A Regime Diagram for Autoignition of Homogeneous Reactant Mixtures with Turbulent Velocity and Temperature Fluctuations

Im, Hong G.; Pal, Pinaki; Wooldridge, Margaret S.; Mansfield, Andrew B.

doi:10.1080/00102202.2015.1034355

Cited by 68 publications

(64 citation statements)

References 24 publications

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“…It is important to note that at higher temperatures, the chemical reactions proceed at a rapid rate and the ignition event is not affected by the differences in flame thickness. There should be then an analogous of a Damköhler number, which relates the ignition delay time to the characteristic time of the flow defined by the ratio of the flame thickness and flame speed [38]. By our observation, whenever Da* = τign / τchar > 0.015, preignition can likely affect the ignition process.…”

Section: Thermal Diffusivity and Laminar Flame Thicknessmentioning

confidence: 80%

Shock tube studies of ethanol preignition

Figueroa-Labastida

Badra

Elbaz

et al. 2018

Combustion and Flame

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CitationFigueroa-Labastida M, Badra J, Elbaz AM, Farooq A (2018) Shock tube studies of ethanol preignition. . Available: http://dx. AbstractUnderstanding premature ignition or preignition is of great importance as this phenomenon influences the design and operation of internal combustion engines. Preignition leading to super-knock restricts the efficiency of downsized boosted engines. To gain a fundamental understanding of preignition and how it affects an otherwise homogeneous ignition process, a shock tube may be used to decipher the influence of fuel chemical structure, temperature, pressure, equivalence ratio and bath gas on preignition. In a previous work by Javed et al.[1], ignition delay time measurements of nheptane showed significantly expedited reactivity compared to well-validated chemical kinetic models in the intermediate-temperature regime. In the current work, ethanol is chosen as a representative fuel that, unlike n-heptane, does not exhibit negative temperature coefficient (NTC) behaviour. Reactive mixtures containing 2.9% and 5% of ethanol at equivalence ratios of 0.5 and 1 were used for the measurement of ignition delay times behind reflected shock waves at 2 and 4 bar. Effect of bath gas was studied with mixtures containing either Ar or N2. In addition to conventional side-wall pressure and OH* measurements, a high-speed imaging setup was utilized to visualize the shock tube crosssection through a transparent quartz end-wall. The results suggest that preignition events are more likely to happen in mixtures containing higher ethanol concentration and that preignition energy release is more pronounced at lower temperatures. High-speed imaging shows that low-temperature ignition process is usually initiated from an individual hot spot that grows gradually, while hightemperatures ignition starts from many spots simultaneously which consume the reactive mixture almost homogeneously.

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Section: Thermal Diffusivity and Laminar Flame Thicknessmentioning

confidence: 80%

Shock tube studies of ethanol preignition

Figueroa-Labastida

Badra

Elbaz

et al. 2018

Combustion and Flame

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“…In single-fuel (SF) constant-volume conditions, there is a body of literature available that scrutinize the importance of ignition and subsequent combustion modes, where effects of temperature [23,[27][28][29][30][31][32][33][34][35][36][37][38][39] , and/or composition [33][34][35]39,40] , and/or velocity [28,31,35,36,38] fluctuations are taken into account. For instance, Pal et al [28,38] proposed regime diagrams which specify different modes of combustion with velocity and temperature fluctuations.…”

Section: Introductionmentioning

confidence: 99%

A numerical study on combustion mode characterization for locally stratified dual-fuel mixtures

Karimkashi

Kahila

Kaario

et al. 2020

Combustion and Flame

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a b s t r a c tCombustion modes in locally stratified dual-fuel (DF) mixtures are numerically investigated for methanol/n-dodecane blends under engine-relevant pressures. In the studied constant-volume numerical setup, methanol acts as a background low-reactivity fuel (LRF) while n-dodecane serves as high-reactivity fuel (HRF), controlling local ignition delay time. The spatial distribution of n-dodecane is modeled as a sinusoidal function parametrized by stratification amplitude ( Y ) and wavelength (0.01 mm <λ< 15 mm). In contrast, methanol is assumed to be fully premixed with air at equivalence ratio 0.8. First, onedimensional setup is investigated by hundreds of chemical kinetics simulations in ( Y , λ) parameter space. Further, the concepts by Sankaran et al. (2005, Proceedings of the Combustion Institute ) and Zeldovich (1980, Combustion and Flame ) on ignition front propagation speed are applied to develop a theoretical analysis of the time-dependent diffusion-reaction problem. The theoretical analysis predicts two combustion modes, (1) spontaneous ignition and (2) deflagrative propagation, and leads to an analytical expression for the border curve called β-curve herein. One-dimensional chemical kinetics simulations confirm the presence of two combustion modes in ( Y , λ) parameter space while the β-curve explains consistently the position of phase border observed in the simulations. Finally, the role of convective mixing is incorporated to the theoretical expression for the β-curve. The effect of convection on combustion modeis assessed by carrying out two-dimensional fully-resolved simulations with different turbulence levels. Two-dimensional numerical simulation results give evidence on combustion mode switching, which is consistent with predictions of the modified β-curve for turbulent cases. The practical output of the paper is the β-curve which is proposed as a predictive tool to estimate combustion modes for various fuels or fuel combinations.

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“…A recent experimental study using iso-octane confirms consistent behaviour [36]. Extension of the Zel'dovich-Sankaran criterion to predict weak versus strong ignition regimes in turbulent conditions has been proposed with a scaling analysis by Im et al [22], and validation by multi-dimensional simulations is underway. Future work should also investigate the extension of the current theoretical framework to generalised turbulent mixing conditions including composition fluctuations.…”

Section: Effects Of Local Hot Spotsmentioning

confidence: 78%

“…Extension of the Zel'dovich-Sankaran criterion to turbulent conditions has been attempted and a regime diagram has been proposed [22]. Further validation of the concept in multi-dimensional simulations will be conducted in future work.…”

Section: Resultsmentioning

confidence: 99%

“…However, since the Zel'dovich-Sankaran criterion is based on the local temperature gradient, it cannot readily be used as a predictive metric in practical devices in which only statistical mean quantities in turbulent fluctuations are available. Im et al [22], by a scaling analysis, proposed a turbulent ignition regime diagram as an extension of the criterion to be applicable in bulk turbulent combustion systems. Downloaded by [New York University] at 07:46 31 July 2015 Combustion Theory and Modelling 3 As a complementary work to the regime diagram, the objective of the present study is to validate the Zel'dovich-Sankaran criterion as a predictive indicator of the ignition regime of a reactant mixture.…”

Section: Introductionmentioning

confidence: 99%

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A computational study of syngas auto-ignition characteristics at high-pressure and low-temperature conditions with thermal inhomogeneities

Pal

Mansfield

Arias

et al. 2015

Combustion Theory and Modelling

Self Cite

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A computational study was conducted to investigate the characteristics of auto-ignition in a syngas mixture at high-pressure and low-temperature conditions in the presence of thermal inhomogeneities. Highly resolved one-dimensional numerical simulations incorporating detailed chemistry and transport were performed. The temperature inhomogeneities were represented by a global sinusoidal temperature profile and a local Gaussian temperature spike (hot spot). Reaction front speed and front Damköhler number analyses were employed to characterise the propagating ignition front. In the presence of a global temperature gradient, the ignition behaviour shifted from spontaneous propagation (strong) to deflagrative (weak), as the initial mean temperature of the reactant mixture was lowered. A predictive Zel'dovich-Sankaran criterion to determine the transition from strong to weak ignition was validated for different parametric sets. At sufficiently low temperatures, the strong ignition regime was recovered due to faster passive scalar dissipation of the imposed thermal fluctuations relative to the reaction timescale, which was quantified by the mixing Damköhler number. In the presence of local hot spots, only deflagrative fronts were observed. However, the fraction of the reactant mixture consumed by the propagating front was found to increase as the initial mean temperature was lowered, thereby leading to more enhanced compression-heating of the end-gas. Passive scalar mixing was not found to be important for the hot spot cases considered. The parametric study confirmed that the relative magnitude of the Sankaran number translates accurately to the quantitative strength of the deflagration front in the overall ignition advancement.

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A Regime Diagram for Autoignition of Homogeneous Reactant Mixtures with Turbulent Velocity and Temperature Fluctuations

Abstract: (150 words)A theoretical scaling analysis is conducted to propose a diagram to predict weak and strong

Cited by 68 publications

References 24 publications

Shock tube studies of ethanol preignition

Shock tube studies of ethanol preignition

A numerical study on combustion mode characterization for locally stratified dual-fuel mixtures

A computational study of syngas auto-ignition characteristics at high-pressure and low-temperature conditions with thermal inhomogeneities

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