Internal combustion engine

An internal combustion engine including a two-stroke engine for a portable handheld work apparatus, the internal combustion engine having a predetermined piston displacement measured in cm3 and comprising:

• a crankcase;
• a cylinder connected to said crankcase;
• said cylinder having a cylinder wall defining a cylinder bore;
• a piston displaceably mounted in said cylinder bore and said piston and said cylinder conjointly defining a combustion chamber;
• a crankshaft rotatably mounted in said crankcase;
• a connecting rod connecting said piston to said crankshaft so as to permit said piston to drive said crankshaft as said piston reciprocates in said cylinder between bottom dead center and top dead center;
• said cylinder having a discharge outlet formed therein for conducting exhaust gases away from said combustion chamber;
• an inlet for conducting an air/fuel mixture to said crankcase;
• a plurality of transfer windows;
• a plurality of transfer channels having respective first ends communicating with said combustion chamber via corresponding ones of said transfer windows and having respective second ends communicating with said crankcase for conducting said air/fuel mixture from said crankcase into said combustion chamber;
• a plurality of controlled openings;
• a plurality of bypass channels for conducting essentially fuel-free air;
• said controlled openings being interposed between said bypass channels and corresponding ones of selected ones of said transfer channels;
• said bypass channels communicating with said selected ones of said transfer channels via corresponding ones of said controlled openings;
• said transfer windows each having an area measured in mm2;
• and,
• the sum of said areas and said piston displacement defining a ratio lying in a range of approximately 1.4 mm2/cm3 to 5.90 mm2/cm3.