Combination of piston rings, and combination structure of piston and piston rings

A combination structure of a piston and piston rings in a diesel engine, comprising the piston fitted in a cylinder in the diesel engine and a plurality of piston rings assembled to the piston, the combination of the plurality of piston rings including:

• a first compression ring assembled at a position closest to a combustion chamber, a second compression ring assembled at a position close to the combustion chamber next to the first compression ring, an oil ring assembled at a position farthest from the combustion chamber, and a third compression ring assembled at a position between the second compression ring and the oil ring, wherein when an axial width of the first compression ring is h1(1), an axial width of the second compression ring is h1(2), an axial width of the third compression ring is h1(3), and an axial width of the oil ring is h1(4), h1(1)≥h1(2) and h1(1)≥h1(3),
• when h1(TOTAL)=h1(1)+h1(2)+h1(3)+h1(4),10 mm≥h1(TOTAL)≥3.9 mm,
• the piston has an outer peripheral surface that is formed with a first ring groove in which the first compression ring is fitted, a second ring groove in which the second compression ring is fitted, a third ring groove in which the third compression ring is fitted, and an oil ring groove in which the oil ring is fitted,
• when a length from an end face of the first ring groove on a combustion chamber side to an end face of the oil ring groove on a crank chamber side in an axial direction of the piston is Lp, Lp≥6.3 mm,
• when a length, in the axial direction of the piston, of a second land portion that is a region defined by the first ring groove and the second ring groove in the outer peripheral surface of the piston is Lp2, and a length, in the axial direction of the piston, of a fourth land portion that is a region defined by the third ring groove and the oil ring groove is Lp4, Lp2>Lp4,
• the first compression ring has an outer peripheral surface formed in a barrel shape,
• the second compression ring has an outer peripheral surface formed in a tapered shape or a tapered undercut shape, and
• the third compression ring has an outer peripheral surface formed in a tapered shape or a tapered undercut shape.