Understanding the miscibility of polyoxymethylene dimethyl ethers (OME<inf>n</inf>) and diesel blend using molecular dynamics simulation

Abstract

Polyoxymethylene dimethyl ethers (OMEn) as an alternative fuel have attracted considerable interest in recent years, owing to their much reduced environmental impact. Since OMEn is often blended with diesel, the miscibility and stability of OMEn/diesel mixtures are important for engine operation. In this study, molecular dynamics method was used to investigate the miscibility of OME1-6 and diesel blends. The results suggest that the miscibility of OMEn and diesel blends decreases with the increasing number of oxymethylene units. The aromatics and heteroatomic molecules help maintain the stability of OMEn/diesel blends. The intermolecular interactions between OME1-6 and diesel molecules were investigated, which revealed that the electrostatic interaction plays a significant role in the liquid–liquid equilibrium of OMEn/diesel blends. The molecules in diesel having strong electrostatic interaction with OMEn are prone to accumulate around OMEn. The electrostatic interaction between diesel and OMEn molecules depends on the molecular structure and electronegativity differences of atoms in diesel molecules. The analyses of MD results coupled to minimum-distance distribution functions show an accumulation of paraffins and naphthenes close to OMEn at ∼ 2.36 Å, and suggest a strong interaction of OMEn with diesel carbazole molecules via hydrogen bonds. The results also indicate that the chain length and structure of alkanes have little impact on the molecular distribution around OMEn.