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

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**A numerical study on combustion mode characterization for locally stratified dual-fuel mixtures.** / Karimkashi Arani, Shervin; Kahila, Heikki; Kaario, Ossi; Larmi, Martti; Vuorinen, Ville.

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*Combustion and Flame*, Vuosikerta. 214, Sivut 121-135. https://doi.org/10.1016/j.combustflame.2019.12.030

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*Combustion and Flame*,

*214*, 121-135. https://doi.org/10.1016/j.combustflame.2019.12.030

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TY - JOUR

T1 - A numerical study on combustion mode characterization for locally stratified dual-fuel mixtures

AU - Karimkashi Arani, Shervin

AU - Kahila, Heikki

AU - Kaario, Ossi

AU - Larmi, Martti

AU - Vuorinen, Ville

PY - 2020/4/1

Y1 - 2020/4/1

N2 - Combustion 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, one-dimensional 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 mode is 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.

AB - Combustion 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, one-dimensional 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 mode is 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.

KW - Dual-fuel

KW - Combustion modes

KW - Stratified mixtures

KW - Methanol

KW - RCCI

UR - http://www.scopus.com/inward/record.url?scp=85077363679&partnerID=8YFLogxK

U2 - 10.1016/j.combustflame.2019.12.030

DO - 10.1016/j.combustflame.2019.12.030

M3 - Article

VL - 214

SP - 121

EP - 135

JO - Combustion and Flame

JF - Combustion and Flame

SN - 0010-2180

ER -

ID: 40887569