No abstract

3-Methyltetrahydrofuran (3-MTHF) is proposed to be a promising fuel component among the cyclic oxygenated species. To have detailed insight of its combustion kinetics, intramolecular hydrogen shift reactions for the ROO to QOOH reaction class are studied for eight ROO isomers of 3-MTHF. Rate constants of all possible reaction paths that involve formation of cyclic transition states are computed by employing the CBS-QB3 composite method. A Pitzer-Gwinn-like approximation has been applied for the internal rotations in reactants, products, and transition states for the accurate treatment of hindered rotors. Calculated relative barrier heights highlight that the most favorable reaction channel proceeds via a six membered transition state, which is consistent with the computed rate constants. Comparing total rate constants in ROO isomers of 3-MTHF with the corresponding isomers of methylcyclopentane depicts faster kinetics in 3-MTHF than methylcyclopentane reflecting the effect of ring oxygen on the intramolecular hydrogen shift reactions.

Ignition delays of stoichiometric mixture of 2,5-dimethyltetrahydrofuran/O 2 /inert mixtures were measured at temperatures ranging from 650 to 1300 K in a RCM and in a shock tube. Operating pressures ranged from 10 to 40 bar at higher temperature (ST) and 10 to 20 bar at lower temperatures (RCM). The ignition delay times exhibit a slight deviation from Arrhenius behaviour, and limited low-temperature reactivity. This behaviour is similar to other cyclic ethers studied in comparable conditions namely THF, 2-MTHF and 3-MTHF, where 2,5-dimethylterahydrofuran (2,5-DMTHF) is showing the lowest reactivity of this series of cyclic ethers.Detailed speciation and quantification of the intermediates formed by a stoichiometric 2,5-DMTHF/O 2 /N 2 mixture in the combustion chamber of the RCM was performed at different times between top dead center and the ignition event for T c = 712 K and p TDC = 10 bar. The major fuel specific species observed are 2,5-dimethylfuran, 2,6-dimethyl-1,3-diox-4-ene, hexa-2,5-dione, 1-(2methylcyclopropyl)ethanone, and hex-3-en-2-one.To provide further insight into the kinetics of the oxidation of 2,5-DMTHF, a comprehensive kinetic model was developed and validated upon the acquired experimental data. Reaction pathway analysis and sensitivity analysis give an overview of the oxidation process of 2,5-DMTHF and elucidates the formation of the experimentally observed fuel-specific intermediates.

2‐Methyltetrahydrofuran (2‐MTHF) is one of the potential fuel components based on its combustion behavior, engine efficiency, and emission performance as proposed by the Cluster of Excellence “Tailor Made Fuels from Biomass (TMFB)” at RWTH Aachen University, Germany. Reaction kinetics of intramolecular hydrogen shift (ROO to QOOH) reactions in 2‐MTHF is theoretically investigated in this work. High‐pressure limit rate constants (500–2000 K) are determined from the transition state theory by employing the CBS‐QB3 composite method. Carbon sites neighboring a ring oxygen atom are favorable abstraction sites in 2‐MTHF due to its weak C─H bond strengths. The size of the transition state ring (six‐ and five‐membered) also plays an important role in the isomerization reaction kinetics. Further, effects of ring oxygen and methyl group position in 2‐MTHF are investigated. At 500 K, total rate constants for the isomerization reactions in ROO2 and ROO5t are 51 and 67 times faster in 2‐MTHF than in methylcyclopentane.

Isopentanol is a potential next-generation biofuel for future applications to Homogeneous Charge Compression Ignition (HCCI) engine concepts. To provide insights into the combustion behavior of isopentanol, especially to its auto-ignition behavior which is linked both to efficiency and pollutant formation in real combustion systems, detailed quantum chemical studies for crucial reactions are desired. H-Abstraction reaction rates from fuel molecules are key initiation steps for chain branching required for auto-ignition. In this study, rate constants are determined for the hydrogen atom abstraction reactions from isopentanol by the H atom and HO2˙ radical by implementing the CBS-QB3 composite method. For the treatment of the internal rotors, a Pitzer-Gwinn-like approximation is applied. On comparing the computed reaction energies, the highest exothermicity (ΔE = -46 kJ mol-1) is depicted for Hα abstraction by the H atom whereas the lowest endothermicity (ΔE = 29 kJ mol-1) is shown for the abstraction of Hα by the HO2˙ radical. The formation of hydrogen bonding is found to affect the kinetics of the H atom abstraction reactions by the HO2˙ radical. Further above 750 K, the calculated high pressure limit rate constants indicate that the total contribution from delta carbon sites (Cδ) is predominant for hydrogen atom abstraction by the H atom and HO2˙ radical.