Theoretical study on the mechanism, heat sink and product distribution for thermal decomposition of endothermic hydrocarbon fuel n-decane

The geometry optimizations and vibrational frequencies of reactions, products and transition states involved in pyrolysis of n-decane were performed using the hybrid method B3LYP with 6-311G (d,p) basis set based on density functional theory. The potential energy surfaces of n-decane were built by the B3LYP/aug-cc-pVTZ methods. The rate constants of all reactions with Eckart correction were calculated by the TheRate program package. The heat capacity and entropy (C_p,m^θ and S_{298 K}^θ) at different temperatures were obtained by statistic thermodynamics. In order to calculate the standard formation enthalpy (△_fH_{298 K}^θ) for all species, isodesmic reactions were designed. The Chemkin II program was used to model the product distribution and heat sink. The effects of the temperature and pressure on the heat sink and product distribution were discussed. The results show that the C-C bond breaking process is the initial step of all reactions and H-abstraction reaction is easier to proceed than the β-scission reaction. The cracking initial temperature is 500 ℃ and the reactions mainly occur in the range of 600~700 ℃. The major products are hydrogen, methane, ethylene, ethane, propylene and 1,3-butadiene and the product distributions vary with temperatures. The total heat sink of n-decane is 2.334 MJ/kg at 600 ℃ and 2.5 MPa, with the conversions of 25.9%, which could meet the cooling requirement of aircrafts at 5~6 Mach number.