Experimental and theoretical investigations of methyl formate oxidation including hot β-scission

Abstract Recently the possibility of hot β -scission pathways gained attention. These reactions give a shortcut during the important fuel consumption phase in combustion processes leading from H-atom abstraction directly to the β -scission products without fuel radical thermalization. Methyl formate (MF) was shown to be prone to hot β -scission due to a low β -scission barrier height. Furthermore, MF as smallest methyl ester can be considered as biodiesel surrogate and it is an important intermediate product during combustion of various ethers. In this work a predominantly ab-initio derived detailed kinetic model of MF combustion is developed including hot β -scission pathways and compared to a sophisticated literature model based on classical estimation methods. For this, new stoichiometric MF in air ignition delay time measurements in a shock tube and a rapid compression machine over a wide temperature range (790 K–1250 K) and pressures of 10, 20 and 40 bar served as validation targets. The experimental ignition delay times (IDT) show Arrhenius type behavior in both facilities at all conditions. The newly developed quantum-based model catches the pressure dependency and low-temperature reactivity well although overpredicting the IDT at higher temperatures. It was found that hot β -scission is the major depletion pathway of formate group-centered MF radicals. This, however, does not change the overall reactivity of MF combustion due to the low stability of the alkyl peroxide (RO 2 ) at the formate group. For species with competing thermal β -scission and RO 2 formation, however, hot β -scission may have a significant impact.