Flow diagram of the air inlet and exhaust system
(3) Air inlet
The components of the air inlet and exhaust system control the quality of air and the amount of air that is available for combustion.
Naturally aspirated engines pull outside air through air inlet (3) of an air cleaner directly into the inlet manifold. The air flows through the inlet manifold which directs an even distribution of the air to each engine cylinder. The air is pulled into the engine cylinder during the intake stroke of the piston. Fuel is mixed with the air in the engine cylinders during the compression stroke. After the fuel combustion occurs in the engine cylinder, the exhaust gases flow directly to the outside air through exhaust (2) .
Turbocharged engines pull outside air through air inlet (3) of an air cleaner into the air inlet of turbocharger (1). The suction is caused by the turbocharger compressor wheel. Then, the turbocharger compressor wheel compresses the air. The air flows through the inlet manifold which directs an even distribution of the air to each engine cylinder. The air is pulled into the engine cylinder during the intake stroke of the piston. Fuel is mixed with the air in the engine cylinders during the compression stroke. After the fuel combustion occurs in the engine cylinder, the exhaust gases flow to the exhaust manifold. The exhaust gases from the exhaust manifold enter the turbine side of the turbocharger in order to turn the turbocharger turbine wheel. The turbine wheel is connected to the same shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through the exhaust outlet and to exhaust (2) .
Each piston makes four strokes for one complete cycle in two revolutions of the crankshaft.
During the intake stroke, the piston moves down and air is drawn into the cylinder through the open inlet valve.
During the compression stroke, the valves are closed and the piston moves up in the cylinder in order to compress the air. As the air is compressed, the temperature increases. As the piston nears the top of the stroke, fuel is injected into the combustion chamber on top of the piston. The fuel mixes with the hot compressed air in order to cause combustion.
During the power stroke, the valves are closed as the forces from combustion push the piston and connecting rod down turning the crankshaft.
During the exhaust stroke, the inertial force of the turning flywheel helps continue the rotation of the crankshaft in order to push up the piston in the cylinder. This action forces the burned gases out of the exhaust valve. This completes the four strokes of the piston.
Turbocharger (if equipped)
Components of a turbocharger (typical example)
(1) Air inlet
(2) Compressor housing
(3) Compressor wheel
(5) Oil inlet port
(7) Turbine housing
(8) Turbine wheel
(9) Exhaust outlet
(10) Oil outlet port
(11) Exhaust inlet
The turbocharger is mounted on the exhaust manifold. All the exhaust gases from the engine go through the turbocharger. The exhaust gases enter turbine housing (7) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (8). The turbine wheel is connected by a shaft to compressor wheel (3) .
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 (4) and (6) for the turbocharger use engine oil under pressure for lubrication and cooling. The oil comes in through oil inlet port (5). The oil then goes through passages in the center section in order to lubricate the bearings. This oil also cools the bearings. Oil from the turbocharger passes through oil outlet port (10) in the bottom of the center section. The oil then returns to the engine oil pan.
Valve System Components
Valve system components
(1) Rocker arm
(2) Valve spring
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 upper idler gear. The camshaft must be timed to the crankshaft in order to get the correct relationship 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. Each cylinder has one inlet valve and one exhaust valve. As the camshaft rotates, the lobes cause lifter (5) to move pushrod (3) up and down. Upward movement of the pushrod against rocker arm (1) results in downward movement (opening) of valve (4). Valve spring (2) closes the valves when the lifters move down.