Modeling Lifted Jet Flames in a Heated Coflow Using an Optimized Eddy Dissipation Concept Model

Evans, Michael J.; Medwell, Paul R.; Tian, Zhao Feng

doi:10.1080/00102202.2014.1002836

Cited by 98 publications

(92 citation statements)

References 45 publications

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“…Fig. 4c shows the Re Ã from the modified local coefficients, indicating values in the range 3-5 in the ignition region, in agreement with the modified EDC model recently proposed by Evans et al [29]. The distribution of C c (Fig.…”

Section: Determination Of Edc Coefficientssupporting

confidence: 78%

“…The results were further confirmed for the analysis of the Adelaide JHC flames with methane/hydrogen mixtures [27] and with several ethylenebased blends [28]. Recently, Evans et al [29] showed that adjusting the EDC coefficients C s and C c from their default value, 0.4083 and 2.1377, to 3.0 and 1.0, respectively, results in significantly improved performance of the EDC model under MILD conditions. Although the modification of the coefficients was shown to provide improved agreement between experiments and numerical simulations, it is still necessary to identify clear guidelines for the modification of the model coefficients in the context of MILD combustion, based on the specific turbulence and chemical features of such a regime.…”

Section: Introductionmentioning

confidence: 67%

“…As pointed out in the introduction, this has led several research groups to modify the classic EDC model coefficients to achieve better predictions of experimental data. In particular, the choice of the coefficients proposed by Evans et al [29] has interesting implications for what concerns the fine structure characteristics. Using the values of 3.0 and 1.0 for C s and C c , respectively, in Eq.…”

Section: Determination Of Energy Cascade Coefficients In Mild Combustionmentioning

confidence: 98%

See 2 more Smart Citations

Extension of the Eddy Dissipation Concept for turbulence/chemistry interactions to MILD combustion

Parente

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Contino

et al. 2016

Fuel

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Section: Determination Of Edc Coefficientssupporting

confidence: 78%

Section: Introductionmentioning

confidence: 67%

Section: Determination Of Energy Cascade Coefficients In Mild Combustionmentioning

confidence: 98%

See 1 more Smart Citation

Extension of the Eddy Dissipation Concept for turbulence/chemistry interactions to MILD combustion

Parente

Malik

Contino

et al. 2016

Fuel

206

135

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“…Since the initial publication of the EDC in the 1970s, several modifications of the EDC were proposed in literature [4][5][6][7][8], all of them claiming to improve the modeling results. In recent years, emphasis is on the extension of the EDC for Moderate or Intense Low oxygen Dilution (MILD) combustion conditions [7][8][9]. In contrast to classical turbulent combustion, MILD combustion features widely distributed reaction zones and slower reactions due to lower oxygen concentrations as well as slightly lower turbulence [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

The Eddy Dissipation Concept—Analysis of Different Fine Structure Treatments for Classical Combustion

et al. 2018

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The Eddy Dissipation Concept (EDC) is common in modeling turbulent combustion. Several model improvements have been proposed in literature; recent modifications aim to extend its validity to Moderate or Intense Low oxygen Dilution (MILD) conditions. In general, the EDC divides a fluid into a reacting and a non-reacting part. The reacting part is modeled as perfectly stirred reactor (PSR) or plug flow reactor (PFR). EDC theory suggests PSR treatment, while PFR treatment provides numerical advantages. Literature lacks a thorough evaluation of the consequences of employing the PFR fine structure treatment. Therefore, these consequences were evaluated by employing tests to isolate the effects of the EDC variations and fine structure treatment and by conducting a Sandia Flame D modeling study. Species concentration as well as EDC species consumption/production rates were evaluated. The isolated tests revealed an influence of the EDC improvements on the EDC rates, which is prominent at low shares of the reacting fluid. In contrast, PSR and PFR differences increase at large fine fraction shares. The modeling study revealed significant differences in the EDC rates of intermediate species. Summarizing, the PFR fine structure treatment might be chosen for schematic investigations, but for detailed investigations a careful evaluation is necessary.Energies 2018, 11, 1902 2 of 21 mixing rate only, and an infinitely fast chemistry assumption is possible. However, if turbulence and turbulent mixing decrease, the reaction progress can be limited by either mixing or chemistry. In this regime, finite rate chemistry is necessary to accurately describe the turbulence-chemistry interaction [7,12,13]. When using detailed chemistry with the EDC, the fine structures are typically treated as perfectly stirred reactors (PSRs), since educts are mixed on a molecular scale and mass is exchanged with the surroundings [4]. The fine structure state is determined by solving the PSR to steady-state, which is numerically expensive due to the strong nonlinearity in the reaction source terms. Some EDC implementations, therefore, treat the fine structures as plug flow reactors (PFR) [7,[16][17][18][19]. These PFRs are solved for the fine structure residence time, implying that the fine structures are spatially isolated structures in the fluid only evolving in time. Since fine structure residence times are typically small (approx. O 10 −7 to O 10 −3 seconds) for classical turbulent combustion, the numerical effort to solve the detailed chemistry in a PFR is significantly reduced. However, the latter approach is not in line with the EDC theory. Although the PFR fine structure treatment was employed in many published research works, e.g., [16][17][18][19][20][21], only De et al. [17], Li et al. [16], and Lewandowski and Ertesvaag [18] commented on the consequences of the PFR simplification. However, none of them performed an in-depth analysis of species profiles and species consumption rates.De et al. [17] state that the PSR and PFR results are only sim...

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“…The inclusion of finite-rate chemistry has a significant impact on the accuracy of turbulent, MILD flame models, 14 and may require model adjustment against experimental data for different fuels and flow conditions. [15][16][17][18] Experimentally, non-premixed MILD jet flames have shown resilience to inlet conditions. 4,19 Beyond of the MILD regime, however, the lift-off heights of autoigniting jet flames may rapidly increase or decrease with small increases in oxygen, temperature or velocity depending on small differences in initial ambient conditions.…”

mentioning

confidence: 99%

Ignition Characteristics in Spatially Zero-, One- and Two-Dimensional Laminar Ethylene Flames

Evans

Medwell

Tian

et al. 2015

22nd AIAA Computational Fluid Dynamics Conference

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Combustion in next-generation aero-engines may occur in conditions in, or approaching, moderate or intense low oxygen dilution (MILD) combustion. Under these conditions, fresh fuel is injected into a hot, low oxygen environment. Autoignition delays for ethylene, with detailed chemical kinetics, in three different oxidants are systematically analysed in a simulated perfectly-stirred batch reactor (batch PSR), with initial conditions based on the composition and adiabatic mixing temperature of the separate fuel and oxidant streams. The analysis of the same non-premixed streams in a transient, one-dimensional, opposed laminar dffusion flame shows ignition initiating at the same equivalence ratio for a diluted ethylene fuel with a high temperature air oxidant, albeit over-predicting ignition delay. Further analysis through means of a two-dimensional simulation shows good agreement between the batch PSR analysis and the location of the flame base. These analysis are subsequently applied to a MILD flame and a flame bordering the MILD and autoignitive lifted-flame regimes. Whilst the batch PSR analysis is able to predict the ignition equivalence ratio of the transitional flame, agreement with lift-off height is superior using a measure of 10K increase above oxidant conditions. This temperature metric is also applied to a MILD flame to show good agreement between a 10K temperature increase and visible chemiluminescence, however occurring in richer conditions than predicted by the batch PSR. The onset of thermal runaway in a batch PSR shows good predictive value for ignition in hot, vitiated environments, such as those anticipated in next generation aero-engines, despite the signicant differences in flame structure between ignition in the lifted and MILD combustion regimes

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Modeling Lifted Jet Flames in a Heated Coflow Using an Optimized Eddy Dissipation Concept Model

Cited by 98 publications

References 45 publications

Extension of the Eddy Dissipation Concept for turbulence/chemistry interactions to MILD combustion

Extension of the Eddy Dissipation Concept for turbulence/chemistry interactions to MILD combustion

The Eddy Dissipation Concept—Analysis of Different Fine Structure Treatments for Classical Combustion

Ignition Characteristics in Spatially Zero-, One- and Two-Dimensional Laminar Ethylene Flames

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