Chapter 3 - Turbine Engines Flashcards
What are the four types of Jet Propulsion?
Rocket
Ramjet
Pulsejet
Gas Turbine Engine
What are the four types of Gas Turbine Engines?
Turbojet
Turbopropeller
Turboshaft
Turbofan
With Turbojet engines, the difference in velocity between the air entering and the air exiting the engine produces what?
Thrust
What is EPR?
What is it dependent on?
Engine Pressure Ratio
An engine’s EPR is the ratio of the turbine discharge pressure to the engine inlet pressure. EPR gauge readings are an indication of the amount of thrust being produced for a given power lever setting. They are often used to verify power settings for takeoff, climb, and cruise.
EPR readings are affected by and are dependent on pressure altitude and outside air temperature (OAT).
Air entering an inlet duct and proceeds to the compressor, ignited with fuel at the combustor section, moves past the turbine section and exits the engine at a much higher velocity than when it entered is what type of engine?
Turbinejet Engine
A gas turbine engine that delivers power to a propeller is referred to as what?
Turbopropeller Engine
What is the biggest difference between a turbojet and a turboshaft engine?
With a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust.
The output of a turboprop or turboshaft engine is measured in ____ rather than thrust.
The output of a turboprop or turboshaft engine is measured in shaft horsepower rather than thrust.
Turbofans were developed to provide a compromise between the best features of what two engines?
Turbojet and turboprop
What is the difference between
Thrust ratio
Bypass ratio
Fan pressure ratio
Aspect Ratio
Thrust ratio - a comparison of the thrust produced by the fan to the thrust produced by the engines core exhaust
Bypass ratio - the ratio of incoming air that bypasses the core to the amount of air that passes through the engine’s core.
Fan pressure ratio - ratio of air pressure leaving the fan to the air pressure entering the fan
Aspect ratio - the ratio of a blade’s length to it’s width, or chord
What are the three classifications for bypass ratio and what is it determined by?
Low bypass (1:1)
Medium bypass (2:1 or 3:1)
High bypass (4:1 or greater)
Fan diameter determines a fan’s bypass ratio and thrust ratio
What are ducted fans?
The bypass air is ducted along the entire length of the engine. Full fan ducts reduce aerodynamic drag and noise emissions.
Weight savings in low aspect ratio blads have been achieved with what type of materials?
Hollow titanium blades with inner reinforcements made of composite materials.
Name the seven basic sections within every gas turbine engine.
Air inlet duct
Compressor section
Combustion section
Turbine section
Exhaust section
Accessory section
The air inlet to a turbine engine is designed to recover as much of the total pressure of the free airstream as possible and diliver it to the compressor. What is this known as?
Ram recovery
An air inlet that consists of a fixed geometry duct with a diameter that progressively increases from front to back is called what?
Divergent
The divergent shape works like a venturi; as the intake air spreads out, the velocity of the air decreases and the pressure increases
An air inlet that consists of a fixed geometry duct with a diameter that progressively decreases, then increases from front to back is called what?
Convergent-divergent
This shape is used to slow the incoming airflow to subsonic speed before it reaches the compressor.
Engines that use a _____direct high-pressure bleed air from the compressor to prevent formation of a low-pressure vortex that can pull debris into the engine.
Vortex dissipater
Name and explain the parts of this compressor
Centrifugal Flow Compressor
Impeller - Draws in air and accelerates it outward by centrifugal force.
Diffuser - The air becomes dispersed, velocity is decreased and its pressure is increased.
Compressor Manifold - Distributes the air in a smooth flow to the combustion section
Describe the Axial Flow Compresser’s two main elements.
Rotor - rows of blades fixed on a rotating spindle. The angle and airfoil contour of the blades force air rearward, much like a propeller
Stator vanes - arranged in fixed rows between the rows of the rotor blades and act as a diffuser
At each stage, air velocity decreases and pressure increases. Each consecutive row of rotor blades and stator vanes comprises a pressure stage.
In a basic axial flow compressor, the compressor and turbine are connected by a shaft and rotate as a single unit. If there is only one compressor unit, what would it commonly be called?
What if it has two or three compressors?
Single-spool compressor - For only one compressor
Dual-spool compressors - For two compressors.
- The front section of a dual-spool compressor is called the low pressure or N1 compressor.
- The second compresor is called the high-speed or N2 compressor.
Triple-spool compressor - For three compressors
- The compressor in the middle is called the intermediate or N2 compressor
What is a compressor stall?
An imbalance between two vector quantities: inlet velocity and compressor rotational speed. Compressor stalls occur when the compressor blade angle of attack exceeds the critical angle of attack. At this point, smooth airflow is interrupted creating turbulence and pressure fluctuations
Compressor air that is used for cabin pressurization, heating, and cooling is called____and it is supplied from the______.
Compressor bleed air
Bleed port
Name three types of compressor rotor blades root
Bulb
Fir tree
dovetail
The only way to overcome a compressor stall is to reduce the angle of attack on the rotor blades. This can be accomplished by ______ as well as stator vanes that change the direction of air contacting the rotor blades.
Variable inlet guides
What are the basic elements of a combustion section?
One or more combustion chamber
Fuel injection system
Fuel drain system
What is Newton’s 1st law of motion?
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
This is often called the Law of Inertia
What is Newton’s 2nd Law of Motion
The force is proportional to the product of mass times acceleration. Furthermore, the acceleration produced when a force acts on a mass is directly proportional to the force and is inversly proportional to the mass. This relationship is expressed by the formula:
F = M x A
F= force
M= mass
A= acceleration
What is Newton’s 3rd Law of Motion?
For every action there is an equal and opposite reaction.
What are the three main components of a centrifugal flow compressor?
Impeller - Draws in and accelerates the air
Diffuser - Divergence duct
Compressor manifold - Distributes the air in a smooth flow.
What is the purpose of swirl vanes?
They slow down air in a vortex motion and helps mix the air/fuel for better combustion.
Is the air inlet duct on a turbojet engine normally considered part of the airframe or the powerplant section?
Airframe Section
What is the difference between a subsonic and a supersonic inlet?
Subsonic inlet - divergent shape
Supersonic inlet - convergent-divergent shape
Name a few applications for compressor bleed air.
Where does it come from?
Bleed air is supplied by bleed ports anywhere along the compressor or along the difusser and can be used for:
- Cabin pressurization
- Air conditioning
- Deicing and anti-icing
- Pneumatic starting of the engine
What are the two basic types of compressors?
Centrifugal flow compressors
- Impeller
- Diffuser
- Compressor Manifold
Axial flow compressors
- Rotor
- Stator
What are the two types of flameouts?
Lean die-out
Usually occurs at high altitudes where low engine speeds and low fuel pressure form a waek flame that is extinguished in a normal airflow
Rich blowout
Typically occurs during rapid engine acceleration with an overly rich mixture, in which either the fuel temperature drops below the temperature necessary for combustion or there is insufficient airflow to support combustion.
Which section of a turbine engine forces air into the engine?
The compressor section
Which components make up the hot and cold sections of a turbine engine?
Hot section
- Combustors
- Turbine
- Exhaust
Cold Section
- Air inlet ducts
- Compressor
- Accessories
What is an APU?
Auxiliary Power Unit
Meets the demand for ground electrical and pneumatic power when the aircraft engine is not running.
Which ATA chapter covers APU?
Air Transport Association of America (ATA) Chapter 49 -
Auxillary Power Units
What two components does the APU engine need to start?
- Its own electric starter motor
- Aircraft battery power
With fuel supplied from one of the aircraft’s main fuel tanks, an APU can start up, provide electric power, heat or cool the cabin, and start the main engines without the need for a ground power source
What three main components are included in a high-energy capacitor discharge system?
- Exciter unit
- Two high-tension cables
- Two spark igniters
When year did the world’s first successful powered jet flight occur?
August 27, 1939
Heinkel He-178 Aircraft
What is the purpose of the turbine nozzle?
To collect the high-energy airflow from the combustors and direct the flow to strike the turbine rotor at the appropriate angle
It is located directly aft of the combustion section and immediately ahead of the turbine wheel.
What attachment is most common for the base of turbine blades?
Fir Tree
The loose fit of a fir tree base permits the base of a turbine blade to expand as it heats to operating temperatures.
What type of air inlet is used on helicopters?
Bellmouth Inlets
Bellmouth inlet ducts have convergent profile that is designed for obtaining high aerodynamic efficiency when in stationary or in slow flight.
What is a Vortex Dissipater?
A high-velocy stream of compressor bleed air blown from a nozzle onto the ground to prevent a vortex from forming and sucking in debris such as sand, stones, and water.
Which is the low speed and high speed compressor?
Low Speed Compressor - N1 Compressor
High Speed Compressor - N2 Compressor
Name the 3 sections.
What two common types of bearings are used to support the main compressor & turbine shaft?
What are the three common type of oil lubrication is used?
What is the main purpose of the bearings?
Two Common types of bearings:
- Ball
- Rotor
Three Common types of oil lubrication:
- Labyrinth seal
- Helical Seal
- Carbon Seal
Main purpose: Keeps shaft aligned
What are the different types of combustion chambers?
Muliple-Can Combustors (flame propagation tubing)
Annular Combustors (fuel nozzle at several locations)
Can-Annular (flame propagation tubing and most efficient)
What is a flame propagation tube?
Tubes that connect individual combustors to allow flames to travel through and ignite the air/fuel mixture.
What is the purpose of a turbine and what are the four main sections of a jet engine’s turbine?
A turbine transform a portion of the kinetic energy in the hot exhaust gases into mechanical energy to drive the compressor and accessories
Case -
- Encloses stator & rotor
Stator -
- Vanes that do not rotate
- Used to increase velocity and direct flow of air to rotor ar proper angle
- A.K.A - Turbine Nozzle
Shroud - Encloses the vanes (stator) and holds them in place
- Inner shroud
- Outter Shroud
Rotor
- Rotes from the exhaust gases
What are the three types of turbine blades?
Impulse - Produces minimum change in pressure or velocity
Reaction - Produces a turning force based on aerodynamic action. Acts like a wing on a plane.
Impulse-reaction - Impulse shaped at the base, reaction shaped at the tip for uniform pressure and velocity
What two types of cooling is used for turbine blades?
Convection cooling (film cooling) -
- bleed air is routed to the tip leading edge and trailing edge.
Transpiration cooling -
- bleed air is ducted into the vanes and exits through the porous material
What are the different sections of an exhaust assembly?
Cone Assembly - Attached to turbine case and further directs the exhaust gases in a streamline
Tailpipe (duct) - used to protect the fuselage from the exhaust gases, not always needed
Exhaust Nozzle - Final boost in velocity
What is the four stroke cycle of a reciprocating engine?
What is the name of this cycle?
Four-Stroke Otto Cycle
- Air/fuel Intake
- Compression
- Combustion
- Exhaust
What is a Brayton Cycle (constant pressure cycle) ?
Energy transformation for a gas turbine engine similar to a four-stroke Otto Cycle. The Brayton cycle has intake, compression, combustion, and exhaust that occur SIMULTANEOUSLY and CONTINUOUSLY.
What three factors effect thrust?
Temperature
Altitude
Airspeed
When the variables of Teperature, Airspeed, and Altitude (factors that effect thrust) is represented as a SINGLE variable is called?
Stagnation Density
What three primary factors determine the thermal efficiency of a gas turbine engine?
Turbine inlet temperature
Compression ratio
Compressor and turbine component efficiencies
What is the standard temperature and air pressure according to the ISA?
Internation Standard Atmosphere (ISA)
Temperature : 15 degrees C (59 degrees F)
Pressure : 29.92 in.Hg, or 14.69 psi, or 1013 millibars
What is a VIGV?
Variable Inlet Guide Vanes
- Automatically controlled by the fuel control unit
- Used to change the angle of attack of the stator vanes to prevent compressor stalls.
