POWEPLANT - MODULE 07: Performance and Thrust Augmentation

MODULE 07: Performance and Thrust Augmentation

Density or weight of the airflow

The maximum power output of a gas turbine engine depends to a large extent upon the ___________________________ passing through the engine.

Methanol

When _______________________ is added to the water it gives anti-freezing properties and also provides an additional source of fuel.

Water injection

In conditions of high altitude and/or high temperature the use of _________________ can restore the thrust of a turbo-jet engine and boost the output of a turbo-prop engine.

Water injection system

The ____________________ is typically activated by moving the throttle to the take-off position.

Mass of air

The power output of a gas turbine engine depends to a large extent upon the ___________________________ flowing through it.

decreases

In conditions of high altitude and/or high temperature, the density, and therefore the mass of the airflow through the engine ____________________, causing a reduction of thrust or shaft horsepower.

Cooled with water

To restore, or with some types of engines, boost, the power output of that engine, the airflow can be _______________________________.

Power limiter circuit

The engine power does not increase above its flat rated 100% power, which is controlled by the ______________________________.

Engine carcass splitting under excessive stress

By Increasing the compressor speed the maximum compressor outlet pressure (P3max), must be limited to prevent the ______________________________.

Pure water injection system

A ________________________ does have some drawbacks, not least because the water must all be used up on take-off if it is not to freeze in the tanks as the aircraft climbs to altitude.

Methanol

Serves primarily as an anti-freeze.

Water methanol control system

In order to regulate the amount of heat added, the quantity of water methanol injected into the engine must be carefully regulated, this is done by a _______________________________.

1. 40%

2. 60%

The proportion of methanol added to the water must also be carefully controlled, a ratio of (1) _________________ methanol to (2) ________________ water (by volume) ensures that the TGT limits should never be exceeded during use of the water methanol system.

1. Engine intake

2. Compressor inlet

Some centrifugal compressor engines, and some small American designed axial flow compressor engines, injected the water into the (1) ________________ or also known as the (2) __________________.

Combustion chamber

Injection of water into the ______________________________ increases the mass flow through the turbine relative to that through the compressor.

1. Free turbine

2. Jet pipe pressure

This results in an increase in the amount of power available, either to drive the propeller through a (1) ______________________, or as an increase in the (2) _________________________.

Compressor inlet injection system

The _________________________________ is a typical system for a turbo-propeller engine.

control unit

The _____________________ meters the flow of mixture to the compressor inlet through a metering valve that is operated by a servo piston

1. Servo system

2. Servo valve

The (1) _______________________ uses engine oil as an operating medium, and a (2) _________________ regulates the supply of oil.

Control system

The degree of servo valve opening is set by a ___________________ that is sensitive to propeller shaft torque oil pressure and to atmospheric air pressure acting on a capsule assembly.

Control unit high pressure oil cock control lever

The _________________________ is interconnected to the throttle control system in such a manner that, until the throttle is moved towards the take-off position, the oil cock remains closed, and thus the metering valve remains closed, preventing any mixture flowing to the compressor inlet.

Servo piston.

Movement of the throttle control to the take-off position opens the oil cock, and the oil pressure passes through the servo valve to open the metering valve by means of the _____________________________.

Combustion chamber injection system

The __________________________ is a typical system for a turbojet engine.

Sensing unit

The water passes from the _______________________ to each fuel spray nozzle and is sprayed from two jets onto the flame tube swirl vanes, thus cooling the air passing into the combustion zone.

Fuel control system

The water pressure between the sensing unit and the discharge jets is sensed by the _________________________, which automatically resets the engine speed governor to give a higher maximum engine speed.

Water flow sensing unit

The ___________________________ opens only when the correct pressure difference is obtained between compressor delivery air pressure and water pressure.

Sensing unit

The ________________________ also forms a non-return valve to prevent air pressure feeding back from the discharge jets and provides for the operation of an indicator light to show when water is flowing.

Thrust augmentation by afterburning (reheat)

__________________________________ makes use of the unburnt oxygen in the exhaust to release more heat energy by burning more fuel between the turbine and the propelling nozzle.

Afterburning

_______________________ is used to improve takeoff and climb or combat performance, mainly restricted to military aircraft.

Four low by-pass ratio turbojets with afterburners

The one notable exception is Concorde, currently the only supersonic passenger carrying aircraft using _________________.

Fuel

______________ is introduced into the jet pipe through discharge nozzles centrally disposed around the axis of flow to enable some of the relatively cooler turbine discharge gas to flow along the jet pipe walls to aid cooling as the afterburner flame temperature may be in excess of 1700°C.

1700°C.

Fuel is introduced into the jet pipe through discharge nozzles centrally disposed around the axis of flow to enable some of the relatively cooler turbine discharge gas to flow along the jet pipe walls to aid cooling as the afterburner flame temperature may be in excess of _____________.

Variable area propelling nozzle

An afterburning jet pipe will have a __________________________________, closed, to provide for non-afterburning operation and open, to allow for an increased volume of gas during afterburning operation.

Detent or 'gate'.

Control of the nozzle is automatic with the selection of afterburner which is typically initiated by moving the throttle lever through a __________or ‘___________’.

Atomized fuel spray

When selected an __________________________ is introduced into the jet pipe through the burners and ignited by an igniter plug or a hot streak of flame from the combustion chamber.

750 to 1,200 feet per second

The gas stream from the engine turbine enters the jet pipe at a velocity of _________________________, but as this velocity is far too high for a stable flame to be maintained.

Flame stabilizer (vapor gutter)

A form of _________________________________ is, therefore, located downstream of the fuel burners to provide a region in which turbulent eddies are formed to assist combustion and where the local gas velocity is further reduced to a figure at which flame stabilization occurs whilst combustion is in operation.

Catalytic igniter

Combustion is then initiated by a _________________________, which creates a flame as a result of the chemical reaction of the fuel/air mixture being sprayed on to a platinum-based element.

'Hot-shot' ignition.

Combustion is then initiated by a catalytic igniter, which creates a flame as a result of the chemical reaction of the fuel/air mixture being sprayed on to a platinum-based element, by an igniter plug adjacent to the burner, or by a hot streak of flame that originates in the engine combustion chamber this latter method is known as _________________________.

1. 700 degrees Celsius

2. 800 degrees Celsius

This is not so, for although cool flames form at temperatures up to (1) ______________________, combustion will not take place below (2) ____________________.

Stable flame

For smooth functioning of the system, a _____________________ that will burn steadily over a wide range of mixture strengths and gas flows is required.

Burner system

The ____________________ consists of several circular concentric fuel manifolds supported by struts inside the jet pipe.

Flame stabilizers

The ______________________ are blunt nosed V-section annular rings located downstream of the fuel burners.

Latter system

The typical burner and flame stabilizer shown in the figure below is based on the ____________________.

Jet pipe

The afterburning __________________ is made from a heat resistant nickel alloy and requires more insulation than the normal jet pipe to prevent the heat of combustion being transferred to the aircraft structure.

Jet pipe

The ___________________ may be of a double skin construction with the outer skin carrying the flight loads and the inner skin the thermal stresses.

heatshield

The _____________________ comprises a number of bands, linked by cooling corrugations, to form a single skin.

Overlapping 'tiles'

The rear of the heatshield is a series of riveted __________________ to the surrounding skin.

Propelling nozzle

The _____________________ is of similar material and construction as the jet pipe, to which it is secured as a separate assembly.

Two-position propelling nozzle

A __________________________ has two movable eyelids that are operated by actuators, or pneumatic rams, to give an open or closed position.

Variable-area propelling nozzle

A ____________________________ has a ring of interlocking flaps that are hinged to the outer casing and may be enclosed by an outer shroud.

1. Fuel flow

2. Propelling nozzle area

It is apparent that two functions, (1)_____________________ and (2)_________________, must be coordinated for satisfactory operation of the afterburner system,

Pressure ratio control unit

The _____________________________ ensures the pressure ratio across the turbine remains unchanged and that the engine is unaffected by the operation of afterburning, regardless of the nozzle area and fuel flow.

Pump

This _______________ is usually of the centrifugal flow or gear type and is energized automatically when afterburning is selected.

'fail safe'

The system is fully automatic and incorporates _______________ features in the event of an afterburner malfunction.

Hydraulically or pneumatically operated rams

To operate the propelling nozzle against the large 'drag' loads imposed by the gas stream, a pump and either _________________________ or ___________________ are incorporated in the control system.

Hydraulic operating rams

Nozzle movement is achieved by the _________________________ which are pressurized by an oil pump, pump output being controlled by a linkage from the pressure ratio control unit.

Pressure ratio control unit

The ________________________________ alters oil pump output, causing an out-of-balance condition between the hydraulic ram load and the gas load on the nozzle flaps.

Ratio of the absolute jet pipe temperatures

The increase in thrust due to afterburning depends solely upon the ______________________ before and after the extra fuel is burnt.

High thrust boosts

___________________________ can be achieved on low by-pass engines because of the large amount of oxygen in the exhaust gas stream and the low initial temperature of the exhaust gases.

Increase in specific fuel consumption

Afterburning always incurs an __________________________ and is, therefore, generally limited to periods of short duration.