Direct Injection E65, E66 N73/N73TU
Direct injection E65, E66 N73/N73TU
Introduction
With the N73B60 engine, direct injection technology is used for the first time on a BMW spark-ignition engine. Direct injection means that the fuel is injected under high pressure directly into the combustion chamber.
There are 2 concepts for spark-ignition engines with direct injection:
- Direct injection with lean running: GDI engine (not used by BMW)
Direct injection is used to reduce fuel consumption in the part-load range.
The disadvantage of direct injection with lean running is the complex and expensive exhaust gas aftertreatment, which uses deNOx converters. The deNOx catalytic converter is a three-way catalytic converter with a special coating. Operation with the deNOx catalytic converter requires the use of sulphur-free fuel.
- Direct injection without lean running: N73B60 engine
Direct injection is used to increase power output.
The advantage of direct injection without lean running is the use of exhaust gas aftertreatment with a conventional three-way catalytic converter. The three-way catalytic converter can be used with sulphurous fuel. On the N73B60 engine, the Valvetronic system is used to reduce fuel consumption in the part-load range. The disadvantages of direction injection with lean running are thus avoided.
The combination of Valvetronic and direct injection (without lean running) allows low fuel consumption with high specific power output and high torque. Compared to the M73 engine, the N73 engine uses 3,6 % less fuel. Power output is increased by 87 kW to 327 kW and torque from 490 Newton-meters to 600 Newton-meters.
The N73B60 engine can be used all around the world as it does not require sulphur-free fuel.
The N73B60 engine will be installed for the first time in March 2003 in 760i/760Li (E65/E66) vehicles.
> N73TU with introduction 09/06
The N73TU satisfies the legal emissions limits, e.g. Euro 4 standard for Europe or LEV II for the USA (LEV: Low Emission Vehicle).
Measures on the direct injection system:
- MED 9.2.2 engine management system, based on ME 9.2.1 engine electronics
Brief description of components
The direct injection system consists of the following components:
- Digital engine electronics DME
(development status: MED 9.2.1/MED 9.2.2 engine electronics for direct injection)
The 2 DMEs actuate the respective cylinder bank of the engine.
[For further information, please refer to SI Technology (SBT) 12 01 03 033] Engine Management Status MED 9.2.1/MED 9.2.2 E65, E66 N73/N73TU
- Electric fuel pump
The electric fuel pump supplies fuel to the two high-pressure pumps.
[For further information, please refer to SI Technology (SBT) 16 01 03 024] Fuel System E65, E66 N73/N73TU
- Fuel filter with pressure regulator and leakage filter
The fuel filter with pressure regulator regulates the fuel pressure in the feed line.
[for further information, please refer to SI Technology (SBT) 16 01 03 024] Fuel System E65, E66 N73/N73TU
- High-pressure pump
The 2 high-pressure pumps compress the fuel and feed it to the rails.
- Pressure damping vent valve
The pressure damping vent valve allows the fuel to flow back to the return line and ventilates the fuel pressure regulator.
- Return cut-off valve
The return cut-off valve prevents a loss of pressure in the injection system.
- Rail with pressure limiter valve
The 2 rails store the compressed fuel and distribute it to the high-pressure injectors.
- Rail pressure sensor
The 2 rail pressure sensors measure the current fuel pressure in the rails and report this to the DMEs.
- High-pressure injector
The high-pressure injectors inject the fuel at high pressure directly into the combustion chamber.
- HDEV control unit
The 2 HDEV control units actuate the high-pressure injectors.
System functions
The direction injection system works in the following way:
- Inhomogeneous mixture preparation with lean running
- Homogenous mixture preparation without lean running
- Improved efficiency and knock characteristics
Inhomogeneous mixture preparation with lean running (not used by BMW)
With direct injection with lean running, a homogenous mixture is only created around the spark plugs. But an inhomogeneous mixture (Lambda > 1) is created throughout the combustion chamber. An inhomogeneous mixture means that the fuel-air ratio is greater than 14.8 kilograms of air to 1 kilogram of fuel. The excess air means that the combustion temperature is greater than with Lambda = 1. This causes the NOx level in the exhaust gas to increase drastically, making aftertreatment with a deNOx converter necessary. Sulphur reduces (throttles) the effectiveness of the deNOx converter. For this reason, sulphur-free fuel must be used.
Homogenous mixture preparation without lean running
The use of direct injection without lean running creates a homogenous mixture in the entire combustion chamber. A homogenous mixture means that the fuel-air ratio is stoichiometrically controlled in the same way as it is in manifold injection systems (Lambda = 1)
("stoichiometric" means a fuel-air ratio of 14.8 kilograms of air to 1 kilogram of fuel.) This homogenous mixture allows a conventional exhaust gas aftertreatment system to be used.
Improved efficiency and knock characteristics
With direct injection, the fuel is vaporized in the combustion chamber and the mixture is cooled. The density is increased (the cooler it is, the greater the density) and improves the efficiency of the N73B60 engine by up to 10 %. This also improves the knock characteristics, making it possible to raise the compression ratio of the N73B60 engine (from 10:1 to 11.5:1).
Notes for service staff
Service staff should note the following points:
- General information: ---
- Diagnosis: ---
- Encoding/programming: ---
Subject to change.