Effects of fuel constituents and injection timing on combustion and emission characteristics of a compression-ignition engine fueled with diesel-DMM blends

The effects of DMM addition and fuel injection timing on combustion characteristics, fuel efficiency and emissions of a compression-ignition engine fueled with diesel-dimethoxymethane (DMM) blends are investigated experimentally in this study. Three diesel-DMM blends with 15%, 30% and 50% volume fraction of DMM addition respectively are tested at different engine loads and engine speeds. Not only HC, CO, smoke and NO_x emissions, but also particle-size distribution and number concentration in exhaust gas have been measured. According to the measured in-cylinder pressure history, the in-cylinder combustion process is promoted by using diesel-DMM blends and can be further improved with early fuel injection. We find that using diesel-DMM blends can improve thermal efficiency and is beneficial to the reduction of smoke and CO emissions as well as particle number of both nanoparticles and ultrafine particles in exhaust gas with slightly increased NO_x emission. Both fuel efficiency and thermal efficiency are improved with advanced fuel injection timing. Advancing fuel injection timing reduces smoke emission and particle number at the cost of increased NO_x emission. We find that early fuel injection can either increase or decrease nanoparticles in exhaust gas. When advancing fuel injection from 20 to 23 CA BTDC, the number of nanoparticles is reduced; the further advanced fuel injection timing from 23 to 26 CA BTDC produces more nanoparticles. In this study, the lowest nanoparticle number in exhaust gas was achieved by injecting diesel-DMM blends with 50% DMM addition at 23 CA BTDC.