Exploring low-temperature oxidation of methacrolein with insights into fuel molecular structure effects

Methacrolein is a typical α, β-unsaturated aldehyde in the combustion of various hydrocarbons and oxygenated biofuels. The oxidation behavior of fuels that contain resonant C=C and CHO groups in the molecular structure has not been well established in the literature. Understanding the effects of these functional groups on oxidation chemistry is also significant in developing a comprehensive core mechanism. In this work, the oxidation of methacrolein is studied in a jet-stirred reactor at atmospheric pressure at temperatures ranging from 475 to 875 K, employing synchrotron vacuum ultraviolet photoionization mass spectrometry technology to identify and quantify the intermediates. A kinetic model is developed following our previous works on trans-crotonaldehyde and examined against the present experimental datasets. Based on experimental observations and modeling analyses, the crucial pathways governing the oxidation reactivities are illustrated. A new pathway is proposed to interpret theformation of ketene during the oxidation process of methacrolein and trans-crotonaldehyde. Furthermore, the effects of molecular structures on the oxidation reactivities are discussed for methacrolein, trans-crotonaldehyde, n-butanal, and isobutanal. Hydrogen abstractions from the -CHO group dominate the initial fuel consumption for the four fuels producing R-CO radicals. The different R radicals produced from R-CO radicals’ dissociation subsequently influence the oxidation reactivities.