Exploration of suitable injector configuration for dual-mode dual-fuel engine with diesel and OMEx as high reactivity fuels

Dual-mode dual-fuel (DMDF) combustion stands over other low temperature combustion strategies as it is able to operate over the entire engine map by transitioning between reactivity controlled compression ignition and diffusive combustion depending on the engine load. In combination with non-sooting e-fuels, it is able to achieve low NOx and soot levels even at high loads. Oxygenated fuels like poly-oxymethylene dimethyl ethers (OMEx) have been already proved to present an outstanding NOx-Soot trade-off improvement when used in combination with a DMDF combustion strategy. One drawback of OMEx is that, despite having a high reactivity, it has a low lower heating value, which requires considerably longer injection events compared to other traditional fuels in order to achieve the same engine power output. The long injections limit the flexibility of the injection strategy and result in extremely long combustion durations. A possible solution to this problem resides in moving towards injectors with higher flow rate capacities, but this may compromise the mixing and combustion processes. This work aims to shed some light on the implications of changing the engine hardware to overcome this limitation by testing a DMDF mull-cylinder engine using gasoline as the low-reactivity fuel and diesel or OMEx as the high reactivity fuels with injectors of different flow capacity. The results show that a concise analysis of the involved phenomenology of the combustion process allows to find out the trade-off between the engine-out emissions and the mixing capacity of the injection system while the engine performance is not significantly affected.