Diesel engine

A diesel engine comprising:

• a cylinder;
• a piston which reciprocates in said cylinder;
• a cylinder head on which an intake valve and an exhaust valve are arranged;
• a fuel injector which is arranged on said cylinder head and injects fuel radially approximately from a center of said cylinder;
• a circular cavity which is formed on a top of said piston and is concaved away from said cylinder head;
• and
• a combustion chamber which is defined by said top of said piston including said cavity, said cylinder, and a face of said cylinder head that faces said top of said piston,
• wherein a wall shape of said cavity on a cross section including a center axis of said cylinder consists of an inward protruding portion located at the periphery of an opening of said top of said piston for said cavity, a center portion projecting toward said fuel injector and located at the bottom of said cavity, and a peripheral portion which connects said inward protruding portion and said center portion and is made with arcs having their centers on the inner side of said cavity,
• wherein said fuel injector and said cavity are configured so that fuel injected from said fuel injector directs to a proximity of the border between said inward protruding portion and said peripheral portion,
• wherein said peripheral portion consists of a first portion located farthermost from said fuel injector among the entire peripheral portion, a second portion located between said inward protruding portion and said first portion, and a third portion located between said first portion and said center portion,
• wherein radii of arcs of said peripheral portion decrease from said second portion to said first portion and increase from said first portion to said third portion, and
• wherein said second portion and said third portion are formed symmetric with respect to a line connecting a point in said first portion located farthermost from said fuel injector and an injection hole of said fuel injector such that the radii of the arcs of the second portion and the third portion are equal and the centers of the arcs of the second portion and the third portion are located at symmetric positions with respect to said line.