Outside air enters the induction system through an intake port on the front of the engine cowling. This port normally contains an air filter that inhibits the entry of dust and other foreign objects. Since the filter may occasionally become clogged, an alternate source of air must be available. Usually, the alternate air comes from inside the engine cowling, where it bypasses a clogged air filter. Some alternate air sources function automatically, while others operate manually.
Two types of induction systems are commonly used in small airplane engines:
- The carburetor system, which mixes the fuel and air in the carburetor before this mixture enters the intake manifold, and
- The fuel injection system, which mixes the fuel and air just before entry into each cylinder.
