The classification of fuel injection system of gasoline engine is based on the injection position of injector.

The fuel injection system of gasoline engine can be divided into intake pipe injection system and in-cylinder injection system according to the different injector components. Among them, intake pipe injection can be divided into single-point injection (SPI, TBI or CFI) and multi-point injection (MPI), and multi-point injection can be divided into pressure-type (D-type) and flow-type (L-type) multi-point injection systems.

1. Intake pipe injection system

For the intake pipe injection system, it can be divided into single-point injection system and multi-point injection system according to the different installation parts of the injector.

(1) single-point injection system

Single-point fuel injection system (SPFI or SPI for short), also known as throttle body injection or centralized injection system, refers to a fuel injection system in which one or two injectors are installed above the throttle of the throttle body (throttle body) of a multi-cylinder engine.

(2) Multipoint injection system

Multipoint fuel injection system (MPFI or MPI) refers to a fuel injection system in which an injector is designed and installed on the intake manifold in front of the intake valve of each cylinder of the engine. When the engine is working, fuel is injected into the intake manifold near the intake valve in time, and air and fuel are mixed near the intake valve, so that each cylinder can get a uniform mixture.

2. In-cylinder injection system

In-cylinder injection system, also known as in-cylinder direct injection system, is mainly characterized in that the injector is installed on the cylinder head, and the injector directly injects gasoline into the engine cylinder at a high fuel pressure (about 3~4MPa) and mixes it with air to form a combustible mixture, as shown in figure 1-7.

At present, companies such as VAG, BMW, Mercedes-Benz, General Motors and Toyota Lexus have started to use in-cylinder injection systems.