Propulsion 2 Marks Answers

AERONAUTICAL ENGINEERING NOTES

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Aeronautical Engineering Notes

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PROPULSION-1 TWO MARKS

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1.Define specific fuel consumption?

experimental stress analysis

It is the rate of fuel consumed pe r unit work work output. output. efficiency eff iciency decreases with increase increase in specif ic

propulsion I two marks

fuel consumed cons umed .its unit is kg/k whr. whr.

rockets and missles propulsion ii two marks

2.Define propulsive efficiency?

Airframe maintanance and

Propulsive Propulsive eff iciency defined as the ratio of propulsive power or thrust thrust power to the p ower output

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of the engine.

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3.what are the condition for maximum propulsive efficiency?

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For max .propulsive .propulsive efficiency ef ficiency the jet velocity must be twice more than free stream velocity for

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which which the propulsive eff iciency 66.7%.

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4.What is multispool e ngine?

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Aircraft Aircraft f lying lying at the high speed should operate at the high spe ed temperatu tempe rature. re. So they used high

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pressure compresso r and turbine.th turbine.this is is known as as multispool engines.

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5.Define intercooler? In multistage multistage compressor,th c ompressor,the e compressed comp ressed air coming out of the first stage is co oled to the intial intial temperature temperature with the help of the heat exchanger exchanger before bef ore being be ing passed to the next stage .this heater exchanger is called intercooler.



6.Draw the PV and TS diagram for an open joules cycle with inter cooler,reheater and regenerator? 7.Define spe cific impulsive? impulsive? It is defined as the thrust produced pe r unit weight weight flow rate through the the propulsiv p ropulsive e device. d evice. 8.Define spe cific thrust? thrust? It is defined d efined as the the thrust produced pe r unit mass mass flow rate through the the propulsiv prop ulsive e device. de vice. 9.Give the classification of air breathing engine? Air breathing breathing engine may be classified into turbojet e ngine, turboprop engine, pulsejet and ramjet ramjet engine. 10.Define work ratio? ratio? Work ratio is defined as the ratio of net work done by the engine to the work done by b y the turbine. turbine. 11.Define thrust augmentation? Increasing the thrust output of the aircraft power plant for a short interval of the time to achieve better take-off performance, higher rate of climb etc..is called thrust thrust augmentation. augmentation.

12.What are the various types of thrust augmentation? The after burner, injection of water, alcohol mixtures and the bleed burn cycle are the different types of thrust augmentation 13.Give the advantage advantage of turbojet engine? *it is suitable for long distance flight at high speed and altitude. altitude. *lower frontal area and shorter landing gears. *lower weight per unit thrust at design speed and altitude. *pressure rise through the inlet diffuser is suff icient. *reheat can be employed f or increased thrust. 14.What are the disadvantage disadvantage of turbojet engine? *it requires a long run way. way. *TSFC is comparatively high at low speed and altitude. *uneconomical on short distance flight. *lower thrust thrust and propulsive efficiency at lower spee d. 15.What are the advantage advantage of turboprop engine? It is produced high thrust at lower speed. so it require short run way. *The TSFC is based on thrust is low.



*propulsive efficiency within the range of operation is high. *Thrust reversal is easily achieved with variable pitch propeller blades. 16.What are the disadvantage disadvantage of the turboprop engine? *Application *Application is limited to power speed spe ed and altitude. *Due to large diameter prope ller the landing landing gear g ear should be long. *engine is heavier and more c omplicated. *higher weight per unit thrust. 17.Why doesn't ramjet engine need a compressor and turbine? turbine? Flight speed o f the ramjet engine is very high, high, say M=2 M=2 to 4.due to this pressure rise in diffuser(Ram pressure) is very very high, high, at this this flight speed c ontribution ontribution of the compressor to the total static pressure rise insignificant. Thus the ram jet engine has a no compressor and turbine.

18.What are the advantage of ram jet engine? *High *High temperature can be employed. *its construction is easy as there are no rotary parts. *it can operate efficiently at high supersonic mach numbers. *it produced high thrust per unit weight and frontal area. 19.What are the disadvantage of ramjet engine? *It requires a launching launching device at s upersonic speed . *it is unsuitable for subsonic. *it has low thermal efficiency and high TSFC. *its maximum operating altitude is limited. 20.What are the two methods o f rating and inlet duct? Duct pressure efficiency ratio and ram recovery point are two methods of rating an inlet duct. 21.Define duct press ure efficiency ratio? ratio? It is defined d efined as the ability of the duct to c onvert the the dynamic dynamic pressure press ure at the inlet inlet of the duct to static pressure at the the energy at the inlet of the co mpressor without without a loss of total pressure. 22.Define ram recover point? It is the velocity of the aircraft aircraft at which which the the ram pressure is equal to the fractional pressure lose . For a goo d inlet duct the ram recover point is less. 23.What are the factor affecting the des ign of an inlet? *inlet total pressure ratio. *Drag to the design speed.



*location of the engine on the wing. *nose suppression required. 24.What are the three three region reg ion of flow f low separation separation internal internal flow of subsonic inlet? *outer surface of the nacelle. *internal surface. *on the centre body.

25.How is flow separation separation caused caused on o n the centre body in subsonic inlet? inlet? For the internal flow in a subsonic inlet, flow separation may be caused in centre body bod y due to in strong adverse pressure gradient; because flow accelerator as the temperature temperature increase and decelerates as the curvature curvature decrease. 26.Define external external flow? Flow which is passing through the external surface of the inlet or nacelle is called an external flow. 27.What are the uses uses of normal and oblique shock in super sonic inlet? inlet? Even for the s upersonic inlet the air entering entering the compress or must be subsonic. The normal shock reduced the velocity of the air supersonic to subso nic .while .while the oblique reduced the velocity of the air, air, but not less than than1. 1. The o blique shock are used scramjet engines. 28.What do you mean by reverse nozzle nozzle diff user? For achieving achieving isentropic deceleration, the the supersonic CD nozzle can be used as a diffuser by operating it in the reverse manner. But this type will cause a greater flow instability due to the interaction of the normal with the boundary layer. 29.What are the factors affecting the range and performance of the supersonic inlet? *Total pressure recovery *cowling drag *boundary *boundary layer bleed flow *capture area ratio *weight 30.How are supersonic supersonic inlets inlets classified based on the the percentage of compression? Based on the pe rcentage of co mpression, supersonic inlets are classified into internal internal compression, external external compression and mixed compression inlets. inlets.

31.write the thrust equation?



F=ma(V j-Vi)+(Pe-Pa)Ae. 32.Define interal interal and external compression inlets? inlets? If the pressure rise occ urs due to change in the area between the the cowl lip and the throat it is is called internal internal compression inlet.Here inlet.Here compression comp ression is achieved by a s eries of internal internal oblique shock followed by a normal shock.If the pressure rise oc curs due to the change in area infront infront of the cowl lip then it is called external compression inlet. 33.Define pilot p ilot inlet? inlet? The external compressor inlet that achives compression through a single normol shock is called the pilot inlet. 34.Define mixed compress ion inlets? inlets? The compress ion inlet inlet in which compression is achieved with the help of external external oblique shocks,interna shocks,internall reflected shocks and terminal normal normal shocks are called mixed compress ion inlets. 35.Why is 2D supersonic inlet preferred over axis-symmetric axis-symmetric supersonic inlet? inlet? The 2D inlets are simple to design and it provides a large variation in inlet airflow. Also the axis-symmetr axis-symmetric ic inleta have have the added des ign problem of getting boundary layer layer bleed air out from the centre bod y through through the support suppo rt struts. struts. 36.How are are supersonic inlets classified b ased on the mass f low required? *subcritical inlet operation *critical inlet operation *supercritical inlet operation 37.Explain sub critical inlet operation? In this operation,normal shock is produced externalto the inlet,which reduces the mass of air entering entering into the inlet causes s pillage.It pillage.It matches the mass flow required by the engine. 38.Explain critical inlet operation? In this operation,shock is produced jusjust inside the inlet which increases the mass of air entering the inlet and and decreases d ecreases the mass of air flowing flowing through the outer surface.It matches the mass f low required by the engine. 39.Explain supercritical operation? In this operation,terminal of normal shock is sucked down into the diffuser which increases the mass flow of air and and decrease d ecrease the p ressure rise. In this op eration thrust thrust produced is very low and and SFC is very high. 40.Define the phenomena of b uzz in supersonic supersonic inlets? Buzz is a low frequency,high amplitude pressure oscillation that is liked through shock/shock interaction or shock/boundary layer at relatively low inlet mass flow rate. 41.Define combustion c ombustion chamber? chamber?



The place where the burning burning or combustion combustio n of the air fuel mixture occurs and the chemical energy of f uel is converted into heat enery which which is used to de velop power by turbin turbine. e. 42.What are the types of combustion chamber? *can type *annular type *can-annular type 43.What are types of combustion mechanism? mechanism? *carbon preferential burning *hydrogen preferential burning *hydroxylation 44.Define ann annula ularr combuster? c ombuster? Annular combuster consists of a single combustion chamber co-axially connected with the engine axis. 45.Define can/tubula can/tubularr combustion co mbustion chamber? Can type combustor consists of a number number of combustion chamber located around around the engine axis,each combustion chamber getting air through separate pipelines. 46.Define can-annular combustor? It consists of can and annular type combustion chamber getting air through a common pipeline. 47.What are the factor affecting combustion chamber design? *gas temperature *pressure loss in combustion chamber *carbon format fo rmation ion *combustion chamber inlet mass flow,density and velocity. 48.What are the factors affecting the pe rformance rformance of o f combustion co mbustion chamber? chamber? *pressure lose in combustion chamber *combustion intensity *efficiency of combustion 49.How is parasitic parasitic loss caused in combustion chamber? a.friction *hot loss *cold loss b.turbulance mixing



*hot loss *cold loss 50.Define combustion intensity? intensity? Combustion intensity intensity is def ined as the rate of heat released per unit volume for co mbustion taking taking place at co nstant nstant pressure. press ure. 51.Define combustion efficiency? Combustion efficiency is d efined as the ratio of actual actual temperature rise in the combustor to the theoretical temperature rise. 52.What are the requirements of combustion chamber? *complete co mbustion must be activated activated *pressure loss must be minimized minimized *carbon formation in inner wall surface must be prevented *combustion should be reliable. 53.Explain in brief about dilution zone? The dilution zone zone is used for cooling co oling down the hot gases formed by combustion.In this this zone air is mixed with with the product of combustion to cool it to the temperature temperature required at the inlet of the turbine. 54.What are the various methods of flame stabilization? Flame stabilization can be achieved using swirl vanes and using bluff bodies and upstream or reverse f low. low.

55.What is the f lame function of swirl in combustion chamber? Swirl vanes are used to provide proper mixing and flame stabilization in combustion chamber,by creating a region of back flow or recirculation within the central or forward part of combustion chamber. 56.How is flame stabilization achieved using a bluff body? The bluff body creates a low pressure recirculation zone or wake region which helps in mixing of fuel in the recirculation zone and helps in flame stabilization. 57.What are the disadvantages disadvantages of can type combustor? *separate air pipelines pipelines are needed for each combustion chamber *they do not make the best use of the space available and hence result in a large triangular engine. 58.What are the advantage of annular type combustor? *improved exceed temperature distribution and increased durability



*less space to volume ratio ratio *has *has highest compressor ef ficiency 59.What are the main objectives objectives of combustion chamber geometry ? *to get complete and stable combustion *to reduce c hamber size *to increase chamber life 60.Define upstream injection? injection? In tnis type of flow,the flow,the fuel is injected in the direction opposite the direction opposite to that of the air flow. This results in better mixing of the air and fuel. 61.What is the purpose of exhaust exhaust nozzle? The purpose o f the exha e xhaust ust nozzle nozzle is to increase increase the velocity of the e xhaust xhaust gas,before discharging discharging from f rom the nozzle. It also co llects the gas f rom the turbine and straightens straightens the gas f low. low. 62.What are types of nozzles? nozzles? *convergent nozzle *convergent-divergent nozzle. 63.write about converging nozzle ? Converging nozzle is a simple converging duct, which is use when the nozzle pressure ratio is less than 4. It is g enerally enerally used in engines f or subsonic aircraft. 64.What is the use variable area nozzle? If the engine incorporates after burners, the nozzle must be designed in such a way that the operating conditions of the engine upstream of the after burner remains remains unchanged. unchanged. 65.What are the functions of nozzle? nozzle? *accelerates the flow to high velocity with minimum total pressure loss *match *match the exit and ambient pressure as close ly as possible *allow thrust reversal if necessary *suppression of noise and infra-red infra-red radiation radiation if desired. de sired. 66.Define ejector e jector nozzle? nozzle? In nozzle which which contains contains bypass air passage for mixing of by-pass air with with the hot gases befo before re or after the nozzle based o n the mass flow requirement is called e jector nozzle. nozzle. 67.Define chocking in nozzle? nozzle? In nozzle at the throat region the mach number is equal to 1. In this region the mass flow rate is maximum and this condition is called chocking. 68.Explain the the c haracteristi haracteristics cs o f supersonic after burner ejector nozzle? nozzle?



*the flow inside the nozzle is secondary flow. *there is a mixing layer between the primary and secondary stream. *the primary flow is supersonic 69.Explain supersonic nozzle configuration with no after burner? *the primary nozzle is at minimum area. *there is a region of separation in external flow. *secondary nozzle at minimum area. *the primary flow is sonic. 70.Explain supersonic nozzle configuration with no after burner? *the flow into the nozzle is tertiary flow. *it consists of a reversible hinge or latch. *it consists movable secondary nozzle.

71.Define under expansion in nozzle? When the exit pressure o f the nozzle nozzle is greater g reater than than the ambient pressure,the pressure,the expansi e xpansion on of gases does not take take place p lace to the desired d esired extent and this condition is called under expansion. 72.Define over expansion in nozzle? When the exit pressure f rom the nozzle is less than the ambient pressure, the expansion of the exhaust gas is more than the desired extent. This condition is called over expansion. 73.Define optimum expansion? expansion? When the exit pressure is equal to the ambient pressure,the expansion of gases is optimum and it gives the des ired velocity without without affecting the perfo rmance rmance of the aircraft. aircraft. 74.Define nozzle efficiency? Nozzle efficiency is defined as the ratio of actual drop in temperature to the theoretical temperature drop. 75.What are the various losses in a nozzle? *boat drag loss *pressure loss *losses due to friction *losses due to cooling 76.Give the shapes o off nozzles based on air inlet condition? condition? *M<1(subsonic)

: the nozzle is a convergent converge nt nozzle



*M=1(sonic)

: the area is constant (throat)

*M>1(supersonic) *M>1(superso nic)

: the nozzle is a divergent diverge nt nozzle.

77.Define stagnation stagnation state? Stagnation Stagnation state is def ined as the c ondition obtained obtained when the the fluid f luid flow is dec elerated to zero velocity at zero elevation in adiabatic or isentropic condition. 78.What are the limitations limitations of the design of nozzle? nozzle? *Diameter of the nozzle in the divergent portion should be less than the overall diameter of the engine. Otherwise Otherwise there will be an external drag in the divergence portion due to thrust thrust offset. of fset. *The angle of inclination inclination of diver d ivergence gence portion p ortion should should be less than 30' to avoid the f ormation ormation of shock in the divergent portion.

79.What do you mean by thrust reversal? When is the need f or sudden reduction of lift or to attain sudden descent, the direction of the exhaust gas are changed which produces additional drag and thus acts as thrust revesers. 80.Define critical critical state? The flow flo w properties at the throat where where the mach number number is unity is is called critical state. 81.What are the functions functions of co mpressors? *to supply sufficient sir to the combustion chamber. chamber. *to increase the pressure and tempe rature rature of air entering entering the combustion chamber to the desired exhaust. *supply bleed air fo r various various purposes in the engine and aircraft aircraft 82.What are types of compressor? *axial *axial flow compresso r *centrifugal *centrifugal compres sors 83.What is the ce ntrifugal ntrifugal compressor? If the air entering the compressor is in the radial direction and air leaves out in the axial direction then it is called centrifugal compressor. 84.What is axial axial floe compressor? If the air enters in and leaves out in the axial direction then it is called axial flow compressor. 85.Define degree of reaction? Degree o f reaction is def ined as the change in enthalpy enthalpy in the the rotor divided by the change in stagnation enthalpy in the stage. 86.Define stage?



A pair of rotor and stator blade is tog ether called called a stage. 87.Define blade profiles? Compressor b lade tips are reduced in thickness,by thickness,by cutouts called profiles. These profiles p revent serious damage to the blades. 88.What are the advantage advantage of centrifugal centrifugal compress ors? *high pressure rise rise per p er stage. *good efficiencies e fficiencies over wide rotational speed range. *low weight *low starting power requirements. 89.What are the disadvantages disadvantages of centrifugal centrifugal compresso rs? *large frontal area for given airflow. *more than two two stages are not possible,because pos sible,because of losses in turns between the stages. 90.What are the advantage advantage of axial axial flow compresso rs? *high peak efficiencies. *small frontal area for given airflow. *straight through flow,allowing high ram efficiency. 91.What are the disadvantages disadvantages of axial axial flow compressors? *good efficiencies only over narrow narrow rotational rotational speed range. range. *difficulty of manufacture and high cost. *relative heavy weight. *high starting power requirements. 92.What is the f unction unction of inlet guide vanes? vanes? The variable inlet guide vanes deflect and direct the air entering into the compressor at a proper angle. 93.Define compressor efficiency? Compressor ef ficiency is defined as the ratio of work done on the compressor to the work done by the compressor. 94.Define flow coefficient? Flow coeff icient is defined as the ratio of relative relative velocity to to the velocity of jet. 95.Define pressure coefficient? Pressure coeff icient is defined as the ratio of the workdone workdone to the square of the outlet velocity. velocity. 96.Define stage efficiency?



Stage eff iciency is defined as the ratio between ideal work done to actual actual workdone. 97.define slip factor? Slip factor is the ratio between actual whirl velocity to the ideal whirl velocity. 98.What do you mean by eddy loss in compressor? The energy transfer occurring in the impeller corresponding to thus velocity profile is less than that have been obtained with one dimensional flow. This reduction of flow or energy transfer is called eddy loss. 99. what are are the applications applications of compressor? *used for f or supercharger. *used for fo r turbo turbo propeller p ropeller units. units. *refrigeration unit. *petrochemical plants. 100.What are types of impeller blades? *straight blades. *curved *curved blades.

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Propulsion 2 Marks Answers

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