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| Illustration 1 | g01120694 |
Air inlet and exhaust system (1) Inlet valves (2) Exhaust valves (3) Exhaust manifold (4) Inlet manifold (5) Muffler (6) Air cleaner (7) Compressor side of turbocharger (8) Turbine side of turbocharger | |
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
- Turbocharger
- 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 air cleaner (6) into the air inlet of the turbocharger compressor (7). A turbocharger is used in order to increase the flow of air into the engine. This increase in air flow pressurizes the combustion air supply for the engine. The pressure that is placed on the inlet air allows a larger volume of air to be compressed into the cylinder. This compressing of the inlet air is referred to as engine boost.
The compressing of air causes the air temperature to rise to about 204 °C (400 °F). Compressing the inlet air increases the combustion efficiency of the engine. This also increases the engine's horsepower output.
From the turbocharger, air enters inlet manifold (4). Air flow from the inlet manifold to 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 of the piston. When the inlet valves open, compressed air enters the cylinder through the inlet ports. The inlet valves close as the piston reaches the bottom center position. This is called the inlet stroke of the engine. As 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 compressed 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 (3) 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
The exhaust gases from the cylinder are forced into exhaust manifold (3). The flow of exhaust gases from the exhaust manifold enter the turbine side of the turbocharger (8). The flow of the exhaust gas and the heat of the exhaust gas causes the turbine wheel in the turbocharger to spin. The turbine wheel is connected to a shaft that drives the compressor wheel. Exhaust gases from the turbine wheel exit the turbocharger and flow through muffler (5) .
Turbocharger
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| Illustration 2 | g01056645 |
Water cooled turbocharger (1) Compressor inlet (2) Compressor housing (3) Compressor wheel (4) Shaft bearing (5) Oil Inlet port (6) Shaft bearing (7) Turbine housing (water cooled housing) (8) Turbine wheel (9) Turbine outlet (10) Turbine inlet (11) Oil outlet port | |
All of the air that enters the engine passes through the turbocharger's compressor. All of the exhaust gases from the engine pass through the turbocharger's turbine.
The exhaust gases enter turbine housing (7) through turbine inlet (10). The flow of the exhaust gas pushes on the blades of the turbine wheel (8) and exits through turbine outlet (9). The turbine wheel is connected by a shaft to compressor wheel (3) .
As the compressor wheel rotates, a vacuum is created in the turbocharger's compressor housing (2). Air is pulled through the air filters into the compressor housing through compressor inlet (1). Impeller vanes are manufactured into the compressor wheel. The vanes are used to compress the incoming air. The compressed air is directed to the turbocharger's compressor outlet into the inlet piping. The air is then directed toward the inlet side of the engine. Boost pressure is created as the flow that is developed by the compressor wheel exceeds the needs of the engine. This results in a positive inlet manifold pressure that exceeds atmospheric pressure. The increased pressure allows the engine to burn more fuel during fuel combustion. Through optimum fuel efficiency, this strategy allows the engine to produce more power and lower emission levels.
When the throttle is opened, more fuel is injected into the cylinders. The combustion of this additional fuel produces an increased flow of exhaust and greater exhaust temperature. The additional flow and the increased temperature of the exhaust causes the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, air flow into the engine's air inlet system creates an increase in the pressure that is in the inlet manifold. This increased air pressure allows the engine to burn additional fuel with greater efficiency.
Turbocharger's shaft bearings (4) and (6) use pressurized oil from the engine for lubrication and for 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 (11) in the bottom of the center section. The oil then flows back to the engine oil pan.
Valve System Components
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| Illustration 3 | g01120765 |
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.