Skewed combustion chamber for opposed-piston engines

1. A piston for an opposed-piston engine, comprising a flat end surface without a ridge, the flat end surface having an elongated, concave bowl formed therein to define a combustion chamber with an elongated bowl formed in a flat end surface of an opposing piston; the flat end surface meeting a piston sidewall at a peripheral edge having a circular shape that is centered on a longitudinal axis of the piston and that is disposed at a single longitudinal level of the piston; a pair of notches formed in the end surface and positioned in opposition on the peripheral edge, in alignment with an end surface diameter; the concave bowl having an oblong shape that is elongated along the end surface diameter, between the notches; the concave bowl being flanked on either side by flat end surface portions that extend to the peripheral edge; the concave bowl having opposing sidewalls and a curved bottom portion which connects the sidewalls smoothly in a vertical section; and, the concave bowl having a maximum depth D max between the curved bottom portion and a plane P ES which intersects the longitudinal axis and is positioned at the longitudinal level, the maximum depth D max being measured at a point on the curved bottom portion which is offset in an orthogonal direction from a longitudinal plane P L which contains the longitudinal axis of the piston and the end surface diameter.

2. The piston of claim 1 , wherein a bowl depth D is a maximum distance between the curved bottom portion of the bowl and the plane P ES in a longitudinal sectional view of the piston taken along the end surface diameter; the bowl depth D is measured from a point of the curved bottom portion that is offset in an orthogonal direction from the longitudinal plane P L ; and, the planes P L and P ES are mutually orthogonal.

3. The piston of claim 2 , wherein the bowl depth D diminishes smoothly from the maximum bowl depth D max when the maximum bowl depth D max is at a position aligned with a midpoint M of the end surface diameter in plan, toward each of the notches, such that the depths D are traced along the bottom portion by a curved arc shape having a concave side that faces the longitudinal plane P L .

4. The piston of claim 3 , wherein the depth D diminishes at the same rate in each direction from the midpoint M such that the curved arc shape is symmetrical with respect to the longitudinal plane P L .

5. The piston of claim 2 , in which the bowl depth diminishes smoothly from the maximum bowl depth D max when the maximum bowl depth D max is located between a midpoint M of the end surface diameter in plan and a respective one of the notches.

6. A two-stroke cycle, compression ignition, opposed-piston engine including at least one cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which:

each piston has a flat end surface without a ridge, and each flat surface has a concave bowl formed therein that defines a combustion chamber with the concave bowl formed in the flat end surface of the other piston when the pistons are near top center locations in the bore;

two fuel injectors are disposed in diametrical opposition and in alignment with a centerline of the combustion chamber;

in a first longitudinal section of the combustion chamber, the combustion chamber has a rotationally skewed shape that is symmetrical with respect to the centerline of the combustion chamber; and,

in a second longitudinal section of the combustion chamber that is orthogonal to the first longitudinal section, the combustion chamber has an elongated shape with opposite end portions that taper along the centerline of the combustion chamber toward the fuel injectors.

7. The opposed-piston engine of claim 6 , in which each flat end surface meets a piston sidewall at a peripheral edge having a circular shape that is centered on a longitudinal axis of the piston and that is disposed at a single longitudinal level of the piston, a pair of notches is formed in the end surface, and the notches are positioned in opposition on the peripheral edge, in alignment with an end surface diameter, wherein:

each concave bowl has an oblong shape that is elongated along an end surface diameter, between the notches;

the bowl is flanked on either side by flat end surface portions that extend to the peripheral edge;

the bowl has opposing sidewalls and a curved bottom portion which connects the sidewalls smoothly in a vertical section; and,

a maximum depth of the bowl is measured from a point of the curved bottom portion, the point being offset in an orthogonal direction from a plane P ES which intersects the piston longitudinal axis and is positioned at the longitudinal level.

8. The opposed-piston engine of claim 7 , in which:

a bowl depth D is the maximum distance between the curved bottom portion and the plane P ES that is measured in a longitudinal section taken along the end surface diameter;

the bowl depth D is measured from a point of the bottom portion that is offset in an orthogonal direction from a longitudinal plane P L ;

the plane P L intersects the longitudinal axis and the end surface diameter; and,

the planes P L and P ES are mutually orthogonal.

9. The opposed-piston engine of claim 8 , in which the bowl depth D diminishes smoothly from a maximum bowl depth D max that is located between a midpoint M of the end surface diameter in plan and a respective one of the notches.

10. A two-stroke cycle, compression ignition, opposed-piston engine including at least one cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, comprising:

each piston having a flat end surface without a ridge, each end surface having an elongated bowl formed therein;

a combustion chamber formed between the elongated bowls;

two fuel injectors disposed in diametrical opposition and in alignment with a centerline of the combustion chamber;

in a first longitudinal section of the combustion chamber, the combustion chamber having a rotationally skewed shape that is symmetrical with respect to the centerline of the combustion chamber; and,

in a second longitudinal section of the combustion chamber that is orthogonal to the first longitudinal section, the combustion chamber having an elongated shape with opposite end portions that taper along the centerline of the combustion chamber toward the fuel injectors.

11. The opposed-piston engine of claim 10 , in which each flat end surface meets a piston sidewall at a peripheral edge having a circular shape that is centered on a longitudinal axis of the piston and that is disposed at a single longitudinal level of the piston, a pair of notches is formed in the end surface, and the notches are positioned in opposition on the peripheral edge, in alignment with an end surface diameter, wherein: each concave bowl has an oblong shape that is elongated along an end surface diameter, between the notches;

the bowl is flanked on either side by flat end surface portions that extend to the peripheral edge;

the bowl has opposing sidewalls and a curved bottom portion which connects the sidewalls smoothly in a vertical section; and,

a maximum depth of the bowl is measured from a point of the bottom portion which is offset in an orthogonal direction from a plane P ES which intersects the piston longitudinal axis and is positioned at the longitudinal Level.

12. The opposed-piston engine of claim 11 , in which:

a bowl depth D is the maximum distance between the curved bottom portion and the plane P ES that is measured in a longitudinal section taken along the end surface diameter;

the bowl depth D is measured from a point of the bottom portion that is offset in an orthogonal direction from a longitudinal plane P L ;

the plane P L intersects the longitudinal axis and the end surface diameter; and,

the planes P L and P ES are mutually orthogonal.

13. The opposed-piston engine of claim 12 , in which the bowl depth D diminishes smoothly from a maximum bowl depth D max aligned with a midpoint M of the end surface diameter in plan of the notches, such that the depths D are traced along the bottom portion by a curved arc shape having a concave side that faces the longitudinal plane P L .

14. The opposed-piston engine of claim 13 , in which, the D max position is aligned with the midpoint M, and the depth D diminishes at the same rate in each direction from the midpoint M such that the curved arc shape is symmetrical with respect to the longitudinal plane P L .

15. The opposed-piston engine of claim 14 , in which each fuel injector is constructed to emit a fuel spray with three or four plumes.

16. The opposed-piston engine of claim 12 , in which the bowl depth D diminishes smoothly from a maximum bowl depth D max that is located between a midpoint M of the end surface diameter in plan and a respective one of the notches.

17. The opposed-piston engine of claim 16 , in which each fuel injector is constructed to emit a fuel spray with three or four plumes.