A spark ignition scenario in a temporally evolving mixing layer

Wawrzak, Agnieszka; Tyliszczak, Artur

doi:10.1016/j.combustflame.2019.07.045

Cited by 21 publications

(8 citation statements)

References 16 publications

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“…Furthermore, ignition was found to occur even when the kernel was introduced in a region located outside the flammability limits [9], which suggests that turbulence and mixing far from the igniter (non-local effects) can influence the ignition outcome. Similar non-local effects were recently evidenced through direct numerical simulations of a turbulent mixing layer [10]. In isotropic turbulence with inhomogeneous mixing, it was found that turbulence could also have an adverse effect on ignition by accelerating the dissipation of heat prior to establishing the flame front [4].…”

Section: Introductionsupporting

confidence: 73%

“…The effect of turbulence on the ignition process has been studied using simulations and experiments in the past [4,[8][9][10][11][12][13][14][15][16][17][18]. In premixed flames, fundamentals of vortex-kernel interaction have been investigated both experimentally [11,12] and numerically [13][14][15][16], leading to advances in understanding the cause of misfire and in characterizing ignition success and failure pathways.…”

Section: Introductionmentioning

confidence: 99%

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Data-driven analysis of relight variability of jet fuels induced by turbulence

Hassanaly

Tang

Barwey

et al. 2021

Combustion and Flame

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For safety purposes, reliable reignition of aircraft engines in the event of flame blow-out is a critical requirement. Typically, an external ignition source in the form of a spark is used to achieve a stable flame in the combustor. However, such forced turbulent ignition may not always successfully relight the combustor, mainly because the state of the combustor cannot be precisely determined. Uncertainty in the turbulent flow inside the combustor, inflow conditions, and spark discharge characteristics can lead to variability in sparking outcomes even for nominally identical operating conditions. Prior studies have shown that of all the uncertain parameters, turbulence is often dominant and can drastically alter ignition behavior. For instance, even when different fuels have similar ignition delay times, their ignition behavior in practical systems can be completely different. In practical operating conditions, it is challenging to understand why ignition fails and how much variation in outcomes can be expected. The focus of this work is to understand relight variability induced by turbulence for two different aircraft fuels, namely Jet-A and a variant named C1. A detailed, previously developed simulation approach is used to generate a large number of successful and failed ignition events. Using this data, the cause of misfire is evaluated based on a discriminant analysis that delineates the difference between turbulent initial conditions that lead to ignition or failure. From the discriminant analysis, a compressed sensing algorithm is then applied to help pinpoint the locations of relevant turbulent features. Findings from the discriminant analysis are confirmed with the time history of near kernel properties. Next, a clustering strategy is used to identify ignition and misfire modes. With this approach, it was determined that the cause of ignition failure is different for the two fuels. While it was found that Jet-A is influenced by fuel entrainment, C1 was found to be more sensitive to small scale turbulence features. A larger variability is found in the ignition modes of C1, which can be subject to extreme events induced by kernel breakdown.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Data-driven analysis of relight variability of jet fuels induced by turbulence

Hassanaly

Tang

Barwey

et al. 2021

Combustion and Flame

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“…The SAILOR code has been thoroughly verified in previous studies devoted to nonreactive flows [38,39] and number of combustion problems in jet flows [23,40,41] and mixing layers [22,42,43]. In all these cases it turned out to be very accurate.…”

Section: Methodsmentioning

confidence: 85%

“…Compared to the auto-ignition phenomenon a situation in spark-ignition problems seems even more complex. Here, the born flames can have very complex structures, e.g., a tribrachial one as shown by Chakraborty and Mastorakos [21], or their occurrence can be significantly conditioned by shear stresses, which arise between flow streams [22]. The presence of strong shear stresses causes that an initially assumed isotropic field evolves and becomes highly anisotropic leading to significantly different regimes than in the HIT conditions.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Hydrogen Auto-Ignition Process in an Isotropic and Anisotropic Turbulent Field

Wawrzak

Tyliszczak

2021

Energies

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The physical mechanisms underlying the dynamics of the flame kernel in stationary isotropic and anisotropic turbulent field are studied using large eddy simulations (LES) combined with a pdf approach method for the combustion model closure. Special attention is given to the ignition scenario, ignition delay, size and shape of the flame kernel among different turbulent regimes. Different stages of ignition are analysed for various levels of the initial velocity fluctuations and turbulence length scales. Impact of these parameters is found small for the ignition delay time but turns out to be significant during the flame kernel propagation phase and persists up to the stabilisation stage. In general, it is found that in the isotropic conditions, the flame growth and the rise of the maximum temperature in the domain are more dependent on the initial fluctuations level and the length scales. In the anisotropic regimes, these parameters have a substantial influence on the flame only during the initial phase of its development.

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“…The convective terms in the stochastic field equations equations are discretized applying TVD scheme with van Leer limiters. The applied code has been thoroughly verified in previous studies 19,25,[29][30][31] and it turned out to be very accurate.…”

Section: Methodsmentioning

confidence: 89%

Control of a Lifted H2/N2 Flame by Axial and Flapping Forcing: A Numerical Study

Tyliszczak

Wawrzak

2021

Preprint

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The large eddy simulation (LES) method combined with the Eulerian stochastic field approach has been used to study excited lifted hydrogen flames in a stream of hot co-flow air in a configuration closely corresponding to the so-called Cabra flame. The excitation is obtained by adding to an inlet velocity profile three types of forcing ((i) axial; (ii) flapping; (iii) combination of both) with amplitude of 15% of the fuel jet velocity and frequency corresponding to the Strouhal numbers St=0.30, 0.45, 0.60 and 0.75. It is shown that such a type of forcing significantly changes the lift-off height Lh of the flame and its global shape, resulting in a flame occupying large volume or the flame, which downstream the nozzle transforms from the circular one into a quasi-planar flame. Both the Lh and their spreading angles of the flames were found to be a function of the type of the forcing and its frequency. The minimum value of Lh has been found for the case with the combination of axial and flapping forcing at the frequency close to the preferred one in the unexcited configuration. The impact of the flapping forcing manifested through a widening of the flame in the flapping direction. It was shown that the excitation can significantly increase the level of the velocity and temperature fluctuations intensifying the mixing process. The computational results are validated based on the solutions obtained for a non-excited flame for which experimental data are available.

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A spark ignition scenario in a temporally evolving mixing layer

Cited by 21 publications

References 16 publications

Data-driven analysis of relight variability of jet fuels induced by turbulence

Data-driven analysis of relight variability of jet fuels induced by turbulence

Numerical Study of Hydrogen Auto-Ignition Process in an Isotropic and Anisotropic Turbulent Field

Control of a Lifted H2/N2 Flame by Axial and Flapping Forcing: A Numerical Study

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