Abstract: A piston for reciprocal movement within a combustion chamber (4) of a compression ignition engine (2) having a fuel injector (20) for forming a fuel injection plume (40) having a relatively deep angle (7.degree. to 40.degree. from a plane perpendicular to the central axis of the combustion chamber) and a piston (8) having a centrally located symmetrical upwardly opening cavity for forming a combustion bowl (30) especially arranged to complement the plume in a manner to maintain very low entrainment of soot in the lubrication oil of the engine and to maintain other engine emissions, e.g., CO and smoke, within acceptable ranges suitable to meet TALuft standards. In particular, the combustion bowl (30) as formed by an upwardly opening cavity formed as a surface of revolution having a centrally raised floor section (42) with relatively large radius of curvature R.sup.1 and an upwardly flared outer bowl section 48 having relatively smaller radius of curvatures R.sub.2. The ratio of R.sub.2 divided by R.sub.