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Title of test: Gas Turbine Engine Description: Aviation Author: Aviation Other tests from this author Creation Date: 22/02/2024 Category: Art Number of questions: 64

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Gas turbine engines operate on the principle of A continuous mass flow with volume maintained constant A continuous mass flow with pressure maintained constant The addition of heat to an airflow causing the air to expand at a constant pressure The release of heat from an airflow causing the air to accelerate through a turbine. In a gas turbine engine, combustion occurs at A constant velocity A Constant pressure A constant volume A constant temperature. As the air flow passes across the turbine Temperature and speed decreases Temperature and speed increases Temperature decreases and speed increases Speed increases and temperature increases. The working cycle of a gas turbine is as follows Compression, expansion, combustion, exhaust Induction, compression, ignition, expansion, exhaust Identical to that of a four stroke piston engine Compression, ignition, combustion, exhaust. Air through a convergent duct causes A decrease in pressure and an increase in velocity An increase in pressure and an increase in velocity An increase in pressure and a decrease in velocity A decrease in pressure and a decrease in velocity. A turbo jet engine produces A large acceleration to a small mass of air A large acceleration to a large mass of air A small acceleration to a small mass of air A small acceleration to the propeller. If the aircraft is stationary on the ground, with engines running, propulsive efficiency Increases if RPM is increased Is at maximum Depends on the ambient air temperature Is at minimum. The efficiency of a gas turbine engine increases with Decrease in ambient temperature Decrease in ambient pressure Increase in ambient temperature Decrease in air density. Engine pressure ratio (EPR) is the ratio of Jet pipe pressure to compressor inlet pressure Compressor discharge to jet pipe pressure Air in the combustion chamber is air by passing it Combustion chamber pressure to compressor discharge. When air is compressed adiabatically There is no change in air temperature Kinetic energy is reduced No heat enters or leaves the gas The air velocity decreases. By pass ratio is The ratio of intake pressure to exhaust pressure The ratio of air entering the cold section to air by-passing the hot section The ratio of LP compressor airflow to HP compressor airflow The ratio of compressor pressure to turbine pressure. In a twin spool gas turbine The HP turbine drives the HP compressor and the LP turbine drive the LP compressor The LP and HP compressor are both driven by the HP turbine The turbines are free to rotate at different speeds to the compressor The LP turbine drives the HP compressor and the HP turbine drives the LP compressor. Variable inlet guide vanes are used to Increase the mass flow at high RPM Increase the mass airflow at low RPM Reduce fan intake noise Reduce the chance of compressor stall. Air intakes are designed to Accelerate the free air flow to the compressor Reduce initial compressor pressure Convert kinetic energy into pressure energy Prevent the compressor from stalling. The majority of the airflow from a single spool compressor is used for Cooling the turbine Combustion Anti-icing Driving the turbine. In a centrifugal compressor the cascade vanes are used To impart an initial swirl to air before entering the compressor To change the direction of the airflow with the minimum loss of energy To reduce the noise of the compressor To create divergent ducts to increase pressure for compression. A compressor bleed valve Opens at high engine RPM and provides a rapid acceleration Decreases the airflow over the HP compressor by closing at high RPM Increases the airflow over the LP compressor by opening at low RPM Allows the airflow to by-pass the hot section at all operating speeds. An Axial flow compressor surges when All compressor stages are stalled Any compressor stage stalls When the HP compressor stalls When the LP compressor stalls. Compression ratio is The ratio of the air intake pressure and the exhaust outlet pressure The ratio of the compressor inlet pressure and the turbine outlet pressure The ratio of the exhaust inlet pressure and the exhaust outlet pressure The ratio of the compressor inlet pressure to the compressor outlet pressure. The main function of the tertiary air introduced in to the combustion chamber is to Stabilise the flame Straighten the axial flow of the nozzle guide vane Cool the gases caused by combustion To circulate the air in the primary zone before combustion. The airflow duct between the compressor and the combustion chamber is Convergent Uniform in diameter Straight Divergent. The swirl vanes in a combustion chamber are fitted to Stabilize the combustion Increase the axial airflow Reduce the pressure in the primary zone Cool the flame tube. The air passing into the annular section of the combustion chamber Is approximately 50% of the total airflow from the high-pressure compressor Is approximately 80% of the total airflow from the high-pressure compressor Is all directed into the primary zone to assist in stabilizing the flame Is all directed into the dilution zone to cool the combustion gases before passing into the turbine section. In a gas turbine engine combustion occurs at Constant pressure Constant velocity Constant volume Constant temperature. The fuel/air mixture ratio required for efficient self-sustaining gas turbine combustion is approximately 1:50 1:2 1:15 1:130. Flame temperature in the primary zone of a combustion chamber Is relatively constant at 2000 degrees Celcius Is restricted to approximately 1500 degrees Celcius to prevent turbine damage Maintains a steady value from compressor to nozzle guide vanes Is controlled in value by the introduction of secondary and tertiary air through holes in the flame tube . Airflow from the compressor is delivered at approximately 2000 ft per second 1500 ft per second 1000 ft per second 500 ft per second. During the combustion process in a gas turbine engine The airflow increases in temperature, reduces in pressure and the velocity is maintained constant The airflow increases in temperature, decreases in volume and increases in velocity The airflow decreases in temperature, increases in volume and increases in velocity The airflow increases in temperature, increases in volume and the pressure is maintained more or less constant . In which of the following circumstances is a flame out most likely to occur During a prolonged cruise climb with a high thrust setting During a high-speed cruise descent at flight idle During high altitude cruise with very high ambient air temperatures On final approach to land with all high lift devices deployed and an intermediate thrust setting. Combustion gases passes through the turbine section experience A reduction in pressure temperature and velocity An increase in pressure and a reduction in temperature and velocity A reduction in pressure and an increase in temperature and velocity An increase in pressure, temperature and velocity. Nozzle guide vanes Direct air on to the initial low-pressure compressor stages at an acceptable angle in order to prevent compressor stall Reduce the degree of swirling caused by the rotating turbine blades and restore an axial flow Direct combustion gases on to the turbine blades causing an impulse rotation of the turbine Divide the compressed air from the LP compressor before entry in to the combustion chamber . Turbine disc and blade creep is A permanent change A temporary expansion due to pressure change A temporary shrinking due to temperature change A temporary expansion due to centrifugal force. A free turbine Is connected to the compressor spool by an independent shaft Is only used to drive the high-pressure compressor Admits intake air into the compressor stages Has no mechanical connection to the compressor stage. The internal gearing of an accessory drive in a gas turbine engine, is most usually fitted A late compression stage A turbine/compressor drive shaft The high pressure turbine The free turbine. Exhaust gases are passed to the atmosphere Through the propelling nozzle, which is a divergent duct causing the gas flow velocity to increase Through the jet pipe, which is a convergent duct causing the gas flow to expand Through the propelling nozzle, which converts kinetic energy into pressure energy Through the propelling nozzle, which is a convergent duct causing the gas flow velocity to increase. The function of the exhaust cone is To prevent hot gases from flowing back over the turbine face To increase the gas flow velocity To prevent any swirling in the jet pipe To increase the pressure of the jet efflux. The jet pipe is A divergent convergent duct fitted to cool the gas flow A duct of uniform diameter fitted to transport the gas flow to the propelling nozzle A divergent duct fitted between the exhaust cone and the propelling nozzle for cooling purposes A convergent duct fitted to increase the kinetic energy and gas flow velocity. The temperature of the gas passing from the turbine section is likely to be between 1150 degrees C – 1400 degrees C 1400 degrees C- 1700 degrees C 850 degrees C –1150 degrees C 550 degrees C-850 degrees C. On most gas turbine engines the jet pipe is insulated from the aircraft structure by means of Ram air from the low-pressure compressor Cooling air and asbestos An asbestos blanket The propelling nozzle. Afterburning is achieved by Increasing the fuel flow to maintain the combustion chambers, and fitting an extra series of igniter plugs at the end of each chamber Injecting a separate supply of jet fuel into the jet pipe and using separate igniters for combustion Spraying jet fuel into the jet efflux as it is expelled from the propelling nozzle Enlarging the area of the combustion chamber network to include a reheat section with spray nozzles and igniters. Reheat is normally used To improve the cruising speed of the aircraft To improve the operational efficiency and decrease the fuel flow over all flight phases For short periods only to improve the take off performance and the rate of climb To increase combustion efficiency at high altitudes. The water/methanol mixture used for injection into the gas turbine engine is Intended for use as an anti-icing agent Used to supplement combustion as an extra source of fuel Used to supplement thrust by lowering the gas flow temperature Used to perform all the function listed in the three answers above. In certain systems coolant is injected into the combustion chamber. This Increases the relative mass flow through the turbine when compared with that through the compressor Decrease the relative mass flow through the compressor when compared to that through the combustion chamber Increases the relative mass flow through the compressor when compared to that through the turbine Increases the relative mass flow through the compressor when compared to that through the exhaust nozzle. Use of water/methanol is Automatic at high ambient temperatures Automatic at all ambient temperatures Controlled by the flight crew Activated by pre-set limits determined during ground maintenance. On a pure turbo jet engine, most noise is transmitted from The air intake The exhaust nozzle The turbine The compressor. The most effective means of noise suppression are Insulation of the rotating parts with acoustic lining, and increased mixing of the exhaust gases and ambient airflow Increasing the length of the jet pipe and reducing the area of the propelling nozzle Cladding the propelling nozzle with acoustic lining and increasing the thickness of the engine nacelle Reducing the incidence angle of the inlet guide vanes, and reducing the turbulent mixing within the propelling nozzle . On a high by-pass ratio engine reverse thrust is achieved by Reversing the hot section gas flow only Reversing the cold section by-pass air flow only Reversing both the hot section gas flow, and the cold stream by-pass flow Reversing the direction of rotation of the HP turbines. On a turbo-propeller engine reverse thrust is achieved by Reversing the jet efflux by use of a clamshell door system Reversing the direction of rotation of the free turbine Reversing the direction of rotation of the reduction gearing /torque meter assembly Reversing the thrust from the propeller by shifting the blades to a negative angle of attack. Clamshell doors are held in the reverse thrust position by The gas flow pressure Hydraulic actuator pressure External ram air pressure Pneumatic pressure. The purpose of a by-pass valve fitted to a fuel cooled oil cooler is To ensure that the oil pressure is always greater than the fuel pressure To direct oil to the main bearing in the event of loss of oil pressure To direct oil to the main bearing in the event of loss of oil pressure To prevent engine oil starvation in the event of a cooler blockage. Magnetic plugs are fitted in order to Neutralize unwanted magnetic fields caused by friction in the oil pipe ways Collect metallic fragments that may be in the bearing housings To attract the roller bearings in order to ensure a small gap is maintained between them and the housing To attract the roller bearings in order to ensure a small gap is maintained between them and the housing. Lubrication of the turbine shaft main bearings is achieved by use of Spray jets Slash delivery Suction attractors Jet fuel. A coarse strainer is fitted in the recirculating system Between the scavenge pump and the oil pump Between the pressure pump and the scavenge pump Between the restrictors and the spray nozzles Between the oil reservoir and the pressure pump. Gas turbine engines use wide-cut gasoline, and kerosene-based fuels, these being AVTUR,AVTAG and AVCAT AVCAT,AVGAS and AVTAG AVTUR,AVGAS and AVTAG AVGAS,AVCAT and AVTUR. To reduce the chance of boiling and vapour locking, the fuel used in a gas turbine engine should have A very high volatility and a low calorific value A high calorific value and a low specific gravity A low volatility and high calorific value A calorific value equal to the volatility. On certain types of aircraft the fuel system includes a low pressure fuel pump to Scavenge the fuel tanks Supply the fuel control unit during low engine RPM operation Supply the high-pressure pump and prevent cavitation Add a safety component to the system for take off. The effect of a change of air density on the fuel/air mixture is corrected by A barometric pressure controller A high-pressure fuel pump A flow controller An altitude relief valve. What limits the maximum output of the HP fuel pump The mass air floe through the engine The maximum RPM governor The accessory drive gearbox The low pressure fuel pump and system. The two forces sensed by the barometric pressure controller are HP pump outlet pressure and HP pump inlet pressure HP inlet pressure and compressor delivery pressure HP pump outlet pressure and air intake pressure HP pump inlet pressure and nozzle delivery pressure. The igniter spark plug caused by Contact breakers Capacitor discharge Impulse reaction Resistor discharge. To motor a gas turbine engine The time cut-off switch circuit breaker should be pulled out The igniters should be selected on to burn fuel The starter motor and ignition systems should both be selected as for normal start up The starting switch should be selected to the off position. In a high energy ignition system, the choke Protects the igniter plug from excessive voltages Protects the HE unit from excessive voltages Prolongs the life of the igniter plug Prolongs the discharge to the igniter plug. An air starter motor Receives charge air to drive its turbine from the main engine compressor Is completely dependent on a charge air supply from an external source for all operation May be supplied by an external power unit or the aircraft APU Can only be used if one of the aircrafts engines has previously been started by an electric motor. The starter system and the ignition system Are operated by the selection by a common starter switch and are both automatically disengaged when the engine reaches self sustaining speed Operate independently of each other but the starter motor circuit can only be activated when the ignition circuit is selected on Operate independently of each other and either system can be selected to function without the other Operate independently of each other but the HE ignition circuit can only be activated when the starter motor has been automatically disengaged .

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