Fuel Injection: Notes

The N55 6-cylinder spark-ignition engine relies on direct fuel injection. The direct fuel injection increases the performance. The maximum fuel pressure is 200 bar (idle: 50 bar, WOT full load: 200 bar). The use of direct fuel injection creates a homogeneous mixture preparation in the entire combustion chamber. Homogeneous mixture formation means that the air/fuel ratio is regulated stoichiometrically in the same way as for intake pipe fuel injection (Lambda = 1). A stoichiometric air-fuel mixture contains a ratio of 14.7 kilograms of air to 1 kilogram of fuel. Homogeneous mixture formation renders it possible to use a conventional emissions control system. Fully-sequential multipoint injection with selective control for each individual cylinder offers the following advantages:

• Optimal fuel mixtures for each individual cylinder
• The injection duration is precisely adapted to the engine's instantaneous operating conditions (engine speed, load factor and temperature)
• For varying load, cylinder-specific correction of fuel injection (during an intake stroke, the injection period can be corrected by extending or shortening it through subsequent fuel injection)
• Selective deactivation of individual cylinders is also available (for instance, in response to a defective ignition coil)
• Allows individual diagnosis of each fuel injector.