Theoretical reaction kinetics predictions for acetone and ketene with NH2 radicals: Implications on acetone/ammonia kinetic modeling

Abstract

The cross-reaction kinetics of acetone/ketene (CH3COCH3/CH2CO) + amino (NH2) radicals are first theoretically reported for a wide range of conditions (T = 300–2500 K and P = 0.1–100 atm) in this work. The high-level electronic structure method CCSD(T)/cc-pVnZ(n = T, Q)//B3LYP-D3BJ/6–311++G(d,p) is used to explore the potential energy profiles on which the temperature- and pressure-dependence kinetic behaviors of the title reactions are characterized using the Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) theory. Corrections of the one-dimensional hindered rotor approximation and asymmetric Eckart tunneling effect are also included in the rate constant calculations. Furthermore, this work delves into the competitive relationships among the H-abstraction, NH2 addition and addition-dissociation reaction pathways. For CH3COCH3 + NH2, the H-abstraction reaction of CH3COCH3 is highly favored over the addition-dissociation reaction and other isomerization channels. For CH2CO + NH2, the reaction channel of addition-dissociation to form CH2NH2 + CO under low temperature conditions is more advantageous, while the H-abstraction reaction plays a dominant role under combustion conditions (T ≥ 1000 K). To reveal the impact of the studied reaction kinetics on model predictions, the rate constants of dominant reaction channels calculated in this work are incorporated into a kinetic model for the auto-ignition, oxidation and pyrolysis of CH3COCH3/NH3 mixtures. The simulated results show that the effect of the updated rate constants on ignition delay time is mainly at low temperatures and the promotion effect of CH3COCH3 addition on the ignition of NH3 presents a nonlinear enhancement. The updated rate constants can also accelerate the consumption of CH3COCH3 and CH2CO formation, while also influence the concentration distributions of other significant species (e.g., NH3, CO). Therefore, the cross-reaction kinetics of CH3COCH3/CH2CO + NH2 are critical in controlling the fuel consumption, important intermediate formation and ignition delay time of CH3COCH3/NH3 mixtures.