1000+ Internal Combustion Multiple Choice Question Answer [Solved]

1. 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

2. Which of the following is false statement? Some of the methods used to reduce diesel smoke are as follows
A. Using additives in the fuel
B. Increasing the compression ratio
C. Adherence to proper fuel specification
D. Avoidance of overloading
Answer : B

3. If the speed of the engine is increased, the indicated power will
A. Increase
B. Decrease
C. Remain same
D. None of these
Answer : A

4. 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

5. Compression loss in I.C engines occurs due to
A. Leaking piston rings
B. Use of thick head gasket
C. Clogged air inlet slots
D. All of the above
Answer : D

6. 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

7. 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

8. 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

9. The minimum cranking speed in case of petrol engine is about
A. Half the operating speed
B. One fourth of operating speed
C. 250 - 300 rpm
D. 60 - 80 rpm
Answer : D

10. The working pressure and temperature inside the cylinder of an internal combustion engine is _________ as compared to a steam engine.
A. Low
B. Very low
C. High
D. Very high
Answer : D

11. A diesel engine has
A. One valve
B. Two valves
C. Three valves
D. Four valves
Answer : C

12. A diesel engine has
A. 1 valve
B. 2 valves
C. 3 valves
D. 4 valves
Answer : C

13. Crankcase explosion in I.C. engines usually occurs as
A. First a mild explosion followed by a bi explosion
B. First a big explosion followed by a mil explosion
C. Both mild and big explosions occurs simultaneously
D. Never occurs
Answer : A

14. A heat engine utilises the
A. Calorific value of oil
B. Low heat value of
C. High heat value of oil
D. Mean heat value of oil
Answer : C

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

16. The compensating jet in a carburettor supplies almost constant amount of petrol at all speeds because the
A. Jet area is automatically varied depending on the suction
B. The flow from the main jet is diverted to the compensating jet with increase in speed
C. The diameter of the jet is constant and the discharge coefficient is invariant
D. Flow is produced due to the static head in the float chamber
Answer : D

17. The higher combustion chamber wall temperature in compression ignition engines will _________ knocking tendency.
A. Increase
B. Reduce
C. Not effect
D. None of these
Answer : B

18. In a petrol engine, the mixture has the lowest pressure at the
A. Beginning of suction stroke
B. End of suction stroke
C. End of compression stroke
D. None of these
Answer : B

19. 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

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

21. Which of the following statement is correct regarding normal cetane?
A. It is a standard fuel used for knock rating of diesel engines
B. Its chemical name is normal hexadecane
C. It has long carbon chain structure
D. All of the above
Answer : D

22. 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

23. The operation of forcing additional air under pressure in the engine cylinder is known as
A. Scavenging
B. Turbulence
C. Supercharging
D. Pre-ignition
Answer : C

24. 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

25. The air standard efficiency of an I.C. engine is given by (where r = Compression ratio, and ? = Ratio of specific heats)
A. 1 - r^{? - 1}
B. 1 + r^{? - 1}
C. 1 - (1/r^{? - 1})
D. None of these
Answer : C

26. Does the supply of scavenging air at a density greater than that of atmosphere mean engine is supercharged?
A. Yes
B. No
C. To some extent
D. Unpredictable
Answer : B

27. The normal heptane (C₇H₁₆) is given a rating of ________ octane number.
A. 0
B. 50
C. 100
D. 120
Answer : A

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

29. Iso-octane (C₈H₁₈) has octane number of
A. 0
B. 50
C. 100
D. 120
Answer : C

30. The loud pulsating noise heard within the cylinder of an internal combustion engine is known as
A. Detonation
B. Turbulence
C. Pre-ignition
D. Supercharging
Answer : A

31. A petrol engine, during suction stroke draws
A. Air only
B. Petrol only
C. A mixture of petrol and air
D. None of these
Answer : C

32. Combustion in compression ignition engines is
A. Homogeneous
B. Heterogeneous
C. Both (A) and (B)
D. Laminar
Answer : B

33. Thermal efficiency of a two stroke cycle engine is ________ a four stroke cycle engine.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : B

34. The correct sequence of the decreasing order of brake thermal efficiency of the three given basic types of engines is
A. Four stroke C.I. engine, four stroke S.I. engine, two stroke S.I. engine
B. Four stroke S.I. engine, four stroke C.I. engine, two stroke S.I. engine
C. Four stroke C.I. engine, two stroke S.I. engine, four stroke S.I. engine
D. Two stroke S.I. engine, four stroke S.I. engine, four stroke C.I. engine
Answer : A

35. An hmh flame speed is obtained in diesel engine when air fuel ratio is
A. Uniform throughout the mixture
B. Chemically correct mixture
C. About 35% of rich mixture
D. About 10% of rich mixture
Answer : D

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

37. The air requirement of a petrol engine during starting compared to theoretical air required for complete combustion is
A. More
B. Less
C. Same
D. May be more or less depending on engine capacity
Answer : B

38. For maximum power generation, the air fuel ratio for a petrol engine for vehicles, is of the order of
A. 9 : 1
B. 12 : 1
C. 15 : 1
D. 18 : 1
Answer : B

39. 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

40. A carburettor is used to supply
A. Petrol, air and lubricating oil
B. Air and diesel
C. Petrol and lubricating oil
D. Petrol and air
Answer : D

41. The reference fuels for knock rating of spark ignition engines would include
A. Iso-octane and alpha-methyl naphthalene
B. Normal octane and aniline
C. Isooctane and normal hexane
D. Normal heptane and isooctane
Answer : D

42. Which of the following fuel has little tendency towards detonation?
A. Benzene
B. Iso-octane
C. Normal heptane
D. Alcohol
Answer : B

43. All heat engines utilize
A. Low heat value of oil
B. High heat value of oil
C. Net calorific value of oil
D. Calorific value of fuel
Answer : A

44. Which of the following does not relate to a spark ignition engine?
A. Ignition coil
B. Spark plug
C. Carburettor
D. Fuel injector
Answer : D

45. The increase in intake temperature of internal combustion engines will _________ efficiency.
A. Have no effect on
B. Increase
C. Decrease
D. None of these
Answer : C

46. Pick up the wrong statement about supercharging
A. Supercharging reduces knocking in diesel engines
B. There can be limited supercharging in petrol engines because of detonation
C. Supercharging at high altitudes is essential
D. Supercharging results in fuel economy
Answer : D

47. 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

48. If one cylinder of a diesel engine receives more fuel than the others, then for that cylinder the
A. Exhaust will be smoky
B. Piston rings would stick into piston grooves
C. Engine starts overheating
D. Scavenging occurs
Answer : D

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

50. 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