I.C Engines Objective Questions with Answers – Set 06

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Q1. The thermal efficiency of diesel engines is about

(A) 15%
(B) 30%
(C) 50%
(D) 70%

Answer: (D) 70%


Q2. The thermal efficiency of a standard Otto cycle for a compression ratio of 5.5 will be

(A) 25%
(B) 50%
(C) 70%
(D) 100%

Answer: (B) 50%


Q3. The theoretically correct air fuel ratio for petrol engine is of the order of

(A) 6: 1
(B) 9: 1
(C) 12: 1
(D) 15: 1

Answer: (D) 15: 1


Q4. In a four stroke cycle petrol engine, the compression

(A) Starts at 40° after bottom dead centre and ends at 30° before top dead centre
(B) Starts at 40° before bottom dead centre and ends at 30° after bottom dead centre
(C) Starts at bottom dead centre and ends at top dead centre
(D) May start and end anywhere

Answer: (A) Starts at 40° after bottom dead centre and ends at 30° before top dead centre


Q5. Detonation is harmful due to

(A) Increase in the rate of heat transfer, there is a reduction in the power output and efficiency of the engine
(B) Excessive turbulence which removes most of the insulating gas boundary layer from the cylinder walls
(C) High intensity of knock causes crankshaft vibration and the engine runs rough
(D) None of the above

Answer: (D) None of the above


Q6. Diesel engine can work on very lean air fuel ratio of the order of 30: 1. A petrol engine can also work on such a lean ratio provided

(A) It is properly designed
(B) Best quality fuel is used
(C) Cannot work as it is impossible
(D) Flywheel size is proper

Answer: (C) Cannot work as it is impossible


Q7. The ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston is called

(A) Mechanical efficiency
(B) Overall efficiency
(C) Volumetric efficiency
(D) Relative efficiency

Answer: (C) Volumetric efficiency


Q8. The knock in diesel engine occurs due to

(A) Instantaneous and rapid burning of the first part of the charge
(B) Instantaneous auto ignition of last part of charge
(C) Delayed burning of the first part of the charge
(D) Reduction of delay period

Answer: (A) Instantaneous and rapid burning of the first part of the charge


Q9. In a four stroke cycle petrol engine, the expansion

(A) Starts at top dead center and ends at bottom dead center
(B) Starts at 30° before top dead center and ends at 50° before bottom dead center
(C) Starts at 30° after top dead center and ends at 50° after bottom dead center
(D) May start and end anywhere

Answer: (B) Starts at 30° before top dead center and ends at 50° before bottom dead center


Q10. In a diesel engine, the fuel is ignited by

(A) Spark
(B) Injected fuel
(C) Heat resulting from compressing air that is supplied for combustion
(D) Ignition

Answer: (C) Heat resulting from compressing air that is supplied for combustion


Q11. The fuel valve in a four stroke cycle diesel engine

(A) Opens at 15° after top dead center and closes at 20° before bottom dead center
(B) Opens at 15° before top dead center and closes at 20° after top dead center
(C) Opens at top dead center and closes at bottom dead center
(D) May open and close anywhere

Answer: (B) Opens at 15° before top dead center and closes at 20° after top dead center


Q12. The cam shaft of a four stroke I.C. engine running at 1500 rpm will run at

(A) 1500 rpm
(B) 750 rpm
(C) 3000 rpm
(D) Any value independent of engine speed

Answer: (B) 750 rpm


Q13. Which of the following does not relate to a compression ignition engine?

(A) Fuel pump
(B) Fuel injector
(C) Governor
(D) Carburettor

Answer: (D) Carburettor


Q14. If the intake air temperature of I.C. engine increases, its efficiency will

(A) Increase
(B) Decrease
(C) Remain same
(D) None of these

Answer: (B) Decrease


Q15. The colour of exhaust from diesel engine is generally

(A) White
(B) Bluish
(C) Black
(D) Violet

Answer: (C) Black


Q16. The effective inhibitor of pre-ignition is

(A) Alcohol
(B) Water
(C) Lead
(D) None of these

Answer: (B) Water


Q17. The specific fuel consumption per B.P. hour for a petrol engine is about

(A) 0.2 kg
(B) 0.25 kg
(C) 0.3 kg
(D) 0.35 kg

Answer: (B) 0.25 kg


Q18. The ignition quality of diesel oil is expressed by

(A) Cetane number
(B) Octane number
(C) Calorific value
(D) None of these

Answer: (A) Cetane number


Q19. The octane number of petrol, generally available, is

(A) 20 to 40
(B) 40 to 60
(C) 60 to 80
(D) 80 to 100

Answer: (D) 80 to 100


Q20. In an internal combustion engine, the process of removing the burnt gases from the combustion chamber of the engine cylinder is known as

(A) Scavenging
(B) Detonation
(C) Supercharging
(D) Polymerisation

Answer: (A) Scavenging


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