Oxygenated molecules such as ethers and esters are very promising biofuel or blend candidates to achieve relatively higher efficiency and cleaner combustion processes. In this work, chemical kinetic models of both ether and ester candidates were developed. Molecules with at least seven carbon alkyl chains were selected to guarantee the occurrence of low temperature chemistry via less strained transition states. The chemical kinetic models were developed using the Reaction Mechanism Generator (RMG) tool, and 0D simulations of these models were validated against a flow reactor experimental result. Important and sensitive reactions in the kinetic mechanisms were updated using calculated rate constants in this study or recent rate constants from literature. For example, rate constants of the C-C/C-O/C-H <i>β</i>-scission reaction of ether radicals were calculated using G4//B3LYP/6-311++G(2df,2pd) composite method in Gaussian16 and the transition state theory in ChemRate software. Applying those rate constants improved the agreement with the experimental results. The models also showed high sensitivity to different sub-mechanisms such as alcohol and aldehydes, as supported by the experimentally detected species. Therefore, detailed sub-mechanisms of these species were included in the kinetic mechanism, and final updated models showed a qualitative agreement with the experimental data. Finally, a detailed analysis was performed by utilizing flux analysis and sensitivity analysis tools to understand the chemistry of the investigated molecules and determine the general mechanism that governs their reactivity.

Ethers and esters combustion chemistry: Experimental and chemical kinetic study

ACS Spring 2022

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