plz read carefully
TURBOCHARGERS
A turbocharger is a way of utilizing the 'left-over' power of the hot exhaust gases busily escaping into the atmosphere. These gases are routed to a turbine (like a water-wheel) which is spun rapidly (up to 100,000 RPM) by them. The turbine is mechanically connected to an impeller via an axle, this impeller compresses the induction air.
The exhaust gases and induction air remain separate, they never touch each other!
The amount of exhaust gas that reaches the turbine is controlled by the waste gate. There are three basic types of waste gate control: manual, fixed and automatic. A manual waste gate is opened and closed by the pilot. You should be able to explain the main drawbacks to this type. A fixed waste gate is simply that, it doesn't move! Why is this inefficient? With regard to the automatic wastegate, there are two systems. Can you name them and describe their differences?
The impeller blades impart a high velocity to the induction air as it is 'flung' outwards (centrifugally) toward the diffuser vanes. The diffuser vanes direct the airflow and converts the high velocity to high pressure. Compressing air heats it, which can rob an engine of power and lead to detonation, so many turbocharger systems use an 'intercooler', a device similar to a car's radiator to cool the compressed air. The hot air flows through tubes in the intercooler whilst fresh outside air flows around these tubes and cools the compressed air. The intercooler may have shutters which open and close to control the amount of air that passes around the intercooler tubes.
When the wastegate is open, a turbocharged engine behaves much the same way as a normally aspirated engine. However, when the wastegate is closed the turbocharged engine behaves differently, in many respects, than the unblown engine. For the most part, this is above 14,000 MSL, although some wastegate systems are closed even below 10,000MSL. In an automatic-controller system, it is very often the case that when the pilot throttles back from climb power to cruise power manifold pressure, levelling off at an altitude below the airplane's stated critical altitude, the turbo wastegates(s) having been partway open during the climb, to prevent overboosting will close all the way as the throttle is reduced for cruise. The altitude at which the wastegate fully closes is thus dependent on throttle setting. At full throttle, the point of wastegate closure defines the airplane's critical altitude. Part-throttle critical altitude is a different matter. If you are ever in doubt as to whether your wastegate has closed all the way, momentarily reduce prop rpm and observe what happens to manifold pressure. If manifold pressure tends to remain constant, the wastegate was not closed before; if instead it drops off with rpm, the wastegate was and is closed.
When the wastegate is closed and all exhaust must pass through the turbocharger on its way out of the engine, a closed feedback loop is formed, such that any increase in fuel or air flow through the engine tends to increase the turbocharger's output, further increasing manifold pressure and flow, adding to turbine speed, etc. Conversely, a decrease in mass flow through the engine causes the turbine to slow down, with the result that turbocharger out put falls off, further reducing flow through the engine, At low altitudes, these bootstrap effects are not as apparent, because much of the exhaust flow is diverted around the turbocharger, and in an automatic-controller system the controller itself (usually nothing more than an aneroid bellows sensing upper deck pressure, and controlling oil flow to the wastegate by means of a poppet valve) functions like a household thermostat to maintain the manifold pressure where the pilot selects it. Above the critical altitude, the controller is effectively taken out of the loop. Considerable potential for manifold pressure fluctuations exists once the turbocharged aircraft has reached high-altitude cruise. What does this mean? Glad you asked! First of all, it means that the MAP/RPM interaction that exists for normally aspirated planes will also exist for turbocharged planes at low altitudes-but when the turbocharged plane has arrived at a high enough altitude to bring about wastegate closure, the MAP/RPM effect will reverse polarity. In other words, when the wastegate is closed, a decrease in rpm will result in a decrease in manifold pressure, while an increase in rpm will cause an increase in MAP. The fact that fuel flow is also part of the turbocharger feedback loop means that changes in fuel flow can have a noticeable effect on manifold pressure. When the mixture is leaned, for instance, fuel flow decreases significantly. This in turn reduces the mass flow through the turbocharger, reducing turbine speed and diminishing compressor output, with a corresponding loss in manifold pressure. Ram air effects are also important. Changes in airspeed can affect air pressure at the engine air-inlet scoop, causing manifold-pressure excursions downstream. If the turbo is operating at a pressure ratio of 2.5-to-1, then a one-inch ram pressure change at the intake air scoop is converted to a two-and-a-half inch change in pressure inside the upper deck. If the throttle is open all the way, manifold pressure will increase 2.5 inches, accordingly. Thus, a very small increase in airspeed can easily translate into a one-or-two-inch manifold pressure change. This effect is very noticeable during the initial level-off period, as airspeed builds, and also during the initial phase of let-down if the airspeed is increased or decreased. Obviously, this must be compensated for by the pilot. The net result of all this is that setting a turbocharged engine up for high-altitude cruise can be a time consuming process, involving as many as five or six iterations of the throttling process to get MAP/RPM and fuel flow set exactly where the pilot wants them.
While the actual climb capability of an aircraft in terms of feet-per-minute is not greatly improved by turbocharging when considered at sea level, the great advantage is that the climb rate can be continued at that rate for the majority of the climb to cruising altitude.
Supercharger
A supercharger is a special air pump whose primary function is to compress the incoming charge so that more weight of air may be handled by the fixed volume of the cylinders, since horsepower output is directly related to weight rather than volume of air. The conventional supercharger is a centrifugal air compressor placed between the carburetor and the air intake pipes. On radial engines, the supercharger is usually housed between the engine power section and the accessory rear section. The principal components of a supercharger consist of three units: the impeller, the diffuser, and the collector or manifold housing.