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| Illustration 1 | g00845676 |
(1) Inlet valves (2) Exhaust valves (3) Inlet manifold (4) Exhaust manifold (5) Water inlet for the aftercooler (6) Water outlet for the aftercooler (7) Aftercooler (8) Air inlet (9) Exhaust outlet (10) Compressor (11) Turbine | |
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 components of the air inlet and exhaust system are the following components:
- Air cleaner
- Turbocharger
- Aftercooler
- Cylinder head
- Valves and valve system components
- Piston and cylinder
- Inlet manifold
- Exhaust manifold
Note: The following description of the operation of the air inlet and exhaust system assumes that the engine is developing boost pressure.
Inlet air passes through the air cleaner into the air inlet (8) of the turbocharger compressor wheel (10). The turbocharger will supply more volume of air into the engine. This compressing of the air is referred to as boost. The compressing of air causes the air temperature to rise to about 204 °C (400 °F). As the air flows through the aftercooler (7) the temperature of the compressed air lowers to about 46 °C (115 °F). Cooling of the inlet air causes the air to become more dense. This increases combustion efficiency and this increases horsepower output.
From the aftercooler, air enters the inlet manifold (3). Air flow from the inlet manifold (3) into the cylinders is controlled by inlet valves (1). There are two inlet valves and two exhaust valves (2) for each cylinder. The inlet valves open at the top center position before the piston moves toward the bottom center position. This is called the inlet stroke. When the inlet valves open, cooled compressed air from the inlet port enters the cylinder. The inlet valves close as the piston reaches the bottom center position. The piston begins to travel back to the top center position on the compression stroke. The air in the cylinder is compressed to a very high temperature. When the piston is near the end of the compression stroke, fuel is injected into the cylinder and mixes with the air. This causes combustion to start in the cylinder. Once combustion starts, the combustion force pushes the piston toward the bottom center position. This is called the power stroke. The exhaust valves open when the piston moves toward the bottom center position and the exhaust gases are pushed through the exhaust port into exhaust manifold (4) as the piston travels toward top center on the exhaust stroke. The exhaust valves close and the cycle starts again. The complete cycle consists of four strokes:
- Inlet
- Compression
- Power
- Exhaust
Exhaust gases from the exhaust manifold (4) enter the turbine side of the turbocharger. The exhaust gas temperature causes the turbine wheel (11) in the turbocharger to turn. The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbine wheel exit the turbocharger (9) .
Turbocharger
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| Illustration 2 | g00294193 |
Turbocharger (1) Air inlet (2) Compressor housing (3) Compressor wheel (4) Bearing (5) Oil Inlet port (6) Bearing (7) Turbine housing (8) Turbine wheel (9) Exhaust outlet (10) Oil outlet port (11) Exhaust inlet | |
All of the air that enters the engine passes through the turbocharger. All of the exhaust gases from the engine pass through the turbocharger.
The exhaust gases enter turbine housing (7) through exhaust inlet (11). The exhaust gas pushes on the blades of the turbine wheel (8). The turbine wheel is connected by a shaft to the compressor wheel (3) .
Air that passes through the air filters enters the compressor housing air inlet (1) by the rotation of compressor wheel (3). The compressor wheel causes the inlet air to be pushed into the inlet side of the engine. Boost pressure is caused when the compressor wheel pushes more air into the inlet side of the engine. This results in a positive inlet manifold pressure that exceeds atmospheric pressure. This allows the engine to burn more fuel. When the engine burns more fuel the engine produces more power.
When the throttle is opened, more fuel is injected into the cylinders. The combustion of this additional fuel produces greater exhaust temperature. The additional exhaust temperature causes the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, more air is forced into the cylinders. The increased flow of air gives the engine more power by allowing the engine to burn the additional fuel with greater efficiency.
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| Illustration 3 | g00761528 |
(12) Canister (13) Actuating lever (14) Line (boost pressure) | |
Some turbochargers use a wastegate. The operation of the wastegate is controlled by boost pressure. At high boost pressures, the wastegate opens bypassing exhaust gases. At low boost pressure, the wastegate closes in order to increase exhaust temperature to the turbocharger.
When the engine is operating under conditions of low boost, a spring pushes on a diaphragm in canister (12). This action moves actuating lever (13) in order to close the valve of the wastegate. Closing the valve of the wastegate allows the turbocharger to operate at maximum performance.
As the boost pressure increases against the diaphragm in canister (12), the valve of the wastegate is opened. When the valve of the wastegate is opened, the rpm of the turbocharger is limited by bypassing a portion of the exhaust gases around the turbine wheel of the turbocharger.
Note: The turbocharger with a wastegate is preset at the factory and no adjustment can be made.
Bearings (4) and (6) for the turbocharger use engine oil under pressure for lubrication and cooling. The oil comes in through oil inlet port (5). The oil then goes through passages in the center section in order to lubricate the bearings. This oil also cools the bearings. Oil from the turbocharger goes out through oil outlet port (10) in the bottom of the center section. The oil then goes back to the engine oil pan.
Valve System Components
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| Illustration 4 | g00761532 |
Valve system components (1) Valve bridge (2) Valve rotator (3) Rocker arm (4) Pushrod (5) Valve springs (6) Valves (7) Valve guide (8) Camshaft (9) Lifter or follower | |
The valve train controls the flow of inlet air and exhaust gases into the cylinders and out of the cylinders during engine operation. The camshaft (6) controls the timing of the valves during engine operation.
The crankshaft gear drives the camshaft gear through an idler gear. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston position and the valve position.
The camshaft has three camshaft lobes for each cylinder. One camshaft lobe operates the inlet valves. One camshaft lobe operates the exhaust valves. One camshaft lobe operates the unit injector. The camshaft lobes cause the follower and the pushrod to push on the rocker arm in order to actuate the valves and the unit injector.
Each cylinder has two inlet valves and two exhaust valves. Valve springs hold the valves closed and the valve springs resist the opening of the valves. This ensures that the valves will close at high rpm and under high boost pressures. Valve rotators cause the valves to rotate while the engine is running. The rotation of the valves prevents the valves from burning by constantly changing the contact area of the valve face and the valve seat. This rotation gives the valves longer service life.