This system mixes the fuel and air together right in the intake port for eachengine cylinder just ahead of the intake valve. An electrical fuel pump pumps fuel from the fuel tank through a fuel filter to the fuel rail assembly , which carries fuel under pressure to the fuel injectors see Figure The fuel rail assembly also may contain the fuel pressure regulator , which maintains proper fuel pressure and meters unused fuel back to the fuel tank. Fuel injectors, one for each cylinder, are attached at one end to the fuel rail and at the other end to the intake port in the engine.
A whole bunch of sophisticated sensors measure a variety of factors and send messages to the ECU , which decides how much fuel to inject at any given time. These sensors are so perceptive that they even check the weather; how much weight you're carrying in the vehicle; and whether you're starting up, speeding up, slowing down, or idling at a light.
This information makes the system respond faster and results in greater fuel economy than older vehicles achieved with throttle-body fuel injection. The ECU completes the electrical circuit to the injector solenoid for the proper injector pulse width , and fuel under pressure is injected into the intake port just before the intake valve.
More recent fuel-injected engines feature sequential fuel injection SFI in which the fuel injectors fire in sequence rather than all at once.
Because each injector opens individually just before its intake valve opens, the fuel isalways sprayed right into an open port and therefore stays in suspension. This type of system is more efficient than a system whose injectors fire simultaneously. In addition, emission levels are lower in an SFI system, but the system requires a separate electricalcircuit for each injector.
The gasoline direct injection GDI system is relatively new in the United States but is expected to grow more popular as time goes on. It resembles diesel technology but uses gasoline instead of diesel fuel. Antuan Goodwin engine writer for Cnet said that readers may have noticed that during the jumps from carburetion to SPFI single port to MPFI multi-port , the point at which fuel is added to the intake charge, has moved from before the throttle to the intake manifold and onward to the individual intake runners — closer and closer to the combustion chamber.
Direct injection takes this evolution to the next level by placing the injector inside the combustion chamber. By moving the injector into the combustion chamber, GDI gasoline direct injection gains a few advantages over the previously discussed systems.
A GDI system also has more flexibility regarding when in the combustion cycle the fuel is added. MPFI systems can only add fuel during the intake stroke of the piston, when the intake valve is open. GDI can add fuel whenever it needs to. For example, some GDI engines can adjust the timing so that a lesser amount of fuel is injected during the compression stroke, creating a much smaller, controlled explosion in the cylinder.
Study Tips Feedback. Fuel Injection Systems Multiport and sequential fuel injection systems both inject atomized fuel into a port just before the intake valve. Multiport Fuel Injection Multiport injection systems fire the injectors in groups. Sequential Fuel Injection Sequential fuel injection systems fire each injector individually.
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