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| Illustration 1 | g02169274 |
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Air Inlet And Exhaust System (1) NOx reduction system (NRS) cooler (2) Exhaust manifold (3) Aftercooler (ATAAC or SCAC) (4) Exhaust outlet (5) Turbine wheel (6) Compressor wheel (7) Air inlet (8) Inlet valve (9) Exhaust valve | |
Clean inlet air from the air cleaners is pulled through air inlet (7) into the turbocharger compressor by compressor wheel (6). The rotation of the compressor wheel compresses the air. The rotation of the turbocharger compressor wheel then forces the air through a tube to aftercooler (3). The aftercooler lowers the temperature of the compressed air before the air enters the inlet chamber in each cylinder head. Air flow from the inlet chamber into the cylinder heads is controlled by the inlet valves.
There are two inlet valves and two exhaust valves for each cylinder. Refer to Systems Operation, "Valve Mechanism". The inlet valves open when the piston moves down on the inlet stroke. The cooled, compressed air is pulled into the cylinder from the inlet chamber.
The inlet valves close and the piston moves up on the compression stroke. When the piston is near the top of the compression stroke, fuel is injected into the cylinder. The fuel mixes with the air and combustion starts. The force of the combustion pushes the piston downward on the power stroke. When the piston moves upward again, the piston is on the exhaust stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (1). After the piston makes the exhaust stroke, the exhaust valves close and the cycle begins again.
Exhaust gases from exhaust manifold (2) go into the turbine side of the turbocharger. The exhaust gases cause turbine wheel (5) to turn. The turbine wheel is connected to the shaft that drives the turbocharger compressor wheel (6). The exhaust gases exit through exhaust outlet (4).
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| Illustration 2 | g06208205 |
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(3) NOx reduction system (NRS) cooler
(2) NRS venturi (3) NRS valve assembly | |
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| Illustration 3 | g06208207 |
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(4) NOx reduction system (NRS) cooler
(1) NRS venturi (2) NRS valve assembly (3) ERV | |
The NOx Reduction System (NRS) sends hot exhaust gas from the exhaust manifold through the NRS system and back into the intake. In order for exhaust gas to be able to mix with pressurized air in the intake, back pressure is needed in the exhaust system. This back pressure is created by the Exhaust Restriction Valve (ERV). The ERV is at the end of the exhaust manifold between cylinders 10 and 12. When NRS flow is requested by the ECM, the ERV valve will partially close, forcing exhaust gas through the NRS system rather than being able to flow freely to the turbochargers.
The hot exhaust gas exits the cylinders and travels into the exhaust manifolds. The exhaust gas is then forced into the NRS system by the partially closed ERV. Exhaust gas then travels to the NRS coolers where the engine coolant flows in parallel to the exhaust gas and cools the gas down. The exhaust gas exits the NRS coolers and passes by the NRS pressure sensor and into the NRS venturi. The NRS differential pressure sensor has a sampling port on either side of the venturi which allows detection of exhaust flow through the NRS system. The gas flows through the electronically controlled NRS valve, where the temperature is taken, and then back to the fresh air intake on the engine.
Both the ERV and NRS valves are electronically controlled and hydraulically actuated using engine oil. When the NRS valve is in the full OFF position, the only source of air for the engine is from the turbocharger compressor. As the NRS valve starts to open and the ERV closes, the flow of cooled exhaust gas from the NRS cooler mixes with the air flow from the turbocharger.
In Cat ET the valves are referred to as:
- The NRS valve is referred to as the "Engine Exhaust Gas Recirculation (EGR) Valve"
- The ERV is referred to as the "Engine Exhaust Gas Recirculation (EGR) Valve 2"