Power Augmentation Flashcards
Rated power.
Power available at a particular rpm.
Cruise power.
% of maximum power.
Effect of density. Power-TAS graph.
As altitude increases, power available decreases for the same TAS.
Supercharging - Altitude boosted.
Superchargers pump compressed air into the cylinder to delay drop in power due to reduced density.
Needs a control system to prevent over boosting on the ground.
Supercharging - Ground boosted
Increase maximum power available at sea level.
Requires stronger engine structure and better cooling system.
Types of supercharging unit.
Superchargers (internal superchargers)
Turbochargers (external superchargers )
Superchargers.
Powered from the crankshaft; upstream of the carburettor.
Increase the intake manifold pressure of the engine. Higher pressure increases the mass of air drawn into the cylinders.
critical altitude is known as the full throttle height here.
Turbochargers.
Powered by the exhaust gas stream; ideally suited to a fuel injected engine.
Increases an internal combustion engine’s efficiency and power output by forcing extra air into the combustion chamber.
Intercooler.
Fitted at the induction manifold to cool the air from the turbocharger.
Will increased the charged airs density through cooling.
Detonation is prevented.
Turbocharged engines.
Very effective.
Control required to prevent over boosting.
Advantages and disadvantages of turbocharged engines.
No power lost from the engine.
Less complex and lighter.
Takes time to spool, lag.
Overboost valve.
Turbine speed depends on amount of exhaust gas directed into its vanes.
Fixed valve in exhaust is flow bleeds excess pressure overboard.
Triggers overboost light in the cockpit.
The waste gate.
Provides basic control of the turbocharger through control of its speed.
Fitted upstream and parallel to turbo charger turbine inlet.
It controls the flow of exhaust gases.
Critical alitutde.
For a given power setting a point is reached where the waste gate is completely closed.
Above critical altitude manifold pressure, engine power decreases.
Back pressure now occurs and reduce volumetric efficiency
Waste gate operation.
Engine start - waste gate held open by spring pressure
Idle power - waste gate fully opens.
Takeoff - waste gate is partially open.
Climb - waste gate closes as density decreases. Rpm increases.
Critical altitude - waste gate fully closed. Turbine at maximum speed.
Above critical altitude - waste gate fully closed. Maximum manifold absolute pressure decreases.
