Large eddy simulation of OME3 and OME4 spray combustion under heavy-duty conditions

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The synthetic diesel fuel (Poly-)oxymethylene ether (OME) has various interesting properties for the transport sector. OME reduces emissions in direct injection (DI) diesel engines, e.g., soot and NOx, and is considered CO2 neutral. While most studies have examined a mixture of OMEs with different chain lengths, recent studies have focused on neat OME3 and OME4. In the literature similar chemical ignition delay times were shown under homogeneous conditions and significant differences were reported in their thermophysical properties. Furthermore, differences between OME3 and OME4 in terms of the mixture formation were shown on a heavy-duty injector under non-reactive conditions. The question of how this mixture formation affects the ignition and flame characteristics of neat OME3 and OME4 spray flames remains unresolved. To address this topic, this study conducts a combined experimental and numerical investigation under inert and reactive spray conditions for OME3 and OME4 on a heavy-duty injector. Large Eddy Simulations (LESs) and high-pressure, high-temperature spray chamber measurements are conducted. The distinct differences between neat OME3 and OME4 are analyzed along the cause–effect chain comprising the mixture formation, ignition behavior and its effects on the overall heat release rate. Based on the differences in the thermophysical properties, e.g., density and vapor pressure, the investigations in inert conditions reveal differences in the liquid penetration and mixture formation. The reactive spray flame measurements and simulations show a significant offset in the ignition delay time for OME3 and OME4. An explanation is found in the significantly different distribution of the scalar dissipation rate due to the differences in the mixture formation. Despite the differing ignition delay times, similar local flame structures are found for both fuels.