Air-cooled, four-stroke aviation engine
An improved air-cooled aviation engine includes a compact combustion chamber having an intake valve opening, an exhaust valve opening, and a generally elliptical shape. The elliptical shape has a major axis and a minor axis, with the major axis intersecting both the intake valve opening and the exhaust valve opening. In some examples, the major axis is the same length or shorter than a diameter of a cylinder bore of the engine, and the minor axis is smaller than the major axis. Combustion is thus constrained to a smaller area than that of the cylinder bore.
1. An engine, comprising:
an engine block having a cylinder bore that contains a piston constructed and arranged to move reciprocally within the cylinder bore; and
a cylinder head having an interior surface that faces the cylinder bore, the interior surface having an intake valve opening, an exhaust valve opening, a first crescent-shaped squish region, and a second crescent-shaped squish region,
wherein the intake valve opening and the exhaust valve opening are disposed between the first crescent-shaped squish region and the second crescent-shaped squish region, and
wherein the first crescent-shaped squish region and the second crescent-shaped squish region are constructed and arranged to direct more of an air-fuel mixture toward the exhaust valve opening than toward the intake valve opening during compression;
wherein an elliptical combustion chamber is disposed between the first crescent-shaped squish region and the second crescent-shaped squish region, the elliptical combustion chamber extending over a cross-sectional area smaller than a cross-sectional area of the cylinder bore.
2. The engine of claim 1 , wherein the elliptical combustion chamber extends to respective ends of the cylinder bore, and
wherein the first crescent-shaped squish region is disposed on one side of a major axis of the elliptical combustion chamber and the second crescent-shaped squish region is disposed on another side of the major axis.
3. The engine of claim 2 , wherein the intake valve opening is disposed on one side of a minor axis of the elliptical combustion chamber and the exhaust valve opening is disposed on another side of the minor axis, and
wherein the elliptical combustion chamber is asymmetrical about the minor axis to direct more of the air-fuel mixture toward the exhaust valve opening than toward the intake valve opening during compression.
4. The engine of claim 3 , wherein the intake valve opening and the exhaust valve opening intersect the major axis.
5. The engine of claim 1 , wherein a minor axis of the elliptical combustion chamber separates the cylinder head into an intake side and an exhaust side, the intake valve opening being disposed on the intake side and the exhaust valve opening being disposed on the exhaust side, and
wherein the first crescent-shaped squish region and the second crescent-shaped squish region extend over a greater area on the exhaust side than on the intake side to direct more of the gases toward the exhaust side than toward the intake side during compression.
6. The engine of claim 1 , wherein the exhaust valve opening is smaller than the intake valve opening.
7. The engine of claim 1 , wherein the piston includes a top surface that faces the interior surface of the cylinder head, the top surface having a first raised outer region, a second raised outer region, and a depression that is depressed relative to the first raised outer region and the second raised outer region, and
wherein the first raised outer region and the second raised outer region directly oppose the first crescent-shaped squish region and the second crescent-shaped squish region, respectively, to direct the air-fuel mixture toward the elliptical combustion chamber during compression.
8. The engine of claim 7 , wherein the interior surface of cylinder head further has a raised dome portion that extends downwardly toward the first crescent-shaped squish region and the second crescent-shaped squish region, and
wherein the elliptical combustion chamber is formed between the raised dome portion and the depression.
9. The engine of claim 8 , wherein the piston further includes a centrally disposed raised portion surrounded by the depression, and
wherein the centrally disposed raised portion directly opposes the raised dome portion to form a kidney-shaped cross-sectional area when the piston is in an uppermost position within the cylinder bore.
10. The engine of claim 1 , wherein the elliptical combustion chamber has a perimeter that maintains a convex curvature entirely around the elliptical combustion chamber.
11. A method of operating an engine, the engine including:
an engine block having a cylinder bore that contains a piston constructed and arranged to move reciprocally within the cylinder bore, and
a cylinder head having an interior surface that faces the cylinder bore, the interior surface having an intake valve opening, an exhaust valve opening, a first crescent-shaped squish region, and a second crescent-shaped squish region,
wherein the intake valve opening and the exhaust valve opening are disposed between the first crescent-shaped squish region and the second crescent-shaped squish region,
the method comprising:
moving the piston to compress an air-fuel mixture inside the cylinder bore such that the first crescent-shaped squish region and the second crescent-shaped squish region direct more of the air-fuel mixture toward the exhaust valve opening than toward the intake valve opening; and
as the piston approaches an uppermost position within the cylinder bore, igniting the air-fuel mixture to provide mechanical power;
wherein an elliptical combustion chamber is disposed between the first crescent-shaped squish region and the second crescent-shaped squish region, the elliptical combustion chamber extending over a cross-sectional area smaller than a cross-sectional area of the cylinder bore.