Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels
KAUST DepartmentChemical Engineering Program
Clean Combustion Research Center
Combustion and Pyrolysis Chemistry (CPC) Group
Computational Reacting Flow Laboratory (CRFL)
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Embargo End Date2020-01-01
Permanent link to this recordhttp://hdl.handle.net/10754/659072
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AbstractSynergistic octane blending behavior of ethanol with gasoline and its surrogates has been observed by many researchers. The nonlinear octane boosting tendency is observed at mid and high molar blends of ethanol in primary reference fuels. The present work aims to provide chemical insight into this nonlinear blending behavior of ignition processes when ethanol is blended with primary reference fuels. To this end, ignition delay time (IDT) calculations, using a well-validated mechanism, were performed for several fuel blends of iso-octane, n-heptane, and ethanol. Temperature and pressure values were found, correlating experimentally measured octane numbers and simulated homogenous batch reactor IDTs. The temperature and pressure conditions obtained, were then used to study the evolution of heat release and reactivity before the onset of auto-ignition in a homogeneous premixed reactor. Markers of low- and high-temperature reactivity (OH and HO2) were analyzed for various molar blends of n-heptane with ethanol-iso-octane. Ethanol was observed to be better at radical scavenging than iso-octane at a higher mole fraction. A computational singular perturbation analysis was conducted for a selection of blends to clarify the reactions responsible for the synergistic blending behavior of ethanol in n-heptane. The role of the H-abstraction reactions was highlighted during the first ignition stage; reactions related to n-heptane were found to compete with the H-abstraction reactions of iso-octane or ethanol. Notably, the H-abstraction path of ethanol was more favored than that of the iso-octane, as a result of the smaller activation energies of the related reactions in ethanol. The competition of the H-abstraction paths resulted in a smaller radical pool in the n-heptane-iso-octane-air case, and an even smaller pool in n-heptane-ethanol-air. In all the cases considered, the second stage was dominated mainly by hydrogen-related reactions, regardless of the initial mixture, with H2O2 (+M) → 2OH (+M) and H + O2 → O + OH playing the most important roles. This work employed a novel approach to examine specific reactions responsible for auto-ignition in ethanol blends, which can be used for fuel design, primarily around the generation/consumption of radical pool intermediates by interaction with fuel components.
CitationSingh, E., Tingas, E.-A., Goussis, D., Im, H. G., & Sarathy, S. M. (2019). Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels. Energy & Fuels. doi:10.1021/acs.energyfuels.9b01423
SponsorsThe research reported in this publication was supported by competitive research funding from King Abdullah University of Science and Technology (KAUST), awarded to the Clean Combustion Research Center (CCRC). Additional support was obtained from the KAUST Clean Fuels Consortium and its member companies.
PublisherAmerican Chemical Society (ACS)
JournalEnergy and Fuels