Potential of oxymethylene ethers as renewable diesel substitute

Abstract

Oxymethylene ethers (OMEx), are a promising renewable replacement fuel for compression ignition engines. OMEx are largely compatible with current engines, can help to significantly reduce engine-out and tail-pipe emissions while simultaneously reducing the transport sector’s net carbon emissions by gradually replacing fossil diesel fuel. This paper aims to compile and critically review recent research progress on OMEx, following the entire value chain from production to engine application. First, pathways for OMEx production are compiled and compared regarding energy efficiency, fuel production costs and life cycle CO2 balance, showcasing advantages and disadvantages of more advanced production pathways with reduced hydrogen consumption. On the application side, chemical kinetics play a fundamental role in understanding OMEx combustion. Recent progress in understanding the decomposition and combustion of OMEx is discussed and resulting detailed chemical reaction mechanisms from the literature are investigated regarding their accuracy and capabilities. Furthermore, the liquid fuel properties of OMEx are presented and compared with conventional fossil diesel fuel as well as selected other renewable and surrogate fuels, pointing out possible issues and potentials for engine application. In particular, material compatibility is discussed, and suitable sealing materials are identified. Subsequently, the application of OMEx in CI engines is discussed in detail, including the fuel’s potential for engine efficiency increase and significant decrease in engine-out particulate and NOx emissions. Necessary and possible changes to engine design and control, such as longer injection duration or larger injector holes, are outlined. Finally, on a high level, the potential for large-scale application of e-fuels such as OMEx is discussed, and necessary political incentives are pointed out.