Operation At Low Rotation Speeds; Operation At High Rotation Speeds; Exhaust Gas Circuit - Fiat 1998 Marea Service Manual

Engine
Fuel system

EXHAUST GAS CIRCUIT

The engine exhaust gases flow through the manifold to the turbocharger and then, by means of a pipe, to
the catalytic converter and the silencer.
Special protection limits the heat transmitted to the bodyshell.
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Marea- Marea Weekend

Operation at low rotation speeds

When the engine is rotating slowly, the exhaust
gases possess a small amount of kinetic energy:
under these circumstances a traditional turbine
would rotate slowly, providing a limited super-
charging pressure.
In the variable geometry turbine (1) on the other
hand, the moving vanes (2) are in the fully
closed position and the small sections between
the vanes increase the speed (C) of the inlet
gases.
Increased inlet speeds involve increased periph-
eral speeds (U) of the turbine and consequently
the compressor.
The speed of the gases flowing inside the im-
peller is indicated by the vector (W).
1. Turbine
2. Moving vanes
3. Pneumatic actuator
4. Rotary seal

Operation at high rotation speeds

Increasing the engine rotation speed gradually
increases the kinetic energy of the exhaust
gases.
As a result, the speed of the turbine (1) in-
creases and therefore the pressure of the super-
charging, also acting on the actuator (3).
The actuator (3) opens the moving vanes (2),
by means of a rod, according to the super-
charging pressure, until the fully open position is
reached.
The section therefore increases and there is a
consequent slowing down in the flow of the ex-
haust gases passing through the turbine (1) with
speeds equal to or less than the low speed con-
dition.
The speed of the turbine (1) decreases and set-
tles down at a suitable value for the correct op-
eration of the engine at high speeds.
1. Turbine
2. Moving vanes
3. Pneumatic actuator
4. Rotary seal
ft * » f t ™
99 range
Print n° 506.763/14