Combustion kinetics of [formula omitted]-propylamine: Theoretical calculations and ignition delay time measurements

Abstract

To better understand the combustion chemistry and improve the model performance of aliphatic amines, the kinetics of H-abstraction reactions from n-propylamine (NPA) by H, CH3, OH, and NH2 radicals and the ignition characteristics of NPA are investigated. The CCSD(T)-F12/cc-pVTZ-F12 method is selected as the benchmark, and the performances of several density functional theory methods are evaluated by comparing the calculated reaction energies and barrier heights against the benchmark values. The M06-2X/jun-cc-pVTZ method is identified as the best one with a mean unsigned deviation of 0.59 kcalmol−1. With the selected method, the rate constants are calculated using the variational transition-state theory combined with the small-curvature tunneling and multi-structural torsional anharmonicity (MS-CVT/SCT) options at 298–2000 K. The H-abstraction reactions at the α-C site are the dominant channels for NPA + H/CH3/NH2, but this channel is less important for NPA + OH due to the significant variational effect. The ignition characteristics of NPA is studied in a shock tube at 1105–1441 K, 4–20 atm, and different equivalence ratios (0.5, 1.0, and 2.0). The ignition delay time of NPA decreases noticeably with increasing temperature and pressure, while it is insensitive to equivalence ratio. Based on our calculations, a literature model is updated and then assessed against the measured ignition delay times. The updated model shows a better agreement with the measurements but fails to predict the ignition behavior of NPA under certain conditions. The reaction pathway and sensitivity analyses demonstrate that the unsaturated aliphatic amines and imines (such as CH3CHCHNH2 and CH2NH) are the important nitrogen-containing intermediates, and further investigation of the subset of these species is needed to improve the combustion model of aliphatic amines.