The fuel itself is useless: it needs oxygen from the outside air to burn. Basically, this happens by itself: as the piston falls during the intake stroke, air flows through the open intake valve to fill the expanding chamber.
Then, when the compression and power strokes are complete, the Performance Exhaust opens and the rising piston forces the exhaust gases out, ready for a fresh intake of fresh air.
In practice, however, the engine requires an air filter to stop dirt, moisture and debris from being sucked into its cylinders and requires an exhaust system to expel the hot exhaust gases safely and quietly.
In order to save a separate filter and exhaust pipe for each cylinder of a multi-cylinder engine, intake air is supplied to the cylinders through a tubular structure called the intake manifold, and exhaust gases are discharged through a similar structure called the exhaust manifold.
Unlike its cousins, motor tractors and dredgers, marine diesel engines typically operate in a relatively clean environment: there is little risk of dealing with hay, dust, or road debris. This means that the air filter is relatively simple, allowing some engines to function flawlessly for years if they only contain a metal box with a few compartments inside.
However, most have something more elaborate, including wire mesh or porous paper. Paper tends to restrict airflow. To compensate for this, it is necessary to increase its area by folding it in the form of a base. It is also difficult to clean, so once the paper filter is clogged, it must be replaced with a new one.