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13-04-2010, 03:38 AM
my self zoheb abdul jaleel studying in b.tech mechanical final year my aim to give a seminar and presentation on turbo chargers in technical seminar and presentation which will be held in my ollege so i want 15 pages theory on turbo chargers.
please kindly help me and supprot me and send total thery about turbochargers.
zoheb abdul jaleel
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Joined: Apr 2010
15-04-2010, 09:56 PM
visit this thread for turbocharger:
Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
Joined: Apr 2012
27-09-2012, 12:12 PM
TURBOCHARGERS[.docx (Size: 748.9 KB / Downloads: 15)
Variable geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R Ratio) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. In many configurations, VGTs do not even require a wastegate, however this depends on whether the fully open position is sufficiently open to allow boost to be controlled to the desired level at all times. Some VGT implementations have been known to over-boost if a wastegate is not fitted.
A turbocharger is a turbine that is driven by exhaust gases that compresses incoming air into the engine. The “hot” side of the turbo receives its energy from the heat and flow energy of the exhaust system. The “cold” side of the turbocharger pressurizes fresh air and forces it into the engine. The pressure generated by the “cold” side is called the boost.The “cold” side is driven by a shaft that is connected to the “hot” side.
DRAWBACKS OF CONVENTIONAL TURBOCHARGERS
The main drawback to a turbocharger, besides cost, is its fixed geometry. The Aspect Ratio (A/R) of a turbo, which is based on its geometry, has a direct relation to both the power increase generated and the motor speed at which the power increase is generated. A smaller A/R will produce boost pressure at a lower engine speed, but will be unable to provide a high
enough flow rate at higher engine speeds. This leads to higher exhaust manifold pressures,
lower pumping efficiencies, and lower power output. A larger A/R will create boost at higher
engine speeds, and thus create more power, but it will be unable to produce boost at lower
engine speeds. So an A/R must be picked to either; produce power at lower engine speeds for
quicker acceleration, or for higher engine speeds to produce a greater total power.
CONCEPT OF LAG
The time it takes for the engine to produce boost between transients is called lag. A
large A/R turbo will have a longer lag time than a smaller A/R turbo due its larger requirement
of energy from the engine to produce boost.
VARIABLE GEOMETRY TURBOCHARGER (VGT)
Variable Geometry Turbochargers are turbochargers whose geometry and thus
effective A/R can be altered as needed while in use. The most common design includes several
adjustable vanes around a central turbine. As the angle of the vanes change, the angle of air
flow onto the turbine blades changes, which changes the effective area of the turbine, and thus
the aspect ratio (A/R) changes.
A Variable Turbine Geometry turbocharger is also known as avariable geometry turbocharger (VGT), or a Variable Nozzle Turbine (VNT). A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angle of the vanes vary throughout the engine RPM range to optimize turbine behavior.
In this cut-through diagram, you can see the direction of exhaust flow when the variable vanes are in an almost closed angle. The narrow passage of which the exhaust gas has to flow through accelerates the exhaust gas towards the turbine blades, making them spin faster. The angle of the vanes also directs the gas to hit the blades at the proper angle.
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