C9.3 Tier 4 Final Engines Air Inlet and Exhaust System Caterpillar


Air Inlet and Exhaust System
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Illustration 1g03876527
Air inlet and exhaust system
(1) Air-to-air aftercooler (ATAAC)
(2) Exhaust manifold
(3) Turbocharger
(4) Clean Emissions Module (CEM)
(5) NOx Reduction System (NRS) cooler
(6) NRS venturi
(7) NRS valve
(8) Exhaust valve solenoid
(9) Intake manifold
(10) Cylinder head

The engine has an electronic control system. The system controls the operation of the engine and communicates with the Clean Emissions Module (CEM) Aftertreatment Electronic Control Module (ECM). The CEM consists of the following components: Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and systems.

The system consists of the following components:

  • Electronic Control Module (ECM)

  • Wiring

  • Sensors

  • Actuators

Inlet air is pulled through the air cleaner . The inlet air is then compressed and heated by the compressor wheel of turbocharger to about 150 °C (300 °F). The inlet air is then pushed through air-to-air aftercooler core and the inlet air is moved to the air inlet elbow. The temperature of the inlet air at air inlet elbow is about 43 °C (110 °F). Cooling of the inlet air increases the combustion efficiency. Increased combustion efficiency helps to lower fuel consumption. Also, increased combustion efficiency helps to increase horsepower output.

Aftercooler core is a separate cooler core. The aftercooler core is installed in front of the core of the engine radiator. Air that is ambient temperature is moved across the aftercooler core by the engine fan. The aftercooler core cools the turbocharged inlet air.

From aftercooler core , the air is forced into the cylinder head to fill the inlet ports. Air flow from the inlet port into the cylinder is controlled by the inlet valves.



Illustration 2g01880505
Air inlet and exhaust system
(11) NRS cooler
(12) Exhaust manifold
(13) Aftercooler
(14) Exhaust outlet from turbocharger
(15) Turbine side of turbocharger
(16) Compressor side of turbocharger
(17) Air inlet
(18) Inlet valve
(19) Exhaust valve

There are two inlet valves and two exhaust valves for each cylinder. Inlet valves open when the piston moves down on the inlet stroke. When the inlet valves open, cooled compressed air from the inlet port is pulled into the cylinder. The inlet valves close and the piston will move up on the compression stroke. The air in the cylinder is compressed. 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. During the power stroke, the combustion force pushes the piston downward. After the power stroke is complete, the piston moves upward. This upward movement is the exhaust stroke. During the exhaust stroke, the exhaust valves open, 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 will start again. The complete cycle consists of four stages:

  • Inlet stroke

  • Compression stroke

  • Power stroke

  • Exhaust stroke

Exhaust gases from the 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.

NOx Reduction System (NRS)

The NRS sends hot exhaust gas from the exhaust manifold that is connected to cylinders one, two, and three through the NRS system. In order for exhaust gas to be able to mix with pressurized air from the ATAAC, back pressure is needed in the exhaust system. This back pressure is created by the turbocharger and DPF. The hot exhaust gas is first cooled in the NRS cooler. The now cooled exhaust gas passes through the NRS venturi. The venturi takes a measurement of the flow of exhaust gas through the NRS system. After the gas flow is measured by the NRS venturi, the gas flows through the electronically controlled NRS valve. The electronic controlled NRS valve is hydraulically actuated. When the NRS valve is in the full OFF position, the only source of air is from the turbocharger compressor. As the valve starts to open the flow of cooled exhaust gas from the NRS cooler mixes with the air flow from the turbocharger. As the demand for more cooled exhaust gas increases, the valve opens wider. The increase in the flow of cooled exhaust gas from the NRS cooler. As the demand for more cooled exhaust gas increases, the demand for air flow from the engines turbocharger decreases.

Turbocharger



Illustration 3g01945375
Turbocharger
(20) Air inlet
(21) Compressor housing
(22) Compressor wheel
(23) Bearing
(24) Oil inlet port
(25) Bearing
(26) Turbine housing
(27) Small path
(28) Balance Valve chamber
(29) Large path
(30) Turbine wheel
(31) Exhaust outlet
(32) Oil outlet port

The turbocharger is installed on the exhaust manifold. Most of the exhaust gases flow through the turbocharger. A metered amount of exhaust gases flow through the NRS system. The compressor side of the turbocharger is connected to the aftercooler by a pipe.

The exhaust gases go into turbine housing (26) through the exhaust inlet. The turbine housing of the turbocharger is of the asymmetric design. The asymmetric design consists of the turbine housing that has two different-sized paths for the exhaust to flow. Path (27) receives exhaust gas from cylinders one, two, and three. Path (29) receives exhaust gas from cylinders four, five, and six. The smaller path restricts the flow of the exhaust. This restriction helps force the exhaust gas through the NRS system to the intake manifold of the engine. The energy from the heat in the exhaust gases pushes the blades of turbine wheel (30). The turbine wheel is connected by a shaft to compressor wheel (22). The turbine housing also contains the exhaust balance valve and the actuator for the exhaust balance valve. The actuator for the exhaust balance valve receives boost pressure from the intake manifold. This boost pressure is first regulated by the solenoid for the exhaust balance valve. The exhaust balance valve solenoid will open allowing the boost pressure to act on the exhaust balance valve actuator if the valve needs to open. The actuator then opens the exhaust balance valve. The exhaust balance valve allows the flowing exhaust gas from the small path of the turbine housing to enter the large path. This action causes less exhaust gas to act on the turbine wheel from the smaller flow path. This action slows down the speed of the turbine wheel to protect the turbocharger. A secondary effect is reduced flow through the NOx Reduction System (NRS).

Clean air from the air cleaners is pulled through compressor housing air inlet (20) by the rotation of compressor wheel (22). The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more 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. The combustion of this additional fuel produces more exhaust gases. The additional exhaust gases cause the turbine and the compressor wheels of the turbocharger to turn faster. 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.

Bearings (23) and (25) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through oil inlet port (24). The oil then goes through passages in the center section to lubricate the bearings. Oil from the turbocharger goes out through oil outlet port (32) in the bottom of the center section. The oil then goes back to the engine lubrication system.

Balance Valve Solenoid Circuit



Illustration 4g02395837
(33) Balance valve actuator
(34) Line from the intake manifold
(35) Balance valve solenoid

The balance valve solenoid circuit is used to control the balance valve actuator (33) on the turbocharger. Line (34) directs the boost air from the intake manifold to the balance valve actuator. Balance valve solenoid (35) either prohibits or allows airflow to the balance valve actuator (33). Also, the engine ECM must send an electronic signal to the balance valve solenoid commanding the solenoid to permit airflow.



Illustration 5g02395958
Balance valve solenoid in closed position
(36) Path to balance valve actuator
(37) Vent
(38) Armature
(39) Path from the NRS mixer

The balance valve actuator is normally closed. The solenoid must be energized by the ECM to keep the balance valve actuator closed. The armature (38) in the balance valve solenoid is responsible for allowing or prohibiting the pressurizing of the entire balance valve system. The armature physically blocks the boost air from flowing to the balance valve actuator. The vent (37) is responsible for purging residual pressure from the balance valve system once the pressure is no longer needed. Without the vent, there would constantly be pressure on the balance valve actuator and not allow the actuator to close. When the charge air pressure supplied to the balance valve actuator exceeds a predetermined limit, the balance valve actuator will open. The actuator opening causes the turbocharger speed to decrease and protects the engine. Engine speed must be present for in order for the electrical current to command the balance valve solenoid to close. If the key is on but the engine is not running, the balance valve solenoid will remain open.



Illustration 6g02396096
Balance valve solenoid in open position
(36) Path to balance valve actuator
(39) Path from the NRS mixer

The balance valve solenoid is activated to the open position by the ECM when the conditions of the performance map are met. Typical engine conditions are when the pressure difference between the two turbine paths becomes greater than desired. These conditions can occur during engine powering or engine braking (if applicable). When the balance valve solenoid is open the armature blocks the vent passage, not allowing any leakage.

Valve System Components



Illustration 7g02396141
Valve system components
(40) Rocker arms
(41) Bridge
(42) Spring
(43) Pushrods
(44) Valves
(45) Lifter

The valve system components control the flow of inlet air into the cylinders during engine operation. The valve system components also control the flow of exhaust gases out of the cylinders during engine operation.

The crankshaft gear drives the camshaft gear through an idler gear. The camshaft must be timed to the crankshaft to get the correct relation between the piston movement and the valve movement.

The camshaft has two camshaft lobes for each cylinder. The lobes operate the inlet and exhaust valves. As the camshaft turns, lobes on the camshaft cause lifters (45) to move pushrods (43) up and down. Upward movement of the pushrods against rocker arms (40) results in downward movement (opening) of valves (44).

Each cylinder has two inlet valves and two exhaust valves. Valve springs (42) close the valves when the lifters move down.

Open Crankcase Ventilation System



Illustration 8g02396148
Typical crankcase ventilation system
(46) Crankcase ventilation filter
(47) Hose from the breather
(48) Filter housing
(49) Fumes disposal tube
(50) Oil drain tube
(51) Crankcase pressure sensor

The engine is equipped with an open crankcase ventilation system. Differential pressure sensor (51) monitors the level of crankcase pressure. Hose from the breather (47) contains passages that route crankcase pressure and atmospheric pressure to the sensor. Filter (46) filters the blowby before venting the blowby through fumes disposal tube (49). Oil is returned to the oil pan through oil drain tube (50).

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