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General information
As opposed to the petrol engine, the diesel engine does not need an ignition system
because the diesel engine is a “compression ignition engine”.
This means that only air is aspirated and compressed with a diesel engine.
Fuel is injected into the combustion chamber just ahead of TDC.
The diesel self-ignites due to the temperature generated by the compression.
Diesel burns more slowly than petrol. Therefore the maximum pressure in the cylinder
is maintained for longer than with a petrol engine.Cayenne Diesel
Fuel and glow system
2 Fuel and glow system
General information23
Glow system24
Ignition delay28
Fuel system29
Low-pressure fuel supply30
High pressure fuel supply35
Value measuring43
Injector technology45
Intake system52
Turbocharging56
Exhaust gases from diesel engines61
Measures for reducing emissions 62
on the 3.0 l V6 TDI engine
Measures inside the engine62
Measures outside of the engine63
Exhaust gas recirculation63
Design of the exhaust system67
Diesel particulate filter DPF69
Differences between EURO III and EURO IV76
System overview of the DME control unit77
1_128_09
1Start of compression
2Plunger at TDC with pmax
3Plunger towards BDC at end of pmax
4Outlet valve opens
TDCPlunger positionBDC
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24Fuel and glow system
Cayenne Diesel
This is the reason for the high torque of the 3.0 l V6 TDI engine.
Due to the viscosity and the adhesive characteristics of the diesel oil, significantly
higher injection pressures are needed than for atomising petrol.
The common rail 3 system with piezo technology facilitates a maximum injection
pressure of 1,800 bar.
The highly-pressurised fuel is injected into the combustion chamber through multiple
spray nozzles which have microscopic fuel outlet holes.
The speed and the quality of the fuel droplets formed, as well as the movement of
air and the speed, are very important factors for clean, efficient combustion.
In addition to the main injection, up to two pre-injections and two post-injections are
now customary.
The common rail system is ideally suited to implementing these injection strategies
as it is the only diesel injection system on the market that enables injection to be
modulated, irrespective of the operating condition of the engine.
The injections following in quick succession can only be achieved with the very fast
switching piezo injectors used, in order to facilitate
Smooth running
Optimised exhaust emissions
Active regeneration of the diesel particulate filter
Another diesel-specific system also helps to achieve the aforementioned targets -
the glow system.
Glow system
As is customary for a diesel engine in a passenger car, the 3.0 l V6 TDI engine has
a glow system.
The glow system consists of:
Glow control unit
One glow plug per cylinder
Glow indicator light
Retainer for glow plugs
The advantages of the glow system are as follows:
Very fast glow plug heating time, to 1,000° C in approx. 2 seconds
More reliable, faster starting, even at temperatures down to -24° C
Reduced soot particle emissions
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