Radiation Model of Horizontal Jet Flame Governed by Buoyancy and Momentum

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Liu Changchun ◽  
Deng Tiandiao ◽  
Zhou Shasha ◽  
Liu Xinlei ◽  
Deng Jun ◽  
...  
Keyword(s):  
Predictive Accuracy ◽  
Flame Length ◽  
Length Ratio ◽  
Flame Height ◽  
Laptop Computer ◽  
Jet Flame ◽  
New Model ◽  
Trajectory Model ◽  
Data Points ◽  
Lift Off

AbstractBuoyancy causes a horizontal jet flame to bend upward when it loses sufficient initial momentum. Therefore, the variation in flame trajectory must be considered to accurately predict the thermal radiant flux of a horizontal jet flame governed by buoyancy and momentum. We introduce the flame trajectory equation into the linear source equation of radiation to establish a new model. The flame length ratio is calculated by flame trajectory length, horizontal projected flame length, and vertical projected flame height in the new model. This paper also presents a formula for flame lift-off distance and flame radiant fraction. We further list the geometric parameters of the horizontal-kite shape, tile-kite shape, and flame trajectory models. Comparing the experimental data and model predictions shows that the flame trajectory model is more accurate than the horizontal-kite and tile-kite models, especially when the Froude number is low. We also study the effects of flame lift-off distance and flame length ratio on predictive accuracy. The flame trajectory model computes quickly, and a normal laptop computer needs only 1.08 s to get a picture with 24,000 data points.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2005 ◽  
Vol 127 (1) ◽  
pp. 187-196 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven nonpremixed turbulent flames.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2001 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

Abstract The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty, direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven, non-premixed turbulent flames.

The effects of wind on the flame characteristics of individual leaves

2011 ◽  
Vol 20 (5) ◽  
pp. 657 ◽  
Author(s):  
Wesley J. Cole ◽  
McKaye H. Dennis ◽  
Thomas H. Fletcher ◽  
David R. Weise
Keyword(s):  
Froude Number ◽  
Flame Length ◽  
Flame Height ◽  
Combustion Model ◽  
Small Scale ◽  
Single Leaf ◽  
Small Branch ◽  
Flame Burner ◽  
Broadleaf Species ◽  
Semi Empirical

Individual cuttings from five shrub species were burned over a flat-flame burner under wind conditions of 0.75–2.80 m s–1. Both live and dead cuttings were used. These included single leaves from broadleaf species as well as 3 to 5 cm-long branches from coniferous and small broadleaf species. Flame angles and flame lengths were determined by semi-automated measurements of video images. Additional data, such as times and temperatures corresponding to ignition, maximum flame height and burnout were determined using video and infrared images. Flame angles correlated linearly with wind velocity. They also correlated with the Froude number when either the flame length or flame height was used. Flame angles in individual leaf experiments were generally 50 to 70% less than flame angles derived from Froude number correlations reported in the literature for fuel-bed experiments. Although flame angles increased with fuel mass and moisture content, they were unaffected by fuel species. Flame lengths and flame heights decreased with moisture contents and wind speed but increased with mass. In most cases, samples burned with wind conditions ignited less quickly and at lower temperatures than samples burned without wind. Most samples contained moisture at the time of ignition. Results of this small-scale approach (e.g. using individual cuttings) apply to ignition of shrubs and to flame propagation in shrubs of low bulk density. This research is one of the few attempts to characterise single-leaf and small-branch combustion behaviour in wind and is crucial to the continued development of a semi-empirical shrub combustion model.

scholarly journals A New Model Approach for Convective Wall Heat Losses in DQMOM-IEM Simulations for Turbulent Reactive Flows

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Yeshaswini Emmi ◽  
Andreas Fiolitakis ◽  
Manfred Aigner ◽  
Franklin Genin ◽  
Khawar Syed
Keyword(s):  
Experimental Data ◽  
Heat Losses ◽  
Reacting Flow ◽  
Jet Flame ◽  
New Model ◽  
Turbulent Reactive Flows ◽  
Novel Method ◽  
The One ◽  
The Impact ◽  
Model Approach

A new model approach is presented in this work for including convective wall heat losses in the direct quadrature method of moments (DQMoM) approach, which is used here to solve the transport equation of the one-point, one-time joint thermochemical probability density function (PDF). This is of particular interest in the context of designing industrial combustors, where wall heat losses play a crucial role. In the present work, the novel method is derived for the first time and validated against experimental data for the thermal entrance region of a pipe. The impact of varying model-specific boundary conditions is analyzed. It is then used to simulate the turbulent reacting flow of a confined methane jet flame. The simulations are carried out using the DLR in-house computational fluid dynamics code THETA. It is found that the DQMoM approach presented here agrees well with the experimental data and ratifies the use of the new convective wall heat losses model.

Calibration and Field Testing of Passive Flame Height Sensors

1992 ◽  
Vol 2 (3) ◽  
pp. 115 ◽  
Author(s):  
MA Finney ◽  
RE Martin
Keyword(s):  
Experimental Test ◽  
Prescribed Burning ◽  
Fire Retardant ◽  
Field Testing ◽  
Flame Length ◽  
Flame Height ◽  
Video Tape ◽  
Fire Damage ◽  
String Type

The concept of a passive flame height sensor involves thin strings permeated with fire retardant or solder which record heights of flame contact. Both types of sensors were calibrated during 12 experimental test fires with respect to flame heights measured on video tape. Three thresholds of fire damage to string-type sensors were identified: singeing of fine string fibers, complete blackening of the string, and thorough charring or consumption. These damage thresholds were found to exceed95%, 71% and48% of all flame heights measured from video tape, respectively. 18-gauge solder melted to a height exceeding 86% of measured flame heights. Field testing of 512 sensors during prescribed burning affirmed the potential practicality of this technique for estimating flame length.

scholarly journals Forecasting Realized Volatility Using a Nonnegative Semiparametric Model

2019 ◽  
Vol 12 (3) ◽  
pp. 139 ◽  
Author(s):  
Anders Eriksson ◽  
Daniel P. A. Preve ◽  
Jun Yu
Keyword(s):  
Predictive Accuracy ◽  
Estimation Method ◽  
Semiparametric Model ◽  
Error Component ◽  
New Model ◽  
Finite Samples ◽  
Proposed Model ◽  
Forecasting Performance ◽  
Out Of Sample ◽  
Using Data

This paper introduces a parsimonious and yet flexible semiparametric model to forecast financial volatility. The new model extends a related linear nonnegative autoregressive model previously used in the volatility literature by way of a power transformation. It is semiparametric in the sense that the distributional and functional form of its error component is partially unspecified. The statistical properties of the model are discussed and a novel estimation method is proposed. Simulation studies validate the new method and suggest that it works reasonably well in finite samples. The out-of-sample forecasting performance of the proposed model is evaluated against a number of standard models, using data on S&P 500 monthly realized volatilities. Some commonly used loss functions are employed to evaluate the predictive accuracy of the alternative models. It is found that the new model generally generates highly competitive forecasts.

Determination of underexpanded hydrogen jet flame length with a complex nozzle geometry

2019 ◽  
Vol 44 (17) ◽  
pp. 8988-8996 ◽  
Author(s):  
M. Henriksen ◽  
A.V. Gaathaug ◽  
J. Lundberg
Keyword(s):  
Flame Length ◽  
Nozzle Geometry ◽  
Jet Flame

Nitrogen-Diluted Methane Flames in the Near-and Far-Field

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
James Kribs ◽  
Nancy Moore ◽  
Tamir Hasan ◽  
Kevin Lyons
Keyword(s):  
Reynolds Number ◽  
Natural Gas ◽  
Low Reynolds Number ◽  
Industrial Applications ◽  
Flame Height ◽  
Far Field ◽  
Jet Flames ◽  
Jet Flame ◽  
Lifted Flame ◽  
Nitrogen Dilution

With the increased utilization of multicomponent fuels, such as natural gas and biogas, in industrial applications, there is a need to be able to effectively model and predict the properties of jet flames for mixed fuels. In addition, the interaction of these diluted fuels with outside influences (such as differing levels of coflow air) is a primary consideration. Experiments were performed on methane jet flames under the influence of varying levels of nitrogen dilution, from low Reynolds number lifted regimes to blowout, observing the influence of the nitrogen on lifted flame height and flame chemiluminesence images. These findings were analyzed and compared with existing lifted jet flame relations, such as the flammable region approximation proposed by Tieszen et al., as well as to undiluted flames. The influence of nitrogen dilution was seen to have an effect on the liftoff height of the flame, as well as the blowout velocity of the flame, but was seen to have a less pronounced effect compared with flames with coflowing air.

Prediction of Rodent Carcinogenesis: An Evaluation of Prechronic Liver Lesions as Forecasters of Liver Tumors in NTP Carcinogenicity Studies

2004 ◽  
Vol 32 (4) ◽  
pp. 393-401 ◽  
Author(s):  
D.G. Allen ◽  
G. Pearse ◽  
J.K. Haseman ◽  
R.R. Maronpot
Keyword(s):  
Predictive Accuracy ◽  
Liver Tumors ◽  
Liver Weight ◽  
Supplementary Information ◽  
Liver Lesions ◽  
Short Term ◽  
Hepatocellular Necrosis ◽  
Carcinogenic Potential ◽  
Data Points ◽  
The Cost

The National Toxicology Program (NTP) developed the chronic 2-year bioassay as a mechanism for predicting the carcinogenic potential of chemicals in humans. The cost and duration of these studies has limited their use to small numbers of selected chemicals. Many different short-term methods aimed at increasing predictive accuracy and the number of chemicals evaluated have been developed in attempts to successfully correlate their results with evidence of carcinogenicity (or lack of carcinogenicity). Using NTP studies, the effectiveness of correlating prechronic liver lesions with liver cancer encompassing multiple studies using mice (83 compounds) and rats (87 compounds) was assessed. These lesions include hepatocellular necrosis, hepatocellular hypertrophy, hepatocellular cytomegaly, bile duct hyperplasia, and hepatocellular degeneration, along with increased liver weight. Our results indicate that pooling 3 of these prechronic data points (hepatocellular necrosis, hepatocellular hypertrophy, and hepatocellular cytomegaly) can be very predictive of carcinogenicity in the 2-year study ( p < 0 .05). The inclusion of increased liver weight as an endpoint in the pool of data points increases the number of rodent liver carcinogens that are successfully predicted ( p < 0 .05), but also results in the prediction of increased numbers of noncarcinogenic chemicals as carcinogens. The use of multiple prechronic study endpoints provides supplementary information that enhances the predictivity of identifying chemicals with carcinogenic potential.

scholarly journals Morphology and Dynamics of a Premixed Hydrogen-Methane-Air Jet Flame in Hot Vitiated Turbulent Crossflow

2020 ◽  
Author(s):  
R. Solana-Pérez ◽  
L. Miniero ◽  
S. Shcherbanev ◽  
M. Bothien ◽  
N. Noiray
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Equivalence Ratio ◽  
Thermal Power ◽  
Atmospheric Condition ◽  
Flame Length ◽  
Fuel Blend ◽  
Time Resolved ◽  
Jet Flame ◽  
Air Jet

Abstract The effect of hydrogen enrichment of a premixed hydrogen-methane-air jet in hot vitiated crossflow was studied at atmospheric condition. The hot turbulent vitiated crossflow is generated by a symmetric array of 4 × 4 jet flames burning a lean mixture of natural gas and air in fully premixed condition at equivalence ratio φcf = 0.7 and total thermal power of 50 kW. This crossflow is then used to ignite the premixed perpendicular jet of hydrogen-methane-air at ambient temperature. Three jet parameters are varied to study the effect of hydrogen addition on the flame morphology and stabilization mechanism: the hydrogen mass fraction of the H2/CH4 fuel blend (ξ = 0 – 100%), the jet equivalence ratio (φ = 0.8 – 2.0) and the jet-to-crossflow momentum ratio (J = 3 – 12). High-speed hydroxyl (OH) chemiluminescence is used to obtain the time-resolved imaging of the reactive jet and to compute its time averaged morphology. OH planar laser induced fluorescence (OH-PLIF) is used to acquire OH concentration fields at the jet center plane. The jet morphology is analyzed by considering its mean trajectory, extracted from the experimental data and fitted with empirical correlations available from the literature. New correlations are proposed for the flame length, width and center of gravity as function of the hydrogen content. It is shown that with increasing hydrogen fraction, the flame is shortened and more compact, and it stabilizes close to the jet root. Another finding of this work is the reattachment of the flame at the base of the windward jet shear layer when hydrogen fraction is increased. Robust flame anchoring is observed for H2 mass fractions of the CH4/H2 fuel blend that exceed 50%. Moreover, it is shown using instantaneous OH-PLIF images that for these conditions of increasing hydrogen concentration, the windward shear layer features larger-scale coherent structures that govern the aerodynamics of the reactive premixed jet in turbulent vitiated crossflow.

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