GEAR (84 teeth) 4S5948 - Caterpillar

Illustration 1 g01107004
Basic air inlet and exhaust system
(1) Inlet valves
(2) Exhaust valves
(3) Inlet manifold
(4) Exhaust manifold
(5) Air to air aftercooler
(6) Air inlet
(7) Exhaust outlet
(8) Compressor
(9) TurbineThe 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 manifoldNote: 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 (6) of the turbocharger compressor (8). A turbocharger is used 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 (5), the temperature of the compressed air is cooled to about 46 °C (115 °F). The aftercooler utilizes a heat exchanger to cool the inlet air. 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 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 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 action 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 repeats. The complete cycle consists of four strokes:
Inlet
Compression
Power
ExhaustThe exhaust gases from the cylinder are forced into exhaust manifold (4). The flow of exhaust gases from the exhaust manifold enters the turbine side of the turbocharger. The flow of the exhaust gas and the heat of the exhaust gas