5K32500TP Mercruiser STERNDRIVE, Bravo-II X Diesel (2.20:1)

Illustration 1 g06412421
Air inlet and exhaust system
(1) Aftercooler core
(2) Air filter
(3) Clean Emissions Module (CEM)
(4) Back pressure valve
(5) Low-pressure turbocharger
(6) High-pressure turbocharger
(7) Wastegate actuator
(8) Exhaust gas valve (NRS)
(9) Exhaust cooler (NRS)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
Exhaust cooler (NRS)
Exhaust gas valve (NRS)
Turbochargers
Aftercooler
Inlet manifold
Cylinder head, injectors, and glow plugs
Valves and valve system components
Piston and cylinder
Exhaust manifold
Clean Emissions Module (CEM)Air is drawn in through the air cleaner into the air inlet of the low-pressure turbocharger by the low-pressure turbocharger compressor wheel. The air is compressed to a pressure of about 75 kPa (11 psi) and heated to about 120° C (248° F). From the low-pressure turbocharger, the air passes to the high-pressure turbocharger. The air is compressed to a pressure of about 220 kPa (32 psi) and heated to about 240° C (464° F) before the air is forced to the aftercooler. 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 emissionFrom the aftercooler, the air flows to the inlet manifold. The air and exhaust gases are then mixed in the inlet manifold. Air flow from the inlet manifold to the cylinders is controlled by inlet valves. There are two inlet valves and two exhaust valves for each cylinder. The inlet valves open when the piston moves down on the intake stroke. When the inlet valves open, cooled compressed air from the inlet port is forced into the cylinder. The complete cycle consists of four strokes:
Inlet
Compression
Power
ExhaustOn the compression stroke, the piston moves back up the cylinder and the inlet valves close. The cool compressed air is then 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. The piston moving upwards initiates the exhaust stroke. The exhaust valves open. The exhaust gases are forced through the open exhaust valves into the exhaust manifold.The NOx Reduction System (NRS) operates with the transfer of the hot exhaust gas from the exhaust manifold to the exhaust gas valve (NRS), and exhaust cooler (NRS). The hot exhaust gas is cooled in the exhaust cooler (NRS). The exhaust gas valve (NRS) regulates the amount of exhaust gas that flows into the exhaust gas cooler (NRS).The reed valve that is located between the exhaust gas cooler (NRS) and the inlet manifold has one main function. The one main function is to prevent the reverse flow of charge air from the inlet side of the engine to the exhaust side of the engine.As the electronically controlled valve starts to open the flow of cooled exhaust gas from the exhaust cooler mixes with the air flow from the charge air aftercooler. The mixing of the cooled exhaust gas and the air flow from the charge air aftercooler reduces the oxygen content of the gas mixture. This results in a lower combustion temperature, so decreases the production of NOx.As the demand for more cooled exhaust gas increases the electronically controlled valve opens further. The further opening of the valve increases the flow of cooled exhaust gas from the exhaust cooler. As the demand for cooled exhaust gas decreases, the electronically controlled valve closes. This decreases the flow of cooled exhaust gas from the exhaust cooler.Exhaust gases from the exhaust manifold enter the inlet of the high-pressure turbocharger to turn the high-pressure turbocharger turbine wheel. The turbine wheel is connected to a shaft that rotates. The exhaust gases travel from the high-pressure turbocharger. The exhaust gases then travel through the duct on the turbine side into the turbine inlet of the low-pressure turbocharger to power the low-pressure turbocharger. The exhaust gases pass from the low-pressure turbocharger through the following components: exhaust outlet, back pressure valve, Clean Emissions Module, and exhaust pipe.Turbochargers
Illustration 2 g00302786
Typical example of a cross section of a turbocharger
(1) Air intake
(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 inletThe high-pressure turbocharger is mounted on the outlet of the exhaust manifold. The low-pressure turbocharger is mounted on the side of the cylinder block. The exhaust gas from the exhaust manifold enters the exhaust inlet (11) and passes through the turbine housing (7) of the turbocharger. Energy from the exhaust gas causes the turbine wheel (8) to rotate. The turbine wheel is connected by a shaft to the compressor wheel (3).As the turbine wheel rotates, the compressor wheel is rotated. This causes the intake air to be pressurized through the compressor housing (2) of the turbocharger.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, air is compressed to a higher pressure and more air is forced into the cylinders. The increased flow of air into the cylinders allows the fuel to be burnt with greater efficiency. This produces more power.The shaft that connects the turbine to the compressor wheel rotates in bearings (4) and (6). The bearings require oil under pressure for lubrication and cooling. The oil that flows to the lubricating oil inlet port (5) passes through the center of the turbocharger which retains