Turbocharger Operation

How a Turbocharger Works The heat energy and pressure in the engine exhaust gas is utilized to drive the turbine wheel. The speed of the ro­tating assembly and output of the compressor wheel is controlled by the design and sizing of the turbine housing. The housing acts as a nozzle to direct the exhaust gas flow to the turbine wheel blades which, in turn, drive the compressor. Clean air from the air cleaner is drawn into the compressor housing and wheel where it is com­ pressed and delivered to the charged air cooler and then to the engine air intake manifold. The amount of air pressure rise and air volume delivered to the engine from the compressor outlet is determined by wheel size, housing size, and performance matching of the turbocharger to a given engine. Each engine size must be properly matched.

What a Turbocharger Does
There are a number of benefits to be gained by turbo­ charging a diesel engine because the turbocharger deliv­ers an abundance of compressed air to the engine. Com­bustion of the fuel is more complete, resulting in cleaner exhaust. The positive air pressure head (above atmo­spheric pressure) that is maintained in the engine intake manifold benefits the engine in several ways. During en­gine valve overlap (before intake stroke starts on four­ cycle engines), clean air is pushed across the combustion chamber, scavenging all remaining burning gases, cool­ing cylinder heads, pistons, valves and exhaust gas. The cleaner burning of the fuel plus the engine cooling which results help to extend engine life.

Many turbochargers are used primarily for what is called normalizing or altitude compensating of a naturally aspirated engine. By this we mean that an engine and turbo­ charger are matched to give only a mild boost of air pressure to improve combustion, reduce smoke, and give a moderate power increase with no increase in fuel deliv­ery.

It is possible to safely increase power output of some engines by as much as 40% to 50% with the correct selection and/or matching of a turbocharger. Care must be exercised to select exactly the right turbocharger and engine fuel settings, since the turbocharger has air delivery and pressure capabilities that could exceed engine tolerances. Failure to exercise proper care can result in engine overheating, excessive combustion chamber firing pressure and increased temperatures, which have detrimental effects on engine life. These conditions can cause deterioration of engine components, such as cracked heads, scored pistons and liners, blown head gaskets, damaged bearings, malfunctioning turbochar­ger, etc. Changing the engine fuel delivery schedule in the field on any turbocharged engine should only be made by following Detroit Diesel’s recommendation, and procedures.

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