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| Illustration 1 | g00761428 |
Air inlet and exhaust system components (1) ATAAC (2) Air inlet (3) Inlet valves (4) Exhaust valves (5) Exhaust outlet (6) Inlet manifold (7) Exhaust manifold (8) Cylinder head (9) Muffler (10) Air cleaner | |
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
- Exhaust manifold
Inlet air is pulled through the air cleaner into air inlet (2) by turbocharger compressor wheel (3). The air is compressed and heated to about 150 °C (300 °F) before the air is forced to aftercooler (1). As the air flows through the aftercooler the temperature of the compressed air lowers to about 46 °C (115 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:
- Lower fuel consumption
- Increased horsepower output
From the aftercooler, air is forced into inlet manifold (8). Air flow from the inlet chambers into the cylinders is controlled by inlet valves (4). There are two inlet valves and two exhaust valves (5) for each cylinder. The inlet valves open when the piston moves down on the intake stroke. When the inlet valves open, cooled compressed air from the inlet port is pulled into the cylinder. The inlet valves close and the piston begins to move up on the compression stroke. The air in the cylinder is compressed. 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. During the power stroke, the combustion force pushes the piston downward. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (9) as the piston rises on the exhaust stroke. After 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 exhaust manifold (9) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel (6). The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (7), a muffler and an exhaust stack.
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 | |
The turbocharger is installed on the center section of the exhaust manifold. All the exhaust gases from the engine go through the turbocharger. The compressor side of the turbocharger is connected to the aftercooler by pipe.
The exhaust gases enter turbine housing (7) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (8). The turbine wheel is connected by a shaft to compressor wheel (3) .
Clean air from the air cleaners is pulled through compressor housing air inlet (1) by the rotation of compressor wheel (3). The action of the compressor wheel blades causes a compression of the inlet air. This compressor allows the engine to burn more fuel. When the engine burns more fuel the engine produces more power.
When the load on the engine increases, more fuel is injected into the cylinders. The combustion of this additional fuel produces more exhaust gases. The additional exhaust gases cause 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) Boost pressure link | |
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 boost pressure.
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 system components control the flow of inlet air into the cylinders during engine operation. The valve system components also time the flow of exhaust gases out of the cylinders during engine operation.
The crankshaft gear drives the camshaft gear through an idler gear. Camshaft (8) must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.
The camshaft has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and one operates the unit injector mechanism. As the camshaft turns, the camshaft lobes cause the lifter or follower (9) to move pushrod (4) up and down. Upward movement of the pushrod against rocker arm (3) results in downward movement (opening) of valves (6) .
Each cylinder has two inlet valves and two exhaust valves. Valve springs (5) close the valves when the lifters move down. Valve rotators (2) cause the valves to rotate while the engine is running. The rotation of the valves keeps the carbon deposits on the valves to a minimum. Also, the rotation gives the valves longer service life.