A diesel engine in which a lubrication oil on the wall surface of the cylinder liner is prevented from being burned and diluted, and a smoke resulting from the local lack of air in the combustion chamber is also prevented from being generated. The diesel engine comprises a group injection hole nozzle 20 and a piston 110 . A step 115 having a height gradually increased toward the radial outer circumference of the piston is formed over the entire circumference of the top surface 111 of the piston. Furthermore, a tilted part 115 b is formed as the step surface of the step 115.
1. A diesel engine comprising:
a group injection hole nozzle including a plurality of injection holes;
a piston having a top surface; and
a step provided on the top surface,
wherein the height of the step increases in an outward direction along a diameter of the piston,
wherein the plurality of injection holes include a plurality of sets of injection holes such that each set of injection holes has an opening angle, which is the angle between the center axes of the injection holes within the set,
wherein the group injection hole nozzle has a first compound spraying angle, which is the angle between the middle of the opening angle of a first set of group injection holes and the middle of the opening angle of a second set of group injection holes located on an opposite side of the group injection hole nozzle,
wherein the group injection hole nozzle has a second compound spraying angle, which is the angle between the middle of the opening angle of a third set of group injection holes and the middle of the opening angle of a fourth set of group injection holes located on an opposite side of the group injection hole nozzle, and
wherein the first compound spraying angle is different than the second compound spraying angle.
2. The diesel engine as set forth in claim 1 , wherein
a step surface of the step is perpendicular to the piston top surface.
3. The diesel engine as set forth in claim 1 , wherein
a step surface of the step is tilted with respect to the piston top surface.
4. The diesel engine as set forth in claim 1 , wherein
a step surface of the step is curved.
5. The diesel engine as set forth in claim 1 , wherein
each of the plurality of group injection holes is the same distance from the step.
6. The diesel engine as set forth in claim 1 , wherein
when the piston is at a top dead point, spray from each of the plurality of injection holes collides with a wall surface of a combustion chamber.