Реферат: Forced Air Induction Essay Research Paper The

Forced Air Induction Essay, Research Paper

The Garret Aviation VNT-25 The idea of forced air induction by turbine, or

turbo, is not new and has it’s mass production roots in WWII fighter planes.

What is new, however, is its application to passenger automobiles. Unlike a near

constant high RPM fighter engine, an automobile requires wide-open throttle (WOT)

power availability throughout its entire operating range. Previous automotive

turbo applications acted like an on-off power switch with a five second delay,

decreasing drivability, rather than providing the smooth linear powerband of a

normally aspirated engine. Because the turbine is in a fixed position in the

exhaust stream, it was plagued with sometimes uncontrolled production from the

compressor at high engine speeds, commonly referred to as boost creep, and a

significant decrease fuel economy versus a similar, but naturally aspirated

engine. The Garret Aviation produced VNT-25 solved all of these problems with

its innovative Variable Nozzle Turbine. Hands down it is the most advanced turbo

ever mass-produced and it was the first of its kind on production cars. One of

the most talked about problems with turbo charged engines is the lengthy time it

takes for the turbo itself to accelerate to operational speeds. This is commonly

referred to as turbo lag or turbo spool up time. Under WOT, turbo lag results in

a seemingly underpowered engine that suddenly comes to life as a delayed tire

melting rush of acceleration. Previously, turbo lag was limited by decreasing

the size of the turbo itself. This resulted in lower rotating mass and more

importantly, a smaller cross sectional area, which accelerated exhaust gasses at

lower engine speeds. Although the turbo is able to spool quicker due to its

size, for the same reason its ability to move and compress large amounts of air

efficiently is significantly reduced. Inherently a smaller turbo will produce

less maximum horsepower than if it were replaced by larger turbo on the same

engine. Previous turbochargers also used a fixed position turbine that powered

the centrifugal compressor directly. Because the turbine is located directly in

the exhaust stream, the turbine is a huge exhaust restriction. This restriction

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