This document is printed from SPI². Not for RESALE
The components of the air inlet and exhaust system
control the quality of air and the amount of air that is
available for combustion. The air inlet and exhaust
system consists of the following components:
• Air cleaner
• Exhaust cooler (NRS)
• Exhaust gas valve (NRS)
• Turbocharger
• Aftercooler
• Inlet manifold
• Cylinder head, injectors, and glow plugs
• Valves and valve system components
• Piston and cylinder
• Exhaust manifold
• Diesel oxidation catalyst
• Diesel particulate filter
• Throttle valve
Air is drawn in through the air cleaner into the air inlet
of the turbocharger by the turbocharger compressor
wheel. The air is compressed to a pressure of about
150 kPa (22 psi) and the compression heats the air
to about 120° C (248° F) before the air is forced to
the aftercooler. As the air flows through the
aftercooler the temperature of the compressed air
lowers to about 55° C (131° F). Cooling of the inlet air
assists the combustion efficiency of the engine.
Increased combustion efficiency helps achieve the
following benefits:
• Lower fuel consumption
• Increased power output
• Reduced NOx emission
• Reduced particulate emission
From the aftercooler, air is forced into the inlet
manifold. Air flow from the inlet manifold to the
cylinders is controlled by inlet valves. There is one
inlet valve and one exhaust valve for each cylinder.
The inlet valve opens when the piston moves down
on the intake stroke. When the inlet valve opens,
cooled compressed air from the inlet port is forced
into the cylinder. The complete cycle consists of four
strokes:
• Inlet
• Compression
• Power
• Exhaust
On the compression stroke, the piston moves back
up the cylinder and the inlet valve closes. The cool
compressed air is compressed further. This additional
compression generates more heat.
Note: If the cold starting system is operating, the glow
plugs will also heat the air in the cylinder.
Just before the piston reaches the top center (TC)
position, the ECM operates the electronic unit
injector. Fuel is injected into the cylinder. The air/fuel
mixture ignites. The ignition of the gases initiates the
power stroke. Both the inlet and the exhaust valves
are closed and the expanding gases force the piston
downward toward the bottom center (BC) position.
From the BC position, the piston moves upward. This
initiates the exhaust stroke. The exhaust valve opens.
The exhaust gases are forced through the open
exhaust valve into the exhaust manifold.
UENR0623 11
Engine Operation
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