Gas Turbine Engine - Midterms

combustion chamber or combustor

must contain the burning mixture of air, and fuel, in order to generate the maximum heat release, at a substantially constant pressure, so the turbine receives a uniformly expanded, heated, and accelerated stream of gas

primary zone

a region of lower velocity recirculation immediately downstream of the fuel spray nozzle

primary zone

stable combustion is achieved within this zone

primary air

about 20% of the total airflow exiting the high pressure compressor

primary air

this air is mixed, in a ratio of approximately 15:1 by weight, with the fuel, and burnt

secondary air

reacts with the primary air, which is flowing through the swirl vanes to form a toroidal vortex

secondary air

20% of the remaining air is allowed into the flame tube through the secondary air holes

toroidal vortex

secondary air reacts with the primary air, which if flowing through the swirl vanes to form a _____

tertiary air

the remaining 60% of the air leaving the HP compressor

tertiary air

fed into the flame tube through corrugated joint sand dilution air holes in the flame tube

tertiary air

used to cool both the air casing and the gas exiting the chamber

inter-connector

it passes the starting flame between the combustion chambers

sealing ring

_____ at the turbine end of the combustion chamber allows for elongation of the chamber due to expansion

sealing ring

allows the chamber to expand into the nozzle box, which is the portion of the engine immediately preceding the nozzle guide vanes while maintaining a gas tight seal

multiple combustion chamber system

tubo-annular system

annular combustion chamber system

types of combustion system

centrifugal compressor

the straight through flow multiple combustion chamber system was supplied with air by a _____

multiple combustion chamber system

this was later used on some earlier types of axial flow engine, and is still in use on centrifugal compressor engines, such as the Rolls Royce Dart

multiple combustion chamber system

consists of a number of the individual combustion chambers, which each consist of flame tube, which has its own air casing

snout

this is the primary air scoop in a multiple combustion chamber system

interconnectors

this allow the passage of the starting flame

drain tubes

allow the drainage of excess fuel from the combustion chambers in the unlikely event of the engine failing to start

torching

a very dangerous jet of flame from the rear of the engine

blowout cycle

any remaining traces of fuel within the engine must be evaporated by motoring the engine over on a _____

blowout cycle

this is when the engine is rotated for the time normally allocated to a full start cycle, but with the HP fuel cock shut, and the ignition system deselected

tubo-annular combustion chamber system

sometimes also called the cannular or can-annular system

tubo-annular system

does not have individual air casings for each of the flame tubes

tubo-annular system

a number of flame tubes are fitted within an inner and outer air casing, which makes the system a more compact unit

annular combustion chamber system

has only one flame tube, which is contained by an inner and outer casing

annular combustion chamber system

have a shorter length with the same diameter for the same power output, no flame propagation problems, less cooling air is required, high combustion efficiency, and improved pressure distribution to turbine

15:1

chemically correct or stoichiometric ratio of air and fuel

combustion stability

smooth burning of the mixture, coupled with the ability to remain alight over a large range of air/fuel and air mass flows

relight

restarting the engine in the air while it is windmilling is called a _____

combustion efficiency

the efficiency with which the combustor assembly extracts the potential heat actually contained in the fuel

one or more combustion chambers (combustors)

fuel injection system

ignition source

fuel drainage system

basic elements of all combustion sections

combustion section

its primary function is to burn the fuel/air mixture, thereby adding heat energy to the air

fuel injection system

meters the appropriate amount of fuel through the fuel nozzles into the combustors

fuel drainage system

draining the unburned fuel after engine shutdown

combustor chambers

where the fuel and air are mixed and burned

multiple-can type combustion chamber or tubular

consists of a series of individual combustor cans which act as individual burner units

annular combusion chamber or basket type

consists of a housing and perforated inner liner, or basket

can-annular or tuboannular type

represent a combination of the multiple-can combustor and the annular type combustor

can-annular or tuboannular type

invented by Pratt & Whitney and consists of a removable steel shroud that encircles the entrie combustion section

flameout

situation wherein an excessively high velocity airflow could literally blow the flame out of the engine/combustion chamber

lean die out and rich blow out

two types of flameout

lean die out

usually ocurs at high altitude where low engine speeds and low fuel pressure form a weak flame that can die out in a normal airflow

rich blow out

occurs during rapid engine acceleration when an overly-rich mixture causes the fuel temperature to drop below the combustion temperature or when there is insufficient airflow to support combustion

nozzle guide vane

first part of the turbine which directs the air axially onto the blades of a rotor section

turbine

extracts energy from the hot gases that flow through it, and converts that energy into mechanical energy, to drive the compressor and gearbox connected to it

one row of stationary nozzle guide vanes and one row of rotating turbine blades

two elements within the turbine stage

blade shroud

fitted in an attempt to minimize losses due to leakage across the turbine blade tips and it also reduces the vibration of the blades

abradable lining

used in the turbine casing area, to reduce gas leakage through this clearance between the blade tips and the turbine casing, but active clearance control can be more effective throughout the flight cycle

free turbine or free power turbine

a turbine which is not connected to the compressor, it is connected only to the reduction gear for propeller

increase drag and greater stresses

two detrimental effects of increasing the diameter of the turbine

convergent duct

the space between two nozzle guide vanes form a _____

impulse type

reaction type

impulse-reaction

3 types of turbine blades

impulse type

similar in action to a water wheel

reaction type

these blades rotate as a reaction the the lift they create as the gas stream flow over them

fir tree fixing

most commonly used turbine blade fixing on modern engines

creep

stretching of the metal of the blade beyond its ability to reform back to its original length

boundaries of the crystal

these create a weakness in the structure, and are usually the starting point of any failure

single crystal casting

this eliminates corrosion and creates an extremely creep resistant blade

turbine section

located downstream of the combustion section

case, stator, shroud, and rotor

4 basic elements of turbine section

turbine nozzle

located directly aft of the combustion section and immediately forward of the turbine wheel

turbine nozzle

collects the high energy airflow from the combustors and direct the flow to strike the turbine rotor at the appropriate angle

shaft and turbine rotor (wheel)

rotation elements of a turbine section

turbine wheel

is a dynamically balanced unit consisting of blades attached to a rotating disk

turbine disk

anchoring component for the turbine blades and is bolted or welded to the main shaft

growth or creep

phenomena in which extreme stress on turbine blades may cause the turbine blades to grow in length due to severe centrifugal loads imposed by high rotational speeds

turbine blades

airfoil shaped components designed to extract the maximum amount of energy from the flow of hot gases

impulse turbine blades

the blades merely change the direction of airflow coming from the turbine nozzle and cause relatively no change in gas pressure or velocity

reaction turbine blades

producing a turning force based on an aerodynamic action

impulse-reaction turbine blades

combination of impulse and reaction blades, the workload along the length of the blade is evenly distribbuted

exhaust cone

a conical shaped device positioned close up to the rear turbine disc rear face

exhaust cone

prevents the hot gases flowing across the rear disc face of the turbine, further reducing disturbance, and preventing overheating of the disc

low bypass exhaust

combines the bypass air and the hot exhaust gases in a mixer unit

mixer unit

ensures thorough mixing of the two streams of air before they are ejected into the atmosphere

compressor, turbine, and exhaust

most significant sources of noise from the engine originate from the _____

lobe type nozzles

caused the gases to flow in separate exhaust jets that rapidly mix with slowly moving air which is trapped by the lobes

exhaust section

direct the flow of hot gases rearward in such a manner as to prevent turbulence and impart a high final or exit velocity to the gases

exhaust cone

exhaust duct or tailpipe

exhaust nozzle

components of exhaust section

tailpipe

an extension of the exhaust section that directs exhaust gases safely from the exhaust cone to the exhaust, or jet nozzle

tailpipe

used almost exclusively with engines that are installed within an aircraft's fuselage to protect the surroundind airframe

converging design and converging-diverging design

two types of exhaust nozzle designs

converging exhaust nozzle

this produces a venturi that accelerates the exhaust gases and increases engine thrust

converging-diverging nozzle

the converging portion of the exhaust nozzle accelerates the turbine exhaust gases to

supersonic speed at the narrowest part of the duct, then, they are accelerated further in

the nozzle's divergent portion, so the exhaust gases exit the nozzle

well above the speed of sound.

mixer unit

in a low by-pass engine, the flow of cool and hot air are combined in a _____ that ensures mixing of the two streams prior to exiting the engine

windmilling compressor

supply sufficient air to support combustion

high-energy capacitor discharge system

the typical ignition source for gas turbine engines