TM 9-6115-729-24
0003
AIR INLET AND EXHAUST SYSTEM - Continued
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. Inlet air is pulled through
the air cleaner. The inlet air is then compressed and heated by the compressor wheel of the turbocharger to
about 150C (300F). The inlet air is then pushed through the air-to-air aftercooler core and the inlet air
temperature drops to about 110F (43C). Cooling the inlet air increases the combustion efficiency which helps to
lower fuel consumption and increases horsepower output. The aftercooler core is a separate cooler core installed
above the core (standard) of the engine radiator. The engine fan moves air at ambient temperature
across the aftercooler core to cool the turbocharged inlet air. From the aftercooler core the air is forced into the
cylinder head to fill the inlet ports. The inlet valves control air flow from the inlet port into the cylinder. There are
two inlet valves and one exhaust valve for each cylinder. Inlet valves open when the piston moves down on the
inlet stroke to pull air 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 and 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.
Then the piston moves upward in 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. Exhaust gases from exhaust manifold enter
the turbine side of turbocharger 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, the muffler
and the exhaust stack.
Turbocharger
The turbocharger is installed on the center section 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 pipe.
The exhaust gases go into the turbine housing through the exhaust inlet. The exhaust gases spin the blades of a
turbine wheel that is connected by a shaft to the compressor wheel. The rotation of the compressor wheel pulls
clean air from the air filters through the compressor housing air inlet. The compressor wheel blades compress the
inlet air. Air compression increases engine 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 producing more
exhaust gases to increase the turbocharger speed. 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. The turbocharger uses engine oil under pressure for lubrication. The oil comes in
through an oil inlet port, lubricates turbocharger bearings, and returns through an outlet port to the engine
lubrication system.
Inlet Air Preheater
The engines are equipped with an electric heater that is located behind the air inlet elbow. The electric heater
functions to aid in starting and to clean up white smoke during start-up. Under the proper conditions, the ECM
turns on the electric heater based on jacket water coolant temperature, inlet manifold temperature, and duration.
The system can deliver heat for 30 seconds prior to start-up and during cranking of the engine. After the engine
has started, the system can deliver heat constantly for 7 minutes, or the system can cycle the heat for 13 minutes.
During the heating cycle, the heat is on for ten seconds and off for ten seconds. If the air inlet heater
malfunctions, the engine will still start and the engine will still run. There may be a concern regarding the amount
of white smoke that is present and the need for an alternative starting aid. The engine ECM controls an inlet air
heater system to improve the cold starting capability. The ECM measures coolant temperature and controls an
air inlet heater relay to apply 24 Vdc from the batteries to the heater to preheat the air as necessary. Regardless
of temperature, power is applied to the heater for two seconds when power is applied to the ECM. If the sum of
the coolant temperature and the inlet manifold temperature is less than 109F (25C), the ECM will turn on the
heater for 30 seconds as a preheating cycle. If the operator attempts starting during this preheating cycle, the
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