PURPOSE: To provide an engine excellent in reliability and economical efficiency by mounting an injector in such a way that its nozzle end is oriented to the center of a piston whose top center part is recessed into a cross-sectional profile of approximately upturned omega shape, and supplying fuel from an engine- driven fuel pump to the injector.

CONSTITUTION: The cylinder head 4 of a multicylinder diesel engine for an aircraft is provided with a pair of valves 6 for each cylinder, to open and close an intake and exhaust port 7. A fuel injector 8 connected to a fuel pump system 9 is placed at the cylinder head 4, with the nozzle end of the fuel injector 8 oriented to the center of the top of a piston 2 in a combustion chamber 5. The piston 2 is recessed at the center of its top into a cross-sectional profile of approximately upturned omega shape, thereby providing a central bulge 5c forming a cavity 5b of doughnut geometry, with fuel ejected toward the central bulge 5c from the injector 8. A crankshaft 3 is rotated by the reciprocating movement of the piston 2 to rotate a propeller 16 for the aircraft.