Stratified-charge two-stroke internal combustion engines

A stratified-charge two-stroke internal combustion engine comprising:

• a combustion chamber having an exhaust port, a first inlet port, and a second inlet port positioned closer to said exhaust port than said first inlet port;
• a piston reciprocable in said combustion chamber;
• a crankcase chamber;
• a first duct extending from the first inlet port in the combustion chamber to a position in the crankcase chamber remote from said combustion chamber;
• a first admission port connecting with said first duct at a position intermediate its ends for introducing a fuel-air mixture into said first duct;
• a second duct extending between the second inlet port in the combustion chamber and said crankcase chamber;
• and a second admission port communicating with said crankcase chamber for introducing air into said crankcase chamber, communication between said combustion chamber and said crankcase chamber through said first and said second ducts being controlled by movement of said piston, the arrangement of said first and second second inlet portions being such that air introduced into said combustion chamber through said second duct substantially separates a fuel-air mixture introduced into said combustion chamber through said first duct from gases being exhausted through said exhaust port.