At some point after the air cleaner, depending on the engine, fuel is added to the air-stream by either a fuel injection system or, in older vehicles, by the carburetor.

• 根据不同的发动机类型，在空气滤清器后的某个部件，燃油通过燃料喷射系统或化油器（在老型号的汽车里）加入到气流中。