Abstract: An internal combustion aircraft engine comprising a cylinder head having a cylindrical head bore formed therein, a piston, and spark plugs, the cylinder head bore and piston designed to reduce engine knock. The cylinder head is fixedly attached to a top end of a cylinder barrel formed with cylindrical walls, the cylinder head bore and the cylindrical walls defining a cylinder. The cylinder head bore has formed therein an outwardly protruding cavity with respect to the top end of the cylinder barrel. The piston has a piston crown, and the piston contained within the cylinder, the piston crown, the cylinder walls, and the cylinder head bore define a combustion chamber. The piston crown has a concavity formed therein, and the piston is constructed and arranged to reciprocate within the cylinder. The concavity of the piston crown and the cavity cooperate at a top dead center position of the piston to form a swirl chamber.

Abstract: An internal combustion aircraft engine comprising a cylinder head having a cylindrical head bore formed therein, a piston, and spark plugs, the cylinder head bore and piston designed to reduce engine knock. The cylinder head is fixedly attached to a top end of a cylinder barrel formed with cylindrical walls, the cylinder head bore and the cylindrical walls defining a cylinder. The cylinder head bore has formed therein an outwardly protruding cavity with respect to the top end of the cylinder barrel. The piston has a piston crown, and the piston contained within the cylinder, the piston crown, the cylinder walls, and the cylinder head bore define a combustion chamber. The piston crown has a concavity formed therein, and the piston is constructed and arranged to reciprocate within the cylinder. The concavity of the piston crown and the cavity cooperate at a top dead center position of the piston to form a swirl chamber.