Cayenne Direct Fuel Injection (DFI)

Direct Fuel Injection (DFI)







A totally redesigned generation of engines with DFI is used for the new Cayenne models: a 3.6 l V6 engine for the Cayenne, a 4.8 l V8 naturally aspirated engine for the Cayenne S and a 4.8 l V8 bi-turbo engine for the Cayenne Turbo.

Development objectives for the new DFI engines:
- More power and torque.
- Reduced fuel consumption.
- Reduced weight.

These objectives have been achieved thanks to the following enhancements and new technologies:
- Increased displacement for more power and torque.
- Use of direct fuel injection (DFI).
- Higher compression ratio.
- Sport button as standard.
- VarioCam Plus (for V8 engines).
- Demand-controlled oil pump (for V8 engines).
- New intake systems adapted specifically for each engine.
- VarioCam Plus (for V8 engines) for controlling the intake camshaft and valve lift.
- New sports exhaust system (optional for Cayenne S with Tiptronic S).
- Demand controlled variable oil pump for improved engine efficiency (for V8 engines).

The most important technical components of the direct fuel injection system are:
- The fuel low pressure system.
- The fuel high pressure system.
- The fuel rail (central high pressure distribution pipe).
- The fuel injectors.
- Modifications to the cylinder head.
- Special recessed pistons for the relevant engine.

Porsche is using direct fuel injection (DFI) for the first time in its new generation of Cayenne engines. DFI offers numerous advantages compared to intake manifold injection. The main objective here is to achieve an air/fuel mixture adapted specifically to the respective operating and charge states of the engine using an injection system and mixture formation. This provides the perfect solution for meeting the various demands relating to economy, power, vehicle handling and emissions.

With direct fuel injection, the fuel is injected directly into the combustion chamber and mixture formation takes place almost completely in the combustion chamber.

The direct fuel injection system used in the new Cayenne models is characterized by the following:
- Homogeneous operation.
- Better cylinder filling.
- Reduced knock sensitivity.
- Higher compression ratio.
- High pressure stratified charge ignition.
- Dual injection.

The direct fuel injection system used in the new Cayenne engines is based on homogeneous operation. The mixture of air and fuel is distributed as evenly as possible in the combustion chamber, thereby allowing optimal combustion. With this system, the fuel is injected directly into the combustion chamber at a pressure of up to 1740 psi (120 bar).

Within the injector, the fuel jet creates a vortex (rotated around the longitudinal axis). This rotation forms a conical cloud of fuel. The fine atomization produced by this allows faster evaporation of the fuel. The fuel evaporation process takes the required heat energy from the air, thereby cooling the air. This reduces the cylinder charge volume and additional air is drawn in through the open intake valve, which in turn improves cylinder filling. The reduced temperature level also helps to meet the prerequisites for the higher compression ratio in all new Cayenne engines since knock sensitivity has been improved. The higher compression ratio in turn increases engine efficiency.

Start Phase of DFI Engines

High pressure stratified charge ignition is used in the DFI systems of the new Cayenne engines in order to optimize cold starting with regard to fuel consumption and emissions. With this ignition system, fuel injection occurs very late - just before the end of the compression stroke - when starting the engine. The high pressure stratified charge ignition system injects fuel directly only once into the specially molded piston recess so that a stratification, which creates an ignitable mixture, is formed around the spark plug. The piston recess ensures that the injected fuel is directed straight to the spark plug. This reduces both the amount of fuel required and the emissions compared to intake manifold injection.

Catalytic Converter Heating Phase in DFI Engines







Once the high pressure stratified charge ignition system starts the engine, engine management switches to the catalytic converter heating phase. In this operating state, a dual injection system helps to bring the catalytic converter to the temperature required for optimal conversion as quickly as possible by increasing the exhaust emissions temperature.

The 2nd injection of fuel into the piston recess occurs just before the end of the compression stroke with the intake valves closed. The air/fuel mixture is ignited very late and this increases the exhaust emissions temperature. As a result, emissions during the start phase are reduced and the secondary air pumps are no longer required for all engines.

Upper Load Range of DFI Engines

Dual injection always occurs in the upper load range up approx. 3500 rpms. The amount of fuel required for combustion is distributed in two consecutive injection processes. In the upper load range, both injections occur during the intake stroke (intake synchronous injection) with the intake valves open, thereby ensuring reduced fuel consumption through improved homogenization.

Piston Recesses in DFI Engines

The piston recesses are important for high pressure stratified charge ignition and for dual injection during the catalytic converter heating phase. They allow late injection of fuel in order to create an ignitable air/fuel mixture around the spark plug for late ignition. 2

NOTE:

Intake manifold injection

- With the intake manifold injection system, the fuel is injected into the intake duct earlier and mixture formation takes place partly in the intake duct and partly in the combustion chamber. During the intake process, fuel is deposited on cylinder walls and valves and as a result, this fuel is no longer available for combustion. This is particularly the case during the start phase of the engine at low temperatures and the consequence of this is that the amount of fuel used exceeds the amount of fuel that is actually needed for combustion.

Sport Button







All new Cayenne models already have a Sport button as standard, which is located centrally in the center console under the shift lever or Tiptronic S gear selector. This button allows the driver to choose between the vehicle's fuel consumption tuning (normal mode) and sport tuning (sport mode). When the Sport button is pressed, a "SPORT" logo lights up in the instrument cluster.

In the Motronic area, pressing the Sport button (in High-Range mode only) affects the following systems, depending on the vehicle equipment:
- When the Sport button is activated, a more sporty accelerator pedal characteristic produces a more spontaneous engine response, underpinning the sporty character. This is achieved via a steeper rise for the electronic throttle characteristic. This means that the throttle is opened further and faster with the same accelerator pedal travel when the Sport button is pressed.
- Maximum full-load torque is available at all times in the Sport button's sport mode. In normal mode, electronic engine management restricts the engine management functions in order to optimize fuel consumption. If full power is required in a certain driving situation (e.g. when passing), it can be achieved at any time by initiating a kick down. Engine management switches to the sport mode map at this time.
- The Sport button lends a sportier feel to the transitions between traction and deceleration, as well as between deceleration and traction. This means that throttle activation and ignition are switched to a more direct map when accelerating and particularly when decelerating, resulting in a more spontaneous and dynamic load cycle.
- The sports exhaust system available for the Cayenne S in combination with Tiptronic S is also activated using the Sport button.

Sport mode remains active until either the Sport button is pressed a second time or the driver switches off the ignition. This deactivates sport mode and the settings revert to normal mode.