Laminar Flame Speeds and Kinetic Modeling of n-Pentanol and Its Isomers

A comprehensive experimental and computational study was conducted on the laminar combustion characteristics and chemical kinetics of four pentanol isomer-air mixtures (n-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and 2-methyl-2-butanol). Experiments were performed at the equivalence ratios ranging from 0.6 to 1.8, three initial temperatures (393, 433, and 473 K), and four pressures (0.1, 0.25, 0.5, and 0.75 MPa) using outwardly propagating flames. Results show that the laminar flame speeds of the four pentanol isomers decrease in the order of n-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-methyl-2-butanol. The most significant differences among the isomers are observed around the stoichiometric mixture. Simulations on the laminar flame speeds of n-pentanol and 3-methyl-1-butanol were respectively performed using the model of Heufer et al. and Sarathy et al. Comparisons between the simulations and experimental data show the n-pentanol model yields satisfactory agreement with the data at most conditions but slight overpredictions at rich mixtures and atmospheric pressure and the 3-methyl-1-butanol model yields close agreement with the data at all conditions. For 2-methyl-1-butanol, a model based on the model proposed by Tang et al. was developed and validated against the data of laminar flame speed as well as ignition delay times. Sensitivity analysis indicates that the laminar flame speeds of the isomer-air flames (n-pentanol, 3-methyl-1-butanol, and 2-methyl-1-butanol) are mainly sensitive to small molecule reactions involving H₂-O₂ and C₁-C₃ species but not to fuel-specific reactions. The concentrations of H₂-O₂ and C₁-C₃ intermediates are responsible for the laminar flame speed difference among the isomers. Additionally, butene isomers working as the important intermediates occupy different fractions in various pentanol isomer flames, confirming the differences on the chemical structure and the reaction pathways of the isomers.