Repair manual

SULEV 2.0L TFSI Engine
39
Operating Modes
After cold-starting the engine, various operating modes
and fuel injection strategies are implemented:
– Stratified start (high-pressure fuel injection)
– Catalyst heating by homogeneous split dual injection,
in conjunction with secondary air injection
– Dual injection during the engine warm-up phase
Stratified Start
(high-pressure fuel injection)
When the rail pressure exceeds 60 bar (absolute) the
injection enable signal is issued by the ECM. This occurs
when the full starting fuel charge is injected during the
compression phase until 60° crankshaft angle before
ignition TDC.
At this stage in the process, both cylinder pressure and
temperature are already considerably elevated, enabling
the injected fuel to evaporate more efficiently.
Ingress of raw fuel into the combustion chamber is
considerably reduced. The resulting, minimal fuel film on
the cylinder walls is necessary to ensure extremely low
raw hydrocarbon emissions at engine start-up.
A richer mixture forms in proximity to the spark plug,
thereby creating more stable ignition conditions.
Fuel Quantity [%]
Crankshaft Angle [°]
1
2
3
Charge Cycle TDC
BDC
Ignition TDC