Potential of e-Fischer Tropsch diesel and oxymethyl-ether (OMEx) as fuels for the dual-mode dual-fuel concept

The dual-mode dual-fuel combustion strategy allows operating over the entire engine map by implementing a diffusive dual-fuel combustion at high engine loads. This requires increasing the amount of exhaust gas re-circulation to control the NOx emissions, which penalizes the soot levels. At these conditions, the use of nonsooting fuels as the e-Fischer Tropsch Diesel (e-FT) and oxymethylene dimethyl ethers (OMEx) could be a potential way to avoid the NOx-soot trade-off. The experimental results acquired in a compression ignition multi-cylinder medium-duty engine evidence that the higher oxygen content of OMEx allows reducing the soot emissions at high loads to near zero levels, while e-FT promotes a soot reduction of around 20% as compared to diesel. Nonetheless, the low lower heating value of OMEx leads to excessive injection durations, enlarging the combustion process and increasing the fuel consumption around 1.3-7.2% and 1.4-5.3% as compared to diesel and e-FT, respectively, depending on the engine load. Finally, the well to wheel analysis confirms the potential in reducing the carbon dioxide footprint of OMEx (14.8-69%) and e-FT (0.3-38.5%) compared to diesel, as they can be synthetized via direct air capture as a source of carbon and using renewable energy.