Measurements and simulations of ignition delay times and laminar flame speeds of nonane isomers

Ignition delay times (IDTs) and laminar flame speeds (S_L) of C₉H₂₀ (nonane) isomers are systematically investigated. IDTs of normal nonane (n-C₉), 2-methyloctane (2mC₈), 2,4-dimethylheptane (24mC₇), and 2,2,4,4-tetramethylpentane (2244mC₅) are experimetally obtained by a shock tube facility and numerically simulated by a chemkin 0-D reactor model. Further, laminar flame speeds (S_L) of n-C₉ and 2244mC₅ are measured by spherical expanding flames in a constant-temperature, constant-pressure dual-chamber cruciform burner over a wide range of the equivalence ratio (Φ = 0.7–1.4), which are used to compare with numerically simulated results obtained by chemkin 1-D flame speed model. Detailed reaction mechanisms of KUCRS, LLNL and JetSurF ver.02 are used for numerical simulations. It is found that experimental IDTs increase with the number of methyl branches, especially in low-temperature and negative temperature coefficient (NTC) regions, where the increase of IDT with the number of methyl branches are well predicted by KUCRS. We also find that the measured values of S_L of highly branched 2244mC₅ are smaller than those of n-C₉ at all values of Φ studied, of which measured S_L data are successfully reproduced by the 1-D flame speed model with KUCRS. These results are important to our understanding of reaction characteristics for highly branched nonane isomers and for the designing of optimal alternative fuels in internal combustion engines.