589,988. Two-stroke engines. AKTIEBOLAGET ATLAS DIESEL. April 6, 1945, No. 8596. Convention date, April 6, 1944. [Classes 7 (ii) and 7 (iii)] A two-stroke internal combustion engine with uniflow scavenging from cylinder inlet ports at one end of the cylinder to an outlet at the opposite end has a number of substantially parallel passages 11-13, Fig. 2, leading from opposed passages 10 to the cylinder ports and arranged substantially perpendicular to and. on each side of a longitudinal plane containing the cylinder axis so that the scavenging streams from 'the opposed passages impinge on each other in the said plane without any tendency to cause rotation of the cylinder contents during the scavenging period. In Fig. 1, an opposed piston engine has interconnected crank-shafts 4, 5 the scavenging inlet ports being controlled by the upper piston 7 and the scavenging flow passing downwards to exit ports 20 controlled by the lower piston. The outer scavenging streams 11 are confined by walls 15 and directed towards the cylinder axis. In some cases the outer walls of adjacent passages 12 may also be curved to direct the flow towards the axis. The tops of both pistons are provided with ridges 16, 19 respectively, which may have 'arcuate side walls, Fig. 2, the centres of the arcs being adjacent the cylinder walls. For a diesel type engine, two injector devices 18 may be located on opposite sides of the cylinder. Alternatively, for a spark ignited engine, spark plugs may be located at 18. At the inner position of the pistons, the arcuate ridges define two combustion spaces, Fig. 3, connected by a narrow slit 23 which causes air to be driven outwards.to mix with fan shaped fuel jets from the injectors and produce strong turbulence. In a modification, the lower piston has a shallower ridge than the upper one so that air forced out of the slit 23 is directed over the surface of the lower piston. In another modification, the upper piston only is provided with a parallel sided ridge while the lower piston has a plane upper surface. In another modification, a single-piston cylinder, Fig. 9, has scavenging ports arranged as described above and the piston has a ridge 41 forming with the exhaust valve 39, and the cylinder head, a narrow gap separating two combustion spaces, each associated with an injector 40. In another modification, Fig. 11, the upper piston has a bevelled portion 48, and the 'scavenging air streams are directed downwardly through inclined passages 47. The piston tops may be either flat, as shown, or ridged as above described. In another modification, Fig. 13, the scavenging air is supplied from opposed conduits 55, 56 each conduit supplying half the cylinder by opposed streams which meet along a central zone 63. The guide surfaces are arranged to counteract any swirling tendency. The upper piston may have a ridge at 75 or 76 or at both positions. In the latter case injection valves or injection means may be located in the planes 77 and 78. In a further modification, all the passages leading into the cylinder from one conduit are parallel to each other, and in opposed relation to corresponding passages in the other conduit.