Fuel injection, basic function

Fig 1: Calculation Of Fuel Mass/Combustion

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The current air mass/combustion is divided by 14.7 and moved to section 2. The unit is now mg fuel/combustion.

In cases of cold engine, short time after start, fast load changes, knocking or high load, the current value is multiplied by a compensation factor.

The lambda control value is multiplied in. The value is moved to section 4.

Multiply by the value for purge adaptation. The value is moved to section 5.

The value from the multiplicative adaptation is multiplied in and the new value moved to section 6.

The value from the additative adaptation is multiplied in and the new value moved to section 7.

If the engine has not yet started, the start fuel mass is determined.

Fig 2: Fuel Mass/Combustion - Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The fuel mass/combustion is the mass of petrol to be added to the engine on each combustion.

Converts the fuel mass to injector opening time in ms.

Before the engine is synchronized, i.e. the camshaft position found by means of the ignition system, injection occurs twice per combustion. The injection time calculated in block 12 is divided by two.

The voltage-dependent needle lift time is added to the injection time. This compensates for the delay between activation of the current in the injector coil and supply of the fuel.

Under certain conditions, e.g. on engine braking, car immobilized, the fuel shut-off can apply. The injection time is then zero.

The ECM controls the injector which is currently supplying fuel, and the sequence is controlled by the ignition sequence. The camshaft angle at which injection takes place depends on the prevailing operating conditions.