Flame Self-interaction and Flow Topology in Turbulent Homogeneous Mixture n-Heptane MILD Combustion

Abo-Amsha, Khalil; Chakraborty, Nilanjan

doi:10.1007/s10494-023-00401-w

Cited by 2 publications

(4 citation statements)

References 26 publications

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“…In all cases, the majority of FSI events occur at , with the peak FSI frequencies occurring between and in most cases. This aligns with the results reported by Abo-Amsha and Chakraborty 19 for n-heptane MILD combustion where the peak frequency of FSI events was also found to be within the flame front ( ). A notable exception to this trend is the inhomogeneous mixture case at low dilution where the peak frequency of FSI events is clearly shifted further towards the burned gas side.…”

Section: Resultssupporting

confidence: 91%

“…This ensures that a satisfactory level of statistical convergence has been achieved. The above numerical procedure has been extensively used in the literature for the study of turbulent MILD combustion 7 – 12 , 19 , 23 , 35 …”

Section: Methodsmentioning

confidence: 99%

“…It was observed that the most common reaction zone structure has a pancake-like shape, which is consistent with experimental findings by Dally et al 6 The pancake shaped reaction structures were found to be the result of events such as autoignition, flames propagating into mixtures of reactants, products, intermediates and radicals, as well as the interactions between these flames 9 . Recently, Abo-Amsha and Chakraborty 19 employed an approach based on the critical point theory to analyse FSI topologies in turbulent homogeneous mixture MILD combustion of n-heptane. It was found that the cylindrical, tunnel like-topologies have the highest frequency of all FSI topologies, and the peak FSI frequency occurred at .…”

Section: Introductionmentioning

confidence: 99%

“…It was found that the cylindrical, tunnel like-topologies have the highest frequency of all FSI topologies, and the peak FSI frequency occurred at . Abo-Amsha and Chakraborty 19 also qualitatively assessed the effects of dilution level and initial turbulence intensity of the distribution on FSI events.…”

Section: Introductionmentioning

confidence: 99%

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Flame self-interactions in MILD combustion of homogeneous and inhomogeneous mixtures

Abo-Amsha,

Awad,

Chakraborty

2024

Sci Rep

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Flame self-interaction (FSI) events in Moderate or Intense Low-Oxygen Dilution (MILD) combustion of homogeneous and inhomogeneous mixtures of methane and oxidiser have been analysed using three-dimensional Direct Numerical Simulations (DNS). The simulations have been conducted at the same global equivalence ratio ($$\langle \phi \rangle = 0.8$$ ⟨ ϕ ⟩ = 0.8 ) for different levels of $$\mathrm {O_2}$$ O 2 concentration (dilution) and initial turbulence intensities. It has been reported that both homogeneous and inhomogeneous mixture MILD combustion cases exhibit significant occurrences of FSI events, with the peak frequency of FSI events occurring towards the burned gas side in all cases. Moreover, the frequency of FSI events increases with increasing dilution level and turbulence intensity, but the presence of mixture inhomogeneity leads to a reduction in total FSI events. In all cases, the cylindrical FSI topologies (i.e. tunnel formation and tunnel closure) were found to have a higher likelihood of occurrence compared to spherical FSI topologies (i.e. unburned and burned gas pockets). The geometries of FSI topologies were also analysed using the mean and Gaussian curvatures. It has been shown that the inward propagating spherical FSI topologies (i.e. unburned gas pockets) are associated with negative mean curvature, while outward propagating spherical FSI topologies (i.e. burned gas pockets) are associated with positive mean curvature. Moreover, tunnel formation (tunnel closure) FSI topologies predominantly exhibit either elliptic geometries with positive (negative) mean curvature or hyperbolic saddle geometries with negative (positive) mean curvature. It has been shown for the first time in MILD combustion that the mean values of kinematic restoration and dissipation terms in the transport equation of the magnitude of the reaction progress variable conditional upon the reaction progress variable tend to cancel each other in the vicinity of the critical points associated with cylindrical topologies. Thus, the singular contributions in these terms, which are obtained from analytical descriptions in the vicinity of tunnel formation and tunnel closure topologies, do not affect the balance equation of the magnitude of the gradient of the reaction progress variable. Consequently, there is no need for a separate model treatment for singularities in modelling approaches based on the magnitude of the gradient of the reaction progress variable. The FSI events in the reaction dominated and propagating flame regions of MILD combustion have also been analysed for the first time. It has been found that more FSI events occur in the reaction dominated region, particularly towards the burned gas side. However, the majority of spherical FSI topologies are found in the propagating flame region. The findings from this study indicate that turbulence intensity, dilution level and mixture inhomogeneity effects need to be considered in any attempt to extend flame surface-based modelling approaches to MILD combustion.

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