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| Illustration 1 | g01062759 |
Engine with one turbocharger (1) Inlet valves (2) Exhaust valves (3) Inlet manifold (4) Exhaust manifold (5) Water outlet for the aftercooler (6) Water inlet 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 air inlet and exhaust system consists of 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 (10). 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). As the air flows through aftercooler (7) the temperature of the compressed air is cooled to about 46 °C (115 °F). The aftercooler utilizes a water cooled heat exchanger in order to cool the inlet air. Cooling water enters the aftercooler through water inlet (6) and the heated water exits through water outlet (5). Cooling the inlet air causes the air to become more dense. Compressing and cooling the inlet air increases the combustion efficiency of the engine. This also increases the engine's horsepower output.
From the aftercooler, air enters the inlet manifold (3). 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, cooled 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 (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
The exhaust gases from the cylinder are forced into exhaust manifold (4). The flow of exhaust gases from the exhaust manifold enter the turbine side of the turbocharger. The flow of the exhaust gas and the heat of the exhaust gas causes the turbine wheel in the turbocharger's turbine (11) to spin. The turbine wheel is connected to a shaft that drives the compressor wheel. Exhaust gases from the turbine wheel then exit the turbocharger (9) .
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 the 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 the 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.
The 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 | g01062836 |
Valve system components (1) Rocker arm (2) Valve adjusting screw (3) Rocker arm shaft (4) Camshaft follower (5) Camshaft (6) Valve bridge (7) Valve rotator (8) Valve spring (9) Valve (10) Valve seat | |
The valve train controls the flow of inlet air into the cylinders and the flow of exhaust gases out of the cylinders during engine operation. Specifically machined lobes on the camshaft (5) control the following aspects of valve function:
- Height of valve lift
- Timing of valve lift
- Duration of valve lift
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. There is also one camshaft lobe that operates the unit injector. Camshaft followers (4) roll against the surface of the camshaft lobes. The followers are used in order to transfer the lift that is machined into the camshaft lobe to the rocker arm (1) .
The camshaft lobes lift the camshaft follower of the rocker arm which actuates the valves (9). As the camshaft lobe lifts the follower, the rocker arm pivots at the rocker shaft (3). This applies the lifting action to the valve bridge (6). The valve bridge is used to transfer the lift from the rocker arm to the valves. The valve adjustment screw (2) is used in order to adjust the valve lash.
Each cylinder has two inlet valves and two exhaust valves. Valve springs (8) are used to hold the valves in the closed position when lift is not being transfered from the camshaft lobe. The springs provide the force on the valve in order to ensure that the valves will close at high rpm and under high boost pressures.
Valve rotators (7) 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 (10). This rotation gives the valves longer service life.