Engine Performance: System: Turbocharger: Operation
Exhaust gases leaving the cylinders flow through exhaust manifold directly into turbocharger turbine housing. Force of gases turns turbine wheel, which in turn spins compressor wheel at same speed. Turbine and compressor wheel speeds can reach up to 100,000 RPM. See Fig 1 and Fig 2 .
Fresh air drawn in by compressor wheel is compressed and delivered to combustion chamber. When engine is idling, the engine operates like a normal aspirated engine.
With increased speeds and higher RPM, exhaust gases are expelled with increasing velocity. This causes turbine wheel to turn faster, increasing boost pressure at compressor wheel.
Boost pressure is routed to intake manifold and to individual cylinders, completing the cycle. The aneroid compensator on top of fuel injection pump automatically adjusts fuel quantity injected into cylinders depending upon boost pressure, or atmospheric pressure in intake manifold. Correct air-fuel relationship is maintained at all times.
Should wastegate fail, a pressure switch installed in intake manifold closes an electrical circuit, energizing a switch-over valve. This valve closes pressure line to intake manifold and simultaneously opens aneroid compensator to atmosphere. This reduces fuel quantity being injected.
Pressure switch only functions when intake manifold boost pressure reaches 16 psi (1.1 kg/cm2 ). When pressure drops below this figure, pressure switch opens electrical circuit and venting of pressure line is stopped.