Contributions to improving small ester combustion chemistry: Theory, model and experiments

Abstract

Biodiesel combustion models demand detailed understanding of the reactions undertaken by the ester functional group in the molecule. Investigations of the chemistry of small methyl esters can contribute to this goal. We have thus chosen methyl propanonate (MP) as a representative ester molecule in a study combining theory, model, and experiments. As an advantage, its reactions are also amenable to high-level theoretical calculations. Based on recent theoretical calculations (Tan et al., 2015), a new kinetics model for small ester combustion was developed and validated. New experimental results were obtained here in an extensive range of conditions, including full speciation in laminar low-pressure flames at two different stoichiometries (ϕ = 0.8 and 1.5) using electron ionization (EI) molecular-beam mass spectrometry (MBMS) and flame speed measurements in a spherical confined chamber (1–6atm). Comparison of the experimental data to the present model shows overall improved performance. Some specific new reaction pathways to form methanol, methylketene, methyl acetate, and acetic acid from the fuel radicals were identified and will permit more detailed insights into the combustion properties of methyl propanoate.