Fuel Injection is a method or system for metering fuel into an internal combustion engine. The fuel is then burned in air to produce heat, which in turn is converted to mechanical work by the engine. In modern automotive applications, fuel injection is typically only one of several important tasks performed by an engine management system.
The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the engine's air stream. In almost all cases this requires an external pump. The pump and injector are only two of several components in a complete fuel injection system.
The process of determining the amount of fuel, and its delivery into the engine, are known as fuel metering. Early injection systems used mechanical methods to meter fuel (non electronic, or mechanical fuel injection). Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. A CPU calculates the mass of fuel to inject.
Fuel Injection Types
- Throttle Body Injection (TBI or CFI)
The TBI system centrally injects fuel at the throttle body. The induction mixture passes through the intake runners just like a carburetor system.
- Continuous Injection
Gasoline is pumped through a large control valve called a fuel distributor, which sits atop a control vane mounted in the air intake pathway. The fuel goes from there to the injectors on each cylinder's intake port (which were simply nozzles with no valves in them). The system works by varying fuel mixture based on the amount of air flowing past the control vane.
- Central Port Injection (CPI)
A new "in-between" technique called "central port injection" (CPI) or "central port fuel injection" (CPFI). It uses tubes from a central injector to spray fuel at each intake port rather than the central throttle-body. However, fuel is continuously injected to all ports simultaneously, which is less than optimal.
- Sequential Central Point Injection (SCPI)
GM refined the CPI system into a sequential central port injection (SCPI) system in the mid-1990s. It used valves to meter the fuel to just the cylinders that were in the intake phase.
- Multi-Port Fuel Injection (PFI or EFI or SEFI)
The goal of all fuel injection systems is to carefully meter the amount of fuel to each cylinder. On most gasoline applications, the system uses a single injector per cylinder and injects fuel immediately ahead of the intake valves.
- Direct Injection
The injection nozzle is placed inside the combustion chamber and the piston incorporates a depression (often toroidal) where initial combustion takes place.