Engine induction and cooling Flashcards
What is a mixture ratio?
The composition of the fuel/air mixture
What is the perfect mixture for combustion?
15:1
What is a stoichiometric mixture?
A mix where all the fuel and all the oxygen in the air is completely used in the combustion process
What are the two types of induction systems on recip engines?
Naturally aspirated
Supercharged
What is a naturally aspirated engine?
An engine that uses atmospheric pressure to force fuel-air charge into the cylinder
What is a function of an air scoop?
Used to convert some ram air pressure into a pressure that forces air into the cylinders
What are three common types filters?
Metal mesh
Dry papers
Foam filters
Should foam filters be cleaned?
No they should be replaced
Is changing the type of filter a major alteration?
Yes and requires and STC
How is icing prevented in a float carburetor?
By passing induction air through a heat muff around the exhaust system
When is carb heat normally not used?
On the ground
What are two downsides to carb heat?
Loss of power
Possible detonation
What is the purpose of an alternate air system?
To bypass the filter when its clogged and is also non-filtered air
What is the function of an intake manifold?
To equalize the fuel-air mixture flow to each cylinder on the engine
What is manifold pressure?
The absolute pressure in the induction system which forces the air into the cylinders
The higher the manifold pressure, the greater?
Density of air pressure being taken into the cylinders
The amount fuel burnt by an engine is directly proportion to?
The amount of air consumed by the eninge
What is forced induction and why is it used?
The air is compressed using a compressor to increase airflow into the cylinders. The air pressure is lower at higher altitudes
What is volumetric efficiency?
The actual amount of air flowing through an engine compared to theoretical maximum
How does an naturally aspirated engine work?
It uses atmospheric pressure to force the mixture into the cylinders
What is MAP?
The pressure in the intake manifold
What is critical altitude?
Altitude above which a recip engine will no longer produce rated horsepower with its throttle wide open
What are the two types of superchargers?
Internal gear-driven superchargers
External exhaust gas-driven turbocharges
What are the three components of a supercharger?
Impeller
Diffuser
Manifold
What is a supercharger and how is it driven?
Uses a gear driven centrifugal compressor placed between the carb and the intake pipes.
It is driven by the crankshaft through gears
How does a turbo charger work?
It uses a small radial inflow turbine in the exhaust system to drive a centrifugal air compressor. Driven by the velocity of the exhaust gases.
What are the main components of a turbo?
Compressor assembly
Turbine wheel assembly
A full floating shaft bearing assembly
What is the function of lubrication oil in a turbo?
Lube the bearings
Transfer heat away from the turbocharger
How is the speed of a turbocharger controlled?
By controlling the amount of exhaust gases allowed to flow through the turbine.
How does a turbo divert exhaust gases to or around the turbo to control the boost?
By using a waste gate valve parallel with the turbine
When the wast gate is wide open what happens with the exhaust?
Gasses bypass the turbine and pass overboard providing little or no boost
What happens when the waste gate is fully closed?
all the gases are forced through the turbine to provide max boost
When a turbocharged engine is started what position is the waste gate valve in?
wide open
What is the upper deck pressure and what is it also referred to as?
The pressure in the intake manifold before the throttle valve.
Turbocharger discharge pressure
What is overboost?
A condition of excessive manifold pressure
What are the three common methods to control the amount of boos in a turbo?
Waste gate restrictor
Manually controlled waste gate valve
Automatically controlled wast gate
How do you prevent over boosting?
An upper deck pressure relief valve is used
How does Lycoming refer to a waste gate valve?
Exhaust bypass valve
What are the key control components to turbo control system?
Absolute pressure controller
Rate-of-change controller
Pressure ratio controller
How is a waste gate held opened and closed?
Held open by a spring
Closed by engine oil pressure
When can’t manifold pressure increased any further?
When it reaches the critical altitude
What is the function of the absolute pressure controller?
It slows down the compressor, so the upper deck pressure and the manifold pressure is regulated
What is the function of the rate of change controller?
Prevents inadvertent overboosting
What are the key components in a lycoming turbo system?
Density controller
Differential pressure controller
What is the function of the density controller?
Only controls the engine during full throttle operation
How do you prevent boostrapping?
A differential pressure controller
What is bootstraping?
A transient increase in engine power will cause the turbocharger to speed up which in turn causes the engine to produce more power.
Excessive heat in a recip engine could lead to?
Detonation
Loss of power
Excess wear
What are the two types of cooling systems?
Air
Liquid
What are the advantages of air cooled engines?
Simpler
Lighter
Less prone to failure
Cheaper to maintain
What are the key components on an air cooled engine?
Cooling fins
Engine cowling
Baffles
How do cooling fins work?
By increasing the exposed surface area for efficient cooling
What is the main purpose of an engine cowling?
Streamlines the airflow around the engine reducing the drag considerably
How does a pressure cooling system work?
Causes a pressure differential between the upper and lower compartments
In what position should cowl flaps be while on the ground any why?
Wide open for more cooling
Where is the highest temperature on a turbine engine?
At the turbine inlet
What is active clearance control on a turbine engine?
A stream of cold air is blown around the case to shrink the case to minimize tip losses
