Air-compressing internal combustion engine

An air compressing internal combustion engine, comprising at least one reciprocating piston (1), in particular for swirl-free or low-swirl combustion, 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) adjoining the trough bottom (4) and having a maximum inner first trough diameter (d1), thereafter a second section (6b) forming a constriction and having a minimum inner second trough diameter (d2) smaller than the inner first trough diameter (d1), and thereafter a third section (6c) forming a trough rim section, 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 angle (β) with the first annular surface (8), wherein the first annular surface (8) and the second annular surface (9) are formed to be inclined to a normal plane (ε) on the piston axis (2), and wherein in the transition between the first annular surface (8) and second annular surface (9) an edge (11) is formed with a defined third radius of curvature (R3), wherein as viewed in a meridian section of the piston (1), the first annular surface (8) together with a normal plane (ε) on the piston axis (2) forms a first angle (α) between 10° and 20°, preferably 15.2°.