A diesel engine comprising: a piston received slidably in a cylinder, and including a main body having an annular-shaped upper surface about a central axis and a combustion chamber provided in the main body to be recessed from the upper surface of the main body such that fuel injected from an injector is mixed with air in the combustion chamber; and an injector installed in a cylinder head covering the cylinder to penetrate through the cylinder head and configured to inject fuel into the combustion chamber at a second acute angle with respect to the central axis, wherein the combustion chamber includes a first bowl and a second bowl above the first bowl with a lip interposed between the first bowl and the second bowl, the lip protruding toward the central axis, wherein the second bowl extends in a radial direction from the lip and includes a bowl guide portion that extends in the radial direction from the lip and is inclined at a first acute angle with respect to the central axis, wherein the second bowl is arranged between the lip and the upper surface of the main body such that gas burned in the second bowl flows above the upper surface and particle matters, PM, generated in the second bowl is oxidized, wherein a surface of the lip has a portion of a first circle with a first radius, and a surface of the second bowl has a portion of a second circle with a second radius less than the first radius, wherein a surface of the bowl guide portion has a common tangent line between the first circle and the second circle, wherein an intersection point of the first bowl and the lip has a central angle rotated by a first angle from a midpoint of a circle of a surface of the first bowl, wherein the central angle of the intersection point is determined to be within a half of a fuel injection angle plus/minus 10 degrees, wherein the injector injects the fuel at the second acute angle with respect to the central axis toward the intersection point of the first bowl and the lip at top dead center, TDC, and injects the fuel toward a bottom of the second bowl at end point of fuel injection, EOI, and wherein a surface of the first bowl has a portion of a third circle with a third radius. a piston received slidably in a cylinder, and including a main body having an annular-shaped upper surface about a central axis and a combustion chamber provided in the main body to be recessed from the upper surface of the main body such that fuel injected from an injector is mixed with air in the combustion chamber; and an injector installed in a cylinder head covering the cylinder to penetrate through the cylinder head and configured to inject fuel into the combustion chamber at a second acute angle with respect to the central axis, wherein the combustion chamber includes a first bowl and a second bowl above the first bowl with a lip interposed between the first bowl and the second bowl, the lip protruding toward the central axis, wherein the second bowl extends in a radial direction from the lip and includes a bowl guide portion that extends in the radial direction from the lip and is inclined at a first acute angle with respect to the central axis, wherein the second bowl is arranged between the lip and the upper surface of the main body such that gas burned in the second bowl flows above the upper surface and particle matters, PM, generated in the second bowl is oxidized, wherein a surface of the lip has a portion of a first circle with a first radius, and a surface of the second bowl has a portion of a second circle with a second radius less than the first radius, wherein a surface of the bowl guide portion has a common tangent line between the first circle and the second circle, wherein an intersection point of the first bowl and the lip has a central angle rotated by a first angle from a midpoint of a circle of a surface of the first bowl, wherein the central angle of the intersection point is determined to be within a half of a fuel injection angle plus/minus 10 degrees, wherein the injector injects the fuel at the second acute angle with respect to the central axis toward the intersection point of the first bowl and the lip at top dead center, TDC, and injects the fuel toward a bottom of the second bowl at end point of fuel injection, EOI, and wherein a surface of the first bowl has a portion of a third circle with a third radius.