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| Illustration 1 | g02169274 |
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Typical Example Basic air inlet and exhaust system (1) NOx reduction system (NRS) cooler (2) Exhaust manifold (3) Aftercooler (4) Exhaust outlet (5) Turbine wheel (6) Compressor wheel (7) Air inlet (8) Inlet valves (9) Exhaust valves | |
The 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
- DOC
- NRS
- Turbocharger
- Aftercooler
- Cylinder head
- Valves and valve system components
- Piston and cylinder
- Inlet manifold
- Exhaust manifold
Note: 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 of the turbocharger compressor (6). A turbocharger is used in order 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
From the aftercooler, air enters the inlet manifold. Air flow from the inlet manifold to the cylinders is controlled by inlet valves (8). There are two inlet valves and two exhaust valves (9) 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 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 (2) as the piston travels toward top center on the exhaust stroke. The exhaust valves close and the cycle starts again. The complete cycle consists of four strokes:
- Inlet
- Compression
- Power
- Exhaust
The exhaust gases from the cylinder are forced into exhaust manifold (2). 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 causes the turbine wheel (5) to spin. The turbine wheel is connected to a shaft that drives the compressor wheel. Exhaust gases from the turbine wheel then exit the turbocharger.
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| Illustration 2 | g02137980 |
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Water cooled turbocharger (10) Compressor inlet (11) Compressor housing (12) Compressor wheel (13) Shaft bearing (14) Oil Inlet port (15) Shaft bearing (16) Turbine housing (17) Small scroll (18) Exhaust balance valve chamber (19) Large scroll (20) Turbine wheel (21) Turbine outlet (22) Oil outlet port | |
All of the air that enters the engine passes through the turbocharger's compressor. All of the exhaust gases from the engine pass through the turbocharger's turbine.
The exhaust gas enters the turbocharger through the turbine inlet. The flow of the exhaust gas pushes on the blades of the turbine wheel (20) and exits through the turbine outlet (21). The turbine housing is asymmetrical in design. This design allows the heat energy from two different volumes of exhaust gas that are from the forward exhaust manifold and the rear exhaust manifold to be used efficiently by the turbocharger.
The exhaust balance valve is controlled by the exhaust balance valve solenoid. The solenoid for the exhaust balance valve is electronically controlled by the Electronic Control Module (ECM). When the balance valve is in the open position, the velocity of the exhaust gas in the small scroll is decreased. This equalizes the pressures on the vanes of the turbocharger, and prevents overspeed of the turbocharger. When the exhaust balance valve is in the closed position, the pressure in the two scrolls is unequal. This is due to a higher backpressure in the smaller scroll and a lower backpressure in the larger scroll. The turbine wheel is connected by a shaft to compressor wheel (12).
As the compressor wheel rotates, a vacuum is created in the turbocharger's compressor housing (11). Air is pulled through the air filters into the compressor housing through the compressor inlet (10). Impeller vanes are manufactured into the compressor wheel. The vanes are used to compress the incoming air. The compressed air is directed to the compressor outlet of the turbocharger into the inlet piping. The air is then directed toward the inlet side of the engine. Boost pressure is created as the flow that is developed by the compressor wheel exceeds the needs of the engine. This results in a positive inlet manifold pressure that exceeds atmospheric pressure. The increased pressure allows the engine to burn more fuel during fuel combustion. Through optimum fuel efficiency, this strategy allows the engine to produce more power and lower emission levels.
When the throttle is opened, more fuel is injected into the cylinders. The combustion of this additional fuel produces an increased flow of exhaust and greater exhaust temperature. The additional flow and the increased temperature of the exhaust causes the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, air flow into the air inlet system creates an increase in the pressure that is in the inlet manifold. This increased air pressure allows the engine to burn additional fuel with greater efficiency.
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| Illustration 3 | g02138171 |
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Valve system components (23) Rocker arm (24) Valve adjustment screw (25) Rocker arm shaft (26) Camshaft follower (27) Camshaft (28) Valve bridge (29) Valve rotator (30) Valve spring (31) Valve (32) Valve seat | |
The valve train controls the flow of inlet air into the cylinders and the flow of exhaust gases out of the cylinders during engine operation. Machined lobes on the camshaft (27) control the following aspects of valve function:
- Height of valve lift
- Timing of valve lift
- Duration of valve lift
The crankshaft gear drives the camshaft gear through an idler gear. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston position and the valve position.
The camshaft has three camshaft lobes for each cylinder. One camshaft lobe operates the inlet valves. One camshaft lobe operates the exhaust valves. There is also one camshaft lobe that operates the unit injector. Camshaft followers (26) roll against the surface of the camshaft lobes. The followers are used in order to transfer the lift that is machined into the camshaft lobe to the rocker arm (23).
The camshaft lobes lift the camshaft follower of the rocker arm which actuates the valves (31). As the camshaft lobe lifts the follower, the rocker arm pivots at the rocker shaft (25). This applies the lifting action to the valve bridge (28). The valve bridge is used to transfer the lift from the rocker arm to the valves. The valve adjustment screw (24) is used in order to adjust the valve lash.
Each cylinder has two inlet valves and two exhaust valves. Valve springs (30) are used to hold the valves in the closed position when lift is not being transferred from the camshaft lobe. The springs provide the force on the valve in order to ensure that the valves will close at high rpm and under high boost pressures.
Valve rotators (29) cause the valves to rotate while the engine is running. The rotation of the valves prevents the valves from burning by constantly changing the contact area of the valve face and the valve seat (32). This rotation gives the valves longer service life.
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| Illustration 4 | g02134516 |
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Components of the NRS (top view of the engine) (7) NRS exhaust cooler (33) Absolute pressure sensor (34) Differential pressure sensor (35) Oil return line from NRS actuator (36) NRS venturi (37) NRS valve assembly (38) Solenoid for NRS actuator (39) NRS actuator (40) Oil supply for NRS actuator | |
The NRS is used to reduce the amount of nitrogen oxide that is produced during combustion.
The exhaust gas exits the combustion chamber and flows into the exhaust manifold. A portion of the exhaust gas from the first three cylinders of each bank flows into the NRS exhaust coolers (7). The NRS exhaust cooler (7) utilizes engine coolant, which flows through a heat exchanger in order to cool the exhaust gas. Heat is transferred from the exhaust gas to the engine coolant as the exhaust gas flows through cooler. The maximum temperature of the cooled exhaust gas is approximately
After the exhaust gas is cooled, the gas flows through the NRS venturi (36). Absolute pressure sensor (33) and differential pressure sensor (34) take measurements at the NRS venturi (36) in order to calculate the flow of exhaust gas. The electronic control module (ECM) uses these calculations to control NRS actuator (39) and valve assembly (37).
The NRS actuator (39) and valve assembly (37) is an electronically controlled, hydraulically actuated assembly. When the NRS valve is in the full OFF position, all exhaust gas is blocked from being recirculated into the intake manifold on the engine. As more exhaust gas is required to be recirculated, the NRS valve opens. A signal from the ECM is sent to solenoid (38) on the NRS actuator. Oil is fed to the actuator from line (40). As the spool shifts within the NRS actuator, pressurized engine oil enters the valve and flows into the housing assembly. Oil fills one side of the housing assembly which acts on one side of the vane. As the oil moves the vane, the shaft which is connected to the vane rotates. This causes the butterfly valve which is coupled to the shaft to rotate. Oil is allowed to drain to the rear gear train from the NRS actuator through line (35).
Diesel Oxidation Catalyst (DOC)
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| Illustration 5 | g02138327 |
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(41) Catalytic converter/muffler
(42) Catalyst section (43) Identification tag (44) Aftertreatment identification module | |
The DOC is a flow-through device that consists of a canister that contains a substrate with a catalytic coating that contains precious metals that are applied to the surface. The DOC is used to oxidize certain elements that are in the engine exhaust gases. As the gases flow through the DOC, a chemical reaction causes a reduction in the amount of carbon monoxide, hydrocarbons, and soluble organic fractions of particulate matter that is in the exhaust.
Open Crankcase Ventilation System
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| Illustration 6 | g02152973 |
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(45) Ventilation breather
(46) Oil separator filter (47) Oil drain tube (48) Ventilation hose (49) Check valve assembly | |
The Open Crankcase Ventilation (OCV) system is used to filter out the crankcase emissions which are incorporated into the combustion gasses. Crankcase emissions are separated from the gasses which flow through filter (46). As oil droplets form, the oil is returned to the crankcase by oil drain tube (47). The remaining air that has been filtered, with water vapor is vented to the atmosphere by ventilation hose (48).