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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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adjust the spring force to vary the boost pressure that will open the valve.<br />

Using a wastegate reduces overall fuel consumption efficiency because as the<br />

title implies, energy is ‘‘wasted’’ when exhaust gases bypass the turbine.<br />

There are several alternate wastegate designs. For example, a swinging<br />

arm-type valve can be used (Fig. 21). In smaller engine applications, the<br />

wastegate is integrated into the turbine housing, thus eliminating the need<br />

for external high-temperature exhaust-line joints that can lead to problems.<br />

The other class <strong>of</strong> boost control devices involves a variable-geometry<br />

turbine that effectively changes the A=R ratio and thus the turbine wheel<br />

speed and in turn the boost pressure. The simplest <strong>of</strong> these devices uses a<br />

turbine housing scroll with twin inlet passages, one <strong>of</strong> which can be closed<br />

Figure 21 Turbocharger fitted with swinging arm-type valve. Boost pressure<br />

sensed in the discharge outlet from the compressor is transmitted via the tubing to<br />

the diaphragm side <strong>of</strong> the control valve. When boost pressure exceeds the spring<br />

force, the shaft opens the swing valve so a portion <strong>of</strong> the exhaust gas bypasses the<br />

turbine.<br />

Copyright © 2003 Marcel Dekker, Inc.

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