AE mock exam (Thermodyn/pplant) Part 2

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?

a.

51%

b.

41%

c.

23%

d.

35%

a. 51%

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

a.

Decrease

b.

Increase

c.

Be constant

d.

Follow Charles's Law

a.

Decrease

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

a.

Hung start

b.

Hot start

c.

Fail start

d.

False start

a.

Hung start

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.

a.

550 hp

b.

415 hp

c.

315 hp

d.

255 hp

d.

255 hp

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?

a.

1149.25 mps

b.

1148.25 mps

c.

1146.25 mps

d.

1147.25 mps

b.

1148.25 mps

An aircraft uses clamshell doors for thrust reversal to.

a.

Block the flow of exhaust gas.

b.

Direct the gas flow rearwards.

c.

Change the direction of the exhaust gas.

d.

Absorb any change in thrust.

c.

Change the direction of the exhaust gas.

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 net-work output per cycle in [kJ/kg], and the thermal efficiency.

a.

57%

b.

58%

c.

56%

d.

59%

b.

58%

Wala naman yung tamang sagot tangina

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

a.

14 CFR 25

b.

Far Part 91

c.

FAR Part 43

d.

Maintenance Manual

c.

FAR Part 43

The correct working cycle of a four-stroke engine is

a.

Power, Exhaust, Compression, Induction

b.

Induction, Power, Compression, Exhaust

c.

Exhaust, Power, Induction, Compression

d.

Compression, Power, Exhaust, Induction

d.

Compression, Power, Exhaust, Induction

The device utilized to measure temperature on a piston engine is

a.

Thermostat

b.

Barometer

c.

Thermocouple

d.

Thermometer

c.

Thermocouple

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.

a.

9580 m/s

b.

8950 m/s

c.

5980 m/s

d.

5890 m/s

d.

5890 m/s

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

a.

94.6 BTU

b.

92.6 BTU

c.

96.4 BTU

d.

100.6 BTU

c.

96.4 BTU

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

a.

Cracking

b.

Galling

c.

Bowing

d.

Distortion

b.

Galling

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

a.

A rich flameout

b.

A lean die out

c.

Detonation

d.

A high EGT

b.

A lean die out

The purpose of the crankcase breather is to.

a.

Maintain the pressure in the oil tank at atmospheric pressure

b.

Ease the task of the oil scraper ring

c.

Prevent distortion of the crankcase

d.

Prevent pressure building up inside the crankcase

d.

Prevent pressure building up inside the crankcase

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

a.

Increases

b.

Decreases

c.

Remains constant

d.

Increases up to ground idle and thereafter decreases

c.

Remains constant

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

a.

Decreases

b.

Increases up to the ground idle and thereafter decreases

c.

Increases

d.

Remains Constant

d.

Remains Constant

EPR is a.

a.

Ratio between intake pressure and compressor delivery pressure

b.

Ratio between exhaust pressure and intake pressure

c.

Ratio between ambient pressure and exhaust pressure

d.

Ratio between ambient pressure and fan pressure

b.

Ratio between exhaust pressure and intake pressure

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?

a.

+30 J

b.

+130 J

c.

-30 J

d.

130 J

a.

+30 J

Cv is less than Cp.

a.

Always

b.

Sometimes

c.

Never

d.

It depends on the cycle

a.

Always

Variable inlet guide vanes help to prevent

a.

Loss compression

b.

Foreign object on the compressor blades

c.

Compressor stalling

d.

Ice build-up on the compressor blades

c.

Compressor stalling

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?

a.

62%

b.

45%

c.

69%

d.

53%

a.

62%

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

a.

Blade angle decreases

b.

Blade angle does not change

c.

Blade angle increases

d.

Blade angle may increase or decrease depending on the particular system

c.

Blade angle increases

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.

a.

170.13 hp

b.

169.14 hp

c.

175.11 hp

d.

180.12 hp

a.

170.13 hp

The length of the stroke is.

a.

Determined by the size of the piston

b.

Inversely proportional to the engine power output

c.

Equal to the length of the cylinder

d.

Equivalent to twice the crank throw

d.

Equivalent to twice the crank throw

The maximum thrust that a jet engine can develop will be.

a.

Max static thrust

b.

Max climb thrust

c.

Go-around thrust

d.

Take-off thrust

a.

Max static thrust

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

a.

Constant Pressure Process

b.

Adiabatic Process

c.

Constant Volume Process

d.

Isothermal Process

a.

Constant Pressure Process

In a gas turbine engine.

a.

Ram pressure is unaffected by airspeed.

b.

Thrust is unaffected by the aircraft's forward speed.

c.

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

d.

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

c.

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

Ram effect is

a.

The increase of dynamic pressure at the face of the compressor

This answer is incorrect.

b.

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

c.

The increase of static energy at the face of the compressor

d.

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

b.

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

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

a.

Shortly after the piston reaches the top of the compression stroke

b.

Shortly before the piston reaches the top of the compression stroke

c.

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

d.

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

b.

Shortly before the piston reaches the top of the compression stroke

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.

a.

957

b.

2057

c.

1759

d.

1176

d.

1176

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.

a.

Lower the collective pitch

b.

Increase manifold pressure and rpm

c.

Decrease manifold pressure

d.

Increase the throttle

a.

Lower the collective pitch

Which of the following statement is wrong?

a.

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

b.

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

c.

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

d.

The closed cycle gas turbine plants are external combustion plants.

a.

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

The stator vanes in an axial-flow compressor.

a.

Convert pressure energy into velocity energy

b.

Convert velocity energy into pressure energy

c.

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

d.

Convert kinetic energy into potential energy

b.

Convert velocity energy into pressure energy

The term "Indicated Mean Effective Pressure" refers to.

a.

The maximum working pressure in the engine cylinder.

b.

The pressure achieved during compression.

c.

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

d.

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

c.

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

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.

586 kPa

c.

276 kPa

d.

933 kPa

d.

933 kPa

The purpose of an ignition switch is.

a.

To prevent condensation

b.

To connect the battery to the magneto

c.

To connect the secondary coil to the distributor

d.

To control the primary circuit of the magneto

d.

To control the primary circuit of the magneto

In a convergent duct.

a.

The pressure and velocity remain constant, the temperature decreases.

b.

The pressure and velocity increase, the temperature decreases.

c.

The pressure and temperature decrease, the velocity increases.

d.

The temperature and velocity increase, the pressure decreases.

c.

The pressure and temperature decrease, the velocity increases.

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.

a.

978.7 lbs

b.

1,178.8 lbs

c.

878.9 lbs

d.

788.8 lbs

c.

878.9 lbs

A method of comparing engine efficiencies is by comparing.

a.

Engine thrust rating

b.

Specific fuel consumption

c.

Thrust-to-weight ratio

d.

Fuel consumption

b.

Specific fuel consumption

Excessive cylinder head temperatures are caused by.

a.

The ignition timing being too far advanced.

b.

The ignition being too far retarded.

c.

The prolonged use of rich mixtures.

d.

The prolonged use of weak mixtures.

d.

The prolonged use of weak mixtures.

Shrouding of stator blade tips is designed to.

a.

Prevent tip turbulence

b.

Ensure adequate cooling

c.

Minimize vibration

d.

Prevent tip losses

c.

Minimize vibration

Which of the following statement is incorrect?

a.

A good fuel should have low ignition point

b.

The solid fuels have higher calorific value than liquid fuels

c.

The liquid fuels have higher calorific value than solid fuels

d.

The liquid fuels consist of hydrocarbons

b.

The solid fuels have higher calorific value than liquid fuels

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.

a.

Red

b.

Blue

c.

Green

d.

Yellow

c.

Green

The highest pressure in a gas turbine is.

a.

At the burner exit

b.

Before the nozzle exit

c.

Before the burner

d.

At the nozzle exit

c.

Before the burner

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

a.

process 2-3; process 1-4

b.

process 1-2; process 2-3

c.

process 3-4; process 4-1

d.

process 1-2; process 3-4

d.

process 1-2; process 3-4

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

a.

To increase the volumetric efficiency.

b.

To cool the charge temperature and prevent detonation.

c.

To give excess power.

d.

To give greater thermal efficiency.

b.

To cool the charge temperature and prevent detonation.

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

a.

-364

b.

-456

c.

-355

d.

-576

a.

-364

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.

a.

12 kJ

b.

6.41 kJ

c.

10.44 kJ

d.

5.31 kJ

a.

12 kJ

One cause of after firing in an aircraft engine is.

a.

Sticking intake valves

b.

Poor ignition

c.

Excessively lean mixture

d.

Excessively rich mixture

d.

Excessively rich mixture