Abstract: The invention relates to an air-compressing internal combustion engine, comprising at least one piston (1) having a combustion chamber trough (3) substantially rotationally symmetrical to a piston axis (2), which has a trough bottom (4) with a substantially cone-like elevation (5) and a circumferential trough wall (6), wherein the trough wall (6) forms a substantially torus-like first section (6a) having a maximum inner first trough diameter (d1), a second section (6b) having a minimum inner second trough diameter (d2) smaller than the inner first trough diameter (d1), and a third section (6c), wherein—as seen in a meridian section of the piston (1)—the first section (6a) has a concave first radius of curvature (R1) and the second section (6b) has a convex second radius of curvature (R2), and wherein the third section (6c) forms a first annular surface (8) adjoining the second section (6b) and a second annular surface (9) terminating in the piston end surface (7), which second annular surface (9) defines an a

Abstract: A rotary piston engine is disclosed. In one aspect, the engine includes a rotary piston rotating in a housing. The engine also includes a piston flank wall extending at least between two apex edges adjacent on the circumferential wall of the piston. The engine further includes a combustion chamber formed between the piston flank wall, an inner circumferential wall of the housing, and inner side walls of the housing, wherein the spark plug is connected to the combustion chamber by at least one spark plug channel. The spark plug channel has a substantially circular, elliptical or slot-like formed cross-section and the spark plug is arranged in a spark plug cavity having a larger diameter than the spark plug channel. The volume of the spark plug cavity is arranged relatively to thee spark plug channel substantially at the rear side, seen in the direction of rotation.