Internal Combustion MCQ Solved Paper for UPSC IES

1. 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

2. 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

3. In the crankcase method of scavenging, the air pressure is produced by
A. Supercharger
B. Centrifugal pump
C. Natural aspirator
D. Movement of engine piston
Answer : D

4. 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

5. A stoichiometric air-fuel ratio is
A. Chemically correct mixture
B. Lean mixture
C. Rich mixture for idling
D. Rich mixture for over loads
Answer : A

6. The knocking tendency in compression ignition engines for a given fuel will be
A. Enhanced by decreasing compression ratio
B. Enhanced by increasing compression ratio
C. Dependent on other factors
D. None of the above
Answer : A

7. A supercharged engine as compared to an ordinary engine
A. Requires smaller foundation
B. Is lighter
C. Consumes less lubricating oil
D. All of these
Answer : D

8. Morse test is used to determine the I.P. of a
A. Single cylinder petrol engine
B. Four stroke engine
C. Single cylinder diesel engine
D. Multi cylinder engine
Answer : D

9. Which of the following statement is wrong?
A. A four stroke cycle engine develops twice the power as that of a two stroke cycle engine
B. For the same power developed, a four stroke cycle engine is lighter, less bulky and occupies less floor area
C. The petrol engines are costly than diesel engines
D. All of the above
Answer : D

10. The volumetric efficiency of a well designed engine may be
A. 30 to 40 %
B. 40 to 60 %
C. 60 to 70 %
D. 75 to 90 %
Answer : D

11. The effective inhibitor of pre-ignition is
A. Alcohol
B. Water
C. Lead
D. None of these
Answer : B

12. The fuels in order of decreasing knock tendency for spark ignition engines are
A. Paraffin, aromatic, napthene
B. Paraffin, napthene, aromatic
C. Napthene, aromatics, paraffin
D. Napthene, paraffin, aromatic
Answer : B

13. Which of the following statement is correct regarding petrol engines?
A. A fine fuel spray mixed with air is ignited by the heat of compression which is at a high pressure
B. The fuel supplied to the engine cylinder is mixed with necessary amount of air and the mixture in ignited with the help of a spark plug
C. The fuel is first evaporated after passing through a carburettor and is mixed with air before ignition
D. All of the above
Answer : B

14. Installation of supercharger on a four cycle diesel engine can result in the following percentage increase in power
A. Up to 35%
B. Up to 50%
C. Up to 75%
D. Up to 100%
Answer : D

15. The increase of efficiency of a compression ignition engine, as the load decreases, is due to
A. Higher maximum temperature
B. Qualitative governing
C. Quantitative governing
D. Hit and miss governing
Answer : B

16. In loop scavenging, the top of the piston is
A. Flat
B. Contoured
C. Slanted
D. Depressed
Answer : B

17. The temperature of interior surface of cylinder wall in normal operation is not allowed to exceed
A. 80°C
B. 120°C
C. 180°C
D. 240°C
Answer : C

18. The accumulation of carbon in a cylinder results in increase of
A. Clearance volume
B. Volumetric efficiency
C. Ignition time
D. Effective compression ratio
Answer : D

19. For the same power developed in I.C. engines, the cheaper system is
A. Naturally aspirated
B. Supercharged
C. Centrifugal pump
D. Turbo charger
Answer : B

20. Volatility of diesel fuel oil is
A. Minimum temperature to which oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in contact with a flame
B. Temperature at which it solidifies or congeals
C. It catches fire without external aid
D. Indicated by 90% distillation temperature, i.e., when 90% of sample oil has distilled off
Answer : D

21. Alpha-methyl-naphthalene (C?? H??) has a cetane number of
A. 0
B. 50
C. 100
D. 120
Answer : A

22. Gaseous fuel guarantees are based on
A. Calorific value of oil
B. Low heat value of oil
C. High heat value of oil
D. Mean heat value of oil
Answer : B

23. High speed compression engines operate on
A. Otto cycle
B. Diesel cycle
C. Dual combustion cycle
D. All of these
Answer : C

24. Pick up the wrong statement
A. 2-stroke engine can run in any direction
B. In 4-stroke engine, a power stroke is obtained in 4-strokes
C. Thermal efficiency of 4-stroke engine is more due to positive scavenging
D. Petrol engines occupy more space than diesel engines for same power output
Answer : D

25. The ignition quality of diesel oil is expressed by
A. Cetane number
B. Octane number
C. Calorific value
D. None of these
Answer : A

26. Fuel consumption of diesel engines is not guaranteed at one quarter load because at such low loads
A. The friction is high
B. The friction is unpredictable
C. The small difference in cooling water temperature or in internal friction has a disproportionate effect
D. The engine is rarely operated
Answer : C

27. Supercharging is essential in
A. Diesel engines
B. Gas turbines
C. Petrol engines
D. Aircraft engines
Answer : D

28. The combustion in compression ignition engines is
A. Homogeneous
B. Heterogeneous
C. Both (A) and (B)
D. None of these
Answer : B

29. 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

30. A mixture containing 65% of iso-octane and 35% of normal heptane will have
A. Cetane number 65
B. Octane number 65
C. Cetane number 35
D. Octane number 35
Answer : B

31. In order to mix air and petrol in the required proportion and to supply it to the engine during suction stroke, then _________ is employed.
A. Fuel pump
B. Injector
C. Carburettor
D. None of these
Answer : C

32. The probability of knocking in diesel engines is increased by
A. High self ignition temperature
B. Low volatility
C. Higher viscosity
D. All of these
Answer : D

33. A diesel engine is _________ as compared to petrol engine, both running at rated load.
A. Equally efficient
B. Less efficient
C. More efficient
D. None of these
Answer : C

34. A spark plug gap is kept from
A. 0.3 to 0.7 mm
B. 0.2 to 0.8 mm
C. 0.4 to 0.9 mm
D. 0.6 to 1.0 mm
Answer : A

35. If the compression ratio in I.C. engine increases, then its thermal efficiency will
A. Decrease
B. Increase
C. Remain same
D. None of these
Answer : B

36. The thermal efficiency of diesel engines is about
A. 15 %
B. 30 %
C. 50 %
D. 70 %
Answer : D

37. A diesel engine as compared to petrol engine (both running and rated load) is
A. More efficient
B. Less efficient
C. Equally efficient
D. Other factors will decide it
Answer : A

38. A 5 BHP engine running at full load would consume diesel of the order of
A. 0.3 kg/hr
B. 1 kg/hr
C. 3 kg/hr
D. 5 kg/hr
Answer : B

39. The ratio of indicated thermal efficiency to the corresponding air standard cycle efficiency is called
A. Net efficiency
B. Efficiency ratio
C. Relative efficiency
D. Overall efficiency
Answer : C

40. Flash point of fuel oil is
A. Minimum temperature to which oil is heated in order to give off inflammable vapours in sufficient quantity to ignite momentarily when brought in contact with a flame
B. Temperature at which it solidifies or congeals
C. Temperature at which it catches fire without external aid
D. Indicated by 90% distillation temperature, i.e. when 90% of sample oil has distilled off
Answer : A

41. The brake power (B.P.) of the engine is given by (where W = Brake load or dead load in newtons, l = Length of arm in metres, N = Speed of engine in r.p.m., S = Spring balance reading in newtons, D = Dia. of brake drum in metres, and d = Dia. of rope in metres)
A. B.P = (Wl × 2?N)/60 watts
B. B.P = [(W - S) ?DN]/60 watts
C. B.P = [(W - S) ? (D + d) N]/60 watts
D. All of these
Answer : D

42. The ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time is called
A. Mechanical efficiency
B. Overall efficiency
C. Indicated thermal efficiency
D. Volumetric efficiency
Answer : B

43. The inlet value of a four stroke cycle I.C engine remains open for nearly
A. 180°
B. 125°
C. 235°
D. 200°
Answer : C

44. The ignition quality of petrol is expressed by
A. Cetane number
B. Octane number
C. Calorific value
D. All of these
Answer : B

45. Polymerisation is a chemical process in which molecules of a compound become
A. Larger
B. Slowed down
C. Smaller
D. Liquid
Answer : A

46. The output of a diesel engine can be increased without increasing the engine revolution or size in following way
A. Feeding more fuel
B. Heating incoming air
C. Scavenging
D. Supercharging
Answer : D

47. The increase of cooling water temperature in petrol engine will __________ the knocking tendency.
A. Not effect
B. Decrease
C. Increase
D. None of these
Answer : C

48. The air-fuel ratio of the petrol engine is controlled by
A. Fuel pump
B. Governor
C. Injector
D. Carburettor
Answer : D

49. Fuel oil consumption guarantees for I .C. engine are usually based on
A. Low heat value of oil
B. High heat value of oil
C. Net calorific value of oil
D. Calorific value of fuel
Answer : B

50. Which of the following does not relate to a compression ignition engine?
A. Fuel pump
B. Fuel injector
C. Governor
D. Carburettor
Answer : D