How the fueling system works:
- The gas pedal in your car is connected to the throttle valve. This is the valve that regulates how much air enters the engine. So the gas pedal is really the air pedal.
- When you step on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU, the computer that controls all of the electronic components on your engine) senses the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens, otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it. Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.
- The throttle valve opens and the fuel travels through to the injectors.
The Injector:
- A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second.
- Fuel injectors deliver fuel from the fuel rail into the cylinders by use of a solenoid powered valve. The coils in the solenoid will have electricity applied in short bursts called the pulse width (typically from 2-20ms depending on engine speed and throttle position) which will pull on the valve to open it up spraying the fuel. The nozzle is designed to atomize the fuel creating as fine a mist as possible so that it can burn easily. A spring will reset the valve to the closed position when the solenoid is no longer activated.
- Fuel pressure is kept at a constant value above manifold pressure, so the amount of fuel injected is determined only by the length of time the injector is held open by the ECU. This is called the pulse width of the injector.
- Sensors measure these variables, and then relay the information to the ECU in the form of electrical signals. The ECU then calculates the duration of pulses necessary to provide the fuel required.
- Extra fuel required during cold starting can be supplied by increasing the number of injection pulses, or by fitting a separate cold start injector that operates independently of the main injectors, when the engine is cranking.