Turbochargers Flashcards
How does a turbocharger work
Use excess speeds and pressure of the exhaust gases to spin a turbine which directly spins a compressor which compresses the fresh intake air ready for entry to cylinder.
Use excess energy leftover in exhaust gasses we would not otherwise use
Altitude Boosting (Turbocharger)
Compress air into cylinder to delay the drop in power due to the increase in density altitude
Ground Boosted Supercharger
Increase the overall power at sea level rather than maintain it
Engine will need to be strengthen to withstand + cooling system
Manifold Absolute Pressure Gauge Displays what?
Displays absolute pressure in the manifold measure in Inches of mercury
Should always be positive
MAP indication is lower at takeoff than on the ground why?
At take off power engine will not get back to the static pressure value
Turbocharger is comprised of
Turbine linked to impeller by shaft - lubricated by engine oil
Driven by exhaust gases
Turbine rotates at very high speed
Connected by shaft to compressor which compresses the incoming air into the manifold
Centrifugal compressor with a diffuser raises the pressure
Critical Altitude
Waste gate is completely closed yet MAP is decreasing - power no longer sufficient for density altitude
Density Controller
Prevents exceeding upper limit of manifold air pressure below critical altitude at full throttle
Waste Gate System
At the exhaust end
Controls speed of turbocharger by directing the amount of outlet gas to the turbine
Waste Gate system in the climb
Will close as air density decreases to increase turbine rpm
Exhaust back pressure increases
Reducing volumetric efficiency
Engine power for a given value of MAP will decrease
Waste Gate position on engine start + idle power + TO
Engine Start - fully open due to spring pressure
Idle power - little exhaust gas so moves to fully closed position
Take off - almost fully open for leeway in QNH increases
Rated Power
Max power which engine can be operated continuously
Rated Boost
The manifold pressure allowed at rated power
Rated altitude
Max altitude continuous power can be maintained on turbocharged engine
Supercharger
Forced induction device utilising the engine to produce more power
Mechanical direct connection to the engine
Less efficient by more responsive than turbocharger
How do you increase the critical altitude
By climbing at a higher MAP
Set a lower MAP therefore on climb wastegate can close a bit more
Where is the inter cooler on a turbocharged engine
After the compressor and is installed to restore density
Air in piston engine turbocharger enter the centrifugal compressor
At the eye of the impeller and leave it almost at a tangent to the periphery
Best conditions for highest engine power
Cold and dry air at high pressure
Increased density and provide best efficiency and power
Exhaust back pressure
Turbochargers lose slight amount of power due to restriction of exhaust gases from engine when wastegate closed.
Exhaust back pressure reduces with
Altitude in normal aspirated or supercharged engine
Two types of compressors are
Axial flow
Centrifugal compressor
Centrifugal compressor composed of
An impeller
A diffuser
A casing
How centrifugal compressor works
Impeller rotates as air enter the eye of impeller
Picked up by rotating vanes and propelled outwards by centrifugal forces
Diffuser vanes on the outside trade airs kinetic energy for pressure energy
Maintain a constant MAP in climb the power output will…
Increase
Reduce in exhaust back pressure more fuel and air mix into the cylinder
Full throttle heigh
Critical altitude in a supercharged engine
Role of the intercooler in turbocharger
Fitted at induction manifold of turbocharger. Cold ram air ducted from atmosphere after compressor
How do you reach rated altitude
Climbing at rated boost and rated rpm
Rated Boost
Manifold pressure allowed at rated power
Rated Altitude is
Max altitude at which max continuous power can be maintained on supercharged engine
Operation of a turbocharged variable pitch propeller A/C
Rev up Throttle back - increasing power
Reduce throttle first then RPM for reducing power
Purpose of intercooler in turbocharger
Minimise risk of detonation - placed between the supercharger and the inlet valve
Exhaust back pressure is
Back pressure from restrictive flow when wastegate is closed meaning exhaust gases are not removed effectively meaning a small amount of power loss in turbochargers
Exhaust back pressure on a normal/supercharged engine reduces with altitude
