Internal combustion engine

23 23 A two-stroke engine is for a portable handheld work apparatus such as a motor-driven chain saw, cutoff machine, brushcutter or the like. A combustion chamber is configured in the cylinder of the engine and is delimited by a reciprocating piston. The piston drives a crankshaft via a connecting rod. The crankshaft is rotatably journalled in the crankcase. The two-stroke engine includes a discharge opening for conducting exhaust gases out of the combustion chamber and an inlet via which an air/fuel mixture is conducted to the crankcase. The air/fuel mixture passes via at least one transfer channel from the crankcase into the combustion chamber. The transfer channels open at one end with a transfer window into the combustion chamber and are connected at the other end to the crankcase. A bypass channel conducts essentially fuel-free gas and opens via a membrane valve into the transfer channel. The sum of all areas of the inlet windows referred to the piston displacement of the engine is approximately 1.4 mm/cmto approximately 5.90 mm/cmwhereby good exhaust-gas values are obtained at low fuel consumption.