Functions of the turbocharger

Internal combustion engines ignite air and fuel to produce energy that is

converted to power. The waste created by the combustion is expelled.

Compressors in the charging systems increase output by compressing the air used for combustion. There are three basic types of compressors, exhaust gas turbochargers, mechanically driven superchargers and pressure wave superchargers.1 The latter two compress air using power supplied by the crankshaft, while the turbocharger is powered by the exhaust gas. A turbocharger (Fig. 11.1) gives a small engine the same horsepower as a much larger engine and makes larger engines more powerful, increasing power output by as much as 40%.2 Turbocharging was rapidly adopted for commercial diesel applications after the first oil crisis in 1973.3 Stringent emission regulations mean that today, virtually every truck engine is turbocharged.

Turbocharged petrol engines for cars came into fashion because of their power, but their role in reducing emissions is now recognized. The introduction of a turbocharged diesel car in 1978 was the breakthrough for turbocharging in engines. Subsequent improvements in diesel engines for cars have increased efficiency, improved drivability to match that of petrol engines and reduced emissions.

The turbocharger is basically an air pump. It makes the air/fuel mixture more combustible by introducing more air into the engine’s chamber which, in turn, creates more power and torque. It accomplishes this task by condensing or compressing the air molecules, increasing the density of the air drawn in by the engine.

Hot exhaust gases leaving the engine are routed directly to the turbine wheel to make it rotate. The turbine wheel drives the compressor wheel via the shaft. The typical turbocharger rotates at speeds of 200,000 rpm or more.

The rotation of the compressor wheel pulls in ambient air and compresses it before pumping it into the engine’s chambers. The compressed air leaving the compressor wheel housing is very hot, as a result of both compression and friction. The charge-air cooler reduces the temperature of the compressed air so that it is denser when it enters the chamber. It also helps to keep the temperature down in the combustion chamber.

The most recent turbochargers adjust the cross-section at the inlet of the turbine wheel in order to optimize turbine power according to load, a system known as variable geometry. The advantages of the turbocharger include a high power-to-weight ratio, so engines are more compact and lighter, a high torque at low engine speeds, which results in quieter engines, and superiorperformance at high altitudes. Currently, the primary reason for turbocharging is the use of exhaust gas energy to reduce fuel consumption and emissions.

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The science and technology of materials in automotive engines

Hiroshi Yamagata

Woodhead Publishing and Maney Publishing

on behalf of

The Institute of Materials, Minerals & Mining

CRC Press

Boca Raton Boston New York Washington, DC

WOODHEAD PUBLISHING LIMITED

Cambridge England

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