Clean and efficient dual-fuel combustion using OMEx as high reactivity fuel: Comparison to diesel-gasoline calibration

From previous results in a single-cylinder engine platform, it can be concluded that the dual-mode dual-fuel (DMDF) concept can be a potential solution to overcome the major constraints found with other single-fuel low temperature combustion modes. To extend these findings to a real application, this work evaluates the potential of the diesel-gasoline DMDF concept on a multi-cylinder 8L engine in terms of performance and emissions. To do this, a full engine calibration map was obtained following a specific methodology. The emissions results show that diesel-gasoline DMDF allows to achieve EURO VI NOx and soot emissions in a great portion of the engine map. Nonetheless, the levels of these pollutant at high load conditions exceed the EURO VI limits by far due to the need of implementing a diffusive combustion strategy with high EGR levels to avoid excessive in-cylinder pressure gradients. To mitigate this issue, the use of Oxymethylene ether (OMEx) instead of diesel fuel is proposed. A dedicated engine calibration was developed for the OMEx-gasoline DMDF concept following the same methodology. The results show that the oxygen content in the OMEx molecule allows to achieve a fully EUVI compliant engine calibration in terms of NOx with engine-out soot levels lower than 0.01 g/kWh. Moreover, due to the lower stoichiometric air-fuel ratio with this fuel, the air management system requirements are lower, reducing the pumping losses and increasing the brake thermal efficiency in most of the calibration map.