake specific fuel consumption on a volume basis was around 6% higher for the blends when compared to fossil diesel. The brake thermal efficiencies were about 3–6% lower than biodiesel and were similar to fossil diesel. Exhaust gas emissions of the blends contained 4% higher CO2 and 6–12% lower NOx, as compared to fossil diesel. At full load, CO emissions of the blends were decreased by 5–10 times. The cylinder gas pressure diagram showed stable engine operation with the 20% blend, but indicated minor knocking with 30% blend. Peak cylinder pressure of the 30% blend was about 5–6% higher compared to fossil diesel. At full load, the peak burn rate of combustion from the 30% blend was about 26% and 12% higher than fossil diesel and biodiesel respectively. In comparison to fossil diesel the combustion duration was decreased for both blends; for 30% blend at full load, the duration was almost 12% lower. The study concludes that up to 20% blend of de-inking sludge pyrolysis oil with biodiesel can be used in an indirect injection CI engine without adding any ignition additives or surfactants.

Fabrication of uranium oxycarbide kernels and compacts for HTR fuel

Fabrication of uranium oxycarbide kernels and compacts for HTR fuel

Effects of nonequilibrium particle distributions in deuterium-tritium burning

The effects of nonequilibrium particle distributions resulting from rapid deuterium-tritium burning in plasmas are investigated using a Fokker–Planck code that incorporates small-angle Coulomb scattering, bremsstrahlung, Compton scattering, and light-ion fusion. For inertial confinement fusion environments, it is found that deviations away from Maxwellian distributions for either deuterium or tritium ions are small and result in 1% changes in the energy production rates. The deuterium and tritium effective temperatures are not equal, but differ by only about 2.5% near the time of peak burn rate. Simulations with high Z (Xe) dopants show that the dopant temperature closely tracks that of the fuel. On the other hand, fusion product ion distributions are highly non-Maxwellian, and careful treatments of energy-exchange between these ions and other particles is important for determining burn rates.

Diagnosing ignition with DT reaction history

A full range DT reaction history of an ignition capsule, from 10(9) to 10(20) neutronsns, offers the opportunity to diagnose fuel conditions hundreds of picoseconds before and during burn. The burn history begins with a sharp rise when the first shock reaches the center of the capsule. The level of this jump reflects the combined shock strength and the adiabat of DT fuel. Changes to the four laser pulses driving the capsule implosion which are large enough to degrade the yield make measurable changes to the reaction history. Low mode asymmetries grow during convergence but change the reaction history during the final approximately 100 ps. High mode asymmetry or turbulence mixing affects only the reaction history within approximately 50 ps of peak burn rate. A capsule with a tritium fuel layer containing a small amount of deuterium (approximately 1%) creates a reaction history similar to the ignition capsule, but without the final ignition burn. A combination of gas Cerenkov detectors and the neutron temporal diagnostic could be capable of diagnosing the full history of ignition and tritium rich capsules.