Chemical insights into the multi-regime low-temperature oxidation of di-n-propyl ether: Jet-stirred reactor experiments and kinetic modeling

To further understand the combustion characteristics and the reaction pathways of acyclic ethers, the oxidation of di-n-propyl ether (DPE) was investigated in a jet-stirred reactor (JSR) combined with a photoionization molecular-beam mass spectrometer. The experiments were carried out at near-atmospheric pressure (700 Torr) and over a temperature range of 425-850 K. Based on the experimental data and previous studies on ether oxidation, a new kinetic model was constructed and used to interpret the oxidation chemistry of DPE. In DPE oxidation, a high reactivity at low temperatures and two negative temperature coefficient (NTC) zones were observed. These behaviors are explained in this work by taking advantage of the obtained species information and the modeling analyses: the two NTC zones are caused by the competition of chain branching and termination reactions of the fuel itself and specific oxidation intermediates, respectively. Furthermore, the general requirements to have double-NTC behavior are discussed. A variety of crucial fuel-specific C-6 species, such as ketohydroperoxides and diones, were detected in the species pool of DPE oxidation. Their formation pathways are illuminated based on rate of-production (ROP) analyses. Propanal was identified as the most abundant small molecule intermediate, and its related reactions have an important impact on the oxidation process of DPE. Both acetic acid and propionic acid were detected in high concentrations. A new formation pathway of propionic acid is proposed and incorporated into the kinetic model to achieve a more accurate prediction for propionic acid mole fractions. (C) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The oxidation of di-n-propyl ether (DPE) was studied in a jet-stirred reactor combined with a photoionization molecular-beam mass spectrometer to understand the combustion characteristics and reaction pathways. A new kinetic model was developed based on experimental data, revealing two negative temperature coefficient zones and discussing the general requirements for double-NTC behavior. Key fuel-specific species were detected, with the formation pathways elucidated through rate of-production analyses. Propanal was identified as a significant intermediate, with acetic acid and propionic acid present in high concentrations. A new formation pathway for propionic acid was proposed and integrated into the kinetic model for improved prediction accuracy.