Steam and Gas Turbines Multiple Choice Questions on “Classification based on Application, Cycle – 1”.
1. Turbojet is a combination of gas turbine with a propeller engine.
Clarification: Turbojet is an air breathing jet engine which was used in aeroplane. Both gas turbine and propeller together is a turbojet.
2. A compressor in the gas turbine is driven by the Turbine.
Clarification: In a gas turbine both the turbine and compressor are connected to each other where turbine itself drives the compressor eventually.
3. What is bypass ratio in Turbofan?
a) None of the mentioned
b) (Mass of the air passing through the engine)/(Mass of the air bypassing the engine)
c) (Air entering the engine)/(Air leaving the engine)
d) (Mass of the air bypassing the engine)/(Mass of the air passing through the engine)
Clarification: The term bypass ratio is used in turbofan.In turbofan some of the air enters the engine bypass and rotates the fan while the remaining air rotates the turbine where these two fan and turbine provides the drag force required.Bypass ratio is the ratio of air bypassing the engine to the ratio of air passing through the engine.
4. Turbojet emits ______ engine noise when compared to Turbofan.
Clarification: Engine’s noise is directly proportional to the air coming from the engine exhaust.In turbojet more air comes from the engine exhaust which is the reason for more noise.
5. Turboprop engines are used in ________ aircrafts.
Clarification: As the air leaving the engine in turboprop is not sufficient to produce required thrust, turboprop engines are used in conditions where less rpms are required.
6. In turboprop engines ____ torque ____ rpm produced from the engine is converted into high rpm low torque.
a) high, low
b) low, high
c) high, high
Clarification: Turboprop engines generally have low torque and high rpms. In such conditions, a reduction gear is used to convert it into low rpm and high torque so that sufficient drag force can be provided.
7. When turboprop and turbofan operate at same speeds, turboprop consumes ________ fuel.
Clarification: Turbofan produces high rpm, low torque but reduction gear is used to convert it into less rpm and high torque to provide required drag force, but turbo fan operates at high rpms, So for turboprop to operate at same speed as of turbofan they require more fuel when compared to turbofan.
8. In turboprop exhaust fan produces ___________
a) more than 25% of the total thrust
b) more than 40% of the total thrust
c) less than 25% of the total thrust
d) less than 10% of the total thrust
Clarification: Due to additional expansion in the turbine system, Energy in the thrust jet is lesser than 10% of the total energy produced by turboprop.
9. Turboprops are not generally operated in high speeds because of ________
a) while speed of the engine increases it looses it efficiency
b) turboprops are not able to produce high speeds
c) turboprops produce high torques
d) none of the mentioned
Clarification: Turboprops cannot be operated at high speeds. Turboprops are operated in between 0.6 and 0.7. When they are operated more than the mentioned speeds they loose their efficiency.
10. A closed cycle gas turbine follows ________
a) Dual Cycle
b) Brayton Cycle
c) Stirling cycle
d) Carnot cycle
Clarification: Closed cycle Gas turbines follow the Brayton cycle.