# Engineering/Compressors, Gas Turbines and Jet Engines MCQ Practice Test - Set 02 Sample Test,Sample questions

## Question: ` A rocket works with maximum overall efficiency when air craft velocity is equal to the`

1.Jet velocity

2.Twice the jet velocity

3. Half the jet velocity

4.Average of the jet velocity

## Question: ``` A rotary compressor is driven by an ```

1.Electric motor

2.Engine

3.Either (A) or (B)

4.None of these

## Question: ` An ideal air compressor cycle without clearance on P-V diagram can be represented by following processes`

1.One adiabatic, two isobaric, and one constant volume

3. Two adiabatic, one isobaric and one constant volume

4.One adiabatic, one isobaric and two constant volumes

1.Centrifugal

2.Reciprocating

3.Axial

4.Screw

1.D₁/D₂ = p₁ p₂

2.D₁/D₂ = p₁/p₂

3.D₁/D₂ = p₂/p₁

4. None of these

## Question: ` In a centrifugal compressor, the ratio of the ________ to the blade velocity is called slip factor.`

1.Inlet whirl velocity

2.Outlet whirl velocity

3.Inlet velocity of flow

4.Outlet velocity of flow

## Question: ``` Isothermal compression efficiency can be attained by running the compressor ```

1.(A) At very high speed

2.At very slow speed

3.At average speed

4.At zero speed

## Question: ` Losses in a centrifugal compressor are due to`

1.Inlet losses

2.Impeller channel losses

3.Diffuser losses

4.All of the above

## Question: ``` Phenomenon of choking in compressor means ```

1. No flow of air

2.Fixed mass flow rate regardless of pressure ratio

3.Reducing mass flow rate with increase in pressure ratio

4. Increased inclination of chord with air steam

## Question: ` Pick up the wrong statement about advantages of multistage compression`

1. Better lubrication is possible advantages of multistage (B) (D)

2. More loss of air due to leakage past the cylinder

3.Mechanical balance is better

4.Air can be cooled perfectly in between

## Question: ` Ratio of indicated H.P. and brake H.P. is known as`

1.Mechanical efficiency

2.Volumetric efficiency

3.Isothermal efficiency

## Question: ` The absolute pressure of air at the outlet of a compressor is called`

1.Back pressure

2.Critical pressure

3.Discharge pressure

4.None of these

## Question: ` The advantage of multistage compression over single stage compression is`

1.Lower power consumption per unit of air delivered

2.Higher volumetric efficiency

3. Decreased discharge temperature

4.All of the above

1.Same

2.One-half

3.One fourth

4. One sixth

## Question: ` The overall isothermal efficiency of compressor is defined as the ratio of`

1.Isothermal h.p. to the BHP of motor

2. Isothermal h.p. to adiabatic h.p.

3.Power to drive compressor to isothermal h.p.

4. Work to compress air isothermally to work for actual compression

## Question: ` The pressure and temperature conditions of air at the suction of compressor are`

1.Atmospheric

2.Slightly more than atmospheric

3.Slightly less than atmospheric

4.Pressure slightly less than atmospheric and temperature slightly more than atmospheric

1.Reduced

2.Increased

3.Zero

4.None of these

## Question: ` The ratio of work done per cycle to the swept volume in case of compressor is called`

1.Compression index

2.Compression ratio

3. Compressor efficiency

4. Mean effective pressure

## Question: ` The type of rotary compressor used in aeroplanes, is of`

1.Centrifugal type

2.Axial flow type

4.None of these

1.0.1%

2. 0.5%

3. 1%

4.5%

## Question: `. Gas turbine as compared to internal combustion engine`

1. Can be driven at a very high speed

2.Produces uniform torque

3.Has more efficiency

4. All of these

1.0.5 kg

2.1.0 kg

3. 1.3 kg

4.2.2 kg

## Question: `A closed cycle gas turbine consists of a`

1.Compressor

2.Heating chamber

3.Cooling chamber

4.All of these

1.Gas turbine

2.C engine

3.Compressor

4.Air motor

## Question: `A rocket engine for the combustion of its fuel`

1.Carries its own oxygen

2.Uses surrounding air

3.Uses compressed atmospheric air

4.Does not require oxygen

## Question: `Adiabatic compression is one in which`

1. Temperature during compression remains constant

2.No heat leaves or enters the compressor cylinder during compression

3. Temperature rise follows a linear relationship

4.Work done is maximum

## Question: `An ideal air compressor cycle with clearance on P-V diagram can be represented by following processes`

1.One adiabatic, two isobaric, and one constant volume

3.Two adiabatic, one isobaric and one constant volume

4.One adiabatic, one isobaric and two constant volumes

## Question: `Clearance volume in actual reciprocating compressors is essential`

1.To accommodate Valves in the cylinder head

2.To provide cushioning effect

3.To attain high volumetric efficiency

4.To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head

## Question: `Compression efficiency is compared against`

1. Ideal compression

3.Isentropic compression

4.Isothermal compression

## Question: ```Diffuser in a compressor is used to ```

1. Increase velocity

2.Make the flow streamline

3.Convert pressure energy into kinetic energy

4.Convert kinetic energy into pressure energy

## Question: `For a two stage compressor, if index of compression for higher stage is greater than index of compression for lower stage, then the optimum pressure as compared to ideal case will`

1.Increase

2.Decrease

3.Remain unaffected

4.Other factors control it

## Question: `For minimum work in multistage compression, assuming same index of compression in all stages`

1.Work done in first stage should be more

2.Work done in subsequent stages should increase

3.Work done in subsequent stages should decrease

4.Work done in all stages should be equal

## Question: `For perfect intercooling in a three stage compressor`

1.p₂/p₁ = p₃/p₂ = p₄/p₃

2.p₃/p₁ = p₄/p₂

3.p₁ p₂ = p₃ p₄

4.p₁ p₃ = p₂ p₄

## Question: `Gas turbine as compared to steam turbine`

1.equires less space for installation

2.Has compressor and combustion chamber

3.Has less efficiency

4.All of the these

## Question: ```he axial flow compressor is preferred in aircraft gas turbines because of ```

1. Low frontal area

2.Higher thrust

3.High pressure rise

4.None of these

## Question: `High air-fuel ratio in gas turbines`

1.Increases power output

2.Improves thermal efficiency

3.Reduces exhaust temperature

## Question: `In a turbo jet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in`

1.Exit nozzle, which is a constant volume process

2.Exit nozzle, which is essentially an isentropic process

3.Turbine blades, which is a constant volume process

4.Turbine blades, which is essentially an isentropic process

## Question: `In gas turbines, high thermal efficiency is obtained in`

1.Closed cycle

2.Open cycle

3. Both of the above

4. Closed/open depending on other considerations

## Question: `In jet engines, paraffin is usually used as the fuel because of its`

1.High calorific value

2. Ease of atomisation

3. Low freezing point

4.Both (A) and (C) above

## Question: `In jet propulsion power unit, the inlet duct of diverging shape is used in order to`

1.Collect more air

2.Convert kinetic energy of air into pressure energy

3.Provide robust structure

4.Beautify the shape

## Question: `Intercooling in gas turbines`

1.Decreases net output but increases thermal efficiency

2.Increases net output but decreases thermal efficiency

3.Decreases net output and thermal efficiency both

4. Increases net output and thermal efficiency both

## Question: `Isothermal compression though most efficient, but is not practicable because`

1. It requires very big cylinder

2.It does not increase pressure much

3.It is impossible in practice

4.Compressor has to run at very slow speed to achieve it

1.Isothermal

3.Polytropic

4.None of these

1.2 kg/cm²

2.6 kg/cm²

3.10 kg/cm²

4.14.7 kg/cm²

1.2 kg/cm²

2.6 kg/cm²

3.10 kg/cm²

4.14.7 kg/cm²

## Question: `n n₁ and n₂ are the indices of compression for the first and second stage of compression, then the ratio of work-done on the first and second stages (W₁/W₂) with perfect intercooling is given by`

1.W₁/W₂ = n₂(n₁ - 1)/n₁(n₂ - 1)

2.W₁/W₂ = n₁(n₂ - 1)/n₂(n₁ - 1)

3.W₁/W₂ = n₁/n₂

4.W₁/W₂ = n₂/n₁

## Question: ```Only rocket engines can be propelled to space because ```

1.They can generate very high thrust

2.They have high propulsion efficiency

3.These engines can work on several fuels

4.They are not air breathing engines

## Question: `Only rocket engines can be propelled to space because`

1.They can generate very high thrust

2.They have high propulsion efficiency

3.These engines can work on several fuels

4.They are not air breathing engines

## Question: `Only rocket engines can be propelled to space because`

1.They can generate very high thrust

2. They have high propulsion efficiency

3.These engines can work on several fuels

4.They are not air breathing engines

1. 34%

2.50%

3.60%

4.72%

## Question: `Propulsive efficiency is defined as ratio of`

1.Thrust power and fuel energy

2.Engine output and propulsive power

3.Propulsive power and fuel input

4.Thrust power and propulsive power

## Question: ```Reheating in a gas turbine ```

1. Increases the thermal efficiency

2.Increases the compressor work

3.Increases the turbine work

4.Decreases the thermal efficiency

## Question: `Rotary compressors are used for delivering`

1. Small quantities of air at high pressures

2.Large quantities of air at high pressures

3.Small quantities of air at low pressures

4.Large quantities of air at low pressures

## Question: `Rotary compressors are used for delivering`

1.Small quantities of air at high pressures

2.Large quantities of air at high pressures

3.Small quantities of air at low pressures

4.Large quantities of air at low pressures

## Question: `The advantage of multistage compression over single stage compression is`

1.Lower power consumption per unit of air delivered

2.Higher volumetric efficiency

3.Decreased discharge temperature

4.All of the above

## Question: `The assumption made in two stage compression with inter-cooler is that`

1. There is no pressure drop in the inter-cooler

2.The compression in both the cylinders is polytropic

3.The suction and delivery of air takes place at constant pressure

4.All of the above

## Question: `The capacity of a compressor is 5 m/min refers to`

1.Standard air

2.Free air

3.Compressed air

4.Compressed air at delivery pressure

## Question: ```The efficiency of jet engine is ```

1.Lower at low speed

2.Higher at high altitudes

3. Same at all altitudes

4.Higher at high speed

## Question: `The following property is most important for material used for gas turbine blade`

1.Toughness

2.Fatigue

3.Creep

4. Corrosion resistance

## Question: `The indicated work per unit mass of air delivered is`

1. Directly proportional to clearance volume

2.Greatly affected by clearance volume

3.Not affected by clearance volume

4.Inversely proportional to clearance volume

## Question: `The mean effective pressure of the compressor is the`

1.ctual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions

2.Volume of air delivered by the compressor

3.Volume of air sucked by the compressor during its suction stroke

4. None of the above

## Question: `The most efficient method of compressing air is to compress it`

1. Isothermally

3. Isentropically

4.Isochronically

## Question: `The overall efficiency of the compressed air system is the`

1.Ratio of shaft output of the air motor to the shaft input to the compressor

2.Ratio of shaft input to the compressor to the shaft output of air motor

3.Product of shaft output of air motor and shaft input to the compressor

4.None of these

1.Same

2.Lower

3.Higher

4.None of these

## Question: ```The ratio of isentropic work to Euler’s work is known as ```

1.Compressor efficiency

2. Isentropic efficiency

3.Euler's efficiency

4.Pressure coefficient

## Question: ```The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called ```

1.Slip factor

2.Velocity factor

3.Velocity coefficient

4. None of the above

## Question: `The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as`

1.Compressor efficiency

2.Volumetric efficiency

3.Isothermal efficiency

4. Mechanical efficiency

## Question: `The thermodynamic efficiency of rotary compressor is based on`

1. Isothermal compression

3. Isentropic compression

4.Polytropic compression

## Question: `The thrust of a jet propulsion power unit can be increased by`

1.Injecting water into the compressor

2.Burning fuel after gas turbine

3. Injecting ammonia into the combustion chamber

4.All of the above

## Question: ```The volume of air delivered in a medium capacity air compressor per unit time is ```

1.0.1 to 1.2 m³/s

2.0.15 to 5 m³/s

3.Above 5 m³/s

4.None of these

## Question: `Volumetric efficiency of a compressor without clearance volume`

1.Increases with increase in compression ratio

2.Decreases with increase in compression ratio

3. Is not dependent upon compression ratio

4.May increase/decrease depending on compressor capacity

1. Equal to

2.Less than

3.More than

4.None of these

## Question: `Which of the following statement is correct as regard to centrifugal compressors?`

1.The flow of air is parallel to the axis of the compressor

2.The static pressure of air in the impeller increases in order to provide centripetal force on the air

3.The impeller rotates at high speeds

4. The maximum efficiency is higher than multistage axial flow compressors

## Question: `Which of the following statement is correct?`

1.The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency

2. The compression ratio for the compressor is always greater than unity

3.The compressor capacity is the ratio of work-done per cycle to the stroke volume

4.During isothermal compression of air, the work-done in a compressor is maximum

## Question: `Which one of the following is the effect of blade shape on performance of a centrifugal compressor?`

1.Backward curved blades has poor efficiency