The impact of oxymethylene dimethyl ether (OME_x)-diesel blends on combustion and soot-reduction characteristics: experimental and kinetic investigations

Oxymethylene dimethyl ether (OME_x) is a renewable oxygenated fuel with significant potential to break the traditional soot-NO_x trade-off. The combustion and soot-reduction potential of OME_x (x=3-6) and its blends with diesel are investigated with combined high-pressure spray chamber experiments and OME_x-dodecane reaction mechanism simulations at diesel-like conditions. Soot-related metrics from combustion chamber experiments and kinetics modeling show consistent trends with PM measurements performed in a dedicated research engine. The results reveal that the liquid length is reduced with OME_x addition, primarily due to its lower boiling point, with minimal influence from fuel density, thereby reducing the possibility of cylinder wall impingement when fuel mass flow needs to be increased. Heat release rate analysis and natural luminosity measurements indicate a faster fuel consumption rate during the premixed burn phase with increasing OME_x content. Soot reduction is observed for high OME_x ratios across various engine-like conditions. The remarkable soot-reduction for OME_x blends is mainly attributed to the reduced soot formation rather than enhanced oxidation. The soot suppression is caused by the increased total oxygen ratio (Ω( H )) from fuel oxygen content and improved air entrainment due to the extended lift-off length. The high oxygen content of OME_x was found to be more effective in reducing soot than enhanced air entrainment. The kinetic analysis shows that OME_x has little influence on the n-dodecane decomposition pathway in the blends. OME_x produces abundant CH₂O via a series of β-scissions, which differs from conventional fuels like dodecane. This potentially inhibits soot formation from precursors.