Pyrolysis and combustion chemistry of tetrahydropyran: Experimental and modeling study

This paper reports new experimental and numerical data for the pyrolysis and combustion of tetrahydropyran (THP) - a model component for next-generation heterocyclic oxygenated fuels. Pyrolysis experiments were performed using a plug flow reactor at 170 kPa, over the temperature range 913-1133 K at residence times of approximately 0.5 and 0.2 s, with 90% and 96% N2 dilution, respectively. THP combustion was investigated in two premixed flat flame burners and in a shock tube. The first premixed flame burner was operated at 6.7 kPa and was used to study detailed flame structures. Two equivalence ratios (1.0 and 1.3) were investigated with a 78% argon dilution. Ethylene, 1,3-butadiene, formaldehyde, and acrolein were the most important intermediates at both pyrolysis and combustion conditions, while the yield of aromatic species was negligible under flame conditions. Laminar burning velocities of THP-air mixtures using the heat flux method were measured at 298, 358 and 398 K and equivalence ratios from 0.55 to 1.50. Finally, ignition delay times of THP-oxygen-argon mixtures were measured behind reflected shock waves at temperatures from 1350 to 1613 K, pressures from 885 to 914 kPa and mixtures containing 0.15-1% fuel at equivalence ratios between 0.5 and 2.0. A new detailed kinetic model for the THP pyrolysis/combustion was developed by EXGAS, complemented with theoretical calculations for the determining reactions. Good agreements between simulations and acquired experimental data were observed. Reaction path analysis shows that THP is mainly consumed by H-abstractions at both pyrolysis and combustion conditions. The pyrolysis simulations are very sensitive to the unimolecular initiations involving C−C and C−O bond fissions, whereas these reactions play only a very minor role under combustion conditions.