Function

Mixing air and fuel outside the combustion chamber is called outer air/fuel mixture.

How it works

The fuel is either injected via throttle body above the throttle blade called TBI Throttle Body Injection or near the intake valve in Multi Point Injections in every individual cylinder. Fuel is atomized with low pressure 1 - 6 bar and injected. Good for mixing is the low pressure in the intake port. The quantity of injected fuel mostly is determined by the duration injection.

For that a good rate of emission cleaning after leaving the engine is important. This is the job of the lambda-sensor that puts signals about oxygen share to the ECU. Injection and ignition use a common ECU (called Motronic).

Exception

In petrol and Diesel engines the inner air/fuel mixture known as direct injection takes place during or to the end of the compression stroke. In contrast to Diesel petrol engines need a spark plug for firing (spark ignition).