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| Illustration 1 | g01107024 |
Air inlet and exhaust system (typical example) (1) Inlet valves (2) Exhaust valves (3) Cylinder head (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 housing (11) Turbine housing | |
The components of the air inlet and exhaust system control the quality of the air that is available for combustion. These components also control the amount of the air that is available for combustion. The components of the exhaust system are listed below:
- Air cleaner
- Turbocharger
- Aftercooler
- Air inlet heater
- Cylinder head
- Valves and valve system components
- Piston and cylinder
- Water cooled exhaust manifold
Inlet air is pulled through the air cleaner. The inlet air is then compressed and heated by the compressor wheel of the turbocharger. The inlet air temperature is about 230 °C (446 °F) at rated speed and rated load. The inlet air is then pushed through the aftercooler core. The temperature of the inlet air at the aftercooler core is between 43 °C (109 °F) and 48 °C (118 °F) at rated speed and rated load. Cooling of the inlet air increases the combustion efficiency. Increased combustion efficiency helps to lower fuel consumption. Also, increased combustion efficiency helps to increase horsepower output.
From the aftercooler core, the air is forced into the cylinder head in order to fill the inlet ports. The flow of the air into the cylinder is controlled by the inlet valves.
There are two inlet valves and one exhaust valve for each cylinder. Inlet valves open when the piston moves down on the inlet 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. After the power stroke is complete, the piston moves upward. This upward movement is the exhaust stroke. During the exhaust stroke, the exhaust valve opens, and the exhaust gases are pushed through the exhaust port into the exhaust manifold. After the piston completes the exhaust stroke, the exhaust valves close and the cycle starts again. The complete cycle consists of four stages:
- Inlet stroke
- Compression stroke
- Power stroke
- Exhaust stroke
Exhaust gases from exhaust manifold (4) enter the turbine side of turbocharger (11) in order to turn the turbine wheel. The turbine wheel is connected to a shaft which drives the compressor wheel. Exhaust gases from the turbocharger pass through the exhaust outlet pipe.
Turbocharger
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| Illustration 2 | g01231788 |
Water cooled turbocharger (typical example) (12) Air inlet (13) Compressor housing (14) Compressor wheel (15) Bearing (16) Oil Inlet port (17) Turbine housing (18) Turbine wheel (19) Oil outlet port (20) Exhaust inlet (21) Exhaust outlet | |
The turbocharger is installed on the end 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 a pipe.
The exhaust gases go into turbine housing (17) through exhaust inlet (20). The exhaust gases then push the blades of turbine wheel (18). The turbine wheel is connected by a shaft to compressor wheel (14) .
Clean air from the air cleaners is pulled through compressor housing air inlet (13) by the rotation of compressor wheel (14). The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more power by allowing the engine to burn more air and more fuel during combustion.
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.
Bearings (15) for the turbocharger use engine oil for lubrication. The oil comes in through oil inlet port (16). The oil then goes through passages in the center section in order to lubricate the bearings. Oil from the turbocharger goes out through oil outlet port (19) in the bottom of the center section. The oil then goes back to the engine lubrication system.
Valve System Components
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| Illustration 3 | g01231790 |
Valve System Components (typical example) (22) Rocker arms (23) Bridge (24) Spring (25) Pushrods (26) Exhaust valve (27) Inlet valves (28) Lifter (29) Camshaft lobe | |
The valve system components control the flow of inlet air into the cylinders during engine operation. The valve system components also control the flow of exhaust gases out of the cylinders 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 movement and the valve movement.
The camshaft has two camshaft lobes for each cylinder. The lobes operate the inlet and exhaust valves. As the camshaft turns, lobes on the camshaft cause lifters (28) to move pushrods (25) up and down. Upward movement of the pushrods against rocker arms (22) results in downward movement (opening) of valves (26) and (27) .
Each cylinder has two inlet valves and one exhaust valve. Valve springs (24) close the valves when lifters (28) move down.