Direct Numerical Simulation of hydrogen combustion at auto-ignitive conditions: Ignition, stability and turbulent reaction-front velocity

Gruber, Andrea; Bothien, Mirko R.; Ciani, Andrea; Aditya, Konduri; Chen, Jacqueline H.; Williams, Forman A.

doi:10.1016/j.combustflame.2021.02.031

Cited by 41 publications

(14 citation statements)

References 44 publications

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“…For a standard premixed H 2 -air flame with φ = 0.7, the maximum heat release rate occurs at T ∼ 895 K. The fact that the heat release rate profiles show two distinct peaks for the 385 K isotherm and a merged single peak for the 983 K isotherm suggests that these data points represent a typical upstream flame-flame interaction without any possibility of autoignition of the upstream gases between the flames. Thus, S d /S L enhancement observed here is attributed to the interacting flame theory, not due to the acceleration by autoignition front, as reported in ( [53][54][55][56][57]) for higher reactant temperature and/or pressure conditions. Incidentally, the fact that the two heat release rate peaks already merged into a single peak for the 983 K isotherm data is attributed to the unique structure of the hydrogen-air flames where the heat release peak is located further upstream relative to that in hydrocarbon flames.…”

Section: Local Flame Speed and Structuresupporting

confidence: 75%

Local flame displacement speeds of hydrogen-air premixed flames in moderate to intense turbulence

Song,

Dave,

et al. 2021

Preprint

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Comprehensive knowledge of local flame displacement speed, S d , in turbulent premixed flames is crucial towards the design and development of hydrogen fuelled next-generation engines. Premixed hydrogen-air flames are characterized by significantly higher laminar flame speed compared to other conventional fuels. Furthermore, in the presence of turbulence, S d is enhanced much beyond its corresponding unstretched, planar laminar value S L . In this study, the effect of high Karlovitz number (Ka) turbulence on densityweighted flame displacement speed, S d , in a H 2 -air flame is investigated. Recently, it has been identified that flame-flame interactions in regions of large negative curvature govern large deviations of S d from S L , for moderately turbulent flames. An interaction model for the same has also been proposed. In this work, we seek to test the interaction model's applicability to intensely turbulent flames characterized by large Ka. To that end, we investigate the local flame structures: thermal, chemical structure, the effect of curvature, along the direction that is normal to the chosen isothermal surfaces. Furthermore, relative contributions of the transport and chemistry terms to S d are also analyzed. It is found that, unlike the moderately turbulent premixed flames, where enhanced S d is driven by interactions among complete flame structures, S d enhancement in high Re t and high Ka flame is predominantly governed by local interactions of the isotherms.

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Section: Local Flame Speed and Structuresupporting

confidence: 75%

Local flame displacement speeds of hydrogen-air premixed flames in moderate to intense turbulence

Song,

Dave,

et al. 2021

Preprint

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“…All elements with gains larger than 0.5 are well reproduced both in gain and in phase confirming the correctness of the assumptions that are made in deriving Eq. (15). Additionally, this excellent match also verifies the consistency of the system identification methodology applied in Ref.…”

Section: Flame Transfer Matrixsupporting

confidence: 74%

“…Research at Ansaldo Energia of Bothien and co-workers focuses on flame transfer functions and matrices. [8][9][10][11] Schulz and Noiray 12,13 as well as Aditya et al 14 and Gruber et al 15 investigate the occurrence of propagation and autoignition stabilized regimes of reheat flames. In contrast to propagation stabilized flames, only a few studies on analytical modelling approaches for autoignition flame acoustics exist.…”

Section: Introductionmentioning

confidence: 99%

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

Gant¹,

Cuquel²,

Bothien

2022

International Journal of Spray and Combustion Dynamics

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Modern gas turbines need to fulfil increasingly stringent emission targets on the one hand and exhibit outstanding operational and fuel flexibility on the other. Ansaldo Energia GT26 and GT36 gas turbine models address these requirements by employing a combustion system in which two lean premixed combustors are arranged in series. Due to the high inlet temperatures from the first stage, the second combustor stage predominantly relies on autoignition for flame stabilization. In this paper, the response of autoignition flames to temperature, pressure and velocity excitations is investigated. The gas turbine combustor geometry is represented by a backward-facing step. Based on the conservation equations an analytical model is derived by solving the linearized Rankine-Hugoniot conditions. This is a commonly used analytical approach to describe the relation of thermodynamic quantities up- and downstream of a propagation stabilized flame. In particular, the linearized Rankine-Hugoniot jump conditions are derived taking into account the presence of a moving discontinuity as well as upstream entropy inhomogeneities. The unsteady heat release rate of the flame is modelled as a linear superposition of flame transfer functions, accounting for velocity, pressure, and entropy disturbances, respectively. This results in a 3[Formula: see text]3 flame transfer matrix relating both primitive acoustic variables and the temperature fluctuations across the flame. The obtained analytical expression is compared to large eddy simulations with excellent agreement. A discussion about the contribution of the single terms to the modelling effort is provided, with a focus on autoignition flames.

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“…For instance, differential diffusion of atomic hydrogen into negatively curved cusps close to the trailing zone of a turbulent flame brush could promote local autoignition, which substantially accelerates flame propagation. However, such an effect has yet to be found in highly preheated mixtures only (Gruber et al 2021;Rieth et al 2021). At the room temperature and, in particular, under conditions of the present study, turbulent flames appear to be pulled waves.…”

Section: Leading Point Conceptmentioning

confidence: 99%

Influence of molecular transport on burning rate and conditioned species concentrations in highly turbulent premixed flames

et al. 2021

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Apparent inconsistency between (i) experimental and direct numerical simulation (DNS) data that show the significant influence of differential diffusion on the turbulent burning rate and (ii) recent complex-chemistry DNS data that indicate mitigation of the influence of differential diffusion on conditioned profiles of various local flame characteristics at high Karlovitz numbers, is explored by analysing new DNS data obtained from lean hydrogen–air turbulent flames. Both aforementioned effects are observed by analysing the same DNS data provided that the conditioned profiles are sampled from the entire computational domain. On the contrary, the conditioned profiles sampled at the leading edge of the mean flame brush do not indicate the mitigation, but are significantly affected by differential diffusion phenomena, e.g. because reaction zones are highly curved at the leading edge. This observation is consistent with a significant increase in the computed turbulent burning velocity with decreasing Lewis number, with all the results considered jointly being consonant with the leading point concept of premixed turbulent combustion. The concept is further supported by comparing DNS data obtained by allowing for preferential diffusion solely for a single species, either atomic or molecular hydrogen.

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Direct Numerical Simulation of hydrogen combustion at auto-ignitive conditions: Ignition, stability and turbulent reaction-front velocity

Cited by 41 publications

References 44 publications

Local flame displacement speeds of hydrogen-air premixed flames in moderate to intense turbulence

Local flame displacement speeds of hydrogen-air premixed flames in moderate to intense turbulence

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

Influence of molecular transport on burning rate and conditioned species concentrations in highly turbulent premixed flames

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