An experimental and modeling study of the combustion of tetrahydrofuran

Tetrahydrofuran (THF) is a well suited starting point fuel to study the combustion chemistry of saturated cyclic esters that are being considered as promising bio-fuels. To better understand the combustion chemistry of THF, laminar low-pressure premixed flame structure, atmospheric adiabatic laminar burning velocities, and high-pressure ignition delay times were investigated. The structure of laminar premixed low-pressure (6.7 kPa) argon-diluted (78%) flames of THF were studied at three equivalence ratios (0.7, 1.0 and 1.3) using on-line gas chromatography analyses. The results consist of temperature and mole fraction profiles (about 40 species) measured as a function of the height above the burner. Ethylene, propene, formaldehyde, acetaldehyde, and dihydrofurans were observed as important intermediates. Aromatic species were detected in very low amounts. The adiabatic laminar burning velocities of THF-air mixtures were measured using the heat flux burner method at atmospheric pressure (initial temperatures from 298 to 398 K, at equivalence ratios from 0.55 to 1.60). The maximum burning velocity of THF was comparable to that of ethanol and diethyl ether. The ignition delay times of THF-oxygen-argon mixtures were measured behind reflected shock waves (temperatures from 1300 to 1700 K, pressures around 8.5 atm, mixtures containing 0.25-1% of fuel for equivalence ratios of 0.5-2.0). A new detailed kinetic model for THF combustion was developed using a combination of automatic generation (EXGAS), Evans-Polanyi correlations (for H-abstraction kinetic data), and CBS-QB3 theoretical calculations (for unimolecular initiation, H-abstraction and β-scission kinetic data). An overall good agreement between simulations and the present experimental results has been found. The main THF reaction pathways under flame conditions have been identified from flow rate analyses.