A molecular investigation on the effects of OMEX addition on soot inception of diesel pyrolysis

Abstract

This study aimed at revealing the atomic-level chemical pathways involved in the soot inception inhibition of diesel pyrolysis with oxymethylene dimethyl ether (OMEX) addition. Using the reactive force field parameters in molecular dynamics simulation, the results effectively identified the specific pathways of OME3 pyrolysis and soot inception, via the analysis of the conversion of three main species: CH2O, CH3O, and CH3, generated from the initial decomposition of OME3. It has been found that CH2O molecule would be converted to CO through continuous dehydrogenation, and the carbon atoms convertered into CO would not participate in forming soot precursors, thus reducing soot formation. The oxidizing groups (mainly OH) are primarily produced from the CH3O radicals. These oxidizing species would react with small gaseous soot precursors to form stable oxides, thus inhibiting soot formation. However, this influence is relatively small under conditions where no oxygen is involved. The CH3 radicals would participate in the formation of soot precursors. In this study, it was observed that the addition of OME3 did not reduce the number of main gaseous precursors of polycyclic aromatic hydrocarbons such as C2H2, C2H3, and C3H3 during diesel-OME3 co-pyrolysis, because there were reactions between CH3 radicals and C1 and C2 species to form C2 and C3 hydrocarbon products. Based on the simulation results, the process from diesel decomposition to incipient soot production under the effects of OME3 is panoramically demonstrated. It is also found that the chain length increase of OMEX with a fixed molar fraction does not influence soot inhibition noticeably. Increasing the proportion of OMEX added to diesel helps reduce soot as carbon atoms involved in the formation of soot precursors are reduced, and more oxidizing species would be produced to slow the formation of gaseous soot precursors.