(659d) Exploring Combustion Chemistry of 4-Methyl-1-Pentene in Pyrolysis and Laminar Flame Propagation with into Fuel Isomeric Effects of C6 Alkenes

Alkenes play an essential role in transportation fuels, constituting up to ~20% in gasoline, and are crucial intermediates and products in the combustion of hydrocarbon and oxygenated fuels. 4-Methyl-1-pentene (4M1Pen), a typical mono-branched hexene, could serve as a potential fuel to promote the knock resistance in spark-ignition engines, due to its higher research octane number when compared to hexanes. The pyrolysis was conducted in a flow reactor at 0.04 and 1 atm using synchrotron vacuum ultraviolet photoionization mass spectrometry, as well as in a jet-stirred reactor at 1 atm using gas chromatography. The laminar burning velocities (LBVs) of 4M1Pen/air mixtures were measured in a high-pressure constant-volume cylindrical combustion vessel at 373 K, 1-10 atm and equivalence ratios of 0.7-1.5. In addition, a kinetic model of 4M1Pen combustion was developed by incorporating theoretically calculated rate constants of fuel unimolecular decomposition reactions and validated against the present experimental data. Under pyrolysis conditions, the allylic C-C bond dissociation reaction (R1) is the most crucial primary decomposition reaction of the fuel. Subsequent decomposition of the primary products formed from R1 is essential for the formation of dominant product families (i.e. alkenes and dialkenes). Under flame conditions, C₀-C₂ reactions take the dominance among the sensitive reactions, while C₃-involved reactions are also influential for the flame propagation. Moreover, special attention has been paid to the fuel isomeric effects on the pyrolysis and flame propagation of 4M1Pen and 1-hexene. Compared to 1-hexene, 4M1Pen has a higher pyrolysis reactivity, due to the lower bond dissociation energy of the allylic C-C bond and the more efficient formation of H atom. However, the LBVs of 4M1Pen flames are lower than those of 1-hexene flames under the same conditions, which is mainly caused by the less prevalent production of reactive radicals especially H atom in 4M1Pen flames.