Laser Absorption Shock Tube Study of C1 to C4 n-Alkyl Formate Pyrolysis

Abstract

$n$-Alkyl formates are considered as potential alternative fuels or fuel additives. While their oxidation chemistry has been investigated intensely, their pyrolysis chemistry requires more experimental insights. The present work utilizes shock tube experiments in combination with infrared laser absorption measurements to obtain information about the $n$-alkyl formate dissociation and to derive rate coefficients. These experiments are complemented with kinetics predictions. Methyl formate is found to be less reactive than the longer n-alkyl formates, the latter of which have rather similar rate coefficients for dissociation towards n-alkene and formic acid, with n-butyl formate exhibiting the largest rate coefficient. The present experimental rate coefficients for n-alkyl formate decomposition are found to agree well with experimental results from the literature. The decomposition of formic acid formed via dissociation of the longer n-alkyl formates, the present experimental rate coefficient was initially assumed to deviate from theoretical predictions found in the literature. Yet when adjusting the collisional energy transfer parameters in the kinetics predictions, the present results can be reproduced through previous theoretical work. This indicates that formic acid might be very sensitive to the bath gas, which will be investigated in future work. With the present systematic investigation of $C_1$ to $C_4$ n-alkyl formates, detailed chemical kinetic modeling of $n$-alkyl formates will be aided in general. Moreover, the potential to gain insights at the elementary reaction level is revealed in the context of formic acid dissociation.