Turbulence–flame interactions in lean premixed dodecane flames

Aspden, A. J.; Bell, John B.; Day, Marc; Egolfopoulos, Fokion N.

doi:10.1016/j.proci.2016.07.068

Cited by 48 publications

(41 citation statements)

References 21 publications

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“…Recently, a number of studies conducted DNS of freely propagating fuel-lean turbulent premixed flames with different fuels with either detailed (Aspden et al, 2011(Aspden et al, , 2015Carlsson et al, 2014;Aspden et al, 2017) or reduced Lapointe et al, 2015) chemistry for different fuels (e.g. H2, CH4, propane, n-dodecane (in the increasing order of fuel Lewis number) by Aspden et al (2017); H2-air flames with equivalence ratios of 0.31 and 0.4 by Aspden et al (2011Aspden et al ( , 2015 and n-Heptane by Savard and Blanquart (2015) and Lapointe et al (2015)). These analyses also indicated that the overall burning rate quantified by volume-integrating reaction rate of the fuel (e.g.…”

Section: Resultsmentioning

confidence: 99%

Influence of the Lewis Number on Effective Strain Rates in Weakly Turbulent Premixed Combustion

Dopazo

Cifuentes

Alwazzan

et al. 2017

Combustion Science and Technology

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Newcastle University ePrints -eprint.ncl.ac.uk Dopazo C, Cifuentes L, Alwazzan D, Chakraborty N. Influence of the Lewis number on effective strain rates in weakly turbulent premixed combustion. ABSTRACTThe influence of the global Lewis number, Le, on the statistical behaviour of the 'effective' normal and tangential strain rates have been analysed based on three-dimensional DNS data of freely propagating statistically planar turbulent premixed flames with Le = 0.34, 0.60, 0.80, 1.00 and 1.20. The volumetric dilatation rate is found to be mostly positive and its magnitude increases with decreasing Le. The flow normal strain rate predominantly assumes positive values and thus tends to pull adjacent iso-scalar surfaces apart, which reduces scalar gradients.By contrast, the "added" normal strain rate due to derivatives of the displacement speed normal to iso-surfaces has the propensity to push them closer together, and therefore increase the magnitude of scalar gradients. The balance between flow and added normal strain rates along with the advective transport determines whether scalar gradients are enhanced or destroyed.Iso-surface elementary area stretching by the fluid flow increases with decreasing Lewis number, and the added tangential strain rate exhibits predominantly negative values and is determined by the correlation between displacement speed components and flame curvature.It has been found that turbulent flames with small values of Lewis number exhibit flame thinning and high values of the flame surface area and these tendency strengthens with decreasing Lewis number. This behaviour has been explained in detail in terms of the statistical behaviours of effective normal and tangential strain rates.

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Section: Resultsmentioning

confidence: 99%

Influence of the Lewis Number on Effective Strain Rates in Weakly Turbulent Premixed Combustion

Dopazo

Cifuentes

Alwazzan

et al. 2017

Combustion Science and Technology

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“…The pathways for water formation, one of the key products in hydrocarbon combustion, are strongly affected with increasing turbulence intensity for the positively-curved elements (Figure 9(c, left) To summarize, the largest variations in reaction pathways with increasing turbulence intensity occur for positively-curved elements; variations for the negatively-curved elements and saddlepoint elements are much weaker. in literature [10][11][12], is evident. For the lower Ka cases, the flame is thin and slightly wrinkled.…”

Section: Spherical Positively-curved Elements (E) Cylindrical Positivmentioning

confidence: 85%

“…We utilize the DNS data set from Aspden et al [11], which consists of a nominally onedimensional, lean (ϕ=0.7), premixed turbulent n-dodecane/air flame. The DNS is based on a Low-Mach number reacting flow model with mixture-averaged transport for molecular diffusion, Soret and Dufour transport, gravity and radiative processes are neglected [13,14].…”

Section: Methodsmentioning

confidence: 99%

Analysis of chemical pathways and flame structure for n-dodecane/air turbulent premixed flames

Dasgupta

Sun

Day

et al. 2019

Combustion and Flame

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This paper analyzes turbulence-chemistry interactions for an n-dodecane-air flame, focusing on the degree to which fuel oxidation pathways change in turbulent flames relative to their corresponding laminar flames. This work is based on a lean ( =0.7) ndodecane-air flame DNS database from Aspden et al. (Proc. Combust. Institute, 36 (2017) 2005. The relative roles of dominant reactions that release heat and produce/consume radicals are examined at various turbulence intensities and compared with stretched flame calculations from counterflow flames and perfectly stirred reactors.These results show that spatially integrated (i.e. integrated heat release or radical production rate metrics averaged over the entire flame) chemical pathways are relatively insensitive to turbulence intensity and mimic the behavior of stretched flames. In other words, the contribution of a given reaction to heat release or radical production, integrated over the entire flame, is nearly independent to turbulence. Localized analysis conditioned on topological feature of the flame and on temperature is also performed.The former analysis reveals that much larger alteration of pathways occurs in the positively-curved regions of the flame. The latter localized analysis shows that peak activity in the low temperature (i.e. below 1200K) region shift towards higher temperatures with increases in Karlovitz number. This result is particularly interesting given that prior work with lighter fuels showed the opposite behavior suggesting a disparate response of the reactions involved in the fuel oxidation process to increased turbulence.

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“…The simulation database that will be used for the present study consists of a series of DNS with detailed chemistry of statistically-stationary statistically-planar turbulent premixed methane flames in maintained homogeneous isotropic turbulence, [26,27,28]. The simulations were run using the well-established low Mach number combustion solver developed at the Center for Computational Sciences and Engineering at the Lawrence Berkeley National Laboratory.…”

Section: Dns Of Turbulent Premixed Methane Flamesmentioning

confidence: 99%

“…The chemical kinetics and transport were modelled using the GRIMech 3.0 without emissions chemistry [32], resulting in 35 species with 217 elementary reactions. The simulations were conducted at Λ = l/l F = 1, as part of the study reported in [27], matching the Karlovitz numbers of the Λ = 4 calculations reported in [26] (Ka = (u 3 l F )/(s 3 F l) = 1 and 36), along with a higher Karlovitz number case from [28] (Ka = 108) looking at more turbulent conditions. The conditions are shown on the regime diagram in figure 1, and span the conventionally-defined thin reaction zone.…”

Section: Dns Of Turbulent Premixed Methane Flamesmentioning

confidence: 99%

An a priori analysis of a DNS database of turbulent lean premixed methane flames for LES with finite-rate chemistry

Aspden

Zettervall

Fureby

2019

Proceedings of the Combustion Institute

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An a priori analysis of a DNS database of turbulent lean premixed methane flames is presented considering the relative effects of turbulence and LES filtering, along with a potential modelling approach for LES with finite-rate chemistry. The leading-order effect was found to be due to the filter operation; flame response to turbulence was a secondary effect, and manifested primarily as an increase in standard deviations about conditional means. It was found that the radicals O, H and OH were less impacted by the filter than other high-temperature radicals, which were significantly reduced in magnitude by the filter. By considering reaction path diagrams, key reactions have been identified that are responsible for disparities between the desired filtered reaction rates and the reaction rates evaluated using quantities available in LES calculations (i.e. the filtered species and temperature). More specifically, the hydrogen abstraction reactions that take CH 4 to CH 3 (by O, H and OH) were found to have particularly enhanced reaction rates, and dominate the reaction path. Under the conditions presented, reaction paths were found to be independent of turbulence intensity. In general, the filtered reaction rates from the DNS were found to align more closely with the filtered laminar profile than the reaction rate of filtered species and temperature, (but disparities were found to decrease with increasing Karlovitz number). A simple model for scaling reaction rates is considered based on filtered laminar flame profiles, and the resulting reaction paths demonstrate proof-of-concept of a simple approach for formulating a reaction rate model for LES with finite-rate chemistry.

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Turbulence–flame interactions in lean premixed dodecane flames

Cited by 48 publications

References 21 publications

Influence of the Lewis Number on Effective Strain Rates in Weakly Turbulent Premixed Combustion

Influence of the Lewis Number on Effective Strain Rates in Weakly Turbulent Premixed Combustion

Analysis of chemical pathways and flame structure for n-dodecane/air turbulent premixed flames

An a priori analysis of a DNS database of turbulent lean premixed methane flames for LES with finite-rate chemistry

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