DNS study of the optimal heat release rate marker in premixed methane flames

Chi, Cheng; Janiga, Gábor; Zähringer, Katharina; Thévenin, Dominique

doi:10.1016/j.proci.2018.07.095

Cited by 22 publications

(13 citation statements)

References 28 publications

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“…Therefore, when SEF propagates from points B to A, the HRR and radical concentrations both increase, as shown in Figure 2 [OH][CH 2 O] has a slightly better linear correlation with the HRR. This was also observed for turbulent premixed CH 4 /air flames simulated by Chi et al 10 For quantitative comparison, the correlation coefficients are plotted in Figure 5. Consistent with the scatter plots in Figure 4, the correlation coefficient for [OH][CH 2 O] is higher than that for [H][CH 2 O] for both ignition energies.…”

Section: Resultssupporting

confidence: 74%

“…According to their results, the product of CH 2 O and OH concentrations was shown to be a reliable indicator for the HRR distribution. Since then, the combined molar concentration [OH][CH 2 O] has been widely adopted in numerous studies for different flame types (e.g., premixed 4,9,10 and non-premixed flames, 11 autoignition-assisted flames, 1 and conventional freely propagating flames 2 ), different flame configurations (e.g., Bunsen flames 9 and spray flames 1,12 ), different flow conditions (e.g., counterflow flames, 13 jet flames, 14 and turbulent flames 4,9 ), and different fuels (e.g., complex hydrocarbons 1,12 and multi-component fuels 15 In practical turbulent combustion processes, the local flame front might be highly curved and stretched. 16−18 For example, in spark-ignition engines, the self-sustained propagation flame develops from an ignition kernel, which is affected by a high positive stretch rate, and in fuel-lean turbulent combustion, there is local flame quenching and reignition processes caused by a high strain/stretch rate.…”

Section: Introductionmentioning

confidence: 99%

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Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames

et al. 2021

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Accurate quantification of heat release rate (HRR) profiles is useful for identifying important combustion processes in practical engines. This study aims to show whether the conventional HRR markers can still be used for highly stretched premixed methane/air flames with and without hydrogen addition. The correlation of formaldehyde-based molar concentrations, [H][CH 2 O] and [OH][CH 2 O], with HRR is numerically studied for highly stretched premixed CH 4 /air and CH 4 /H 2 /air flames. Two types of premixed flames are considered: the spherically expanding flame (SEF) starting from a highly positively stretched ignition kernel and the Bunsen flame with a high negative stretch rate at the flame tip. It is found that both [H][CH 2 O] and [OH][CH 2 O] can qualitatively describe the spatial distribution of HRR profiles in these two types of flames. In comparison to [H][CH 2 O], [OH][CH 2 O] is slightly better because it has a higher correlation coefficient and weaker sensitivity to the stoichiometry. However, during the ignition-influenced regime of SEFs, the magnitude of HRR cannot be accurately correlated by the concentrations of CH 2 O, OH, and H. Besides, hydrogen addition does not change the good spatial reconstruction qualities of these two HRR markers when its volume fraction in methane/hydrogen binary fuel blends is below 70%. The present results demonstrate that the conventional HRR markers, [OH][CH 2 O] and [H][CH 2 O], can be used to quantify the shape of HRR profiles even for highly stretched premixed flames with a small amount of hydrogen addition. Nevertheless, the magnitude of HRR cannot be accurately correlated by these two HRR markers for a highly stretched ignition kernel and hydrogen-dominated binary fuel blends.

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Section: Resultssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames

et al. 2021

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“…One can deduce the LIF signals using the DNS data and thus it is possible to evaluate the adequacy of these methods by comparing the heat release from the DNS to those obtained using the deduced LIF signals. This has been done in many past studies for premixed combustion (Chi et al, 2018;Minamoto and Swaminathan, 2014;Nikolaou and Swaminathan, 2014;Wabel et al, 2018) and also for premixed MILD combustion (Minamoto and Swaminathan, 2014). However, it is not quite easy to deduce the chemiluminescence signal from DNS unless the…”

Section: Markers For Heat Releasementioning

confidence: 99%

“…Þrather than a single scalar were good in identifying HRR regions in MILD combustion (Chi et al, 2018;Minamoto and Swaminathan, 2014;Nikolaou and Swaminathan, 2014;Wabel et al, 2018). However, these studies are for premixed combustion under either conventional or MILD conditions.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Markers for Combustion Mode and Heat Release in MILD Combustion Using DNS Data

Doan

Swaminathan

2019

Combustion Science and Technology

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Various commonly used markers for heat release are assessed using direct numerical simulation (DNS) data for Moderate or Intense Lowoxygen Dilution (MILD) combustion to find their suitability for nonpremixed MILD combustion. The laser-induced fluorescence (LIF) signals of various markers are synthesized from the DNS data to construct their planar (PLIF) images which are compared to the heat release rate images obtained directly from the DNS data. The local OH values in heat releasing regions are observed to be very small compared to the background level coming from unreacted mixture diluted with exhaust gases. Furthermore, these values are very much smaller compared to those in burnt regions. This observation rises questions on the use of OH-PLIF for MILD combustion. However, the chemiluminescent image obtained using OH Ã is shown to correlate well with the heat release. Two scalar-based PLIF markers,, correlate well with the heat release. Flame index (FI) and chemical explosive mode analyses (CEMA) are used to identify premixed and non-premixed regions in MILD combustion. Although there is some agreement between the CEMA and FI results, large discrepancies are still observed. The schlieren images deduced from the DNS data showed that this technique can be used for a quick and qualitative identification of MILD combustion before applying expensive laser diagnostics.

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“…DINO has been extensively used in numerous combustion studies, e.g. (Chi et al 2017(Chi et al , 2018(Chi et al , 2019(Chi et al , 2021Thévenin 2017, 2019), in which the proper coupling between chemical reactions, turbulent transport, and heat exchange has been fully validated.…”

Section: Numerical Simulations and Configurationsmentioning

confidence: 99%

Transient Ignition of Premixed Methane/Air Mixtures by a Pre-chamber Hot Jet: a DNS Study

Chi

Abdelsamie

Thévenin

2021

Flow Turbulence Combust

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The present study investigates the transient processes controlling ignition by a hot jet issued from a pre-chamber. Direct numerical simulations (DNS) have been performed to study the characteristics of the turbulent jet flow and of the associated flame during the whole ignition process, quantifying the relevant physicochemical interactions between pre-chamber and main chamber. Thanks to a detailed analysis of the DNS results, the transient ignition is found to consist of three main sequential processes: (1) near-orifice local ignition in the main chamber; (2) further flame development supported by the jet flow; and (3) global ignition and propagation of a self-sustained flame in the main chamber, independently from the hot jet. The characteristic time-scale of the hot jet as well as jet-induced effects (local enrichment, supply of radicals and heat) are found to be essential for successful ignition in the main chamber. A more intense turbulence in the main chamber appears to support local ignition. However, it also induces local quenching, thus delaying global ignition. An ignition threshold based on a critical Damköhler number is a promising concept, but is not sufficient to describe the process in all its complexity.

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DNS study of the optimal heat release rate marker in premixed methane flames

Cited by 22 publications

References 28 publications

Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames

Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames

Analysis of Markers for Combustion Mode and Heat Release in MILD Combustion Using DNS Data

Transient Ignition of Premixed Methane/Air Mixtures by a Pre-chamber Hot Jet: a DNS Study

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DNS study of the optimal heat release rate marker in premixed methane flames

Cited by 22 publications

References 28 publications

Heat Release Rate Markers for Highly Stretched Premixed CH4/Air and CH4/H2/Air Flames

Heat Release Rate Markers for Highly Stretched Premixed CH4/Air and CH4/H2/Air Flames

Analysis of Markers for Combustion Mode and Heat Release in MILD Combustion Using DNS Data

Transient Ignition of Premixed Methane/Air Mixtures by a Pre-chamber Hot Jet: a DNS Study

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Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames

Heat Release Rate Markers for Highly Stretched Premixed CH₄/Air and CH₄/H₂/Air Flames