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| Illustration 1 | g00281646 |
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Air inlet and exhaust system (typical example) (1) Exhaust manifold (2) inlet manifold (3) Engine cylinder (4) Air inlet (5) Turbocharger compressor wheel (6) Turbocharger turbine wheel (7) Exhaust outlet | |
Engines which are naturally aspirated pull outside air through an air cleaner directly into inlet manifold (2). The air flows from the inlet manifold to the engine cylinders (3). The fuel is mixed with the air in the engine cylinders. After the fuel combustion occurs in the engine cylinder, the exhaust gases flow directly to the outside air through exhaust manifold (1).
Turbocharged engines pull outside air through an air cleaner into the air inlet (4) of the turbocharger. The suction is caused by the turbocharger compressor wheel (5). Then, the turbocharger compressor wheel compresses the air. The air flows through inlet manifold (2) which directs an even distribution of the air to each engine cylinder (3). Air is pulled into the engine cylinder (3) during the intake stroke of the piston. Then, the air is mixed with fuel from the fuel injection nozzles.
Each piston makes four strokes:
- Intake
Air is drawn into the cylinder through the open inlet valve and fuel is injected into the cylinder by the use of a fuel injector nozzle.
- Compression
The mixture of air and fuel is compressed in the cylinder in order to heat the mixture to the temperature of combustion.
- Power
The mixture of air and fuel ignites at the top of the compression stroke. The expansion of gases from the combustion forces the piston downward. This force creates the power of the engine.
- Exhaust
The piston moves upward in order to force the gases of combustion from the cylinder through the open exhaust valve.
The sequence of the strokes by all of pistons in all of the engine cylinders provide constant air flow to the inlet system during the engine operation.
The exhaust stroke and the timing of the valve mechanism pushes combustion gases out of the open exhaust valve through exhaust manifold (1). The exhaust gases flow through the blades of the turbocharger turbine wheel (6) which causes the turbine wheel and the compressor wheel to turn. Then, the exhaust gases flow through the exhaust outlet (7) of the turbocharger to the outside.
The air inlet system is also equipped with a crankcase ventilation system. The inlet strokes of the pistons pull in atmospheric air to the crankcase.
A turbocharger increases the temperature and the density of the air that is sent to the engine cylinder. This condition causes a lower temperature of ignition to develop earlier in the compression stroke. The compression stroke is also timed in a more accurate way with the fuel injection. Surplus air lowers the temperature of combustion. This surplus air also provides internal cooling.
A turbocharger improves the following aspects of engine performance:
- Power output is increased.
- Engine torque is increased.
- Engine efficiency is increased.
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| Illustration 2 | g00302786 |
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Components of a turbocharger (typical example) (1) Air inlet (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 | |
A turbocharger is installed between the exhaust and inlet manifolds. The turbocharger is driven by exhaust gases which flow through the exhaust inlet (11). The energy of the exhaust gas turns the turbine wheel (8). Then, the exhaust gas flows out of the turbine housing (7) through the exhaust outlet (9).
Turbine wheel (8) and compressor wheel (3) are installed on the same shaft. Therefore, turbine wheel (8) and compressor wheel (3) rotate at the same rpm. The compressor wheel is enclosed by compressor housing (2). The compressor wheel compresses the air. The air flows into the engine cylinders through the inlet valves of the cylinders.
The oil from the main gallery of the cylinder block flows through the oil inlet port (5) in order to lubricate the turbocharger bearings (4) and (6). The pressurized oil passes through the bearing housing of the turbocharger. The oil is returned through the oil outlet port (10) to the oil pan.
The turbocharger has a wastegate. The wastegate is controlled by the boost pressure. This allows some of the exhaust gas to bypass the turbine at higher engine speeds. The wastegate is a type of flapper valve that automatically opens at a preset level of boost pressure in order to allow exhaust gas to flow around the turbine. The wastegate allows the design of the turbocharger to be more effective at lower engine speeds.
The wastegate is controlled by a diaphragm which is open to the atmosphere on one side and open to the manifold pressure on the other side.
An air/fuel ratio control is installed between the turbocharger and the fuel injection pump. The air/fuel ratio control performs the following functions:
- The fuel is limited on acceleration in order to prevent an overspeed condition.
- The generation of black smoke is reduced.
- The fuel efficiency is improved and emissions are reduced at low boost when the fuel rack is limited for low power output.
The valves and the valve mechanism control the flow of the air and the exhaust gases in the cylinder during engine operation. The cylinder head assembly has two valves for each cylinder. Each valve has one valve spring. The ports for the inlet and exhaust valves are on the right side of the cylinder. Steel valve seat inserts are installed in the cylinder head for both the inlet and the exhaust valves. The valve seat inserts can be replaced.
The valves move along steel guides. The guides are treated with phosphate in order to reduce friction and wear. The valve guides can be replaced. The exhaust valve guide has a counterbore in order to prevent the seizure of the valve stem. The seizure of the valve stem is caused by a buildup of carbon under the head of the valve.
The inlet and the exhaust valves are opened and closed by the rotation and movement of the following components:
- Crankshaft
- Camshaft
- Valve lifters
- Pushrods
- Rocker arms
- Valve springs
The camshaft gear is driven by the crankshaft 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 lobes for each cylinder that operate the inlet and exhaust valves. As the camshaft turns, the camshaft lobes cause the valve lifters to move the pushrods up and down. Upward movement of the pushrod against the rocker arm results in downward movement (opening) of the valves. The valve springs close the valves when the valve lifters move down.