The cylinder head is mounted on top of the cylinder block, sealing the cylinders and forming part of the combustion chamber:
Due to contact with high-temperature and high-pressure combustion gases, the cylinder head is subjected to significant thermal and mechanical loads. In water-cooled engines, the cylinder head contains cooling water jackets, which cool high-temperature areas such as the combustion chamber through circulating water. Additionally, the cylinder head also features intake and exhaust valve seats, valve guide bores, as well as intake and exhaust passages. Gasoline engine cylinder heads are machined with holes for spark plugs, while diesel engine cylinder heads have holes for injectors. Overhead camshaft engines also have camshaft bearing bores in the cylinder head for mounting the camshaft.
Cylinder heads are typically made from gray cast iron or alloy cast iron. However, to improve vehicle fuel economy, engine lightweighting has become an inevitable trend. The use of lightweight materials can effectively reduce engine mass. Cylinder heads for light-duty engines (including gasoline engines and diesel engines with displacement less than 3L) widely use alloy materials, which can reduce mass by 40% to 60% compared to cast iron materials under the same structure.
Aluminum alloy possesses excellent thermal conductivity and cooling performance, making it an outstanding cylinder head material. Adding Cu to aluminum alloy improves thermal stability, while adding Mg increases the hardness of the casting. For information on aluminum alloy usage, please refer to the chart below.
The good thermal conductivity of aluminum alloy can increase the compression ratio, thereby improving engine efficiency. Consequently, aluminum alloy cylinder heads have been increasingly adopted in recent years.
The cylinder head is an integral part of the combustion chamber, and the shape of the combustion chamber significantly impacts engine operation. Due to different combustion methods in gasoline and diesel engines, the parts of the cylinder head that form the combustion chamber also differ. In gasoline engines, the combustion chamber is primarily located in the cylinder head; whereas in diesel engines, the combustion chamber is mainly formed by a recess in the piston crown.
