E-Fuel Blend Operation of Small Industral SI-Engines with Carburetors

Intentions for replacing small SI-engines in motor-equipment for professional gardening and forestry by battery-electric solutions are limited by requested disposability and tolerable power-to-weight ratio. Due to this fact experimental investigations for using methanol/gasoline fuel-blends and pure methanol in a small air-cooled industrial SI-engine (4 kW @ 3600 rpm) were carried out. At a first step (only) for these experiments, the serial mechanical carburetor was additionally equipped with a self-developed electronic lambda-control, to enable tests for different fuel-blends (Super E5, M30, M60, M100) with constant boundary conditions during engine operation without exchange of carburetor jets. This concept of control will be presented. Special needs for these SI-engines (exhaust-gas temperature, non-electric start) require a permanent sub-stoichiometric operation. For serial applications free of electronic components, the size of jets would have to be adapted as well as the use of standardized fuel-mixtures will be necessary. In addition to reference tests on different days in operation with gasoline ´Super E5´ to check repeatability, operating values and emissions will be presented for operation with the fuel-blends described. Pressure indications allow statements for changes in heat release and - additionally to acoustical perception - evaluations of combustion stability. Following inspection of engine components showed consequences of sub-stoichiometric combustion of methanol-fuel-blends and resulting recommendation. Lube-oil analysis, afterwards carried out by ATR spectroscopy shows possible contamination inside crankcase. Optical inspections and material measurements at normally used serial components of fuel system (float, housing, sealings, hoses) showed possible incompatibilities with this alcoholic fuel-blends as well as necessary alternative materials.