A study on the pyrolysis of n-hexane initiated by 1-nitropropane: Molecular dynamics simulations and SVUV-PIMS experiments

Abstract

To investigate the influence of 1-nitropropane (1-NP) initiator on the pyrolysis of n-hexane (n-C6H14), molecular dynamics (MD) simulations and synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) experiments were used to analyze the pyrolysis processes of n-C6H14 and n-C6H14 with 10 % 1-NP added. ReaxFF MD simulations were used to analyze the pyrolysis rates and product distributions of n-C6H14 and 1-NP/n-C6H14 at different temperatures. The mechanism of action of n-C6H14 pyrolysis initiated by 1-NP was investigated. Additionally, the pyrolysis products of n-C6H14 and 1-NP/n-C6H14 were identified and quantitatively analyzed using the SVUV-PIMS technique. These experimental results were compared with the ReaxFF MD simulation results to validate the reliability of the simulations and to complement each other. The results indicate that the presence of 1-NP promotes the pyrolysis of n-C6H14 and significantly improves the chemical heat sink of the fuel. The chemical heat sink in the 1-NP/n-C6H14 system differs from that in the n-C6H14 system by 28.78 kJ/kg at 2103 K. A significant increase in C2H4 production in the pyrolysis products of n-C6H14 with the addition of 1-NP. The pyrolysis of 1-NP/n-C6H14 yielded approximately twice as much C2H4 as n-C6H14 at 2103 K. The pyrolysis reactions were described by first-order kinetics, and the activation energy for the pyrolysis of 1-NP/n-C6H14 was determined to be 140 kJ/mol, approximately 48 % lower than that of n-C6H14. The composition of the pyrolysis products was confirmed by SVUV-PIMS experiments, which were in good agreement with the ReaxFF MD simulations. The mechanism of pyrolysis of n-C6H14 initiated by 1-NP was elucidated: the NO2 radicals generated by 1-NP react with H radicals of the system to form OH radicals. The primary reaction of n-C6H14 involves the abstraction of H by OH, leading to the formation of C6H13. Subsequently, C6H13 is further decomposed to form 1-C3H7, 1-C4H8, 1-C5H10 and 2-C6H12.