An experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine

Amine compounds are an important class of nitro-containing fuels and represent as promising renewable fuels. However, the structural effect from the alkyl group on the combustion characteristics of amines remains an urgent problem to promote their usage in practical engines. To probe and replenish the combustion properties of amine fuels, this work reported an experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine over a wide range of conditions. Specifically, a high-pressure shock tube is used to measure the ignition delay times under the temperature range from 1100 K to 1700 K with pressure of 2 and 5 bar and the equivalence ra-tios of 0.5, 1.0 and 2.0. The pyrolysis characteristics is studied using a single-pulse shock tube at fuel concentration of 0.5% diluted by argon in the temperature range 950-1400 K at 5 and 10 bar with the residence time around 1.6 microsecond. A detailed kinetic mechanism is developed to simulate the experimental results. To improve the accuracy of the detailed mechanism, primary initial reactions of cyclohexylamine including the hydrogen abstraction reactions and the C -N decomposition reaction are theoretically studied at G4//M06-2X/6-311 ++G(d, p) level of theory with transition state theory and RRKM/mater equation. The detailed kinetic mechanism shows good prediction accuracy of the ignition delay times and pyrolysis product distributions under different temperature, pressure and equivalence ratio conditions. Sensitivity analysis results indicate that the most sensitive reaction is O 2 + H = O + OH with the most negative sensitivity coefficient and the abstraction reaction of vinylamine with OH radi-cal, C2H3NH2 + OH = C2H3NH + H2O also exhibits large sensitivity coefficients. Reaction path analysis reveals that the abstraction reactions control the initial oxidation of cyclohexylamine and cyclohexen-1-amine, cyclohexen-2-amine, and cyclohexen-3-amine are also major intermediates during the oxidation of cyclohexylamine besides small pyrolysis products.(c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the high-temperature ignition and pyrolysis characteristics of cyclohexylamine through experimental and kinetic modeling approaches. The results show that the ignition delay times and pyrolysis product distributions of cyclohexylamine are influenced by temperature, pressure, and equivalence ratio. A detailed kinetic mechanism accurately predicts the experimental results. Sensitivity analysis identifies the most sensitive reaction as O2 + H = O + OH, and the abstraction reaction of cyclohexylamine with OH radical also exhibits significant sensitivity coefficients. Reaction path analysis reveals the control role of abstraction reactions in the initial oxidation of cyclohexylamine.