I.C Engines Objective Questions with Answers – Set 02

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Q1. In petrol engines, advancing of the spark timing will _ the knocking tendency.

(A) Not effect
(B) Decrease
(C) Increase
(D) None of these

Answer: (C) Increase

Q2. The reason for supercharging in any engine is to

(A) Increase efficiency
(B) Increase power
(C) Reduce weight and bulk for a given output
(D) Effect fuel economy

Answer: (C) Reduce weight and bulk for a given output

Q3. Supercharging is the process of supplying the intake air to the engine cylinder at a density _ the density of the surrounding atmosphere.

(A) Equal to
(B) Less than
(C) Greater than
(D) None of these

Answer: (C) Greater than

Q4. In a typical medium speed 4-stroke cycle diesel engines

(A) Exhaust valve opens at 35° before bottom dead center and closes at 20° after top dead center
(B) Exhaust valve opens at bottom dead center and closes at top dead center
(C) Exhaust valve opens just after bottom dead center and closes just before top dead center
(D) May open and close anywhere

Answer: (A) Exhaust valve opens at 35° before bottom dead center and closes at 20° after top dead center

Q5. Which of the following statement is correct?

(A) Compression ratio for petrol engines varies from 6 to 10
(B) Higher compression ratio in diesel engines results in higher pressures
(C) Petrol engines work on Otto cycle
(D) All of the above

Answer: (D) All of the above

Q6. The size of inlet valve of an engine in comparison to exhaust valve is

(A) More
(B) Less
(C) Same
(D) More/less depending on capacity of engine

Answer: (B) Less

Q7. A fuel of an octane number rating of 75 matches in knocking intensity as a mixture of

(A) 75% iso-octane and 25% normal heptane
(B) 75% normal heptane and 25% iso-octane
(C) 75% petrol and 25% diesel
(D) 75% diesel and 25% petrol

Answer: (A) 75% iso-octane and 25% normal heptane

Q8. The fuel air ratio in a petrol engine fitted with suction carburettor, operating with dirty air filter as compared to clean filter will be

(A) Higher
(B) Lower
(C) Remain unaffected
(D) None of the above

Answer: (A) Higher

Q9. The combustion in compression ignition engines is

(A) Homogeneous
(B) Heterogeneous
(C) Both (A) and (B)
(D) None of these

Answer: (B) Heterogeneous

Q10. Diesel fuel, compared to petrol is

(A) Less difficult to ignite
(B) Just about the same difficult to ignite
(C) More difficult to ignite
(D) Highly ignitable

Answer: (C) More difficult to ignite

Q11. Which of the following statement is wrong?

(A) In compression ignition engines, detonation occurs near the beginning of combustion.
(B) Since the fuel, in compression ignition engines, is injected at the end of compression stroke, therefore, there will be no pre-ignition.
(C) To eliminate knock in compression ignition engines, we want to achieve auto-ignition not early and desire a long delay period.
(D) In compression ignition engines, because of heterogeneous mixture, the rate of pressure rise is comparatively lower.

Answer: (C) To eliminate knock in compression ignition engines, we want to achieve auto-ignition not early and desire a long delay period.

Q12. The cetane (C₁₆H₃₄) which is a straight chain paraffin, is assigned a cetane number of

(A) 0
(B) 50
(C) 100
(D) 120

Answer: (C) 100

Q13. The air standard efficiency of an I.C. engine depends on

(A) Fuel used
(B) Speed of engine
(C) Compression ratio
(D) None of these

Answer: (C) Compression ratio

Q14. The normal heptane (C₇H₁₆) is given a rating of __ octane number.

(A) 0
(B) 50
(C) 100
(D) 120

Answer: (A) 0

Q15. Compression ratio of I.C. Engines is

(A) The ratio of volumes of air in cylinder before compression stroke and after compression stroke
(B) Volume displaced by piston per stroke and clearance volume in cylinder
(C) Ratio of pressure after compression and before compression
(D) Swept volume/cylinder volume

Answer: (A) The ratio of volumes of air in cylinder before compression stroke and after compression stroke

Q16. The ignition quality of petrol is expressed by

(A) Cetane number
(B) Octane number
(C) Calorific value
(D) All of these

Answer: (B) Octane number

Q17. In a four stroke cycle diesel engine, the compression

(A) Starts at 40° after bottom dead center and ends at 10° before top dead center
(B) Starts at 40° before top dead center and ends at 40° after top dead center
(C) Starts at top dead center and ends at 40° before bottom dead center
(D) May start and end anywhere

Answer: (A) Starts at 40° after bottom dead center and ends at 10° before top dead center

Q18. In a naturally aspirated diesel engine, the air is supplied by

(A) A supercharger
(B) A centrifugal blower
(C) A vacuum chamber
(D) An injection tube

Answer: (C) A vacuum chamber

Q19. Stoichiometric ratio is

(A) Chemically correct air-fuel ratio by weight
(B) Chemically correct air-fuel ratio by volume
(C) Actual air-fuel ratio for maximum efficiency
(D) None of the above

Answer: (B) Chemically correct air-fuel ratio by volume

Q20. Polymerization is a chemical process in which molecules of a compound become

(A) Larger
(B) Slowed down
(C) Smaller
(D) Liquid

Answer: (A) Larger

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