Management of fuel injection

The management strategies ensure the best ignition advance and fuel delivery, thus providing the correct mixture strength at all times as the engine load and environmental conditions vary.

The system management strategies are basically as follows:

• -management of fuel injection;
• -management of ignition;
• -management of engine starting block function (Fiat CODE);
• -management of radiator fan;
• -management of engine idle control;
• -management of fuel vapour recirculation;
• -management of fault diagnosis;
• -management of climate control system.

MANAGEMENT OF FUEL INJECTION

The fuel injection management strategy aims to supply to the engine the correct quantity of fuel at the required instant, in accordance with the engine’s operating conditions.

The fuel injection-ignition uses a “SPEED DENSITY-LAMBDA” indirect measuring system, which measures angular speed of rotation, density of intake air and mixture strength control (feedback control).

In practice, the system uses the ENGINE SPEED (rpm) and AIR DENSITY (pressure and temperature) data to measure the quantity of air drawn in by the engine.

The quantity of air drawn in by each cylinder for each engine cycle depends not only on the density of the air drawn in, but also on the unit cylinder capacity and the volumetric efficiency.

Air density is the density of the air drawn in by the engine and calculated in accordance with the absolute pressure and temperature, both measured in the inlet manifold.

Volumetric efficiency is the parameter relating to the cylinder fill coefficient measured in accordance with experimental tests conducted on the engine throughout its operating range, and subsequently stored in the electronic control unit’s memory.

After establishing the quantity of air drawn in, the system must provide the quantity of fuel in accordance with the desired mixture strength.

The end-of-injection or delivery timing pulse is contained in a map stored in the control unit’s memory, and varies depending on the engine speed and pressure in the inlet manifold. In effect these are processing operations carried out by the control unit to control the sequential opening and timing of the four injectors, one per cylinder, for the length of time strictly necessary for forming an air-petrol mixture as close as possible to the stoichiometric ratio.

The fuel is injected directly in the manifold near the inlet valves at a differential pressure of about 3 bar.

The speed (rpm) and air density (pressure and temperature) are used to measure the quantity of intake air; when this has been determined, the quantity of fuel is metered in accordance with the desired mixture strength. The other sensors present in the system (coolant temperature, throttle valve position, battery voltage, etc.) enable the electronic control unit to correct the basic strategy for all the particular operating conditions of the engine.

Making the air-fuel ratio fluctuate around stoichiometric values is the essential condition for both correct and long-lasting operation of the catalytic converter, and for reducing polluting emissions.