Abstract: A two stroke internal combustion engine has two opposed pistons (8) which reciprocate in opposite directions in cylinder (4) and define a common compression chamber (6) therebetween. Blower (10) supplies scavenging air at high pressure to compression chamber (6) through inlet port(s) (15) to pass axially through compression chamber (6) to exhaust port(s) (7) in an amount sufficient to purge substantially all products of combustion from compression chamber (6) and to cool cylinder (4). A small external combustion chamber (3), having restricted communication (9) with compression chamber (6), has a valve (2) permitting injection of a rich fuel/air mixture which in part passes to compression chamber (6) to form a fuel lean mixture with the scavenging air therein. Ignition means (1) ignites the fuel rich mixture in combustion chamber (3), in turn allowing burning fuel to ignite the fuel lean mixture in compression chamber (6).

Abstract: The machine (e.g. an internal combustion engine or pump) has at least one cylinder 4 housing two opposed pistons 5 adapted to reciprocate in opposite directions and a common working chamber 13. A main shaft 1 carries two contoured tracks 3 each having opposed, axially facing, endless, substantially sinusoidal cam surfaces. Bearings 8 and 9 mounted on connecting rod 6 abut the cam surfaces so that reciprocation of pistons 5 imparts rotary motion to main shaft 1, or vice versa.