Turbocharger - Diesel: Operation

At idle and light throttle, the Turbo engine operates like any other diesel engine. When more power is required, the usually wasted exhaust gases from the exhaust manifold enter the turbocharger's turbine housing and flow through the turbine blades.

Exhaust flow and turbine speed increase, as engine RPM increases. The impeller turns with the turbine and forces air into the compressor housing and intake manifold. The faster the impeller and turbine spin, the more pressurized air is provided for the engine.

If boost pressure went too high, engine damage would result. The wastegate opens when exhaust pressure exceeds a predetermined limit and allows exhaust gases to by-pass the compressor. A drain pipe is connected from the wastegate diaphragm housing to the impeller housing. This is to prevent a build up of oil or blowby from the crankcase ventilation system.

A boost pressure safety valve (blow-off valve) is used for protection in case the wastegate fails. The blow-off valve is connected to the intake manifold, and opens whenever boost pressure exceeds 11.7 psi (.8 kg/cm² ). The excess boost pressure is vented to the intake pipe after the air cleaner. Some vehicles are equipped with a warning lamp which is connected to the blow-off valve. The warning lamp will light, whenever the blow-off valve operates.

Since the turbocharger supplies more air to the engine, a boost pressure enrichment device is needed to increase the amount of fuel delivered to the engine. At part throttle when boost pressure is low, no enrichment is necessary. As boost pressure increases the engines fuel requirements also increase.