Fuel Injection: Operation

The injection system is direct type, that is fuel is directly injected inside the cylinder. The main advantages consist in an improved fuel evaporation and an increase of engine volumetric output since heat is removed from intake air rather than from the intake walls. The air and petrol load can have a higher density and be colder, increasing the compression ratio. A high compression ratio is useful for increasing performance and engine power output as well.

Thanks to the direct petrol injection in controlled ignition engines, fuel consumption can be reduced up to 20% compared to the same engine with traditional injection; CO2 emissions can also be reduced in the case of road traffic.

The injection system must comply with the following requirements:

• extreme precision in the quantity of fuel injected:
• generation of the required injection pressure;
• definition of the exact mixture ignition time, depending on the engine operation mode;
• direct and precise fuel filling in the engine combustion chamber.

The fuel injection system principally comprises an accumulator (rail) linked to the fuel injectors. With this system, fuel can be injected directly into the cylinders by high pressure injectors.

Intake air quantity can be adjusted at will by the electronically-operated throttle valve (Electronic Throttle Control): to determine it precisely, a hot film air flow meter is used, located on the air intake circuit after the filter casing.

The air/fuel mixture is indirectly monitored by the universal-type oxygen sensor (which can measure a wide range of oxygen content in exhaust gas), directly fitted in the exhaust pipe immediately before the catalytic converter. It ensures that the λ value (relationship between the measured air/fuel ratio and the reference stoichiometric value for the fuel used) is always as close as possible to 1, to ensure maximum conversion efficiency for harmful gases by the catalytic converter.