Fuel Supply, High-Pressure Side DFI
Fuel Supply, High-pressure Side DFI
The high-pressure fuel system (from the high-pressure pump to the injectors) corresponds to that of the previous Cayenne V8 DFI engines. The direct fuel injection is optimally matched to the characteristics of the V8 naturally aspirated engine and V8 biturbo engine. A radial piston pump is used in both engines. This is driven by the left intake camshaft. In the V8 naturally aspirated engine, the fuel high pressure is built by up 3 pistons. In the V8 twin turbo engine, this is done by 6 pistons. Fuel is distributed in both engines via a central high-pressure fuel rail in the inner-V of the engine with separate lines leading to the fuel injectors. When the engine is running, the high pressure measured by the pressure sensor is regulated to a pressure of between approx. 580 psi (40 bar) and 1740 psi (120 bar) by the quantity control valve (at the inlet of the high-pressure pump).
High-pressure pump
The high-pressure pump provides the high pressure of approx. 580 psi (40 bar) to 1740 psi (120 bar) which is needed for injection. The pump is driven via the intake camshaft of the left cylinder bank.
- Naturally aspirated engine: 3-piston high-pressure pump (HD) with quantity control valve and 1 damper
- Turbo engine: 6-piston high-pressure pump with quantity control valve and 2 dampers
Quantity control valve
The quantity control valve installed at the inlet of the high-pressure pump on the V8 engines regulates the fuel high pressure.
High-pressure rail
The central high-pressure rail (KR) is located within the inner-V of the engine, from where the fuel is supplied to the injectors via individual lines. The volume of the high-pressure rail differs for the naturally aspirated and turbo engines. The high-pressure rail provides the same pressure for all injectors.
Pressure sensor
The pressure sensor (DS) on the high-pressure rail detects the fuel high pressure (pressure measurement from approx. 580 psi/40 bar to 1740 psi/120 bar).
Swirl injectors
The injectors are solenoid-operated and are positioned beneath the intake ducts of each cylinder. They inject the fuel under high pressure directly into the combustion chamber. To open an injector, the activation voltage is briefly raised to up to 75 V by way of a voltage booster in the DME control unit. Fuel injection quantity for V8 naturally aspirated engine 210 g/min, V8 Turbo 349 g/min.
Characteristics of direct fuel injections
- High cylinder charging
- Low knock sensitivity
- High compression ratio
- High-pressure stratified charge injection
- Multiple injection possible
- Homogeneous operation with engine at operating temperature
In the case of direct fuel injection, the fuel is injected directly into the combustion chamber, so that the mixture formation takes place almost entirely within the combustion chamber.
The direct fuel injection system used in the Cayenne DFI engines is based on homogeneous operation when the engine is at operating temperature. The mixture of fuel and air is distributed as evenly as possible in the combustion chamber, thereby enabling optimal combustion. In this process, the fuel is injected directly in the combustion chamber at a pressure of up to 1740 psi (120 bar). The jet and cone angles of the injectors have been optimized to achieve optimum homogenization across the entire operating range. Within the injector, the fuel jet is swirled (rotated about the longitudinal axis). This rotation forms a cone-shaped cloud of fuel. This results in fine atomisation which in turn enables quicker evaporation of the fuel.
The heat energy required for this is removed from the air by the fuel evaporation and this cools the air as a result. 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 create the prerequisites for the high compression ratio in all Cayenne engines, since knock sensitivity and engine efficiency have been improved. The high compression ratio of 12.5:1 for the V8 naturally aspirated engine and 10.5:1 for the V8 twin turbo engine realized through DFI serves to optimize both engine power and fuel consumption.