Measurement of the laminar burning velocity using the confined and unconfined spherical flame methods – A comparative analysis

Omari, Ahmad Al; Tartakovsky, Leonid

doi:10.1016/j.combustflame.2016.03.012

Cited by 60 publications

(32 citation statements)

References 49 publications

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“…First, ( t ) is measured and noise is suppressed with cubic smoothing splines selected to ensure unstructured fit residuals over the useful range of data. The range of smoothed ( t ) is narrowed: data at early times are eliminated for ( t ) < 1.25 P i , which is sufficient to remove ignition transients and electrical noise; data at longer times are eliminated beyond the maximum 2 nd derivative of the pressure trace, which has been suggested as a marker for when the flame begins to interact with the chamber walls [29]. Second, the relationship between the unburned/burned gas thermodynamic states and the flame radius ( R f ) was computed via the Hybrid ThermoDynamic-Radiation (HTDR) model [9] with species thermodynamic data taken from the NIST HFC mechanism [30].…”

Section: Data Reductionmentioning

confidence: 99%

Effects of stretch and thermal radiation on difluoromethane/air burning velocity measurements in constant volume spherically expanding flames

Burrell

Pagliaro

Linteris

2019

Proceedings of the Combustion Institute

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Compared to current refrigerants, next-generation refrigerants are more environmentally benign but more flammable. The laminar burning velocity is being used by industry as a metric to screen refrigerants for fire risk, and it is also used for kinetic model development and validation. This study reports measurements of difluoromethane/air flame burning velocities for equivalence ratios from 0.9 to 1.4 in a spherical, constant volume device. Experimental burning velocities produced with the aid of an optically thin radiation model are about 17 % greater than those obtained with an adiabatic model. Characterization of flame stretch based on the product of Markstein and Karlovitz numbers indicates that while many experimental data are nearly stretch-free, those for slower burning velocities, smaller flame radii, and leaner conditions may not be. Limiting the data to regions estimated to be stretch-free requires extrapolation away from the experimental conditions to extract burning velocities near ambient conditions, e.g., at (298 K, 101 kPa). Lower uncertainty, desirable for kinetic model validation, is obtained by interpolating between experimental conditions, e.g., at (400 K, 304 kPa). Since thermal radiation and flame stretch were found to affect the inferred burning velocities of difluoromethane/air constant volume spherical flames, they should also be considered during data reduction of other mildly flammable refrigerants.

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Section: Data Reductionmentioning

confidence: 99%

Effects of stretch and thermal radiation on difluoromethane/air burning velocity measurements in constant volume spherically expanding flames

Burrell

Pagliaro

Linteris

2019

Proceedings of the Combustion Institute

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“…When required conditions are met, combustion is initiated. Confinement effects are minimized by limiting the use flame radii to 8% of the vessel radius [22]. By employing a Schlieren optical setup, the system generates an image of the working area.…”

Section: Experimental Methodsologymentioning

confidence: 99%

“…(5) is fitted or plotted to attain u L , a safety factor was included, choosing 10 mm as the minimum flame radius for observation in this study. Additionally, in order to minimize radiation uncertainty, flame radii were limited to <2 cm [22].…”

Section: Theory and Analysismentioning

confidence: 99%

Characterization of critical stretch rate using outwardly propagating spherical flames

Rosa-Urbalejo¹,

Martínez-Martínez²,

Sánchez-Cruz³

2018

THERM SCI

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Original scientific paper https://doi.org/10.2298/TSCI170809071ROutwardly propagating spherical flames within a constant volume combustion chamber are studied to analyse the non-linear relationship between flame stretch and flame speed, enabling a critical appraisal of a methodology proposed for characterizing the critical stretch rate. Four fuels, namely methane, propane, methanol, and ethanol in air, are chosen to investigate the correlation between maximum critical stretch rate and the flame extinction across a range of equivalence ratios at various ambient conditions in under-driven flames, and to compare the hypothesis against data from the traditional counter-flowing flame technique. Flame propagation is recorded via high-speed Schlieren photography, and low ignition energies are achieved via a variable capacitive-discharge supply, enabling the critical early stages of flame propagation, critical stretch rate, and the sensitivity of the non-linear methodology to ignition energy to be systematically analysed. The non-linear methodology shows partial agreement with extinction stretch rate from counter flowing flames, particularly in the case of gaseous fuels. Although the fuel vapour data lies between previous extinction stretch rate measurements using the counter-flowing flame methodology, and predictions from chemical kinetic schemes, a 40% deviation is observed. A mathematical expression was produced to determine the critical stretch at the specific conditions of the present work.

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“…accuracy of the models for the burned mass fraction [9], stretch effects [10], influence of burnt gases equilibrium state [11] and of radiation [4]) and problems in flame instability detection [12]. This method has received particular attention in recent years [4,10,[13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

“…and the pressure technique [16,17,19,20]. In these studies, a specific attention was paid to the sphericity of the chamber.…”

Section: Introductionmentioning

confidence: 99%

Laminar flame speed determination at high pressure and temperature conditions for kinetic schemes assessment

Halter

Dayma

Serinyel

et al. 2021

Proceedings of the Combustion Institute

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Given the experimental difficulties, most of the available flame speed database is for relatively reduced thermodynamic conditions and for non-simultaneous variations of pressure and temperature. This limitation may be overpassed by using spherically expanding flames with the constant volume method. This methodology, introduced in the 30s by Lewis and von Elbe, requires the knowledge of the pressure evolution in the combustion chamber. It has been penalized for a long time because of the underlying assumptions and problems in flame instability detection. This method has been greatly renewed recently by Egolfopoulos following a coupled experimental/numerical approach integrating the effects of radiation and dissociation while maintaining moderate computing costs. In parallel with this study, we have worked on an alternative method providing a maximum of information for each test minimizing uncertainties. The current study uses a new experimental device allowing simultaneous recording of pressure and flame radius inside the chamber during the full combustion process. The direct use of these data over the whole flame propagation allows testing kinetic schemes over large pressure and temperature domains with good accuracy. These new experimental targets allowed the identification of key reactions needing improvements.

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Measurement of the laminar burning velocity using the confined and unconfined spherical flame methods – A comparative analysis

Cited by 60 publications

References 49 publications

Effects of stretch and thermal radiation on difluoromethane/air burning velocity measurements in constant volume spherically expanding flames

Effects of stretch and thermal radiation on difluoromethane/air burning velocity measurements in constant volume spherically expanding flames

Characterization of critical stretch rate using outwardly propagating spherical flames

Laminar flame speed determination at high pressure and temperature conditions for kinetic schemes assessment

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