LO 9-2 Describe the functions, construction, composition, types, and applications of diesel engine cylinder head assemblies

Classification of Cylinder Heads and Valve Trains

Cylinder heads are classified in several ways, including by the number of cylinders capped by the head, the type of material used, the way exhaust and intake air ports are arranged, and the valve train arrangement. The variety of cylinder head designs is driven by the function of a cylinder head that requires it to operate while withstanding high combustion temperatures and pressures without distortion. It is essential that the head is constructed with a high degree of strength and temperature resistance. Cooling of the head is also critical to keep oxides of nitrogen (NO_x) emissions low, and the addition of temperature-sensitive components, such as injectors and electronic sensors, and other temperature regulation strategies has made the cooling of cylinder heads particularly important in the latest engines. Air and exhaust gas flow through the cylinder head is another design concern that must be considered in order to achieve the best engine efficiency with high levels of power and performance without generating excessive emissions. The shape and position of the intake and exhaust ports, the position of the valves, and the location of the camshaft determining the overall geometry of the cylinder head have significant influence on power output, fuel consumption, and emissions. In addition to these considerations, manufacturers must be able to construct cylinder heads that meet EURO IV–VI and the U.S. EPA’s durability requirements, require the least amount of maintenance, are economical to produce, and promote outstanding performance accompanied by low emissions and fuel consumption. To meet the constantly improving benchmarks of engine performance, a wide variety of cylinder head designs, construction techniques, and service procedures are currently in use.