The role of low temperature chemistry in combustion mode development under elevated pressures

Pan, Jiaying; Wei, Haiqiao; Shu, Gequn; Chen, Zheng; Zhao, Peng

doi:10.1016/j.combustflame.2016.09.012

Cited by 114 publications

(32 citation statements)

References 44 publications

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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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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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“…However, this effect is significantly reduced when the initial mean temperature, T 0 , falls within the NTC regime the ignition delay time becomes insensitive to the temperature variations. It was found that larger length scale and/or T 0 in the NTC regime induce a greater amplitude of the PRR oscillation, and the ignition-front speed of the cases inside the NTC regime travels faster, leading to more interactions between the pressure wave and the developing reaction fronts, which in turn facilitates the formation of detonation wave [54,55,[55][56][57][58][59][60].…”

Section: Introductionmentioning

confidence: 99%

Prediction of Ignition Regimes in DME/Air Mixtures with Temperature and Concentration Fluctuations

Luong¹,

Pérez²,

Sow³

et al. 2019

AIAA Scitech 2019 Forum

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The objective of the present study is to establish a theoretical prediction of the autoignition behavior of a reactant mixture for a given initial bulk mixture condition. The ignition regime criterion proposed by Im and coworkers based on the Sankaran number (Sa), which is a ratio of the laminar flame speed to the spontaneous ignition front speed, is extended to account for both temperature and equivalence ratio fluctuations. The extended ignition criterion is then applied to predict the autoignition characteristics of dimethyl ether (DME)/air mixtures and validated by two-dimensional direct numerical simulations (DNS). The response of the ignition mode of DME/air mixtures to three initial mean temperatures of 770, 900 K, and 1045 K lying within/outside the NTC regime, two levels of temperature and concentration fluctuations at a pressure of 30 atm and equivalence ratio of 0.5 is systematically investigated. The statistical analysis is performed, and a newly developed criterion-the volumetric fraction of Sa < 1.0, F Sa,S , is proposed as a deterministic criterion to quantify the fraction of heat release attributed to strong ignition. It is found that the strong and weak ignition modes are well captured by the predicted Sa number and F Sa,S regardless of different initial mean temperatures and the levels of mixture fluctuations and correlations. Sa p and F Sa,S demonstrated under a wide range of initial conditions as a reliable criterion in determining a priori the ignition modes and the combustion intensity.

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“…Following much of the literature, the term 'cool flame' is used indiscriminately here to refer both to deflagrative and to ignitive reaction fronts involving low temperature chemistry. Low temperature chemistry can significantly modify the chemical and transport properties of a mixture [3], thereby affecting the laminar flame speed in mixtures well before the onset of high-temperature ignition [6,14]. The response of laminar flame properties to blending of fuels with dissimilar ignition behaviours, such as methane and n-heptane, has not been characterised fully at autoignitive conditions.…”

Section: Introductionmentioning

confidence: 99%

Investigation of flame propagation in autoignitive blends of n-heptane and methane fuel

Soriano

Richardson

2019

Combustion Theory and Modelling

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The effects of pre-ignition chemistry on laminar flame speed in methane/n-heptane fuel blends are investigated numerically, leading to flame speed modelling accounting for these effects. The laminar flame speeds of fuel blends are important input parameters for turbulent combustion models needed to support design of dual-fuel engines. At the autoignitive conditions found in engines, pre-ignition reactions cause the speed of the reaction front to increase. Fuels that exhibit two-stage ignition behaviour, such as n-heptane, also exhibit a two-stage increase in the speed of the reaction front as the reactant residence time increases. There is a corresponding reduction in the flame thickness until the residence time approaches the ignition delay time, whereupon the deflagrative scaling of flame thickness breaks down. The analysis shows that the increase in flame speed is due to distinct contributions of heat release, reactant consumption, and enhanced reactivity ahead of the flame. Addition of methane to n-heptane-air mixtures retards and reduces the first-stage increase in flame speed, in part due to dilution of the more-reactive n-heptane fuel, and in part due to consumption of radical species by the methane chemistry. The effect of methane/n-heptane fuel blending on flame speed is described adequately by a linear mixing rule. The effect of pre-ignition chemistry can then be modelled as a linear function of the progress variable ahead of the flame-accounting for heat release, reactant consumption, and enhanced reactivity ahead of the flame. The flame speed model accurately describes the variation of flame speed across the full range of methane/n-heptane blends at engine-relevant conditions, up to the deflagration/ignition transition.

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The role of low temperature chemistry in combustion mode development under elevated pressures

Cited by 114 publications

References 44 publications

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

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

Prediction of Ignition Regimes in DME/Air Mixtures with Temperature and Concentration Fluctuations

Investigation of flame propagation in autoignitive blends of n-heptane and methane fuel

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