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Abstract
Combustion modes in locally stratified dualfuel (DF) mixtures are numerically investigated for methanol/ndodecane blends under enginerelevant pressures. In the studied constantvolume numerical setup, methanol acts as a background lowreactivity fuel (LRF) while ndodecane serves as highreactivity fuel (HRF), controlling local ignition delay time. The spatial distribution of ndodecane 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 timedependent 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 βcurve herein. Onedimensional chemical kinetics simulations confirm the presence of two combustion modes in (Y′, λ) parameter space while the βcurve 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 βcurve. The effect of convection on combustion mode is assessed by carrying out twodimensional fullyresolved simulations with different turbulence levels. Twodimensional numerical simulation results give evidence on combustion mode switching, which is consistent with predictions of the modified βcurve for turbulent cases. The practical output of the paper is the βcurve which is proposed as a predictive tool to estimate combustion modes for various fuels or fuel combinations.
Original language  English 

Pages (fromto)  121135 
Number of pages  15 
Journal  Combustion and Flame 
Volume  214 
DOIs  
Publication status  Published  1 Apr 2020 
MoE publication type  A1 Journal articlerefereed 
Keywords
 Dualfuel
 Combustion modes
 Stratified mixtures
 Methanol
 RCCI
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Dive into the research topics of 'A numerical study on combustion mode characterization for locally stratified dualfuel mixtures'. Together they form a unique fingerprint.Projects
 2 Finished

TriReactivity Ignition: Simulation and Experiments
Vuorinen, V., Morev, I., Cheng, Q., Kannan, J., Gadalla, M. & Tamadonfar, P.
01/09/2018 → 31/08/2022
Project: Academy of Finland: Other research funding

New insight on the ignition of ultralean gas combustion
Ahmad, Z., Larmi, M., Ainsalo, A., Hassan, G., Cheng, Q., Keskinen, K. & Kaario, O.
01/09/2016 → 31/12/2020
Project: Academy of Finland: Other research funding