scholarly journals Combustion dynamics of large-scale wildfires

2021 ◽  
Author(s):  
Naian Liu ◽  
Jiao Lei ◽  
Wei Gao ◽  
Haixiang Chen ◽  
Xiaodong Xie
Keyword(s):  
Large Scale ◽  
Combustion Dynamics

scholarly journals Review of emissions from smouldering peat fires and their contribution to regional haze episodes

2018 ◽  
Vol 27 (5) ◽  
pp. 293 ◽  
Author(s):  
Yuqi Hu ◽  
Nieves Fernandez-Anez ◽  
Thomas E. L. Smith ◽  
Guillermo Rein
Keyword(s):  
Large Scale ◽  
Field Studies ◽  
Combustion Efficiency ◽  
Combustion Regime ◽  
Mitigation Strategies ◽  
Combustion Dynamics ◽  
Tropical Peat ◽  
Regional Haze ◽  
Key Aspects ◽  
Peat Fires

Smouldering peat fires, the largest fires on Earth in terms of fuel consumption, are reported in six continents and are responsible for regional haze episodes. Haze is the large-scale accumulation of smoke at low altitudes in the atmosphere. It decreases air quality, disrupts transportation and causes health emergencies. Research on peat emissions and haze is modest at best and many key aspects remain poorly understood. Here, we compile an up-to-date inter-study of peat fire emission factors (EFs) found in the literature both from laboratory and from field studies. Tropical peat fires yield larger EFs for the prominent organic compounds than boreal and temperate peat fires, possibly due to the higher fuel carbon content (56.0 vs 44.2%). In contrast, tropical peat fires present slightly lower EFs for particulate matter with diameter ≤2.5 μm (PM2.5) for unknown reasons but are probably related to combustion dynamics. An analysis of the modified combustion efficiency, a parameter widely used for determining the combustion regime of wildfires, shows it is partially misunderstood and highly sensitive to unknown field variables. This is the first review of the literature on smouldering peat emissions. Our integration of the existing literature allows the identification of existing gaps in knowledge and is expected to accelerate progress towards mitigation strategies.

Turning Dynamic Sensor Measurements From Gas Turbines Into Insights: A Big Data Approach

2019 ◽  
Author(s):  
Roman Karlstetter ◽  
Robert Widhopf-Fenk ◽  
Jakob Hermann ◽  
Driek Rouwenhorst ◽  
Amir Raoofy ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Power Plants ◽  
Large Scale ◽  
Time Windows ◽  
Machine Learning Algorithms ◽  
Sensor Data ◽  
Combustion Dynamics ◽  
Measurement Analysis ◽  
Data Pipeline ◽  
Sensor Measurement

Abstract Gas turbine power plants generate an ever growing amount of high frequency dynamic sensor data. One of the applications of this data is the protection against problems induced by combustion dynamics, as, e.g., with the ArgusOMDS system developed by IfTA. In the light of digitalization, this data has the potential to also be used in other areas and ultimately transform maintenance, repair and overhaul approaches. However, current solutions are not designed to cope with the large time windows needed for a general analysis and this can hinder development of advanced machine analysis algorithms. In this work, we present an end-to-end approach for large scale sensor measurement analysis, employing data mining techniques and enabling machine learning algorithms. Our approach covers the complete data pipeline from sensor measurement acquisition to analysis and visualization. We demonstrate the feasibility of our approach by presenting several case studies that prove the benefits over existing solutions.

Application of Adaptive Control to Reduce Cyclic Dispersion Near the Lean Limit in a Small-Scale, Natural Gas Engine

2004 ◽  
Author(s):  
K. Dean Edwards ◽  
Robert M. Wagner
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Large Scale ◽  
Small Scale ◽  
Target Point ◽  
Combustion Dynamics ◽  
Current Cycle ◽  
History Of ◽  
Lean Limit ◽  
Prediction Strategy

Predictive feedback control is applied to achieve reduction in cyclic dispersion in an analytical, lean, spark-ignition model and a two-cylinder, four-stroke, natural gas Kohler Command 25 engine operating at lean conditions. Recent observations of the combustion dynamics are used to define a desired target point for control and to predict future combustion events which may stray from the target point. Fueling perturbations are applied to steer the system back toward the desired behavior. Overall control perturbations are constrained to maintain a constant average fuel-to-air ratio. We present two methods for obtaining the prediction of future combustion events. In the first method, the recent history of cycle heat release is used to construct an adaptive, low-order map which relates the current-cycle heat release to the next-cycle heat release. The second method uses symbolic analysis to determine the relative frequency of successive-cycle combustion events and predict the most probable successor to the current cycle. Results are presented which show a moderate reduction in cycle-to-cycle variation near the lean limit in both the model and the engine. Similarities in behavior have been shown to exist-ignition engines suggesting that a similar prediction strategy could be successfully applied to control cyclic dispersion in large-scale reciprocating engines.

Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers

2014 ◽  
Vol 743 ◽  
pp. 554-584 ◽  
Author(s):  
J. O’Brien ◽  
J. Urzay ◽  
M. Ihme ◽  
P. Moin ◽  
A. Saghafian
Keyword(s):  
Mach Number ◽  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Mixing ◽  
High Speed ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Mixing Layers ◽  
Subgrid Scale ◽  
Combustion Dynamics

AbstractThis study addresses the dynamics of backscatter of kinetic energy in the context of large-eddy simulations (LES) of high-speed turbulent reacting flows. A priori analyses of direct numerical simulations (DNS) of reacting and inert supersonic, time-developing, hydrogen–air turbulent mixing layers with complex chemistry and multicomponent diffusion are conducted here in order to examine the effects of compressibility and combustion on subgrid-scale (SGS) backscatter of kinetic energy. The main characteristics of the aerothermochemical field in the mixing layer are outlined. A selfsimilar period is identified in which some of the turbulent quantities grow in a quasi-linear manner. A differential filter is applied to the DNS flow field to extract filtered quantities of relevance for the large-scale kinetic-energy budget. Spatiotemporal analyses of the flow-field statistics in the selfsimilar regime are performed, which reveal the presence of considerable amounts of SGS backscatter. The dilatation field becomes spatially intermittent as a result of the high-speed compressibility effect. In addition, the large-scale pressure-dilatation work is observed to be an essential mechanism for the local conversion of thermal and kinetic energies. A joint probability density function (PDF) of SGS dissipation and large-scale pressure-dilatation work is provided, which shows that backscatter occurs primarily in regions undergoing volumetric expansion; this implies the existence of an underlying physical mechanism that enhances the reverse energy cascade. Furthermore, effects of SGS backscatter on the Boussinesq eddy viscosity are studied, and a regime diagram demonstrating the relationship between the different energy-conversion modes and the sign of the eddy viscosity is provided along with a detailed budget of the volume fraction in each mode. A joint PDF of SGS dissipation and SGS dynamic-pressure dilatation work is calculated, which shows that high-speed compressibility effects lead to a decorrelation between SGS backscatter and negative eddy viscosities, which increases for increasingly large values of the SGS Mach number and filter width. Finally, it is found that the combustion dynamics have a marginal impact on the backscatter and flow-dilatation distributions, which are mainly dominated by the high-Mach-number effects.

The Effect of Chevrons on the Primary and Secondary Swirlers on the Dynamic Behavior of the Flow Generated by a Counter-Rotating Radial-Radial Swirler

2016 ◽  
Author(s):  
Sheng-Chieh Lin ◽  
Wessam Estefanos ◽  
James Brennan ◽  
Samir Tambe ◽  
San-Mou Jeng
Keyword(s):  
Reynolds Number ◽  
Dynamic Behavior ◽  
High Speed ◽  
Large Scale ◽  
Swirling Flow ◽  
Vertical Plane ◽  
High Energy ◽  
Flow Dynamic ◽  
Trailing Edge ◽  
Combustion Dynamics

An experimental investigation was conducted to study the effect of chevrons on the dynamic behavior of the swirling flow generated by a counter-rotating radial-radial swirler. 3X models of a low swirl number swirler (SN ≈ 0.6) were used to achieve lower velocities for the same Reynolds number (Re) and enhanced visibility of the flow characteristics by enabling high spatial and temporal resolutions. Three swirler configurations were used, including the baseline with no chevrons. Configuration 2 features chevrons on the trailing edge of the primary swirler, and configuration 3 has chevrons on the trailing edge of both primary and secondary swirlers. The swirlers were tested in water flow at Reynolds number (Re) = 51,500 which corresponds to the typical operational pressure drop of 4% of atmospheric pressure for the corresponding 1X model of the swirler at ambient conditions. Water testing was used since it allows additional slowing down of the flow dynamic features so that they can be captured and analyzed. Measurements were conducted in a vertical plane passing through the swirler centerline, and two horizontal (cross-sectional) planes using a High-Speed, Two Dimensional, Particle Image Velocimetry (2D PIV) system to obtain the mean, turbulent and dynamic behavior of the flow. Results of this study introduce the concept of chevrons on swirlers as a promising approach to change the flow dynamic behavior and thus, affect combustion dynamics. The results show that the presence of chevrons break down the region of high modal energy into several smaller regions. However, configuration 2 has few regions of the highest modal energy among the configurations, whereas the modal energy values for configurations 3 has the lowest magnitudes. Thus, the secondary chevrons in configuration 3 play an important role to eliminate these high-energy local spots as well as meet the requirement to break down the large scale structures.

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

Some applications of electron beam microanalysis techniques in VLSI process evaluation

1983 ◽  
Vol 41 ◽  
pp. 160-161
Author(s):  
Simon Thomas
Keyword(s):  
Integrated Circuits ◽  
Process Evaluation ◽  
Large Scale ◽  
Technology Development ◽  
Analytical Techniques ◽  
Successful Implementation ◽  
Analysis Of Failures ◽  
Characterization Of Materials ◽  
Circuits Vlsi

Trends in the technology development of very large scale integrated circuits (VLSI) have been in the direction of higher density of components with smaller dimensions. The scaling down of device dimensions has been not only laterally but also in depth. Such efforts in miniaturization bring with them new developments in materials and processing. Successful implementation of these efforts is, to a large extent, dependent on the proper understanding of the material properties, process technologies and reliability issues, through adequate analytical studies. The analytical instrumentation technology has, fortunately, kept pace with the basic requirements of devices with lateral dimensions in the micron/ submicron range and depths of the order of nonometers. Often, newer analytical techniques have emerged or the more conventional techniques have been adapted to meet the more stringent requirements. As such, a variety of analytical techniques are available today to aid an analyst in the efforts of VLSI process evaluation. Generally such analytical efforts are divided into the characterization of materials, evaluation of processing steps and the analysis of failures.

Electron microscopy study of reactively sputter-deposited Ti/N films on silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1362-1363
Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Large Scale ◽  
Hexagonal Phase ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Process Conditions ◽  
Tin Films ◽  
Wide Range ◽  
Fcc Phase ◽  
Circuits Vlsi

Titanium nitride (TiN) films have historically been used as diffusion barrier between silicon and aluminum, as an adhesion layer for tungsten deposition and as an interconnect material etc. Recently, the role of TiN films as contact barriers in very large scale silicon integrated circuits (VLSI) has been extensively studied. TiN films have resistivities on the order of 20μ Ω-cm which is much lower than that of titanium (nearly 66μ Ω-cm). Deposited TiN films show resistivities which vary from 20 to 100μ Ω-cm depending upon the type of deposition and process conditions. TiNx is known to have a NaCl type crystal structure for a wide range of compositions. Change in color from metallic luster to gold reflects the stabilization of the TiNx (FCC) phase over the close packed Ti(N) hexagonal phase. It was found that TiN (1:1) ideal composition with the FCC (NaCl-type) structure gives the best electrical property.

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