3512B Petroleum Engines Caterpillar

The components of the air inlet and exhaust system control the quality and the amount of air that is available for combustion. There are separate turbochargers and exhaust manifolds on each side of the engine. A common aftercooler is located between the cylinder heads in the center of the engine. The inlet manifold is a series of elbows that connect the aftercooler chamber to the inlet ports (passages) of the cylinder heads. There is one camshaft in each side of the block. The two camshafts control the movement of the valve system components.

Illustration 1	g00281646
Air Inlet And Exhaust System (1) Exhaust manifold. (2) Aftercooler. (3) Engine cylinder. (4) Air inlet. (5) Turbocharger compressor wheel. (6) Turbocharger turbine wheel. (7) Exhaust outlet.

Clean inlet air from the air cleaners is pulled through air inlet (4) into the turbocharger compressor by the turbocharger compressor wheel (5). The rotation of the turbocharger compressor wheel causes the air to compress. The rotation of the turbocharger compressor wheel then forces the air through a tube to aftercooler (2). The aftercooler lowers the temperature of the compressed air before the air goes into the inlet chambers in each cylinder head. This cooled and compressed air fills the inlet chambers in the cylinder heads. Air flows from the inlet chambers in the cylinder heads. Air flow from the inlet chamber into the cylinder is controlled by the inlet valves.

There are two inlet valves and two exhaust valves for each cylinder. Make reference to Valve Mechanism. The inlet valves open when the piston moves down on the inlet stroke. The cooled, compressed air is pulled into the cylinder from the inlet chamber.

The inlet valves close and the piston starts to move up on the compression stroke. 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. The force of the combustion pushes the piston downward on the power stroke. When the piston moves upward the piston is on the exhaust stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (1). After the piston makes the exhaust stroke, the exhaust valves close and the cycle starts again.

Exhaust gases from the exhaust manifold go into the turbine side of the turbocharger. The exhaust gases cause the turbocharger turbine wheel (6) to turn. The turbine wheel is connected to the shaft that drives the turbocharger compressor wheel (5). The exhaust gases exit through the exhaust outlet (7).