07. Piston Engine Power Augmentation Flashcards
Normal aspirated engine
The charge mass that can enter the cylinder is dependant on what 2 things regarding air within the inlet manifold
- DENSITY
- PRESSURE
Pg 165
Density varies with which 3 things
- Temperature
- Altitude
- Humidity
Pg 166
Density varies with ____, ____, and ____, so the best means to determine engine power is by what
- TEMPERATURE
- ALTITUDE
- HUMIDTY
- DENSITY ALTITUDE
DA = PA + ((Actual Temp - ISA temp) x 118)
Pg 166
What is the density altitude formula
Density altitude = Pressure altitude + (Diff. between actual & ISA Temp x 118)
DA = PA + ((Actual - ISA) x 118)
EXAMPLE:
An aircraft plans to take off from an airfield at an altitude of 4000ft.
The OAT is 21℃.
The ISA temp for 4000 ft should be 7℃
ISA temp = 15 - (alt x 2) ⋉ 15 - (4 x 2) ⋉ 15 - 8 = 7℃
21 - 7 = 14
4000 + (14 x 118) ⋉ 4000 + 1652 = 5,652 ft
This means the max power produced by the engine at this airfield on this day is equivilant to an engine operating at almost 5,700 ft
Pg 166
Engines produce the most power when they are HOT & HIGH or when they are LOW & COLD
LOW and COLD
Idea would be winter sea level conditions when air is cold, dry, and dense
Pg 166
Complete the following graph that shows a Normally Aspirated Engine Performance
LINK HERE
- Performance available - Sea Level
- Performance available - Altitude
- TAS
- Power
Pg 167
Piston Engine Power & Performance
When considering power output, the efficiency of which component of the engine must be taken into account
PROPELLER
Pg 167
At high atmospheric densities, the engine produces more power and needs MORE or LESS power to turn the propeller
MORE
Pg 167
Propeller efficiency varies significantly with ____ as well as density
AIRSPEED
Pg 167
What are the 3 operational descriptions of power output
- Take-off
- Rated
- Cruise
- Take-off - is the max power the engine can produce
- Rated - Power available under specific conditions
- Cruise - Expressed normally as a percentage of max power
Pg 168
Normally aspirated engines mass of charge entering the cylinder will INCREASE or DECREASE with increasing density altitude
DECREASE
Read “increasing density altitude” as increase in altitude and not as density increasing.
Density increasing means thicker, denser air, where as altitude increasing means a decreasing density.
Remember - Density Altitude is just a point in the sky (altitude) at which the aircraft is at
Pg 169
By ____ ft, a normally aspirated engine will have lost ____% of its power
- 20,000 ft
- 50%
Pg 169
Supercharging
What type of system helps maintain normal power output during the climb
COMPRESSOR SYSTEM
Altitude boosted supercharger
Pg 169
Supercharging
A compressor system that helps maintain normal power output during the climb is known as what
ATLTITUDE BOOSTED SUPERCHARGER
Pg 169
What are the 2 types of supercharging devices
- Supercharger
- Turbocharger
Pg 169
A superchargers compressor is driven by what
BELT from the CRANKSHAFT
Pg 169
A turbochargers compressor is driven by what
EXHAUST GAS
Pg 169
What does MAP stand for
MANIFOLD ABSOLUTE PRESSURE
(MAP)
MAP guage is a gauge that measures the manifold absolute pressure
Pg 170
What does a MAP GAUGE measure
AIR PRESSURE in INLET MANIFOLD
Gauge measures the pressure of the air being supplied by turbocharger into the inlet manifold
Pg 170
What is the difference in terms of measurements between a boost gauge and a manifold absolute pressure gauge (MAP)
BOOST - measures pressure relative to standard sea level
BOOST - can be negative or positive
MAP - pressure displayed as an absolute pressure
Pg 170
If the MAP and boost gauges indicate atmosopheric pressure whens stopped on the ground, what is this known as
STATIC BOOST
Pg 170
Static boost is a term used to describe what
Engine stopped on the ground
MAP and BOOST gauges indicate atmospheric pressure
Pg 170
What does a turbocharger unit comprise of
TURBINE linked to IMPELLER
Pg 172
What drives the turbine in a turbocharger engine
EXHAUST GAS
Exhaust gas drives the turbine, which then drives the impeller
Pg 172
How does an impeller in a turbocharger engine impart energy to the air.
ACCELERATES AIR to CIRCUMFERENCE
Pg 172
Impeller vanes are designed to CONVERGE or DIVERGE air
DIVERGE
Pg 173
As air diverges to the impeller circumference, the air increases in what 3 things
- Velocity
- Pressure
- Temperature
Pg 173
What is the name of the component which trades velocity for a further increase in pressure and temperature in a turbochargerd engine
DIFFUSER
Pg 173
How does a diffuser function in a turbocharger engine
Trades VELOCITY for increase in PRESSURE & TEMPERATURE
Usually formed by an expanding duct
Pg 173
Some turbochargers use what to cool air before entering the cylinder
INTERCOOLERS
Pg 173
What are 2 key advantages of a turbocharger
- NO ENGINE POWER
- RPM BOOST
Engine Power - No power is taken from the engine to drive the turbocharger
As RPM increases, velocity of exhaust gas increases, which increases the impeller speed, thus icnreasing the amount of boost
Pg 173
What is 1 key disadvantage of a turbocharger
SPOOL TIME
Turbo lag
Turbine is driven by exhaust gases. When RPM increased, it takes a finite amount of time to spool up the turbocharger
Pg 173
What is turbo lag
LAG in BOOST DELIVERED
Turbine is driven by exhaust gases. When RPM increased, it takes a finite amount of time to spool up the turbocharger
Pg 173
If the amount of exhaust gas output is not controlled to drive the turbine, what can this lead to
OVER BOOSTING
Excessive mass of charge is pumped into the cylinders
Pg 175
A sophisticated method of boost control is what
WASTE GATE SYSTEM
Pg 176
What happens to the exhaust gases when the waste gate system is open and when it is closed
OPEN - Exhaust gases go to atmosphere
CLOSED - Exhaust gases to go turbine
Pg 176
The waste gate system is fitted PARALLEL or IN SERIES to the turbocharger.
The waste gate system is fitted UPSTREAM or DOWNSTREAM to the turbocharger
- PARALLEL
- UPSTREAM
Pg 176
What is the name of the component that constantly controls and maintains the right amount of boost to the turbocharger
WASTE GATE CONTROLLER
Pg 177
What does the waste gate controller do
MAINTAINS and CONTROLS BOOST
Maintains the right amount of boost across a range of ambient conditions
Pg 177
As altitude increases and air density decreases, the waste gate controller will OPEN or CLOSE
CLOSE
Closes to try and maintain the optimum level of boost delivered to the cylinders
Pg 177
What is the term given to the point where the waste gate controller has completely closed
CRITICAL ALTITUDE
Pg 177
At critical altitude what will happen to MAP pressure and engine power
REDUCES
Pg 177
On a supercharger engine, the equivilant of critical altitude is known as what
FULL THROTTLE HEIGHT
Pg 177
What is a disadvantage of reaching critical altitude in terms of exhaust gases
BACK PRESSURE
VOLUMETRIC EFFICIENCY
Volumetric efficienty in the cylinder due to back pressure
All exhaust gas is directed towards the turbine, which causes back pressure
THis means some exhaust lags, this remaining in the cylinder, reducing the volumetric efficiency
Pg 177
What is the waste gate position for each of the following stages of flight, and any other significant considerations;
- Engine start
- Idle Power
- Take off
- Climb
- Critical Altitude
- Above critical altitude
- HELD OPEN - spring pressure
- FULLY CLOSED - MAP pressure low as little exhaust gas
- PARTIALLY OPEN
- CLOSED - Turbine RPM increases
- FULLY CLOSED - Turbine at max speed
- FULLY CLOSED - Max value of MAP reduces
Pg 178
In a supercharger system how does the intercooler cool the air entering the engine
COLD RAM AIR
Ducted from atmosphere and passed over induction manifold
Pg 179
What is rated power
MAX POWER at which engine can be operated CONTINUOUSLY
Pg 180
What is rated boost
MANIFOLD PRESSURE allowed for RATED POWER
Pg 180
Supercharger
If an aircraft climbs at rated boost to the full throttle height, it is said to have reached what
RATED ALTITUDE
Rated altitude is the maximum altitude at which maximum continous power can be maintained on a supercharged engine
Pg 180
What is a supercharged engine at significant risk from with rapid throttle movements
THERMAL SHOCK
Pg 180
