Multiple Choice - POWERPLANT

Which of the following is most likely to occur if an overhead valve engine is operated with inadequate valve clearances?

A. The further decrease in valve clearance that occurs as engine temperatures increase will cause damage to the valve-operating mechanism

B. The valve will not seat positively during start and engine warmup

C. The valves will remain closed for longer periods than specified by the engine manufacturer

D. Timing between the tappet and cam lobe will lessen as it approaches strokes of the piston

B

The mixture of impulse and reaction blade shape in the average turbine blade is such that

A. The inner half is impulse and the outer half is reaction

B. The trailing edge is reaction and the leading edge is impulse

C. The inner half is reaction and the outer half is impulse

D. The leading edge is reaction and the trailing edge is impulse

A

Compared to normally aspirated engines, turbocharged engine exhaust systems operate at

A. Higher temperatures and higher pressures

B. Lower temperatures and lower pressures

C. Similar temperatures and higher pressures

D. Similar temperatures and pressures

A

Bleed air for engine anti-icing is provided by

A. The bleed valves

B. The compressor

C. The turbine stages

D. The combustion chambers

A

The Gas Turbine Engine uses the principle/s of

A. Newton's Laws of Motion

B. Expelling air at the same speed as that of the aircraft

C. Creating thrust equal to the weight of the aircraft

D. Newton's Third Law of motion only

A

In a gas turbine engine

A. Thrust is maximum and ram pressure at minimum at the start of the take-off run.

B. Ram pressure is maximum at the start of the take-off run.

C. Thrust is unaffected by the aircraft's forward speed.

D. Ram pressure is unaffected by airspeed.

B

In a gas turbine unit, air is drawn at 1.02 bar and 15 deg C, and is compressed to 6.12 bar. Calculate the thermal efficiency when the maximum cycle temperature is limited to 800 deg C.

A. None of these choices

B. 40.80%

C. 40.10%

D. 38.80%

C

"For all adiabatic processes between two specified states of a closed system, the net work done is the same regardless of the nature of the closed system and the details of the process" This principle comes from the _____.

A. Third Law of Thermodynamics

B. Second Law of Thermodynamics

C. First Law of Thermodynamics

D. Zeroth Law of Thermodynamics

C

Ignition occurs at 28 deg BTDC on a certain four-stroke cycle engine, and the intake valve opens at 15 deg BTDC. How many degrees of crankshaft travel after ignition does the intake valve open? (Consider one cylinder only.)

A. 347 deg

B. 747 deg

C. 373 deg

D. 707 deg

C

In a by-pass engine, the by-pass air

A. Increases the air mass flow and therefore increases the propulsive efficiency.

B. Cools the combustion chamber and therefore increases the thermal efficiency.

C. Increases the air mass flow and therefore reduces the propulsive efficiency.

D. Reduces the air mass flow and therefore increases the propulsive efficiency.

A

In a piston engine, operating on a constant volume air cycle approximation, with a compression ratio of 6, the thermal efficiency is

A. 46%

B. 51%

C. 59%

D. 42%

B

1 kg of air enclosed in a rigid container is initially 4.8 bar and 150 deg.C. The container is heated until the temperature is 200 deg.C. Calculate the heat supplied during the process.

A. 35.9 kJ/kg

B. 28.6 kJ/kg

C. None of these choices

D. 39 kJ/kg

A

During engine operation, if carburetor heat is applied, it will

A. Decrease the air density to the carburetor

B. Increase air-to-fuel ratio

C. Increase engine RPM

D. Decrease RPM

A

Select the correct order of best propulsive efficiency, from low to high airspeed

A. Turbo-prop, High by-pass ratio turbo jet, Low by-pass ratio turbo jet, Pure turbo jet

B. High by-pass ratio turbo jet, Low by-pass ratio turbo jet, Pure turbo jet, Turbo-prop

C. Low by-pass ratio turbo jet, Pure turbo jet, Turbo-prop, High by-pass ratio turbo jet

D. Pure turbo jet, Turbo-prop, High by-pass ratio turbo jet, Low by-pass ratio turbo jet

A

From a standing start with an increase in forward speed jet thrust will

A. Decrease

B. Decrease then recover but will never achieve its initial setting

C. Stay the same

D. Increase

B

The compression ratio of an air-standard Otto cycle is 9.5. Prior to the isentropic compression process, the air is at 100 kPa, 35 deg.C, and 600 cu. cm. The temperature at the end of the isentropic expansion process is 800 K. Using specific heat values at room temperature, determine the highest pressure in the cycle.

A. 7500 kPa

B. 1420 kPa

C. 4326 kPa

D. 6072 kPa

D

The mean effective pressure of an ideal air-standard Diesel cycle can be increased by

A. Increasing the heat transfer into the engine cycle

B. Increasing the size of the intake and exhaust valve

C. Increasing the volume of the fuel injected

D. Increasing the engine displacement

D

Excessive valve clearance results in the valves opening

A. Late and closing late

B. Early and closing early

C. Late and closing early

D. Early and closing late

C

The pressure ratio of a gas turbine engine compressor is

A. Never greater than 5 to 1.

B. The ratio between compressor outlet and compressor inlet pressure.

C. Equal to the number of compression stages.

D. The ratio between exhaust inlet and exhaust outlet pressure.

B

A 2,000 lbs aircraft is accelerated at 10 fps to 80 fps. What is the change of momentum?

A. 4,555 lbs-sec

B. 4,348 lbs-sec

C. 5,380 lbs-sec

D. 4,448 lbs-sec

B

The number of pounds of air present in the engine cylinder per pound of fuel is called

A. Air specific weight ratio

B. Fuel-air mixture

C. Air-fuel ratio

D. Combustion efficiency

C

Consider a 1200-kg car cruising steadily on a level road at 90 kph. Now the car starts climbing a hill that is sloped 30 deg upwards from the horizontal. If the velocity of the car is to remain constant during climbing, determine the additional power that must be delivered by the engine.

A. 170 kW

B. 197 kW

C. 147 kW

D. 200 kW

C

An un-supercharged aircraft reciprocating engine, operated at full throttle from sea level to 10,000 feet, provided the RPM is unchanged, will

A. Lose power due to the reduced volume of air drawn into the cylinders

B. Remains the same as on sea level condition

C. Lose power due to the reduced density of the air drawn into the cylinders

D. Produce constant power due to the same volume of air drawn into the cylinders

C

An ideal Brayton cycle with air as the working fluid has a pressure ratio of 7 and the minimum & maximum temperatures are 300 K and 1300 K, respectively. Now the pressure ratio is doubled without changing the minimum and maximum temperatures in the cycle. Determine the thermal efficiency of the cycle.

A. 14.00%

B. 10.60%

C. 12.60%

D. 7.50%

B

What is the purpose of a turbocharger system for a small reciprocating aircraft engine?

A. Maintains constant air velocity in the intake manifold.

B. Compresses air to maintain manifold pressure constant from sea level to the critical altitude of the engine.

C. Compresses the air to hold the cabin pressure constant after the aircraft has reached its critical altitude.

D. Level the engine efficiency while cruising on an altitude above its regular operational capability.

B

CP is always greater than CV

A. It depends

B. Null

C. False

D. True

D

An ideal diesel engine has a compression ratio of 20 and uses air as the working fluid. The state of air at the beginning of the compression process is 95 kPa and 20 deg.C. If the maximum temperature in the cycle is not to exceed 2200 K, determine the mean effective pressure.

A. 456 kPa

B. 933 kPa

C. 1000 kPa

D. 276 kPa

B

Consider an aircraft powered by a turbojet engine that has a pressure ratio of 12. The aircraft is stationary on the ground, held in position by its brakes. The ambient air is at 27 deg.C and 95 kPa and enters the engine at a rate of 10 kg/s. The jet fuel has a heating value of 42,700 kJ/kg, and it is burned completely at a rate of 0.2 kg/s. Neglecting the effect of the diffuser and disregarding the slight increase in mass at the engine exit as well as the inefficiencies of engine components, determine the force that must be applied on the brakes to hold the plane stationary.

A. 8680 N

B. 10100 N

C. 9089 N

D. 8050 N

C

mechanical device used in aircraft reciprocating engine that increases the manifold pressure above the pressure of the atmosphere so as to provide high power output for take-off and to sustain the maximum power at high altitude

A. Booster pump

B. Afterburner

C. Supercharger

D. Generator

C

Shrouding of stator blade tips is designed to

A. Ensure adequate cooling

B. Minimize vibration

C. Prevent tip turbulence

D. Prevent tip losses

B

n an air compressor the pressures at inlet and outlet are 1 bar and 5 bar respectively. The temperature of the air at inlet is 15 deg.C and the volume at the beginning of compression is three times that at the end of compression. Calculate the increase of internal energy per kg of air.

A. 138 kJ/kg

B. 157 kJ/kg

C. 120 kJ/kg

D. None of these choices

A

Sodium-filled valves are advantageous to an aviation engine because they

A. Dampen valve impact shocks

B. Are lighter

C. Avoid valve deformation

D. Dissipate heat well

D

Cam-ground pistons are installed in some aircraft engines to

A. Equalize the wear on all pistons

B. Provide a better fit at operating temperatures

C. Act as a compensating feature so that a compensated magneto is not required

D. For proper movement of the connecting rod translated to the movement of piston

B

Pressure, temperature and density are examples of thermodynamic ____ properties.

A. Pre-emptive

B. Extensive

C. None of these choices

D. Intensive

D

For a piston engine, the ratio of the brake horsepower to the indicated horsepower is

A. Thermal Efficiency

B. Mechanical Efficiency

C. Volumetric Efficiency

D. Propulsive Efficiency

B

One reason for shrouding turbine blades is

A. To enable thinner blades to be used

B. To minimise blade end erosion

C. To improve efficiency and reduce vibration

D. To reduce "creep" which may occur in the blades

C

The highest pressure in a gas turbine engine occurs

A. Between the compressor and the combustion chamber.

B. In the combustion chamber.

C. In the jet pipe.

D. At the P1 probe.

A

What is the purpose of the supersonic diffuser in the variable throat intake?

A. Increase in velocity prior to compressor face.

B. Interim reduction in velocity to below Mach 1 prior to a further reduction in the subsonic diffuser.

C. Interim reduction in velocity to below Mach .5 prior to a further reduction in the subsonic diffuser.

D. Final reduction in velocity prior to compressor face.

B

The five events of a four-stroke cycle engine in the order of their occurrence are

A. intake, power, ignition, compression, exhaust

B. intake, compression, ignition, power, exhaust

C. intake, power, compression, ignition, exhaust

D. intake, ignition, compression, power, exhaust

B

Determine the energy required to accelerate an 800-kg car from rest to 100kph on a level road.

A. 450 kJ

B. 309 kJ

C. 515.8 kJ

D. 378 kJ

B

The primary concern in establishing the firing order for an opposed engine is to

A. Keep the power impulses on adjacent cylinders as close as possible in order to obtain the greatest mechanical efficiency

B. Create equal distribution of volumetric and thermal efficiency in cylinders

C. Provide for balance and eliminate vibration to the greatest extent possible

D. Keep power impulses on adjacent cylinders as far apart as possible in order to obtain the greatest mechanical efficiency

C

Which of the following requires the least mass flow rate in order for it to function efficiently?

A. Ramjet

B. Turbojet

C. Rocket

D. Scramjet

C

Heat engines are devices for converting heat into

A. Energy

B. Enthalpy

C. Work

D. Cycles

C

The effect on the temperature and pressure of the gases as they pass across the turbine is

A. Their temperature increases and their pressure falls.

B. Their temperature decreases and their pressure rises.

C. Both their temperature and pressure increase.

D. Both their temperature and pressure decrease.

D

Calculate the heat supplied for 0.05 cu.m of a perfect gas at 6.3 bar undergoing a reversible isothermal process to a pressure of 1.05 bar.

A. 50.0 kJ/kg

B. 37.2 kJ/kg

C. 56.4 kJ/kg

D. 49.0 kJ/kg

C

A single cylinder, four stroke cycle, reciprocating engine develops 160 brake horsepower with a brake mean effective pressure of 120 lb/ sq.in and an engine speed of 2000 revolutions per minute. The length of the stroke and the diameter of the bore in the cylinder are equal. Find the piston diameter.

A. 8.20 in.

B. 8.54 in.

C. 8.92 in.

D. 8.76 in.

D

0.05 cubic meter of a perfect gas at 6.3 bar undergoes a reversible isothermal process to a pressure of 1.05 bar. Calculate the heat supplied.

A. 65.8 kJ

B. 56.4 kJ

C. 42.3 kJ

D. 35.4 kJ

B

Some aircraft engine manufacturers equip their product with choked or taper-ground cylinders in order to

A. Provide a straight cylinder bore at operating temperatures

B. Flex the rings slightly during operation and reduce the possibility of the rings sticking in the grooves

C. Increase the compression pressure for starting purposes.

D. Balance the heat applied inside the cylinder during power stroke

A

Which of the following statements regarding volumetric efficiency of an engine is true?

A. It is impossible to exceed 100 percent volumetric efficiency of any engine regardless of the type of supercharger used.

B. Increasing the amount of fuel and air mixture will directly affect volumetric efficiency through the ratio of intake and exhaust volume

C. It is possible to exceed 100 percent volumetric efficiency of some engines by the use of superchargers of the proper type.

D. The volumetric efficiency of an engine will remain the same regardless of the amount of throttle opening.

C

Compressor blades increase in size

A. From the tip to the root to decrease the temperature.

B. From the high-pressure section of the compressor to the low-pressure section.

C. From the root to the tip to increase the temperature.

D. From the low-pressure section of the compressor to the high-pressure section to maintain a constant airflow velocity.

B

The purpose of an ignition switch is

To prevent condensation

To connect the battery to the magneto

To connect the secondary coil to the distributor

To control the primary circuit of the magneto

To control the primary circuit of the magneto

EPR is a

Ratio between ambient pressure and exhaust pressure.

Ratio between exhaust pressure and intake pressure.

Ratio between intake pressure and compressor delivery pressure.

Ratio between ambient pressure and fan pressure.

Ratio between exhaust pressure and intake pressure

Consider as a system the gas contained in the cylinder which is fitted with a piston on which a number of small weights are placed. The initial pressure is 200 kPa and the initial volume of the gas is 0.04 cu.m. Let a Bunsen burner be placed under the cylinder and let the volume of the gas increase to 0.1 cu.m while pressure remains constant. Calculate the work done by the system during the process.

5.31 kJ

7.33 kJ

6.41 kJ

10.44 kJ

7.33 kJ

A single cylinder, four stroke cycle, 1800 rpm piston engine operates on a constant volume air cycle, compression ratio is 6 and the cylinder work input is 15.7 BTU/cycle. What is the thermal efficiency?

41%

23%

35%

51%

51%

Cv is less than Cp...

It depends on the cycle

Sometimes

Always

Never

Always

For a rocket engine to develop a thrust of 10,000 newtons, the 19.2 lb propellant consumed by the rocket per second must generate an exhaust gas jet velocity at atmospheric of what?

1146.25 mps

1149.25 mps

1148.25 mps

1147.25 mps

1148.25 mps

Severe rubbing of turbine of turbine engine compressor blades will usually cause.

Distortion

Cracking

Galling

Bowing

Galling

The stator vanes in an axial-flow compressor

Convert kinetic energy into potential energy

Direct air into the first stage rotor vanes at the proper angle

Convert velocity energy into pressure energy

Convert pressure energy into velocity energy

Convert velocity energy into pressure energy

The highest pressure in a gas turbine is (2Pt)

At the nozzle exit

At the burner exit

Before the nozzle exit

Before the burner

Before the burner

An ideal air-standard Diesel cycle engine has a compression ratio of 18 and a cutoff ratio of 2. At the beginning of the compression process, the working fluid is at 100 kPa, 27 deg C (300 K). Determine the thermal efficiency.

59%

57%

58%

56%

58%

What publication is used for guidance to determine whether a powerplant repair is major or minor?

Maintenance Manual

FAR Part 43

14 CFR 25

Far Part 91

FAR Part 43

An aircraft uses clamshell doors for thrust reversal to

Direct the gas flow rearwards.

Change the direction of the exhaust gas.

Block the flow of exhaust gas.

Absorb any change in thrust.

Change the direction of the exhaust gas.

Calculate the indicated horsepower for a four-cylinder engine that has a bore of five inches and is turning at 2750 rpm with a measured IMEP of 500 psi for all cylinders. Assume square engine.

180.12 hp

175.11 hp

169.14 hp

170.13 hp

170.13 hp

To aid in identifying the different grades of aviation fuel, each fuel grade is color-coded with dye for easy visual identification. The color code for the 100 octane rating aviation gasoline is

Green

Blue

Yellow

Red

Green

With a governor-controlled propeller system, what happens to the propeller blade angle as the aircraft accelerates during the take-off?

Blade angle does not change

Blade angle decreases

Blade angle may increase or decrease depending on the particular system

Blade angle increases

Blade angle increases

A rich mixture is supplied to the cylinders at take-off and climb.

To give excess power.

To give greater thermal efficiency.

To cool the charge temperature and prevent detonation.

To increase the volumetric efficiency.

To cool the charge temperature and prevent detonation.

In a gas turbine engine...

Thrust is maximum and ram pressure at minimum at the start of the take-off run.

Thrust is unaffected by the aircraft's forward speed.

Ram pressure is unaffected by airspeed.

Ram pressure is maximum at the start of the take-off run.

Thrust is maximum and ram pressure at minimum at the start of the take-off run.

For a turbo jet with flight velocity of 310 kilometers per hour and exhaust gas jet velocity of 690 kilometers per hour at atmospheric pressure, What is the propulsive efficiency with the fuel considered negligible?

69%

62%

45%

53%

62%

If the value of n = 0 in the equation pv^n = C, then the process is called...

Isothermal Process

Constant Pressure Process

Adiabatic Process

Constant Volume Process

Constant Pressure Process

A frictionless piston-cylinder device contains 10 lbm of steam at 60 psia and 320degF. Heat is now transferred to the steam until the temperature reaches 400degF. If the piston is not attached to a shaft and its mass is constant, determine the work done by the steam during this process.

96.4 BTU

92.6 BTU

94.6 BTU

100.6 BTU

96.4 BTU

What most likely to happen in an engine that start normal, EGT within limits but engine fails to accelerate in reach the idle rpm?

Hot start

Hung start

False start

Fail start

Hung start

Which of the following statement is wrong?

The closed cycle gas turbine plants are external combustion plants.

The advantage of efficient internal combustion is eliminated as the closed cycle has an external surface

In open cycle gas turbine, atmosphere acts as a sink and coolant are required.

In the closed cycle gas turbine, the pressure range depends upon the atmospheric pressure

In the closed cycle gas turbine, the pressure range depends upon the atmospheric pressure

One cause of afterfiring in an aircraft engine is...

Excessively rich mixture

Poor ignition

Excessively lean mixture

Sticking intake valves

Excessively rich mixture

In the relationship between manifold pressure, rpm, collective, and throttle, if the manifold pressure is LOW and the rpm is HIGH the solution will be...

Lower the collective pitch

Increase the throttle

Increase manifold pressure and rpm

Decrease manifold pressure

Lower the collective pitch

Find the T3 of an otto engine that has a compression ratio of 7. The engine operates on 0.5 lb/s of air from 13 psia and 80 deg F at the beginning of compression. The engine has a clearance of 10% and 200 BTU of heat are added per cycle.

957

1176

1759

2057

1176

Excessive cylinder head temperatures are caused by...

The ignition timing being too far advanced.

The prolonged use of rich mixtures.

The ignition being too far retarded.

The prolonged use of weak mixtures.

The prolonged use of weak mixtures.

Determine the jet thrust if the mass flow of the air is 50 lbs/second, as the inlet velocity is 734 ft/sec and the jet velocity is 1,300 feet/sec.

878.9 lbs

978.7 lbs

788.8 lbs

1,178.8 lbs

878.9 lbs

A method of comparing engine efficiencies is by comparing...

Fuel consumption

Specific fuel consumption

Engine thrust rating

Thrust-to-weight ratio

Specific fuel consumption

A weak fuel-to-air mixture along with normal airflow through a turbine engine may result in

Detonation

A high EGT

A rich flameout

A lean die out

A lean die out

In a convergent duct

The pressure and velocity remain constant, the temperature decreases.

The pressure and velocity increase, the temperature decreases.

The temperature and velocity increase, the pressure decreases.

The pressure and temperature decrease, the velocity increases.

The pressure and temperature decrease, the velocity increases.

The temperature of the gases within the cylinder of a four-stroke engine during the power stroke will...

Decrease

Be constant

Follow Charles's Law

Increase

Decrease

Ram effect is....

The increase of static energy at the face of the compressor

Conversion of kinetic energy to pressure energy at the face of the compressor

Conversion of static energy to kinetic energy at the face of the compressor

The increase of dynamic pressure at the face of the compressor

Conversion of kinetic energy to pressure energy at the face of the compressor

The length of the stroke is...

Equal to the length of the cylinder

Determined by the size of the piston

Inversely proportional to the engine power output

Equivalent to twice the crank throw

Equivalent to twice the crank throw

Which of the following statement is incorrect?

The solid fuels have higher calorific value than liquid fuels

The liquid fuels have higher calorific value than solid fuels

The liquid fuels consist of hydrocarbons

A good fuel should have low ignition point

The solid fuels have higher calorific value than liquid fuels

The term "Indicated Mean Effective Pressure" refers to...

The maximum working pressure in the engine cylinder.

The pressure achieved during compression.

The effective working pressure in the cylinder during the power stroke.

The minimum working pressure applied to the piston during the cycle.

The effective working pressure in the cylinder during the power stroke.

The maximum thrust that a jet engine can develop will be

Max static thrust

Take-off thrust

Max climb thrust

Go-around thrust

Max static thrust

During an ideal Brayton cycle in jet engine, the process is isentropic in...

process 3-4; process 4-1

process 2-3; process 1-4

process 1-2; process 2-3

process 1-2; process 3-4

process 1-2; process 3-4

A large rocket engine delivers hydrogen at 1500oC and 3 MPa, k = 1.41, R = 4124 J/kg-K, to a nozzle which exits with gas pressure equal to the ambient pressure of 54 kPa. Assuming isentropic flow, if the rocket thrust is 2 MN, estimate the exit velocity.

5980 m/s

9580 m/s

8950 m/s

5890 m/s

5890 m/s

Helium (R=0.4968 BTU/lbm-R) is compressed isothermally from 14.7 psia and 68degF, the compression ratio is 4. Calculate the work done by the gas in BTU/lbm.

-355

-364

-456

-576

-364

The device utilized to measure temperature on a piston engine is

Thermostat

Thermocouple

Thermometer

Barometer

Thermocouple

When is the fuel/air mixture ignited in a conventional reciprocating engine?

When the piston has reached top dead center of the intake stroke

Right when the piston reaches the top dead center on the compression stroke

Shortly before the piston reaches the top of the compression stroke

Shortly after the piston reaches the top of the compression stroke

Shortly before the piston reaches the top of the compression stroke

With an increase in the rotational speed of a four-stroke engine, the valve overlap

Remains constant

Increases

Decreases

Increases up to ground idle and thereafter decreases

Remains constant

A system suffers an increase in internal energy of 80 J and at the same time has 50 J of work done on it. What is the heat change of the system?

130 J

-30 J

+30 J

+130 J

+30 J

Compute the indicated horsepower for a six-cylinder engine that has a bore of 5 in, a stroke of 5 in, and is turning at 2750 rpm with a measured IMEP of 125 lbs/sq.in per cylinder.

415 hp

315 hp

255 hp

550 hp

255 hp

The purpose of the crankcase breather is to...

Prevent pressure building up inside the crankcase

Prevent distortion of the crankcase

Maintain the pressure in the oil tank at atmospheric pressure

Ease the task of the oil scraper ring

Prevent pressure building up inside the crankcase

Variable inlet guide vanes help to prevent...

Foreign object on the compressor blades

Loss compression

Ice build-up on the compressor blades

Compressor stalling

Compressor stalling