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

Classification by Intake and Exhaust Port Arrangement

Because intake and exhaust port arrangements strongly influence gas flow and turbulence, or swirl, into the cylinders, configuration of these ports affects engine performance and emissions. The size and number of valve ports and where they are located primarily determines this classification method. For example, when intake and exhaust ports are arranged on either side of the cylinder head, the construction method is called a cross flow cylinder head. Cross flow cylinder head design is the most popular for diesel engines Figure 8. In this configuration, engine breathing characteristics are improved when airflow travels into the intake valve ports and out the exhaust valve ports located on opposite sides of an in-line engine cylinder head. Larger intake and exhaust ports can be used because there is no crowding from a nearby exhaust or intake port. Additionally, this port arrangement avoids the unnecessary heating of intake air as it passes over heated exhaust surfaces. This design provides cooler air for efficient combustion and helps allow for improved fuel economy, maximum efficiency, and reduced emissions. The drawback to this configuration is that exhaust and intake manifolds on opposite sides of the cylinder head create a wider temperature gradient across the head, with the exhaust side having much higher temperatures than the intake side. This makes the head vulnerable to potential cracking, distortion, and head gasket leaks caused by excessive and unequal movement of the cylinder head across the block deck.

A parallel flow head, sometimes referred to as the uniflow design , places the intake and exhaust manifolds on the same side of the engine Figure 9. In this design, joining together shorter, large cylinder head ports provides a more compact engine design with adequate airflow to the cylinders. Less thermal stress of the cylinder head takes place because the cooler intake ports are placed alongside the exhaust ports.

FIGURE 09-8: A cross flow cylinder head arranges the intake and exhaust ports on opposite sides of the cylinder head.

FIGURE 09-9: A parallel flow head arranges the intake and exhaust ports on the same side of the engine.