Cap 7Piston Engine Power Augmentation

Question 1

Power output terminology

Answer 1

~Take off power : max power eng can produce
~rated power : power available at a particular RPM setting ,MAP or both. And can be used continuosly
~cruise power : a percentage of max power

Question 2

Altitude boosted

Answer 2

Altitude boosted supercharger is gonna increase the density as you climb and try to keep the same pressure as at mean sea level without using heavy ground booster

Question 3

Density altitude

Answer 3

Density altitude =Pressure altitude corrected to isa deviation

Question 4

Ground booster

Answer 4

Increases max power availble at sea level.require stronger structure and better cooling sys

Question 5

Two type superchager

Answer 5

~supechager : are poweres from the crankshaft ,upstream the carburettor

~turbochargers: (external superchagers) are powered by the exhaust gas stream ,ideally situeted to a fuel injected

Question 6

Intercooler

Answer 6

An intercooler is fitted at the induction manifold to cool the air from the turbo-charger
This will increase the charger air density through cooling
Through cooling of the charger air ,detonation within the cylinder will be prevented

Question 7

Advantages and disadvatanges of turbocharged (turbine)

Answer 7

Advantage
~ no power is take from the engine to drive the turbocharger
~the drive train is less complex and the whole system is lighter

Disatvantage
~ the exhaust driven turbine takes time to spool up as rpm increases
Can lead to slight lag in delivering the extra boost required

Question 8

Overboost valve

Answer 8

The speed of the turbine depends on the amount of the exhaust gas directed into its vanes.

A fixed valve in the exhaust flow bleeds excess pressure overboard:

Provides rudimentary protection against over boosting.
When the valve operates it triggers an overboost waning light in the cockpit

Question 9

Waste gate

Answer 9

When engine is off,the the waste gate is open,when is running idle the waste gate is closed (little exhaust gas so waste gaste moves to the fully closed),while take off the waste gate is partially open, and then it keeps closing while climbing until critical altitude where is fully closed.Above critical altitude the waste gate is fully closed ,the max value of MAP reduces.

~The waste gate provied rudimentary control of the turbo charger through of its speed

~Waste gate is fitted upstream but parallel to the turbo charger tubine inlet.

~The waste gate actuator is a single acting design fed with engine oil and controlled by a dual pressure control unit
~within the dual pressure control unit an aneroid capsule detects intake manifold pressure and regulates the position of the waste gate to balance speed and pressure

Question 10

Critical altitude

Answer 10

For a given power setting a point is eventually reached where the waste gate controller has completely closed the waste gate.
Above the critical altitude manifold pressure ,and thus engine power will reduce.

Back pressure occurs because all the exhaust now enters the turbine
~Reduced volumetric efficient
~engine power for a given a value of MAP will decrease

On an internal supercharger critical altitude is known as the full trottle height.( is the same as the critical altitude for external turbocharger turbine)

Question 11

Engine managemnet

Answer 11

The operation temp is much higher so oil and cylinder head temp must be monitored

Rated power is max power at which the engine can be operated continuously

Rated boost is the manifold pressure allowed at rated power

Question 12

Engine management

Answer 12

Rated alt its max alt at which max conitnous power can be mainted on superchager eng