Diesel Engine Cylinder Head Design: The Compromises and the Techniques

The cylinder head of a direct-injection diesel engine has to perform many functions. It must bring charge air to the cylinder and exhaust gas from the cylinder, with minimum pumping loss and required swirl and other properties of charge motion. It must provide a mounting for the injector, seal the combustion gases and maintain acceptable temperatures of the components. The cylinder head is therefore a crowded and complex component. This paper discusses the options that can be applied to cylinder head design of four-stroke, direct-injection diesel engines with head-mounted valves. Intake ports generate swirl in two modes; the directed mode and the helical mode. Intake ports generate swirl most efficiently when the swirl generated by the directed mode is about 30 percent of the total. It is possible to measure the magnitude of the directed and helical modes of swirl generation by special flow bench tests. Certain cylinder head layouts can provide more opportune positioning of ports and enhance other attributes of the design.