Effects of turbulent length scale on the bending effect of turbulent burning velocity in premixed turbulent combustion

Varma, Arun Ravi; Ahmed, Umair; Klein, Markus; Chakraborty, Nilanjan

doi:10.1016/j.combustflame.2021.111569

Cited by 19 publications

(7 citation statements)

References 58 publications

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“…7, for both methane/ air and ammonia/air flames examined in this work. This finding is in agreement with previous findings reported in Han and Huh (2008); Chakraborty et al (2014); Nivarti and Cant (2017); Ahmed et al (2019); ; Brearley et al (2020); Klein et al (2020);Varma et al (2021); Song et al (2021). However, the validity of this hypothesis might not be maintained for premixed turbulent planar flames with a global Lewis number smaller or higher than unity (Haworth and Poinsot 1992;Trouvé and Poinsot 1994;Bell et al 2007;Han and Huh 2008;Chakraborty et al 2014), and for flames with significantly non-zero mean flame front curvature, i.e.…”

Section: Assessing the Validity Of Damköhler's First Hypothesissupporting

confidence: 90%

“…According to this well-known hypothesis (Damköhler 1940), the ratio of the turbulent burning velocity to the unstrained premixed laminar burning velocity is equal to the ratio of the wrinkled to the unwrinkled flame surface area. On one hand, this hypothesis was successfully confirmed using DNS studies of Chakraborty and Cant (2005), Hawkes and Chen (2006), Han and Huh (2008), Nivarti and Cant (2017), Ahmed et al (2019), Klein et al (2020), Brearley et al (2020), andVarma et al (2021) for statistically premixed turbulent planar flames with unity Lewis number. It should be emphasized that the primary fuels for these studies are mostly methane and hydrogen.…”

Section: Introductionmentioning

confidence: 71%

“…A similar simplification has been previously performed in the literature, see e.g. Boger et al (1998); Chakraborty (2007); Han and Huh (2008); Dopazo et al (2015); Brearley et al (2020); Kasten et al (2021);Varma et al (2021).…”

Section: Flame Configurationmentioning

confidence: 84%

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Inner Flame Front Structures and Burning Velocities of Premixed Turbulent Planar Ammonia/Air and Methane/Air Flames

Tamadonfar

Karimkashi

Kaario

et al. 2022

Flow Turbulence Combust

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Ammonia ($$\mathrm {NH_3}$$ NH 3 ) has attracted interest as a future carbon-free synthetic fuel due to its economic storage and transportation. In this study, quasi direct numerical simulations (quasi-DNS) with detailed-chemistry have been performed in 3-D to examine the flame thickness and assess the validity of Damköhler’s first hypothesis for premixed turbulent planar ammonia/air and methane/air flames under different turbulence levels. The Karlovitz number is systematically changed from 4.26 to 12.06 indicating that all the test conditions are located within the thin reaction zones combustion regime. Results indicate that the ensemble average values of the preheat zone thickness deviate slightly from the thin laminar flamelet assumption, while the reaction zone regions remain relatively intact. Following the balance equation of reaction progress variable gradient, normal strain rate and the tangential diffusion component of flame displacement speed variation in the normal direction to the flame surface are found to be responsible for thickening the flame. However, the sum of reaction and normal diffusion components of flame displacement speed variation in the normal direction to the flame surface is in charge of flame thinning for ammonia/air and methane/air flames. In addition, the validity of Damköhler’s first hypothesis is confirmed by indicating that the ratio of the turbulent burning velocity to the unstrained premixed laminar burning velocity is relatively equal to the ratio of the wrinkled to the unwrinkled flame surface area. Furthermore, the probability density functions of the density-weighted flame displacement speed show that the bulk of flame elements propagate identical to the unstrained premixed laminar flame.

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Section: Assessing the Validity Of Damköhler's First Hypothesissupporting

confidence: 90%

Section: Introductionmentioning

confidence: 71%

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Inner Flame Front Structures and Burning Velocities of Premixed Turbulent Planar Ammonia/Air and Methane/Air Flames

Tamadonfar

Karimkashi

Kaario

et al. 2022

Flow Turbulence Combust

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“…The values of u ′ / s 0 l and l t / δ z do not change significantly in comparison to their initial values in the timescale of ignition so the initial values can be considered in the context of equation (9). Several analyses on turbulent premixed combustion [72][73][74][75][76][77][78][79] reported that Ξ varies linearly (i.e. n Ξ ≈ 1.0) with u ′ for small turbulence intensities, whereas Ξ becomes less sensitive to the changes u ′ for large turbulence intensities leading to n Ξ < 1.…”

Section: Physical Explanations For the Effects Of Fuel Lewis Number O...mentioning

confidence: 99%

Effects of fuel Lewis number on the minimum ignition energy and its transition for turbulent homogeneous fuel–air mixtures

Papapostolou

Chakraborty

2023

International Journal of Spray and Combustion Dynamics

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The effects of fuel Lewis number on the minimum ignition energy (MIE) requirements for ensuring successful thermal runaway, and self-sustained flame propagation have been analysed for forced ignition of homogeneous fuel–air mixtures under decaying turbulence for a wide range of initial turbulence intensities using three-dimensional direct numerical simulations. The minimum energy demand for ensuring self-sustained flame propagation has been found to be greater than that for ensuring only thermal runaway irrespective of its outcome for large turbulence intensities, and the minimum ignition energy increases with increasing rms turbulent velocity irrespective of the fuel Lewis number. The MIE values have been found to increase more sharply with increasing turbulence intensity beyond a critical value for all fuel Lewis numbers considered here. The variations of the normalised MIE (MIE normalised by its laminar value) with increasing turbulence intensity beyond the critical point follow a power-law and the power-law exponent has been found to increase with an increase in fuel Lewis number. This behaviour has been explained using a scaling analysis. The stochasticity associated with forced ignition has been demonstrated by using different realisations of statistically similar turbulent flow fields for the energy inputs corresponding to the MIE and successful outcomes are obtained in most instances, justifying the evaluation of the MIE values in this analysis.

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“…Nevertheless, fundamental study of the effect of length scales is important in order to explore the combustion physics, to define the constraints on flamelet-based modelling (Driscoll et al 2020;Skiba et al 2017Skiba et al , 2021Hawkes and Chen 2006) and to suggest model improvements. Recent papers have analysed the variations in flame speed with 0 both experimentally (Kim et al 2020;Mohammadnejad et al 2021) and using DNS (Yu and Lipatnikov 2017a, b;Kulkarni and Bisetti 2021a;Kulkarni and Bisetti 2021b;Varma et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Turbulence Intensity and Length Scale Effects on Premixed Turbulent Flame Propagation

Trivedi

Cant

2021

Flow Turbulence Combust

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The effects of varying turbulence intensity and turbulence length scale on premixed turbulent flame propagation are investigated using Direct Numerical Simulation (DNS). The DNS dataset contains the results of a set of turbulent flame simulations based on separate and systematic changes in either turbulence intensity or turbulence integral length scale while keeping all other parameters constant. All flames considered are in the thin reaction zones regime. Several aspects of flame behaviour are analysed and compared, either by varying the turbulence intensity at constant integral length scale, or by varying the integral length scale at constant turbulence intensity. The turbulent flame speed is found to increase with increasing turbulence intensity and also with increasing integral length scale. Changes in the turbulent flame speed are generally accounted for by changes in the flame surface area, but some deviation is observed at high values of turbulence intensity. The probability density functions (pdfs) of tangential strain rate and mean flame curvature are found to broaden with increasing turbulence intensity and also with decreasing integral length scale. The response of the correlation between tangential strain rate and mean flame curvature is also investigated. The statistics of displacement speed and its components are analysed, and the findings indicate that changes in response to decreasing integral length scale are broadly similar to those observed for increasing turbulence intensity, although there are some interesting differences. These findings serve to improve current understanding of the role of turbulence length scales in flame propagation.

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Effects of turbulent length scale on the bending effect of turbulent burning velocity in premixed turbulent combustion

Cited by 19 publications

References 58 publications

Inner Flame Front Structures and Burning Velocities of Premixed Turbulent Planar Ammonia/Air and Methane/Air Flames

Inner Flame Front Structures and Burning Velocities of Premixed Turbulent Planar Ammonia/Air and Methane/Air Flames

Effects of fuel Lewis number on the minimum ignition energy and its transition for turbulent homogeneous fuel–air mixtures

Turbulence Intensity and Length Scale Effects on Premixed Turbulent Flame Propagation

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