 | |
| Illustration 1 | g01205681 |
Air inlet and exhaust system (1) Exhaust manifold (2) Electronic unit injector (3) Glow plug (4) Inlet manifold (5) Aftercooler core (6) Exhaust outlet (7) Turbine side of turbocharger (8) Compressor side of turbocharger (9) Air inlet from the air cleaner (10) Inlet valve (11) Exhaust valve | |
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
- Inlet manifold
- Cylinder head, injectors and glow plugs
- Valves and valve system components
- Piston and cylinder
- Exhaust manifold
Air is drawn in through the air cleaner into the air inlet of the turbocharger (9) by the turbocharger compressor wheel (8). The air is compressed and heated to about 150 °C (300 °F) before the air is forced to the aftercooler (5). As the air flows through the aftercooler the temperature of the compressed air lowers to about 50 °C (120 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:
- Lower fuel consumption
- Increased horsepower output
- Reduced particulate emission
From the aftercooler, air is forced into the inlet manifold (4). Air flow from the inlet manifold to the cylinders is controlled by inlet valves (10). There are two inlet valves and two exhaust valves 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 forced into the cylinder. The complete cycle consists of four strokes:
- Inlet
- Compression
- Power
- Exhaust
On the compression stroke, the piston moves back up the cylinder and the inlet valves (10) close. The cool compressed air is compressed further. This additional compression generates more heat.
Note: If the cold starting system is operating, the glow plugs (3) will also heat the air in the cylinder.
Just before the piston reaches the TC position, the ECM operates the electronic unit injector. Fuel is injected into the cylinder. The air/fuel mixture ignites. The ignition of the gases initiates the power stroke. Both the inlet and the exhaust valves are closed and the expanding gases force the piston downward toward the bottom center (BC) position.
From the BC position, the piston moves upward. This initiates the exhaust stroke. The exhaust valves open. The exhaust gases are forced through the open exhaust valves into the exhaust manifold.
Exhaust gases from exhaust manifold (1) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel (7). The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (6), a silencer and an exhaust pipe.
Turbocharger
 | |
| Illustration 2 | g00302786 |
Turbocharger (1) Air intake (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 mounted on the outlet of the exhaust manifold. The exhaust gas from the exhaust manifold enters the exhaust inlet (11). The gas then passes through the turbine housing (7) of the turbocharger. Energy from the exhaust gas causes the turbine wheel (8) to rotate. The turbine wheel is connected by a shaft to the compressor wheel (3) .
As the turbine wheel rotates, the compressor wheel is rotated. This causes the intake air to be pressurized through the compressor housing (2) of the turbocharger.
The shaft that connects the turbine to the compressor wheel rotates in bearings (4 and 6). The bearings require oil under pressure for lubrication and cooling. The oil that flows to the lubricating oil inlet port (5) passes through the center of the turbocharger which retains the bearings. The oil exits the turbocharger from the lubricating oil outlet port (10) and returns to the oil pan.
Valve System Components
 | |
| Illustration 3 | g01334457 |
Valve system components (1) Bridge (2) Rocker arm (3) Pushrod (4) Lifter (5) Spring (6) Valve | |
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 either a pair of inlet valves or a pair of exhaust valves. As the camshaft turns, lobes on the camshaft cause the lifter (4) to move the pushrod (3) up and down. Upward movement of the pushrod against rocker arm (2) results in a downward movement that acts on the valve bridge (1). This action opens a pair of valves (6) which compresses the valve springs (5). When the camshaft has rotated to the peak of the lobe, the valves are fully open. When the camshaft rotates further, the two valve springs (5) under compression start to expand. The valve stems are under tension of the springs. The stems are pushed upward in order to maintain contact with the valve bridge (1). The continued rotation of the camshaft causes the rocker arm (2), the pushrods (3) and the lifters (4) to move downward until the lifter reaches the bottom of the lobe. The valves (6) are now closed. The cycle is repeated for all the valves on each cylinder.