Role of large scale flow features on cycle-to-cycle variations of spark-ignited flame-initiation and its transition to turbulent combustion

Zeng, Wei; Keum, Seunghwan; Kuo, Tang-Wei; Sick, Volker

doi:10.1016/j.proci.2018.07.081

Cited by 25 publications

(16 citation statements)

References 12 publications

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“…Zeng et al 20 performed further analysis on flame images from the same experiment to determine the flame transition against the flame radius. The flame radius was calculated from burned gas area, and a correlation between the flame radius and flame speed was reconstructed from experimental data, which is shown in Figure 2.…”

Section: Model Developmentmentioning

confidence: 99%

A semi-empirical laminar-to-turbulent flame transition model coupled with G equation for early flame kernel development and combustion in spark-ignition engines

Keum

Zhu

Grover

et al. 2019

International Journal of Engine Research

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It has been reported that early combustion in a spark-ignition engine determines the subsequent combustion. Also, the early combustion has a very strong correlation with cycle-to-cycle variability, which limits engine operating range. As such, accurate modeling of the early flame development is very important in accurate simulation of spark-ignition engine combustion. During the early flame development, the flame kernel, initiated by spark, grows initially at laminar flame speed. As the kernel grows, the flame surface wrinkles due to surface instability and interacts with the flow turbulence as the flame transitions from laminar to turbulent flame. In this study, a semi-empirical model is proposed to simulate the laminar-to-turbulent flame transition process during early spark-ignition combustion. A hyperbolic tangent function was used to emulate the laminar-to-turbulent flame speed transition process. The proposed transition function was evaluated during early flame kernel development for both Reynolds-averaged Navier–Stokes and large eddy simulation models against combustion analysis data from high-speed optical particle image velocimetry. Difference in Reynolds-averaged Navier–Stokes and large eddy simulation transition function was analyzed and discussed.

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Section: Model Developmentmentioning

confidence: 99%

A semi-empirical laminar-to-turbulent flame transition model coupled with G equation for early flame kernel development and combustion in spark-ignition engines

Keum

Zhu

Grover

et al. 2019

International Journal of Engine Research

Self Cite

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“…Even under conditions that lead to misfires, spark ignition was found to successfully initiate a flame kernel, which extinguishes during the early growth phase [6]. By using advanced optical diagnostics, prolonged chemical time scales due to exposure of the small flame to locally lean or diluted mixture [7], or fluctuations in large-scale flow structures [8,9] and kinetic energy [10] could be identified as sources for cyclic variability. Under fully premixed in-cylinder conditions, variations in burning velocity during the transition phase from ignition kernels to fully developed turbulent flames were found to be one major contributor to CCV [9].…”

Section: Introductionmentioning

confidence: 99%

DNS study of the global heat release rate during early flame kernel development under engine conditions

Falkenstein

Kang

Cai

et al. 2020

Combustion and Flame

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Despite the high technical relevance of early flame kernel development for the reduction of cycle-to-cycle variations in spark ignition engines, there is still a need for a better fundamental understanding of the governing in-cylinder phenomena in order to enable resilient early flame growth. To isolate the effects of small-and large-scale turbulent flow motion on the young flame kernel, a three-dimensional DNS database has been designed to be representative for engine part load conditions. The analysis is focussed on flame displacement speed and flame area in order to investigate effects of flame structure and flame geometry on the global burning rate evolution. It is shown that despite a Karlovitz number of up to 13, which is at the upper range of conventional engine operation, thickening of the averaged flame structure by small-scale turbulent mixing is not observed. After ignition effects have decayed, the flame normal displacement speed recovers the behavior of a laminar unstretched premixed flame under the considered unity-Lewis-number conditions. Run-to-run variations in the global heat release rate are shown to be primarily caused by flame kernel area dynamics. The analysis of the flame area balance equation shows that turbulence causes stochastic flame kernel area growth by affecting the curvature evolution, rather than by inducing variations in total flame area production by strain. Further, it is shown that in local segments of a fully-developed planar flame with similar surface area as the investigated flame kernels, temporal variations in flame area rate-of-change occur. Contrasting to early flame kernels, these effects can be exclusively attributed to curvature variations in negatively curved flame regions.

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“…As shown in Fig. 4(a) of Zeng et al [13], there are substantial variations in the flame surface area during the early stage of the burning process where the laminar-to-turbulent flame transition occurs. Schiffmann et al [12] performed a statistical analysis of their PIV and OH fluorescence data obtained in an optical engine in order to look for a root cause of CCV in an SI engine.…”

Section: Laminar-to-turbulent Flame Transition Model: Reproducing Cycle-to-cycle Variations In Si Premixed Burningmentioning

confidence: 93%

“…Early investigations have shown the importance of early-stage burning rates in the CCV, which are affected by the laminar-to-turbulent flame transition occurring in the early-stage flame kernel development. Recent experimental studies by Schiffmann et al [12] and Zeng et al [13] also suggest the importance of variations in the laminar-to-turbulent flame transition in CCV. As shown in Fig.…”

Section: Laminar-to-turbulent Flame Transition Model: Reproducing Cycle-to-cycle Variations In Si Premixed Burningmentioning

confidence: 94%

Development of a Physics-Based Combustion Model for Engine Knock Prediction

Kim

Splitter

2020

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Role of large scale flow features on cycle-to-cycle variations of spark-ignited flame-initiation and its transition to turbulent combustion

Cited by 25 publications

References 12 publications

A semi-empirical laminar-to-turbulent flame transition model coupled with G equation for early flame kernel development and combustion in spark-ignition engines

A semi-empirical laminar-to-turbulent flame transition model coupled with G equation for early flame kernel development and combustion in spark-ignition engines

DNS study of the global heat release rate during early flame kernel development under engine conditions

Development of a Physics-Based Combustion Model for Engine Knock Prediction

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