Theoretical Investigation of Key i-C3H7O2 and n-C3H7O2 Reaction Pathways and Their Impact on Propane Oxidation under High-Pressure Conditions.

Recent high-pressure jet-stirred reactor experiments revealed that significant discrepancies existed in model predictions of the classical negative temperature coefficient region for alkanes such as propane (C3H8) at high pressures. To address this, four key propyl peroxy radical reactions (a) i-C3H7O2 → i-C3H6 + HO2, (b) n-C3H7O2 → n-C3H6 + HO2, (c) i-C3H7O2 + HO2 → i-C3H7O2H + O2, and (d) i-C3H7O2 + CH2O → i-C3H7O2H + CHO were re-evaluated using M06-2X/aug-cc-pVTZ and ROCBS-QB3 methods, and their rate parameters were fitted to the modified Arrhenius eq (298-1000 K). These reactions play a central role in controlling RO2 radical consumption and radical-pool evolution during C3H8 oxidation, particularly in the negative temperature coefficient regime where competing reaction channels become pressure-dependent. The updated rates were implemented into existing models and compared with literature C3H8 oxidation experiments at 100 atm. By changing the unimolecular β-scission channels of RO2 to alkene and HO2 from these computed reaction rates, the present model significantly improved agreements with experimental data, while modifying the relevant bimolecular reactions alone did not. Pathway analyses confirmed the dominance of β-scission under 100 atm and 725 K. Additional ignition delay time (IDT) and laminar flame speed (LFS) simulations using our model demonstrated its comprehensive effectiveness beyond JSR experiments. This work provides an excellent C3H8 mechanism, especially for high to supercritical pressure combustion simulations.