UENR0623-02 13 Engine Operation Air is drawn in through the air cleaner into the air inlet of the turbocharger by the turbocharger compressor wheel. The air is compressed to a pressure of about 150 kPa (22 psi) and the compression heats the air to about 120° C (248° F) before the air is forced to the aftercooler. As the air flows through the aftercooler the temperature of the compressed air lowers to about 55° C (131° F). Cooling of the inlet air assists the combustion efficiency of the engine. Increased combustion efficiency helps achieve the following benefits:
Lower fuel consumption Increased power output Reduced NOx emission Reduced particulate emission From the aftercooler, air is forced into the inlet manifold. Air flow from the inlet manifold to the cylinders is controlled by inlet valves. There is one inlet valve and one exhaust valve for each cylinder. The inlet valve opens when the piston moves down on the intake stroke. When the inlet valve opens, 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 valve closes. The cool compressed air is compressed further.
This additional compression generates more heat. Note: If the cold starting system is operating, the glow plugs will also heat the air in the cylinder. Just before the piston reaches the top center (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 valve opens.
The exhaust gases are forced through the open exhaust valve into the exhaust manifold.