High-Pressure Fuel System (N55): 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 preparation means that the fuel-air 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)
• Responds to changes in load by correcting the injection duration specifically for the individual cylinder (during the intake stroke the injection duration can be corrected with a supplementary post-injection discharge as well as by extending or reducing the injection period)
• Selective deactivation of individual cylinders is also available (for instance, in response to a defective ignition coil)
• Allows individual diagnosis of each fuel injector.