Numerical and experimental investigations on the influence of preheating and dilution on transition of laminar coflow diffusion flames to Mild combustion regime

Abtahizadeh, Ebrahim; Sepman, Alexey; Pérez, Francisco E. Hernández; Oijen, J.A. van; Mokhov, Alexander; Goey, de Lph Philip; Levinsky, Howard

doi:10.1016/j.combustflame.2013.05.020

Cited by 28 publications

(28 citation statements)

References 37 publications

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“…Similar observations were reported in jet in hot crossflow [12]. The importance of autoignition appearing at the most reactive mixture fraction, Z MR , was also noted in [13] at the flame base. These kernels then propagated towards stoichiometric and richer mixture.…”

Section: Introductionsupporting

confidence: 84%

Autoignition and flame propagation in non-premixed MILD combustion

Doan

Swaminathan

2019

Combustion and Flame

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Direct Numerical Simulation (DNS) data of Moderate or Intense Low-oxygen Dilution (MILD) combustion are analysed to gather insights on autoignition and flame propagation in MILD combustion. Unlike in conventional combustion, the chemical reactions occur over a large portion of the computational domain. The presence of ignition and flame propagation and their coexistence are studied through spatial and statistical analyses of the convective, diffusive and chemical effects in the species transport equations. Autoignition is observed in regions with lean mixtures because of their low ignition delay times and these events propagate into richer mixtures either as a flameor ignition. This is found to be highly dependent on the mixture fraction length scale, Z , and autoignition is favoured when Z is small.

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Section: Introductionsupporting

confidence: 84%

Autoignition and flame propagation in non-premixed MILD combustion

Doan

Swaminathan

2019

Combustion and Flame

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“…De Joannon et al [2,3] studied a methane counterflow configuration with various hot and diluted fuel and oxidiser conditions, commenting on significant changes introduced with preheat and dilution to the Heat Release Rate (HRR), including the appearance of a double-peaked HRR profile and a lack of correlation of the highest HRR peak with the stoichiometric mixture fraction, depending on dilution configuration. Steady methane counterflow flames reported by Abtahizadeh et al [12,13] showed extended HRR regions and reduced NO formation with preheat and dilution, while autoignition behaviour depended on whether the reactant oxidiser, fuel, or both were diluted with hot combustion products. Sorrentino et al [14] performed a similar study investigating non-premixed autoignition behaviour with an inert diluent, concluding that, in agreement with [13], autoignition behaviour depended heavily on dilution configuration.…”

Section: Introductionmentioning

confidence: 99%

“…Steady methane counterflow flames reported by Abtahizadeh et al [12,13] showed extended HRR regions and reduced NO formation with preheat and dilution, while autoignition behaviour depended on whether the reactant oxidiser, fuel, or both were diluted with hot combustion products. Sorrentino et al [14] performed a similar study investigating non-premixed autoignition behaviour with an inert diluent, concluding that, in agreement with [13], autoignition behaviour depended heavily on dilution configuration. Coriton et al [5] commented on the lack of sudden extinction associated with MILD flames, a finding also evident in earlier work [1,9,10], and discussed differences in behaviour based on the composition and temperature of hot product diluent in turbulent experimental [15] and laminar numerical [5] methane counterflow flames.…”

Section: Introductionmentioning

confidence: 99%

Simulations of laminar non-premixed flames of kerosene with hot combustion products as oxidiser

Sidey

Giusti

Mastorakos

2016

Combustion Theory and Modelling

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The effects of hot combustion product dilution in a pressurised kerosene-burning system at gas turbine conditions were investigated with laminar counterflow flame simulations. Hot combustion products from a lean (φ = 0.6) premixed flame were used as an oxidiser with kerosene surrogate as fuel in a non-premixed counterflow flame at 5, 7, 9 and 11 bar. Kerosene-hot product flames, referred to as 'MILD', exhibit a flame structure similar to that of kerosene-air flames, referred to as 'conventional', at low strain rates. The Heat Release Rate (HRR) of both conventional and MILD flames reflects the pyrolysis of the primary and intermediate fuels on the rich side of the reaction zone. Positive HRR and OH regions in mixture fraction space are of similar width to conventional kerosene flames, suggesting that MILD flames are thin fronts. MILD flames do not exhibit typical extinction behaviour, but gradually transition to a mixing solution at very high rates of strain (above A = 160, 000 s −1 for all pressures). This is in agreement with literature that suggests heavily preheated and diluted flames have a monotonic S-shaped curve. Despite these differences in comparison with kerosene-air flames, MILD flames follow typical trends as a function of both strain and pressure. Further still, the peak locations of the overlap of OH and CH 2 O mass fractions in comparison with the peak HRR indicate that the pixel-by-pixel product of OH-and CH 2 O-PLIF signals is a valid experimental marker for non-premixed kerosene MILD and conventional flames.

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“…MILD combustion has been studied extensively using computational fluid dynamics (CFD) as well. Abtahizadeh et al and Sepman et al investigated the laminar JHC burner from University of Groningen using detailed chemistry (Abtahizadeh et al, 2013;Sepman et al, 2013b). In the former study, the effects of preheating and dilution were investigated, and it was found that in the presence of both preheating and dilution, the flame transitions into the MILD regime, and stabilizes via autoignition.…”

Section: Introductionmentioning

confidence: 99%

Modeling Temperature Variations in MILD Combustion Using MuSt-FGM

2020

Self Cite

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The energy demand in the world is ever increasing, and for some applications combustion is still the only reliable source, and will remain as such in the foreseeable future. To be able to mitigate the environmental effects of combustion, we need to move to cleaner technologies. Moderate or intense low oxygen dilution (MILD) combustion is one of these technologies, which offer less harmful emissions, especially nitric oxide and nitrogen dioxide (NOx). It is achieved by the recirculation of the flue gases into the fresh reactants, reducing the oxygen content, and thereby causing the oxidation reactions to occur at a milder pace, as the acronym suggests. This results in a flameless combustion process and reduces the harmful emissions to negligible amounts. To assist in the design and development of combustors that work in the MILD regime, reliable and efficient models are required. In this study, modeling of the effects of temperature variation in the oxidizer of a MILD combustion case is tackled. The turbulent scales are fully resolved by performing direct numerical simulations (DNS), and chemistry is modeled using multistage flamelet generated manifolds (MuSt-FGM). In order to model the temperature variations, a passive scalar which is created by normalizing the initial temperature in the oxidizer is defined as a new control variable. During flamelet creation, it was observed that not all the compositions are autoigniting. Several approaches are proposed to solve this issue. The results from these cases are compared against the ones performed using detailed chemistry. With the best performing approach, the ignition delay is predicted fairly well, but the average heat release rate is over-predicted. Some possible causes of this mismatch are also given in the discussion.

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Numerical and experimental investigations on the influence of preheating and dilution on transition of laminar coflow diffusion flames to Mild combustion regime

Cited by 28 publications

References 37 publications

Autoignition and flame propagation in non-premixed MILD combustion

Autoignition and flame propagation in non-premixed MILD combustion

Simulations of laminar non-premixed flames of kerosene with hot combustion products as oxidiser

Modeling Temperature Variations in MILD Combustion Using MuSt-FGM

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