Comparison of Promising Sustainable C1-Fuels Methanol, Dimethyl Carbonate, and Methyl Formate in a DISI Single Cylinder Light Vehicle Gasoline Engine

On the way to a climate-neutral mobility synthetic fuels with their potential of a CO2-neutral production are currently in the focus of the internal combustion research. In this study the C1-fuels methanol (MeOH), dimethyl carbonate (DMC), and methyl formate (MeFo) are tested as pure C1-fuels mixtures and as blends component for gasoline. The study was performed on a single-cylinder engine in two configurations, thermodynamic and optical. As pure C1-fuels the already investigated DMC/MeFo mixture is compared with a mixture of MeOH/MeFo. DMC is replaced by MeOH, because of its benefits in laminar flame speed, ignition limits and production costs. MeOH/MeFo shows benefits in particle number (PN) emissions at a cooling water temperature of 40°C and in high load operating points. But reversed an increase of 60% in NOx emissions related to DMC/MeFo was observed in hot engine conditions. Both mixtures show no sensitivity in PN emissions for rich combustions. Neither triggered by a global rich operating point, nor with a late compression stroke stratified injection with local rich areas. This was also verified in the optical engine. DMC was also used as a blend component for gasoline. Advantages in PN emissions, knock resistance and injector tip coking were observed. Furthermore, to evaluate the knock resistance of the pure C1-fuels, two knock resistant fuels toluol and pure methanol were used as a reference. DMC/MeFo showed the highest knock resistance at the investigated operating point (1500 rpm / 17 bar IMEP / ε=14.91), where the intake air temperature was increased till first knocking combustions were detected. At least DMC/MeFo was used in a fueled pre-chamber to determine the potential of the ultra-low soot combustion inside the pre-chamber. Therefore, the lean limit was extended to λ=2.2 and an indicated efficiency of more than 40% was reached at 7 bar IMEP.