Fuel Supply and Management

Fuel Supply and Management

Direct injection is one of the most decisive cornerstones in the concept of the N54 engine. The complex requirements of the combustion process can only be met with this injection process, which is described in the following.

Direct injection achieves a higher compression ratio when compared with a turbocharged engine with manifold injection. At the same time, the exhaust-gas temperature is reduced under full load. Another advantage of this injection process is the improved efficiency in part-load operation.

The N52KP and N51 engines continue to use the conventional "manifold injection" system from the N52.

High Precision Injection (HPI)
High-precision injection represents the key function in the concept for as economic a use of fuel as possible. The new generation of petrol direct injection satisfies the expectations placed on it with regard to economic efficiency without compromising on the engine's dynamic qualities.

High-precision injection provides for amore precise metering of mixture and higher compression - ideal preconditions for increasing efficiency and significantly reducing consumption.

This is made possible by locating the piezo injector centrally between the valves. In this position, the new injector, which opens in an outward direction, distributes a particularly uniform amount of tapered shaped fuel into the combustion chamber.

The new direct injection of BMW HPI spark ignition engines operate according to the spray-directed process.

HPI Function
The fuel is delivered from the fuel tank by the electric fuel pump via the feed line (5) at a "feed" pressure of 5 bar to the high pressure pump. The feed pressure is monitored by the low-pressure sensor. The fuel is delivered by the electric fuel pump in line with demand.

If this sensor fails, the electric fuel pump continues to run at 100% delivery with terminal 15 ON.

The high pressure pump is driven "in-tandem" with the vacuum pump which is driven by the oil pump chain drive assembly.

The fuel is compressed in the permanently driven three-plunger high-pressure pump and delivery through the high-pressure line to the rail. The fuel accumulated under pressure in the rail in this way is distributed via the high-pressure lines to the piezo injectors.

The required fuel delivery pressure is determined by the engine-management system as a function of engine load and engine speed. The pressure level reached is recorded by the high-pressure sensor (4) and communicated to the engine control unit.

Control is effected by the fuel-supply control valve by way of a setpoint/actual-value adjustment of the rail pressure. Configuration of the pressure is geared towards best possible consumption and smooth running of the N54 engine. 200 bar is required only at high load and low engine speed.